CA1223647A - Filter integrated circuit - Google Patents
Filter integrated circuitInfo
- Publication number
- CA1223647A CA1223647A CA000477618A CA477618A CA1223647A CA 1223647 A CA1223647 A CA 1223647A CA 000477618 A CA000477618 A CA 000477618A CA 477618 A CA477618 A CA 477618A CA 1223647 A CA1223647 A CA 1223647A
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- filter
- pseudofilter
- signal
- reference level
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/12—Frequency selective two-port networks using amplifiers with feedback
- H03H11/1291—Current or voltage controlled filters
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
Abstract
ABSTRACT OF THE DISCLOSURE
A filter integrated circuit having a refer-ence level generator circuit for attenuating its input signal and generating a reference level signal, a pseudofilter circuit including resistors and a variable capacitor as filter elements, and an error amplifier unit for comparing the level of the output signal of the reference level generator circuit with the level of the output signal of the pseudofilter circuit and for generating an automatic adjustment control signal in accordance with the level difference between the output signals. The automatic adjustment control signal is supplied to the pseudofilter circuit to change the capacitance value of the variable capacitor in the pseudofilter circuit so that the output signal level of the pseudofilter circuit may become equal to the level of the reference signal. The automatic adjustment control signal is also supplied to at least one filter circuit to change the capacitance of a variable capacitor included therein. As a result, the deviation in the filter characteristics caused by deviations in the resistance of a resistor and in the capacitance of the capacitor is corrected.
A filter integrated circuit having a refer-ence level generator circuit for attenuating its input signal and generating a reference level signal, a pseudofilter circuit including resistors and a variable capacitor as filter elements, and an error amplifier unit for comparing the level of the output signal of the reference level generator circuit with the level of the output signal of the pseudofilter circuit and for generating an automatic adjustment control signal in accordance with the level difference between the output signals. The automatic adjustment control signal is supplied to the pseudofilter circuit to change the capacitance value of the variable capacitor in the pseudofilter circuit so that the output signal level of the pseudofilter circuit may become equal to the level of the reference signal. The automatic adjustment control signal is also supplied to at least one filter circuit to change the capacitance of a variable capacitor included therein. As a result, the deviation in the filter characteristics caused by deviations in the resistance of a resistor and in the capacitance of the capacitor is corrected.
Description
3~
BACKGROUND OF THE INVENTION
The present invention relates to a filter integrated circuit suitable to integration of a filter into a monolithic IC formed on a silicon wafer or the like.
As lowpass, highpass and bandpass filters or phase equalizers for producing desired signals in conventional electronic circuits, block filters having discrete components of inductance ~, capacitance C and resistance R have been widely used. As more and more electronic circuits are realized as integrated circuits (monolithic IC's), these filters becomP obstacles ~o cost reduction and reduction o~ size and weight of electronic circuits. Especially for portable devices in which mobility is an important factor, reduction in size and weight is important and it is demanded to realize filters in the form of integxated circuits.
Since it is difficult to realize the inductance L as an integrated circuits, filters suitable to integration are active filters which can be formed by using only the capacitance C and resistance R. For example, twin-T-shaped trap filters can be formed by using only capacitors and resistors. The trap frequency fr of the filter is represented as ~.,~,, ~ ~ ~ 3 6 fr ~ 1
BACKGROUND OF THE INVENTION
The present invention relates to a filter integrated circuit suitable to integration of a filter into a monolithic IC formed on a silicon wafer or the like.
As lowpass, highpass and bandpass filters or phase equalizers for producing desired signals in conventional electronic circuits, block filters having discrete components of inductance ~, capacitance C and resistance R have been widely used. As more and more electronic circuits are realized as integrated circuits (monolithic IC's), these filters becomP obstacles ~o cost reduction and reduction o~ size and weight of electronic circuits. Especially for portable devices in which mobility is an important factor, reduction in size and weight is important and it is demanded to realize filters in the form of integxated circuits.
Since it is difficult to realize the inductance L as an integrated circuits, filters suitable to integration are active filters which can be formed by using only the capacitance C and resistance R. For example, twin-T-shaped trap filters can be formed by using only capacitors and resistors. The trap frequency fr of the filter is represented as ~.,~,, ~ ~ ~ 3 6 fr ~ 1
2~CaRa 1 where Ca is the capacitance of the capacitor used in the twin-T-shaped ~rap filter and Ra is the resistance of the resistor used in that filter.
When such a trap filter is to be integra~ed, deviations in the capacitance value and the resistance value pose a problem. That i5 to say, ~he values of the capacitance and resistance in the IC are affected by deviations in the impurity concentra~ions and mask alignment etc.. For example, the absolute value of the capacitance varies by +10 to 15% and the absolute value of the resistance varies by ~10%. These deviations are rather large values. In the above described example, therefore, the trap frequency of the integrated twin-T-shaped trap filter also varies by -~20 to 25% in the worst case, the practical use being exkremely difficult.
In accordance with a countermeasure disclosed in Japanese Patent Publication No. 58083/82, the resistance value o~ the resistor located on the IC chip is changed by using the laser ~rimming to ccrrect the deviation.
Although this countermeasure has been used, many problems still remain with respect to the precision and the yield rate.
In variable attenuation circuits disclosed in Japanese Patent Publication No. 58083/82 and U.S. Patent No. 3761741, the fact that the ~mitter resistance of the transistor is varied by a change in the DC cuxrent 1 is used. It is known that the variation in the filter characterist.ics caused by ~eviations of element values of the IC can be corrected hy using the similar tech~
nique . However, it is difficult to apply this technique to all filters including ~rap filters. In addition, deviations of elements of the IC must be corrected by external adjustment, resulting in a higher cost.
SUMMARY OF T~E INVENTION
An object of the present invention is to pro-vide a filter integrated circuit which is capable ofautomatically correcting the variation in the filter chaxacteristics caused by deviations in the integrated capacitance and the integrat2d resistance without requiring any external adjustment to ensure the pre-determined performance and which is free from the abovedescxibed problems of ~he prior artO
A filter integrated circuit in accordance with the present invention comprises a r~erence level generator circuit for receiving an input signal having a reference frequency and for generating a reference level signal, a pseudofilter circuit filtering said input signal and comprising an integrated rPsistor and an integrated capacitor having a variable capacitance value, an error amplifier unit for receiving the output ~5 signal of said reference level generator and the output signal of said pseudofilter circuit and for generating an automatic adjustment control signal in accordance ~ ~ ~ 3~ ~
1 with the level difference between those output signals, means for supplying the automatic adjustment control signal to the pseudofilter circuit and for thereby changing the capacitance value of the variable capacitor so that the level of the output signal of the pseudo-filter circuit may hecome ~qual to the level of the reference level signal, and a filter circuit including an integrated resistor and an integrated variable capacitor which respectively have high ratio precision with respect to the corresponding elements of the pseudofilter circult, i.e., the resistor and the capacitor of the pseudofilter circuit. The automatic adjustment control signal is supplied to the filter circuit to change the capacitance value o~ the variable capacitor thereof so as to correct the deviation in the filter characteristics.
