CA1224293A - Dtmf-telephone set with multiple use of the logic of the digital tone generator - Google Patents
Dtmf-telephone set with multiple use of the logic of the digital tone generatorInfo
- Publication number
- CA1224293A CA1224293A CA000466175A CA466175A CA1224293A CA 1224293 A CA1224293 A CA 1224293A CA 000466175 A CA000466175 A CA 000466175A CA 466175 A CA466175 A CA 466175A CA 1224293 A CA1224293 A CA 1224293A
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- Prior art keywords
- frequency
- frequency divider
- signal
- telephone set
- additional
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M19/00—Current supply arrangements for telephone systems
- H04M19/02—Current supply arrangements for telephone systems providing ringing current or supervisory tones, e.g. dialling tone or busy tone
- H04M19/04—Current supply arrangements for telephone systems providing ringing current or supervisory tones, e.g. dialling tone or busy tone the ringing-current being generated at the substations
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/26—Devices for calling a subscriber
- H04M1/30—Devices which can set up and transmit only one digit at a time
- H04M1/50—Devices which can set up and transmit only one digit at a time by generating or selecting currents of predetermined frequencies or combinations of frequencies
- H04M1/505—Devices which can set up and transmit only one digit at a time by generating or selecting currents of predetermined frequencies or combinations of frequencies signals generated in digital form
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/26—Devices for calling a subscriber
- H04M1/53—Generation of additional signals, e.g. additional pulses
Abstract
ABSTRACT:
"DTMF-telephone set with multiple use of the logic of the digital tone generator".
Electronic telephone set having DTMF tone dialling.
By some slight additions to the logic circuits of the digital DTMF tone generator this tone generator is made suitable for generating a two-tone ringing signal, for supervising the frequency of the incoming ringing voltage and for generating a tone interval of approximately 0.1 s for the call-back function.
Fig. 3.
"DTMF-telephone set with multiple use of the logic of the digital tone generator".
Electronic telephone set having DTMF tone dialling.
By some slight additions to the logic circuits of the digital DTMF tone generator this tone generator is made suitable for generating a two-tone ringing signal, for supervising the frequency of the incoming ringing voltage and for generating a tone interval of approximately 0.1 s for the call-back function.
Fig. 3.
Description
"DTMF-telephone set with multiple use of the logic of th~
digital tone generator~lO
The invention relates to an eleotronic telephone set having number selection push-buttons and fl~-ther control elements and comprising a digital tone generator for push-button tone diallin~ incorporating an oscilla tor having a fixed oscillator frequenoy and a :Logic cir-cuit comprising a first frequenoy divider for dividing the oscillator frequency~ the divisors of this frequency divider being adjustable for push button tone dialling under the s~ontrol Or the number selection push--buttons~
l Such a telephone set is disclosed in th~ periodical "IEEE Jou~lal of Solid State Circuits", June 1~77, pages 238 -- 242. The set described in this art:icle gener~tes the tone signals required for push-button tona dialling in accordanoe ~ith the DTMF-system with the aid lS of adjustable frequency dividers as is illustrated more specifically b~ Fig, 6 of the relevant article in the above-mentioned periodical~
In electronic telephone sets it is desirable, in addition to per~orm ~unctions other than the ~?ush-button tone dialling with the aid of electronic circuits 9 pre--ferably mon~lithic integrated circuitsO Such additional~unctions are~ ~or exam~le7 generating an apparatus ring-ing signal~ monitoring the frequency o~ an incoming ~0 voltage in the on-hook state o~ the handset or providin~
a non-recurrent brief interruption of the sub~oriber~s line ~or siignalling purposes 9 the ~unction commonly referred to as the call-back function.
It is customary in an electronic telephone set for these other ~unctions to be performed by separate cir-cuits ~hich are especially in*ended ~or those funct1onsO
Thus, "Nac]rrichtentechnische Zeitschri~t" Vcl. 36 (1983) number 5, pa~e 345 discloses an electronio telephone set for D~ tone dial~lin~ in which an apparatu~ riLngiinB
~;242~3 signal can be produced by a separate ringing circuit which is specially pro-vided for that purpose. A considerable portion of the chip surface of the integrated circu:it of which this ringing circuit forms part ;s occupied by this ringing circuit, which is disadvantageous from a technical and economic point of view.