Here, the ratio precision refers to the precision of a ratio between values of circuit compo~
nents. For example, when the ratio between resistance values of two resistors remains unchanged even if indivi-dual resistance value~ deviate from their nominal values~
it is said that th~ ratio precision is high. This holds true also for capacitance values. In a semi-conductor integrated circuit, high ratio precision between circuit component values on one chip can be obtained although individual values devlate from their nominal values.
In a filter integrated circuit in accordance 1 with the present invention, the automatic adjus~ment control signal is generated to make the output signal level of the pseudofilter circult equal to the reference value. That is to say, the automatic adjustment control signal corrects the deviation in the filter charac-teristics of the pseudofilter circuit caused by deviations in the element values and the automatic adjuskment control signal is concurrently supplied to the filter circuit. The ratio precision between an element value of the filter circuit and the corresponding element value of the pseudofilter circuit is high. If the filter characteristics of the pseudofilter circuit vary due to deviations in the element values, therefore, the filter characteristics of the filter circuit vary in the same way a, the pseudofilter circuit. Accord-ingly, it is possible to correct the deviation in the characteristics of the filter circuit by using the automatic adjusbment control. signal which is used to correct the deviation in the characteristics of the pseudofilter circuit~
In ~he filter integrated circuit, the refer-ence level generator circuit can be formed by a plurality of integrated resistors or external resistors having high ratio precision so as to attenua~e the reference input signal by using those resistors to produce the reference level signal. The error amplifier unit can be composed of a detector circuit for detecting the output signal of the reference le~el generator circuit,
When such a trap filter is to be integra~ed, deviations in the capacitance value and the resistance value pose a problem. That i5 to say, ~he values of the capacitance and resistance in the IC are affected by deviations in the impurity concentra~ions and mask alignment etc.. For example, the absolute value of the capacitance varies by +10 to 15% and the absolute value of the resistance varies by ~10%. These deviations are rather large values. In the above described example, therefore, the trap frequency of the integrated twin-T-shaped trap filter also varies by -~20 to 25% in the worst case, the practical use being exkremely difficult.
In accordance with a countermeasure disclosed in Japanese Patent Publication No. 58083/82, the resistance value o~ the resistor located on the IC chip is changed by using the laser ~rimming to ccrrect the deviation.
Although this countermeasure has been used, many problems still remain with respect to the precision and the yield rate.
In variable attenuation circuits disclosed in Japanese Patent Publication No. 58083/82 and U.S. Patent No. 3761741, the fact that the ~mitter resistance of the transistor is varied by a change in the DC cuxrent 1 is used. It is known that the variation in the filter characterist.ics caused by ~eviations of element values of the IC can be corrected hy using the similar tech~
nique . However, it is difficult to apply this technique to all filters including ~rap filters. In addition, deviations of elements of the IC must be corrected by external adjustment, resulting in a higher cost.
SUMMARY OF T~E INVENTION
An object of the present invention is to pro-vide a filter integrated circuit which is capable ofautomatically correcting the variation in the filter chaxacteristics caused by deviations in the integrated capacitance and the integrat2d resistance without requiring any external adjustment to ensure the pre-determined performance and which is free from the abovedescxibed problems of ~he prior artO
A filter integrated circuit in accordance with the present invention comprises a r~erence level generator circuit for receiving an input signal having a reference frequency and for generating a reference level signal, a pseudofilter circuit filtering said input signal and comprising an integrated rPsistor and an integrated capacitor having a variable capacitance value, an error amplifier unit for receiving the output ~5 signal of said reference level generator and the output signal of said pseudofilter circuit and for generating an automatic adjustment control signal in accordance ~ ~ ~ 3~ ~
1 with the level difference between those output signals, means for supplying the automatic adjustment control signal to the pseudofilter circuit and for thereby changing the capacitance value of the variable capacitor so that the level of the output signal of the pseudo-filter circuit may hecome ~qual to the level of the reference level signal, and a filter circuit including an integrated resistor and an integrated variable capacitor which respectively have high ratio precision with respect to the corresponding elements of the pseudofilter circult, i.e., the resistor and the capacitor of the pseudofilter circuit. The automatic adjustment control signal is supplied to the filter circuit to change the capacitance value o~ the variable capacitor thereof so as to correct the deviation in the filter characteristics.
Here, the ratio precision refers to the precision of a ratio between values of circuit compo~
nents. For example, when the ratio between resistance values of two resistors remains unchanged even if indivi-dual resistance value~ deviate from their nominal values~
it is said that th~ ratio precision is high. This holds true also for capacitance values. In a semi-conductor integrated circuit, high ratio precision between circuit component values on one chip can be obtained although individual values devlate from their nominal values.
In a filter integrated circuit in accordance 1 with the present invention, the automatic adjus~ment control signal is generated to make the output signal level of the pseudofilter circult equal to the reference value. That is to say, the automatic adjustment control signal corrects the deviation in the filter charac-teristics of the pseudofilter circuit caused by deviations in the element values and the automatic adjuskment control signal is concurrently supplied to the filter circuit. The ratio precision between an element value of the filter circuit and the corresponding element value of the pseudofilter circuit is high. If the filter characteristics of the pseudofilter circuit vary due to deviations in the element values, therefore, the filter characteristics of the filter circuit vary in the same way a, the pseudofilter circuit. Accord-ingly, it is possible to correct the deviation in the characteristics of the filter circuit by using the automatic adjusbment control. signal which is used to correct the deviation in the characteristics of the pseudofilter circuit~
In ~he filter integrated circuit, the refer-ence level generator circuit can be formed by a plurality of integrated resistors or external resistors having high ratio precision so as to attenua~e the reference input signal by using those resistors to produce the reference level signal. The error amplifier unit can be composed of a detector circuit for detecting the output signal of the reference le~el generator circuit,
3~
1 another detector circuit for detecting the output signal of the pseudofilter circuit, and an amplifi~r for receiving the oUtput signals of both detector circuits, amplifying the level difference between those outpu signals, and generating the automatic adjustment control signal. The frequency o~ the input signal to the filtPr integrated circuit may be variableO In this case, automatic adjustment is carried oUt for signals of respective frequencies~
In accordance with the present invention, the deviation in the characteristics of a filter comprising an integrated resistor and an integrated variable capacitor as elements contained in a semi-conductor integrated circuit is automatically adjusted~
And it is possible to improve the precision of the filter and eliminate the adjus~ment which has been heretofore conducted filter by filter. In accordance with the present invention, therefore, a large-sized block filter which has heretofore been used as an exter-?0 nal part can be integrated without requiring adjustment.
As a result, it becomes possible to reduce the cost of circuits in the filter unit as well as the size, weight and the number of parts of the unit.
BRIEF DESCRIPTION OF TME DRAWINGS
These and othex objects and advantages of the prese~t invention will become apparent hy re~erence to the following description and accompanying drawings ~2~
1 wherein:
Fig. 1 is a circuit diagram of a twin-T-shaped trap filter;
Fig, 2 is a characteristic diayram for S illustrating the deviation in the frequency charac-teristics of the filter illustrated in Fig. l;
~ ig. 3 is a block diagram for illustrating the configuration of an embodiment of a filter integrated circuit according to ~he pxesent invention;
Fig. 4 shows a concrete example of a reference level generating circuit used in the filter integrated circuit of Fig~ 3;
Fig. 5 shows a concrete example of a pseudo-filter circuit used in the filter integrated circuit;
Fig. 6 shows waveforms of signals appearing at various points of the filter integrated circuit;
Fig. 7 is a characteristic diagram of a variable capacitox used in the pseudofilter circuit;
Fig. 8 shows deviations in the frequency characterist.ics o the pseudofilter circuit;
Fig. 9 shows a concrete example of a filter circuit used in the integrated ci.rcuit;
Fig. 10 shows another concrete example of a filter circuit used in the filter integrated cir-cuit;
Fig. 11 is a circuit diagram of anotherembodiment of a filter integrated circuit according to the present invention; and ~2236~'7 1 Fig. 12 is a circuit diagram of still another embodimen-t of a filter integrated circuit according ko the present invention.
DEscRIp~rIoN 9F PREFERRED EMBODIMENTS
Prior to description of an embodiment of the present invention, the configuration o a twin-T-shaped trap filter suitable to integration will now be described.
Fig~ 1 shows the configura~ion of a well known twin T-shaped trap filter. If resistance and capacitance values of FigO 1 are chosen as Rl = R2 = 2R3 - ~a C = C - C /2 - Ca it follows that fr = 2~CaRa . In Fig. 1, vi is an input signal and vO is an output signal.
When a trap filter is integrated, the trap fxequency is deviated as a result of deviations in the capacitance and resistance values of the integrated circuit. In the integrated circuit~ the absolute value of the capacitance may vary as much as +10 to 15% and the absolute value of the resistance may vary as much as +10%~ In this case, the trap frequency fr of the trap filter illustrated in Fig. 1 varies as much as +20 to 25% in the worst case. Fig. 2 shows that the trap frequency varies in a range extending from a to b 1 as a result of variation in the resis-tance and capacitance values of the fil~er circuit illustrated in Fig. 1. The present invention provides a filter integrated circuit having a function of automa~ically correcting such variation o~ the trap ~requency of ~he trap filter.
Embodiments o the present invention will now ~e described by referring to drawings. Fig. 3 is a blo~k diagram for illustrating the configuration of an embodiment of a filter circuit according to the present invention. In Fig. 3, a signal 3 having a ~onstant reference ~requency ~in is applied to an IC pin 2 of an IC 1. The input signal 3 i5 applied to a reference level generator circuit 4 and a pseudofilter circuit 5 in the IC 1. The reference level generator circuit 4 attenuates the input signal to produce a reference level signal. The reference level signal is detected in a detector circuit and the detected output is fed to one input terminal of an error amplifier 7. The pseudoilter circuit S is a filter circuit comprising a resistor and a variable capacitor as elements. The pseudofilter circuit 5 filters the input signal and supplies the filtered~signal to a detector circuit 8.
The detector circuit 8 detects the signal and supplies the detected signal to the other input terminal of the error amplifier 7. The error amplifier 7 amplifies the level difference between the output of the detector circuit 6 and the output of the detector circuit 8.
The resultant voltage signal is supplied to the variable ~ g 1 capacitance in the pseudofil ter circuit 5 via a lead 9.
In the pseudofilter circuit 5, the voltage slgnal supplied from ~he error amplifier 7 changes ~he capa-citance value of the variable capacitor to change the filter characteristics so that the level of the filtered signal level will ~e equal to that o the reference signal level supplied from the reference l~vel generator circuit 4. The reference level generator circuit 4, the pseudofilter circuit 5, the detec~or circuits 6 and 8, and the error amplifier 7 constitute an auto-matic adjustment control signal generator circuit 10.
The automatic adjustment control voltage signal supplied from the error amplifier 7 adjusts and corrects the deviation in the filter characteristics caused by deviations in the resistance and capacitance of the pseudofilter circuit 5. The automatic adjustment control voltage signal is supplied to filter circuits 11 and 12 provided in the IC 1. Each of the circuits 11 and 12 include a resistor and a variable capacitor as its components. The resistor and capacitor in each of filter circuits 11 and 1~ are formed in high ratio precision with respect to the resistor and capacitor of the pseudofilter circuit, respectively. In each of filter circuits 11 and 12, the automatic adjustment control voltage signal changes the capacitance value of the variable capacitor to adjust the devia-tion in the filter charac~eris~ics caused by deviations in ~he resistance and capacitance values. The input and output 1 ~f the filter circuit 11 are respectively connected to IC pins 13 and 14 so as to be used outside the IC 1. The filter circuit 12 is used by the circuit within the IC 1.
TAe embodiment of ~ig. 3 will now be described in more detail. Fig. 4 shows an example of a concrete circuit of the reference level generator circuit 4 and Fig. S shows an example of a concrete circuit of the pseudofilter circuit 5. Fig. 6~a) shows a waveform of the input signal 2. Fig. 6(b3 shows waveforms appearing at the output of the reference level generator circuit 4 and the output of the detector circuit as represented by the solid line and the broken line, respectively. Fig. 6(c) shows waveforms appearing at the output of the pseudofilter circuit 5 and the output of the d~tector circuit 8 as represented by the solid line and the broken line, respectively.
Fig. 7 shows a characteristic diagxam of the variable capacitor included in the pseudofilter circuit 5.
Fig. 8 shows frequency characteristics of the pseudo-filter circuit 5. Fig. 9 shows a concrete example of the circuit diagram of the filter circuit 11. FigO 10 shows a concrete example of the circuit diagram of the filter circuit 12.
The reference level generator circuit 4 attenuates the input signal 3 by a constant ratio with precision. qlhe reference level generatox circuit 4 can be formed by integrated resistors 15 and 16 as ~23~ 7 1 shown in Fig. 4, for example. Since the ratio ofelement values in the IC can be obtained with suf~
~iciently high precision~ the attenuation between the input and outpu~ o~ the reference level generator cir-cuit 4 represented as Output = 16 _ = l Input R15 + R16 ( ~ ) can also be realized with sufficiently high precision.
The pseudofilter circuit 5 i5 a ~ilter circuit including an integrated resistor and an integrated capacitor having a capacitance value varied by the voltage applied thereto.