USA Patent 4,070,551 discloses a telephone set in which a variety of tone signals are generated in response to commands received. These tone signals are obtained with the aid of a tone generator in which a fixed oscillator frequency is divided so as to obtain the desired tone frequencies.
Generating these tone signals is also effected by means of a separate circuit which is specially provided for that purpose, so that a separate oscillator and a separate frequency dividing circuit are necessary. This requires many components or, when implemented by integrated circuit techniques a large portion of the available chip surface or even a separate integrated circuit.
It is an object of the invention to provide an elec-tronic telephone set of the type set forth in the opening paragraph in which cl number of func-tions other than the tone push-button selection can be realized in a way which in the event of monolithic integration occupies only a small additional sur-face area of the integrated circuit.
According to the invention, there is provided in an electronic telephone set having line terminals, number selection push-buttons, digital tone generator means having an oscillator having a fixed oscillator frequency and logic circuit means connected to said oscillator and comprising first frequency divider means for dividing said oscillator frequency by one of a plurality of divisors selectable under control of said number selection push-buttons, a plurality of further control elements, and means for externally ~;~242~3 -2a-generating a control signal, the improvement comprlsing: detection means for detecting sai.d externally generated control signal and generating in response thereto a frequency control signal; additional frequency divider means; and means for interconnecting said additional frequency divider means between said first frequency divider means and a selected one of said further control elements in response to said frequency control signal.
Because of these simple additions the digital tone generator which was originally intended to generate DTMF tones can now also be used for generating different tones or generating desired time interva.ls in dependence on detected commands from the '~2~42~3 PHN 10 814 -3- 2~-8-198 subscriber line or from the further control element~
"Further control elements" must~ ~or axample, be under-stood to mean an additional push-button ~or the oall-baok ~unction or the hook contact of the telephone set.
A ~urther embodiment o~ the telephone set in accordance with the in~ention suitabla ~or gene~ating a ringing signal for the acoustic ringing arrang~ment of the telephone set is characterized in that the det~ction oir~
cuit is arranged for detecting on the subscriber line terminals an a.c. voltage having an amplitude which exoeeds a predetermined threshold value and that the lo~ic circuit comprises a first switch Por coupling the output o~ the frequency divider to the acoustic ringing signa7 generator of the telephone set under *he control of at least the detection circuit. These measures have the advantage that in this way one gets the choice of apparatus ringing signals other than the cutomary a.c. voltage o~ ~or example, 25 H~ on the subscriber~s lines, so th.at the sound produced by the ringing signal generator can be ZO given a spectral composition ~hich can be heard better and is more ag~eable to the car than the customary elec-tromechanical bells. Moreover~ the apparatus r~nging signal generated by the telephone set is independent o~
the frequency of the line ringing signal used ~or ringing ~5 on the subscriber line9 which increases the -fields of app~ication o~ this telephone setO
It s:hould bs noted that ~rom the periodical "Review Or the Electrical Communication Laboratories"
Vol. 22 9 No ~ 3 - 4, March/April 1974, an electronic telephone sa* i8 known in which the DTMF t~e generator is used to generate in the on-hook condition Or the hand-set a 1336 :Hz apparatus ringing signal which pulsates at the ~requency of the re¢eived line ringing signal, in res-pon3e to the line ringing signal on tha subs¢riber line.
This apparatus ringing signal is however not obtained with the aid o~ a digital tone generator compriqing a frequency divider h~v:~ng an add~tional divisor~ but by switching-on an RC-oscillator which is normally intended ~or DTMF tone ~224~g3 selec-tion. The dual-purpose use of the frequency dividers of the digital tone generator is consequently n.ot known from this periodical.