For example, the pseudo~ilter circuit 5 can be formed by inteyrated resistors 17 and 18, a variable capacitor 19; and a constant voltage ~ource 20 as shown in FigO 5 The resistance value R18 of the integrated resi~tor 18 and the capacitance value Clg of the variable capacitor l9 form a CR filter of the first order. The cutoff frequency fc is represented by f _ l 2 R18 l9 The constant voltage source 20 applies the DC voltage to the anode of the variable capacitance l9 via integ-rated resistors 17 and 18. On the other hand, the output voltage of the error amplifier 7 is supplied to the cathode of the variable capacitor 19 in the 1 negative feedback form.
The capacitance value of the variable capacitor 19 is varied by the voltag~ applied across it.
When the c~pacitance of a b~se-emitter juncti.on is used as the variable capacitor 19, the capacikance can be represented as cj = _Cj (? ....
( 1 +
= cj~o or log Cj ~ log ~ + ~) where:
Cj - base-emikter junction capacitance j(0) - base-emitter junction capacitance at zero bias ~j = emitter-base voltage (reverse-biased diode voltage) = built-in vol~age ~ = voltage-dependent coefficient K = log [Cj(O)~]
An example of charactexistics of khe ~ase-emitter junction capacitance is shown in Fig. 7. When the power supply voltage is 5V, Vj may be O to 3~ and Cj can be varied at least by +20 to 25~ w.ith respect 36'~ ~7 1 to its typ:ical value.
The outputs of the reference level genera-tor circuit 4 and the pseudofilter circui.t 5 as represented by the solid lines of Figs. 6(b) and 6(c) respectively are subjected to peak detection in the above described detector circuits to become signals as represented by broken lines of Figs. 6(b) and 6(c), respective.Ly.
These outpu-t signals of the detector cixcuits as represented by broken lines are supplied to the error 10 amplififer 7. As the automatic filter adjustment control voltage signal 9 which has been su~jected to negative feedback, the output of the error amplifier 7 is supplied to one end of the vaxia~le capacitor 19 definin~ the filtering characteristics of the pseudo-filter circuit 5 so that the outputs of the detectorcircuits 6 and 8 may equal each other, i.e., levels 21 and 22 respectively as shown in Figs. 6(b) and 6(c) may become equal to each other. By the automatic adjustment control voltage signal, the capacitance value of the variable capacitor 19 i~ automatically varied to absorb the deviation in the pseudofilter circuit 5.
Each of two filter circuits 11 and 12 comprises an integrated resistor and a variable capacitor to attain the desired filter characteristics and is supplied with the automatic adjustment control signal ~
Since elements integrated on one chip can be formed with high ratio precision, the deviation in the 1 frequency cha.ractexistics o the pseudofilter circui~
5 can be made nearly equal -to that of each of the filter circuits 11 and 12. Accor~ingly, it is possible to automatically absorb deviations in ~he ~requenc~
characteristics of the filter circuits 11 and 12 by using the automatic adjustment control signal 9.
The operation o the circuit of Fig. 3 will now be described in more detail. It is now assumed that the integrated resistors 15 and 16 are defined so that the reference level generator circuit 4 has an attenuation loss of 3 dB. If the sum of de~iations of the integrated resistor and the variable capacitor is -2a~ ~ the pseudofilter circuit 5 has characteristics as represented by 23 in Fig. 8. If the input signal 3 having a fr~quency fin is then supplied to the circuit 3, the output of the pseudofil~er circuit 5 becomes larger than that of the reference level generator cir-cuit 4. And the outputs of the pseudofilter circuit 5 and the reference level generator circuit 4 are fed back to the pseudofilter circuit 5 via the detector circuits 6 and 8 as well as the error amplifier 7 so as to reduce the voltage applied to the variable capacitor o ~he pseudofilter circuit 5. Since the decrease in the voltage applied to the variable capacitor increases the capacitance value as shown in Fig, 7, ~he ~requency characteristics 23 of Fig. 8 is shifted to the left to produce the frequency characteristics 24 of Fig. 8.
That is to say, the capacitance value of the variable ~3~
1 capacitor is so varied ~hat the outputs of the reference level generator circuit 4 and the pseudoilter circuit 5 may become equal to each other at the frequency fin.
Since the capacitance value of the variable capacitor vaxies by +20 to 25~ in accordance with Vj, the maximum deviation can be absorbed, I~ the total deviation of the integrated resistor and the variable capacitor is the maximum value of ~20%, the pseudofilter circuit 5 assumes characteristics 25 as illustrated in Fig. 8.
In this case, it is a matter of couxse ~ha~ the pseudo-filter circuit 5 has eventually the frequency character-istics 24 of Fig. 8 upon receiving the fin input.
As described above, the automatic adjustment control signal 9 for automatically absorbing the deviations of ~he integra~ed resistor 1~ and the variable capacitor 19 is obtained. Because of existence on the same chip, the integrated resistor 18 and the variable capacitor 19 can be formed with sufficiently high ratio precision with respect to the integrated resistors 30 and 31 and the variable capacitors 32 and 33 illustrated in Figs.
~ and 10, respectively. Cutoff frequencies fc~
and fC(12) of the filter circuits 11 and 12 exemplified in Figs..9 and 10 are represented as fc(ll~ 30C32 2~ 9 and ~L2~
f (12) = 1 = _ _ C 2~R31C33 27rn3n4Rl8Cl9 1 where nl to n4 are constants. Thus, deviations in the filter circui-ts 11 and 12 can be automatically absor~ed, resulting in in~egrated ~ilters requiring no adjust-ments.
Further, since the reference of the negakive feedback is the attenuation ~ of the 1 + ( 15 ) reference level generator circuit 4 as described above, the fil-ter charac~eristics depend upon neither the temperature, nor the power supply voltage, nor the level change of the input signal 3. As a result, desired stable filter characteristics can always be attainedO
In the embodiments described above, the input signal 3 is supplied outside the IC 1. However, it is a matter of course that the similar effect can be obtained even if the input signal 3 is supplied from a circuit contained in the same IC. In the video tape recorder, for example, a concrete signal source is the chrominance subcarrier (3.58 MHz in NTSC) generated with high precision in the color signal processing circuit by using a crystal oscillator.
In the above description, the detector cir-cuits 6 and 7 send out the half~wave rectified wave~orms.
~ 17 -~2;3~
1 If full-w ve rectified waveforms are subjected to peak detection, more stable filter circuits can be realized~
Fig. 11 shows another embodiment o~ the pxe-se.nt invention. Reference numerals that are like reference numerals in Fig~ 3 refer to like components.
Constant voltage sources 40, 41 and 42 supply the same voltage. This voltage minus the hase-emitter voltage of a transistor which is approximately 0.7V is supplied to anode sides of the variable capacitors 19, 43, 44 and 45 and also supplied to the detector circuits G and 8. Refexence numerals 46 ~o 48 denote integrated capacitors. Reference numerals 47 to 52 and 53 to 61 denote npn transistors and integrated resistors, respec~ively.
A filter circuit 11 is a twin-T-shaped trap filter described before. If elements are selected as ~58 R59 = 2R60 a Rb C = C - ~43 - C
44 45 ~ 2 b then the trap fre~uency fr can be represented a~
2 7rRbCb Since the elements on one chip can be realized with high ratio precision, Rb and Cb can be represented as ~b = n5R18 and Cb = n6C19 1 where n5 and n6 are constants. Thus, it follows that fr = ~
2 rrn5n6R18Cl9 By the automatic adjustment of the pseudoilter circuit 5, the component deviations in the twin-T-shaped circuik can also b~ absorbed without requiring any ad~us~mentO
Fig. 12 shows still another embodiment of the present invention. Reference numerals that are like reference numerals in Figs. 3 and 11 refer ~o like components. Variable capacitors 62 and 63, npn tran-siskors 64 to 67, cons~ant current sources 68 and 69, integrated resistors 70 to 77~ a constant volkage source 78, an A~ signal bypassing capacitor 79, and an IC pin 80 ar~ shown in Fig. 12. A resistor 74 having a high resistance value is used to supply bias voltage or passing only the DC voltage signal. Since the re~istor 74 has a high resistance value, an AC
signal flowing through the resistor 74 i5 largely attenuated as comparsd with the AC signal flowing to the variable capacitance 62 through the capacitance 79 and is neglizible. The automakic ad~ustment control signal from the error amplifier circuit 7 is supplied to the ~ariable capacitor 62 khrough the resistor 74O
Re~erence numeral 81 denotes a differential amplifier.
The differential amplifier 81 constikutes a positive 1 feedback type lowpass filter o~ the second order in conjunction with resistors 72 and 73 as well as variable capacitors 62 and 63. The effects of the pxesent inven-tion described before are obtained in this embodiment a~ wellO
In ~he embodiment of Fig. 12, ~he filter circuit forms a lowpass filter~ As an alternative~ a highpass filter or a bandpass filter may be used~ In this case, the pseudofilter circuit is ~ormed similarly to FigO 12. And the capacitance value of the variable capacitor included in the filter circuit comprising the highpass filter or the bandpa~s ~ er is changed by the automatic adjustment control signal so as to correct the deviation in the filter characteristics.
In the above described embodiments r the input signal has a constant frequency. However, an input signal having a variable frequency may also be used.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the present invention in the broader aspect.
1 another detector circuit for detecting the output signal of the pseudofilter circuit, and an amplifi~r for receiving the oUtput signals of both detector circuits, amplifying the level difference between those outpu signals, and generating the automatic adjustment control signal. The frequency o~ the input signal to the filtPr integrated circuit may be variableO In this case, automatic adjustment is carried oUt for signals of respective frequencies~
In accordance with the present invention, the deviation in the characteristics of a filter comprising an integrated resistor and an integrated variable capacitor as elements contained in a semi-conductor integrated circuit is automatically adjusted~
And it is possible to improve the precision of the filter and eliminate the adjus~ment which has been heretofore conducted filter by filter. In accordance with the present invention, therefore, a large-sized block filter which has heretofore been used as an exter-?0 nal part can be integrated without requiring adjustment.
As a result, it becomes possible to reduce the cost of circuits in the filter unit as well as the size, weight and the number of parts of the unit.
BRIEF DESCRIPTION OF TME DRAWINGS
These and othex objects and advantages of the prese~t invention will become apparent hy re~erence to the following description and accompanying drawings ~2~
1 wherein:
Fig. 1 is a circuit diagram of a twin-T-shaped trap filter;
Fig, 2 is a characteristic diayram for S illustrating the deviation in the frequency charac-teristics of the filter illustrated in Fig. l;
~ ig. 3 is a block diagram for illustrating the configuration of an embodiment of a filter integrated circuit according to ~he pxesent invention;
Fig. 4 shows a concrete example of a reference level generating circuit used in the filter integrated circuit of Fig~ 3;
Fig. 5 shows a concrete example of a pseudo-filter circuit used in the filter integrated circuit;
Fig. 6 shows waveforms of signals appearing at various points of the filter integrated circuit;
Fig. 7 is a characteristic diagram of a variable capacitox used in the pseudofilter circuit;
Fig. 8 shows deviations in the frequency characterist.ics o the pseudofilter circuit;
Fig. 9 shows a concrete example of a filter circuit used in the integrated ci.rcuit;
Fig. 10 shows another concrete example of a filter circuit used in the filter integrated cir-cuit;
Fig. 11 is a circuit diagram of anotherembodiment of a filter integrated circuit according to the present invention; and ~2236~'7 1 Fig. 12 is a circuit diagram of still another embodimen-t of a filter integrated circuit according ko the present invention.
DEscRIp~rIoN 9F PREFERRED EMBODIMENTS
Prior to description of an embodiment of the present invention, the configuration o a twin-T-shaped trap filter suitable to integration will now be described.
Fig~ 1 shows the configura~ion of a well known twin T-shaped trap filter. If resistance and capacitance values of FigO 1 are chosen as Rl = R2 = 2R3 - ~a C = C - C /2 - Ca it follows that fr = 2~CaRa . In Fig. 1, vi is an input signal and vO is an output signal.
When a trap filter is integrated, the trap fxequency is deviated as a result of deviations in the capacitance and resistance values of the integrated circuit. In the integrated circuit~ the absolute value of the capacitance may vary as much as +10 to 15% and the absolute value of the resistance may vary as much as +10%~ In this case, the trap frequency fr of the trap filter illustrated in Fig. 1 varies as much as +20 to 25% in the worst case. Fig. 2 shows that the trap frequency varies in a range extending from a to b 1 as a result of variation in the resis-tance and capacitance values of the fil~er circuit illustrated in Fig. 1. The present invention provides a filter integrated circuit having a function of automa~ically correcting such variation o~ the trap ~requency of ~he trap filter.
Embodiments o the present invention will now ~e described by referring to drawings. Fig. 3 is a blo~k diagram for illustrating the configuration of an embodiment of a filter circuit according to the present invention. In Fig. 3, a signal 3 having a ~onstant reference ~requency ~in is applied to an IC pin 2 of an IC 1. The input signal 3 i5 applied to a reference level generator circuit 4 and a pseudofilter circuit 5 in the IC 1. The reference level generator circuit 4 attenuates the input signal to produce a reference level signal. The reference level signal is detected in a detector circuit and the detected output is fed to one input terminal of an error amplifier 7. The pseudoilter circuit S is a filter circuit comprising a resistor and a variable capacitor as elements. The pseudofilter circuit 5 filters the input signal and supplies the filtered~signal to a detector circuit 8.
The detector circuit 8 detects the signal and supplies the detected signal to the other input terminal of the error amplifier 7. The error amplifier 7 amplifies the level difference between the output of the detector circuit 6 and the output of the detector circuit 8.