A further embodiment of the telephone set acoording to the invention is parti¢ularly suitable for ~upervising the frequency of aOcO voltages on the subscriber line in the on-h.ook condition of the handsetO In thi.s embodiment the logic circuit ~urther comprises a seoond frequency divider for dividing the oscillator frequency~ the divisor of this second frequency divider being adjusta~le under the control of the push-buttons, and a third frequency divider having a divisor required for push-button tone~
dïalling~ the input of this third frequency divider being connected to the OUtpllt of the second ~requenc~ divider.
This embodi.ment of the telephone set according to the in-vention is characterized in that - the logic circuit comprises a second switch for connect-ing the input o~ the second frequency divider l;o the output of the first frequenc~ divider under the control of the detection circuit~
- the second frequency divider is adJustable under the rontrol of the detection oircuit to at least one additional divisor for establishing an upper limit frequency;
~ the third. frequency divider is adjustable under -the control of the detection circuit to a second divisor ~or establishing a lower cut-off frequency~
- the digital tone generator comprises a comparison cir-cuit for comparing the frequency of the a.cO vo~ge with the lower limit fraquency and with the upper limit ~re-30 queno~y - and that the first switch couples the first frequency divider to the aooustic ringing signal generator of the telephone set under the control of the comparison circuit output si&~lal.
The upper and lower limit frequencies can be chosen such that i.nterfering voltages~ for example owing to induction ~y ~ectrlc rail transport, do not result in the ringing devic~ of the telephone set belng activated.
~ Zz ~ ~3 P~ 10 814 ~5~ 28-8-1984 A ~lrther embodiment of ~he telephone set ac¢ord-ing to the invention i9 also suita~le for the oall-back function. To that end this telephone set is characterized in that it compr:ises a third s~itch ~or interrupting the sub scriber~s ;line) - the digital tone generator comprises a line in-terrupt circuit for controlling the third switchg the digital tone generator also comprises 2 ~ourth frequency <livider whose input is connected to the output of the third frequency divider andwhose output is oonnec-t~
ed to the input of the line interrupt circuit.
- and that under the control of the detection circuit and in dependence on the activation of one of the further control elements o~ the telephone set the line interrupt circuit applies a pulse to the third switch for interrupt-ing the subscriber's line, the pulse duration of this pulse being equal to the period of the output 6ignal of the fourth frequency divider.
The invention will now be described in greater detail by ~tay of example with reference to the accom-panying Fig~1res~ corresponding components in the dif~erent Figures having been given the same reference numeralsO
Herein:
Figo 1 shows an electxonic telephone set as it is known from the prior art 9 Fig. 2 shows an electronic telephone set according to the invention comprising a digital to~e generator ~uitable for generating an apparatus ringing signal, Figu 3 shows an electronic telephone set a¢cording to the invention comprising a digital tone generator suitable for supervising the frequsncy of tha :Line ringing signal and Fig. 4 shows an electronic telephone set according to the invention comprising a digital tone generator suitable fc>r the call-back functionO
~ he prior art telephone set shown in Figo 1 com-prise~ a digital tone genera ~r 1 for generating dialling ~ 2 ~ 3 P.HN 10 814 -6- ~8~8-1984 tones ~or push-button tone dialling in accord~lc0 wi-th the DTMF-systemO This tone generator is connec1;ed to the subscriber line terminals 4 ~ia a switoh 2 and the hook contaots 3, ~he acoustic ringing signal genera~or 5 of` the telephone set is provided between the subscriber line t3rminals 4 and behind the hook contact 3 seen from the telephone set. In Fi~. 1, this acoustic ringing signal generator is constituted by a ringing capacitor and an electro-mechanical bell. A dif~erent~ also kno~m manner o~
ringing is e~fec-ted with a separate ringing signal circuit which appli.es a ringing signal to an electroacoustic transducer~ for example a loudspeaker.
In one o~ the wires o~ the subscribers line a recti~ier circuit 27 is provided between the acoustic ringing signal generator 5 and one of the hook contac~O
~his rectifier circuit renders the telephone set insensi tive to polarity changes o~ the voltage on subscriber line terminals 4.