The resultant voltage signal is supplied to the variable ~ g 1 capacitance in the pseudofil ter circuit 5 via a lead 9.
In the pseudofilter circuit 5, the voltage slgnal supplied from ~he error amplifier 7 changes ~he capa-citance value of the variable capacitor to change the filter characteristics so that the level of the filtered signal level will ~e equal to that o the reference signal level supplied from the reference l~vel generator circuit 4. The reference level generator circuit 4, the pseudofilter circuit 5, the detec~or circuits 6 and 8, and the error amplifier 7 constitute an auto-matic adjustment control signal generator circuit 10.
The automatic adjustment control voltage signal supplied from the error amplifier 7 adjusts and corrects the deviation in the filter characteristics caused by deviations in the resistance and capacitance of the pseudofilter circuit 5. The automatic adjustment control voltage signal is supplied to filter circuits 11 and 12 provided in the IC 1. Each of the circuits 11 and 12 include a resistor and a variable capacitor as its components. The resistor and capacitor in each of filter circuits 11 and 1~ are formed in high ratio precision with respect to the resistor and capacitor of the pseudofilter circuit, respectively. In each of filter circuits 11 and 12, the automatic adjustment control voltage signal changes the capacitance value of the variable capacitor to adjust the devia-tion in the filter charac~eris~ics caused by deviations in ~he resistance and capacitance values. The input and output 1 ~f the filter circuit 11 are respectively connected to IC pins 13 and 14 so as to be used outside the IC 1. The filter circuit 12 is used by the circuit within the IC 1.
TAe embodiment of ~ig. 3 will now be described in more detail. Fig. 4 shows an example of a concrete circuit of the reference level generator circuit 4 and Fig. S shows an example of a concrete circuit of the pseudofilter circuit 5. Fig. 6~a) shows a waveform of the input signal 2. Fig. 6(b3 shows waveforms appearing at the output of the reference level generator circuit 4 and the output of the detector circuit as represented by the solid line and the broken line, respectively. Fig. 6(c) shows waveforms appearing at the output of the pseudofilter circuit 5 and the output of the d~tector circuit 8 as represented by the solid line and the broken line, respectively.
Fig. 7 shows a characteristic diagxam of the variable capacitor included in the pseudofilter circuit 5.
Fig. 8 shows frequency characteristics of the pseudo-filter circuit 5. Fig. 9 shows a concrete example of the circuit diagram of the filter circuit 11. FigO 10 shows a concrete example of the circuit diagram of the filter circuit 12.
The reference level generator circuit 4 attenuates the input signal 3 by a constant ratio with precision. qlhe reference level generatox circuit 4 can be formed by integrated resistors 15 and 16 as ~23~ 7 1 shown in Fig. 4, for example. Since the ratio ofelement values in the IC can be obtained with suf~
~iciently high precision~ the attenuation between the input and outpu~ o~ the reference level generator cir-cuit 4 represented as Output = 16 _ = l Input R15 + R16 ( ~ ) can also be realized with sufficiently high precision.
The pseudofilter circuit 5 i5 a ~ilter circuit including an integrated resistor and an integrated capacitor having a capacitance value varied by the voltage applied thereto.
For example, the pseudo~ilter circuit 5 can be formed by inteyrated resistors 17 and 18, a variable capacitor 19; and a constant voltage ~ource 20 as shown in FigO 5 The resistance value R18 of the integrated resi~tor 18 and the capacitance value Clg of the variable capacitor l9 form a CR filter of the first order. The cutoff frequency fc is represented by f _ l 2 R18 l9 The constant voltage source 20 applies the DC voltage to the anode of the variable capacitance l9 via integ-rated resistors 17 and 18. On the other hand, the output voltage of the error amplifier 7 is supplied to the cathode of the variable capacitor 19 in the 1 negative feedback form.
The capacitance value of the variable capacitor 19 is varied by the voltag~ applied across it.
When the c~pacitance of a b~se-emitter juncti.on is used as the variable capacitor 19, the capacikance can be represented as cj = _Cj (? ....
( 1 +
= cj~o or log Cj ~ log ~ + ~) where:
Cj - base-emikter junction capacitance j(0) - base-emitter junction capacitance at zero bias ~j = emitter-base voltage (reverse-biased diode voltage) = built-in vol~age ~ = voltage-dependent coefficient K = log [Cj(O)~]
An example of charactexistics of khe ~ase-emitter junction capacitance is shown in Fig. 7. When the power supply voltage is 5V, Vj may be O to 3~ and Cj can be varied at least by +20 to 25~ w.ith respect 36'~ ~7 1 to its typ:ical value.
The outputs of the reference level genera-tor circuit 4 and the pseudofilter circui.t 5 as represented by the solid lines of Figs. 6(b) and 6(c) respectively are subjected to peak detection in the above described detector circuits to become signals as represented by broken lines of Figs. 6(b) and 6(c), respective.Ly.
These outpu-t signals of the detector cixcuits as represented by broken lines are supplied to the error 10 amplififer 7. As the automatic filter adjustment control voltage signal 9 which has been su~jected to negative feedback, the output of the error amplifier 7 is supplied to one end of the vaxia~le capacitor 19 definin~ the filtering characteristics of the pseudo-filter circuit 5 so that the outputs of the detectorcircuits 6 and 8 may equal each other, i.e., levels 21 and 22 respectively as shown in Figs. 6(b) and 6(c) may become equal to each other. By the automatic adjustment control voltage signal, the capacitance value of the variable capacitor 19 i~ automatically varied to absorb the deviation in the pseudofilter circuit 5.
Each of two filter circuits 11 and 12 comprises an integrated resistor and a variable capacitor to attain the desired filter characteristics and is supplied with the automatic adjustment control signal ~
Since elements integrated on one chip can be formed with high ratio precision, the deviation in the 1 frequency cha.ractexistics o the pseudofilter circui~
5 can be made nearly equal -to that of each of the filter circuits 11 and 12. Accor~ingly, it is possible to automatically absorb deviations in ~he ~requenc~
characteristics of the filter circuits 11 and 12 by using the automatic adjustment control signal 9.
The operation o the circuit of Fig. 3 will now be described in more detail. It is now assumed that the integrated resistors 15 and 16 are defined so that the reference level generator circuit 4 has an attenuation loss of 3 dB. If the sum of de~iations of the integrated resistor and the variable capacitor is -2a~ ~ the pseudofilter circuit 5 has characteristics as represented by 23 in Fig. 8. If the input signal 3 having a fr~quency fin is then supplied to the circuit 3, the output of the pseudofil~er circuit 5 becomes larger than that of the reference level generator cir-cuit 4. And the outputs of the pseudofilter circuit 5 and the reference level generator circuit 4 are fed back to the pseudofilter circuit 5 via the detector circuits 6 and 8 as well as the error amplifier 7 so as to reduce the voltage applied to the variable capacitor o ~he pseudofilter circuit 5. Since the decrease in the voltage applied to the variable capacitor increases the capacitance value as shown in Fig, 7, ~he ~requency characteristics 23 of Fig. 8 is shifted to the left to produce the frequency characteristics 24 of Fig. 8.
That is to say, the capacitance value of the variable ~3~
1 capacitor is so varied ~hat the outputs of the reference level generator circuit 4 and the pseudoilter circuit 5 may become equal to each other at the frequency fin.
Since the capacitance value of the variable capacitor vaxies by +20 to 25~ in accordance with Vj, the maximum deviation can be absorbed, I~ the total deviation of the integrated resistor and the variable capacitor is the maximum value of ~20%, the pseudofilter circuit 5 assumes characteristics 25 as illustrated in Fig. 8.
In this case, it is a matter of couxse ~ha~ the pseudo-filter circuit 5 has eventually the frequency character-istics 24 of Fig. 8 upon receiving the fin input.
As described above, the automatic adjustment control signal 9 for automatically absorbing the deviations of ~he integra~ed resistor 1~ and the variable capacitor 19 is obtained. Because of existence on the same chip, the integrated resistor 18 and the variable capacitor 19 can be formed with sufficiently high ratio precision with respect to the integrated resistors 30 and 31 and the variable capacitors 32 and 33 illustrated in Figs.
~ and 10, respectively. Cutoff frequencies fc~
and fC(12) of the filter circuits 11 and 12 exemplified in Figs..9 and 10 are represented as fc(ll~ 30C32 2~ 9 and ~L2~
f (12) = 1 = _ _ C 2~R31C33 27rn3n4Rl8Cl9 1 where nl to n4 are constants. Thus, deviations in the filter circui-ts 11 and 12 can be automatically absor~ed, resulting in in~egrated ~ilters requiring no adjust-ments.
Further, since the reference of the negakive feedback is the attenuation ~ of the 1 + ( 15 ) reference level generator circuit 4 as described above, the fil-ter charac~eristics depend upon neither the temperature, nor the power supply voltage, nor the level change of the input signal 3. As a result, desired stable filter characteristics can always be attainedO
In the embodiments described above, the input signal 3 is supplied outside the IC 1. However, it is a matter of course that the similar effect can be obtained even if the input signal 3 is supplied from a circuit contained in the same IC. In the video tape recorder, for example, a concrete signal source is the chrominance subcarrier (3.58 MHz in NTSC) generated with high precision in the color signal processing circuit by using a crystal oscillator.
In the above description, the detector cir-cuits 6 and 7 send out the half~wave rectified wave~orms.
~ 17 -~2;3~
1 If full-w ve rectified waveforms are subjected to peak detection, more stable filter circuits can be realized~
Fig. 11 shows another embodiment o~ the pxe-se.nt invention. Reference numerals that are like reference numerals in Fig~ 3 refer to like components.
Constant voltage sources 40, 41 and 42 supply the same voltage. This voltage minus the hase-emitter voltage of a transistor which is approximately 0.7V is supplied to anode sides of the variable capacitors 19, 43, 44 and 45 and also supplied to the detector circuits G and 8. Refexence numerals 46 ~o 48 denote integrated capacitors. Reference numerals 47 to 52 and 53 to 61 denote npn transistors and integrated resistors, respec~ively.
A filter circuit 11 is a twin-T-shaped trap filter described before. If elements are selected as ~58 R59 = 2R60 a Rb C = C - ~43 - C
44 45 ~ 2 b then the trap fre~uency fr can be represented a~
2 7rRbCb Since the elements on one chip can be realized with high ratio precision, Rb and Cb can be represented as ~b = n5R18 and Cb = n6C19 1 where n5 and n6 are constants. Thus, it follows that fr = ~
2 rrn5n6R18Cl9 By the automatic adjustment of the pseudoilter circuit 5, the component deviations in the twin-T-shaped circuik can also b~ absorbed without requiring any ad~us~mentO
Fig. 12 shows still another embodiment of the present invention. Reference numerals that are like reference numerals in Figs. 3 and 11 refer ~o like components. Variable capacitors 62 and 63, npn tran-siskors 64 to 67, cons~ant current sources 68 and 69, integrated resistors 70 to 77~ a constant volkage source 78, an A~ signal bypassing capacitor 79, and an IC pin 80 ar~ shown in Fig. 12. A resistor 74 having a high resistance value is used to supply bias voltage or passing only the DC voltage signal. Since the re~istor 74 has a high resistance value, an AC
signal flowing through the resistor 74 i5 largely attenuated as comparsd with the AC signal flowing to the variable capacitance 62 through the capacitance 79 and is neglizible. The automakic ad~ustment control signal from the error amplifier circuit 7 is supplied to the ~ariable capacitor 62 khrough the resistor 74O
Re~erence numeral 81 denotes a differential amplifier.
The differential amplifier 81 constikutes a positive 1 feedback type lowpass filter o~ the second order in conjunction with resistors 72 and 73 as well as variable capacitors 62 and 63. The effects of the pxesent inven-tion described before are obtained in this embodiment a~ wellO
In ~he embodiment of Fig. 12, ~he filter circuit forms a lowpass filter~ As an alternative~ a highpass filter or a bandpass filter may be used~ In this case, the pseudofilter circuit is ~ormed similarly to FigO 12. And the capacitance value of the variable capacitor included in the filter circuit comprising the highpass filter or the bandpa~s ~ er is changed by the automatic adjustment control signal so as to correct the deviation in the filter characteristics.
In the above described embodiments r the input signal has a constant frequency. However, an input signal having a variable frequency may also be used.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the present invention in the broader aspect.
Claims (3)
1. A filter integrated circuit including at least a resistor and a capacitor comprising:
a reference level generator circuit for attenuating an input signal and generating a reference level signal;
a pseudofilter circuit for filtering said input signal, said pseudofilter circuit including a resistor and a variable capacitor as filter elements;
a detector circuit for detecting the output signal of said reference level generator circuit;
another detector circuit for detecting the output signal of said pseudofilter circuit;
an error amplifier for receiving the output signals of said detector circuits, comparing signal levels of both output signals, and producing an automatic adjustment control signal in accordance with the difference between said signal levels;
means for supplying said automatic adjustment control signal to said pseudofilter circuit for changing the capacitance value of said variable capacitor to reduce said signal level difference; and a filter circuit including the resistors and variable capacitors formed with high ratio precision with respect to filter elements of said pseudofilter circuit, the capacitance value of said variable capacitor being so changed by said automatic adjustment control signal as to change the filter characteristics of said filter circuit.
a reference level generator circuit for attenuating an input signal and generating a reference level signal;
a pseudofilter circuit for filtering said input signal, said pseudofilter circuit including a resistor and a variable capacitor as filter elements;
a detector circuit for detecting the output signal of said reference level generator circuit;
another detector circuit for detecting the output signal of said pseudofilter circuit;
an error amplifier for receiving the output signals of said detector circuits, comparing signal levels of both output signals, and producing an automatic adjustment control signal in accordance with the difference between said signal levels;
means for supplying said automatic adjustment control signal to said pseudofilter circuit for changing the capacitance value of said variable capacitor to reduce said signal level difference; and a filter circuit including the resistors and variable capacitors formed with high ratio precision with respect to filter elements of said pseudofilter circuit, the capacitance value of said variable capacitor being so changed by said automatic adjustment control signal as to change the filter characteristics of said filter circuit.
2. A filter integrated circuit according to claim 1, wherein said reference level generator circuit comprises resistors, said pseudofilter circuit comprises resistors and variable capacitors, and said filter circuit comprises resistors and variable capacitors.
3. A filter integrated circuit according to claim 1, wherein said reference level generator circuit, said pseudofilter circuit, and said filter circuit further comprises transistors as active components, respectively.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP70828/84 | 1984-04-11 | ||
| JP59070828A JPS60214617A (en) | 1984-04-11 | 1984-04-11 | Filter integrated circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223647A true CA1223647A (en) | 1987-06-30 |
Family
ID=13442824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000477618A Expired CA1223647A (en) | 1984-04-11 | 1985-03-27 | Filter integrated circuit |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4667120A (en) |
| EP (1) | EP0158231B1 (en) |
| JP (1) | JPS60214617A (en) |
| KR (1) | KR900001717B1 (en) |
| BR (1) | BR8501655A (en) |
| CA (1) | CA1223647A (en) |
| DE (1) | DE3582513D1 (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61281613A (en) * | 1985-05-20 | 1986-12-12 | Sanyo Electric Co Ltd | Automatic adjusting device for active filter |
| GB2190255B (en) * | 1986-04-30 | 1989-11-29 | Philips Electronic Associated | Electrical filter |
| JPH0787332B2 (en) * | 1986-07-18 | 1995-09-20 | 株式会社東芝 | Automatic time constant adjustment circuit for filter circuit |
| JPH07120923B2 (en) * | 1986-12-27 | 1995-12-20 | ソニー株式会社 | Filter adjustment device |
| JP2522276B2 (en) * | 1986-12-27 | 1996-08-07 | ソニー株式会社 | Filter adjuster |
| JP2522274B2 (en) * | 1986-12-27 | 1996-08-07 | ソニー株式会社 | Filter adjuster |
| JP2522275B2 (en) * | 1986-12-27 | 1996-08-07 | ソニー株式会社 | Filter adjuster |
| US5023491A (en) * | 1988-01-18 | 1991-06-11 | Nec Corporation | Filter circuit arrangements with automatic adjustment of cut-off frequencies |
| JPH01183907A (en) * | 1988-01-18 | 1989-07-21 | Nec Ic Microcomput Syst Ltd | Filter circuit |
| JPH01183908A (en) * | 1988-01-18 | 1989-07-21 | Nec Ic Microcomput Syst Ltd | Filter circuit |
| JPH0693594B2 (en) * | 1989-02-16 | 1994-11-16 | 株式会社東芝 | Analog filter automatic adjustment circuit |
| US5220220A (en) * | 1989-09-20 | 1993-06-15 | Gennum Corporation | Noise suppression system |
| US5392456A (en) * | 1989-10-06 | 1995-02-21 | Hitachi, Ltd. | Method of controlling filter time constant and filter circuit having the time constant control function based on the method |
| JPH03175714A (en) * | 1989-12-04 | 1991-07-30 | Nec Corp | Filter circuit |
| JP2811928B2 (en) * | 1990-07-17 | 1998-10-15 | 日本電気株式会社 | Automatic adjustment filter |
| DE4025428C2 (en) * | 1990-08-10 | 1994-03-03 | Siemens Ag | Circuit arrangement for generating control voltages |
| JP2962800B2 (en) * | 1990-09-29 | 1999-10-12 | 三洋電機株式会社 | Control circuit for variable bandpass filter |
| US5233245A (en) * | 1991-04-10 | 1993-08-03 | General Electric Company | Rate controlled noise filter |
| US7032189B2 (en) * | 2002-10-31 | 2006-04-18 | Northrop Grumman Corporation | Configurable amplifier array incorporating programmable EHF transmission lines |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3562675A (en) * | 1969-05-16 | 1971-02-09 | Sperry Rand Corp | Automatic tuned interference signal rejection filter including drift compensation means |
| JPS574492Y2 (en) * | 1972-05-13 | 1982-01-27 | ||
| US3761741A (en) * | 1972-06-21 | 1973-09-25 | Signetics Corp | Electrically variable impedance utilizing the base emitter junctions of transistors |
| JPS579530B2 (en) * | 1974-07-08 | 1982-02-22 | ||
| CA1033478A (en) * | 1974-07-18 | 1978-06-20 | Sanyo Electric Co. Ltd. | Automatic tuning apparatus |
| NL7415210A (en) * | 1974-11-21 | 1976-05-25 | Takeda Riken Ind Co Ltd | Filter with automatically controlled variable cut off frequency - has output level maintained constant via amplifier with resistive feedback and FET. |
| US4316108A (en) * | 1979-09-25 | 1982-02-16 | Rogers Jr Walter M | Tracking filter for FM threshold extension |
| JPS58159016A (en) * | 1982-03-16 | 1983-09-21 | Sony Corp | Integrated circuit filter device |
| US4509019A (en) * | 1983-01-27 | 1985-04-02 | At&T Bell Laboratories | Tunable active filter |
-
1984
- 1984-04-11 JP JP59070828A patent/JPS60214617A/en active Granted
-
1985
- 1985-03-27 CA CA000477618A patent/CA1223647A/en not_active Expired
- 1985-03-28 EP EP85103719A patent/EP0158231B1/en not_active Expired - Lifetime
- 1985-03-28 DE DE8585103719T patent/DE3582513D1/en not_active Expired - Lifetime
- 1985-03-30 KR KR1019850002156A patent/KR900001717B1/en not_active IP Right Cessation
- 1985-04-09 BR BR8501655A patent/BR8501655A/en unknown
- 1985-04-10 US US06/721,867 patent/US4667120A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0158231A3 (en) | 1988-01-27 |
| EP0158231B1 (en) | 1991-04-17 |
| JPS60214617A (en) | 1985-10-26 |
| JPH0516696B2 (en) | 1993-03-05 |
| KR850008245A (en) | 1985-12-13 |
| EP0158231A2 (en) | 1985-10-16 |
| BR8501655A (en) | 1985-12-10 |
| DE3582513D1 (en) | 1991-05-23 |
| US4667120A (en) | 1987-05-19 |
| KR900001717B1 (en) | 1990-03-19 |
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