The logic circuit 1 is ~ormed by an osci.llator 13 having a fixed oscilla-tor frequency of, for example~
400 kHz, two~requencr dividers 11 and 12 having an adjustable divisor, two digital-to-analog converters 6 and ~, an a.dder circuit 8 and a keyboard 9. The .~ixed oscillator ~requency is divided by each o~ the two ~re quency dividers 11 and 12 under the control o~ the ke~board 9 to obtain two ~requencies ~rom the DTMF-system. The two ~requencies ara added together after con~ersion by a D/A-converter and applied to the subscriber line.
I~ none o~ the push-buttons of the keyboard 9 i.s activated9 switch 2 is opened A Any speech signals are transmitted to and from a speech circui*, not shown~ via a speech transmission line 10.
Each of the two frequency dividers 11 and 12 is constituted by a series arrangement of a divider having a ~ariable divisor and a divider having a fixed d.ivisor.
When an oscillator frequency o~, ~or example~ 400~Iz is used, the fixed divider o~ frequency divider 11 ha~ a divisor o~, for example, 18 and the ~ixed divid.er o~
:~Z242~3 PHN 10 814 -7- 28~8-1984 ~requenoy clivider 12 then has a di~isor o~ ~or example~
14. By sli~htly extending the logio cirouits ~orming the said ~requency di~iders it is possible to oause the digital tone generator to perform Pun¢tions o*her than generating dialling -tonesO
Figure 2 shows an eIectronic telephone se-t which~
by slightly extending the logic circuits of the digital tone generator can be made suitable ~or detect~ng a line ringing sigrnal on the terminals 4 and generating an apparatus ringing signal in dependence thereona The telephone ~;et shown in Figure 2 is formed by the set shown in Figur0 1 to which a pluralit~ of elements haYe been added and ~rom which the con~entional rin~ing signal generator 5 ha~:been omitted.
In ~ig~re 2, the tone generator 1 compr:ises a detection circuit 14 ~or deteoting -the line ringing signal on the te:~linals 4O To that end the detection circuit 14 comprises a connecting line 18; whi:~h~ in the on-hook condition o~ the handset is connected to the terminals 4O The adj~lstable ~requency divider 11 has some additional logic switc:hiDg elements-so that two extra divisors can be realizedL by means o~ the adjustable portion o~ this ~requency dLivider~ ~or example the divisors 24 ~nd 3O~
So~ in oom~)lnation with the ~ixed portion~ havlng the 25 divisor 18, Or frequenc~ diYider 11, the divisors 432 and 54O are obtainedO
In addition,:the telephone set shown in Figo 2 com-prises an acoustic ringring signal generator 16 ~or produc ingr the acoustic ringing signal and a switch 15 ~or applying the electric ringing signal to ringing signal generator 16O Ringring signal generator 16 is ~d by ringlng supply 29 which converts the line ringing signal rectified by recti~ier clrcuit 27 into supply energy ~or the acoustic ringing signal generator 16.
A capacitor 31 used ~or smoothing the rl~cti~ied, pulsating ~oltage is provided at the input of ringing supply 29. A Zener diode 3O which together with resistor 28 constitutes the overvoltage protection in the on-hoo~
~22~ 3 condition of the handqet is arranged in parallel w-lth capacitor 31. Capaoitor 17 which together with resistor 28 forms a serie~ arrangement has for its ob~ect; to provide the customary separation of direct curre~nt and alternating current in the on-hook condition. I~ the on-hook condition of the handset tone generator 1 is also powered by ringing supply 29 in a manner not shown in the Figure.
Detection circuit 14 compares the amplitude of an aOcO voltage signal on the terminals 4 with a predeter-mined threshold value in the circuit. If the amplitude of the aOoO voltage exceeds this threshold valu~ then frequency divider 11 is alternately set to one of the two extra di~isors by means of a control signalv At the same time~ switch 15 is closed under the control of de-tection circuit 14~ causing ~he apparatus ringillg signal produced by oscillator 13 and frequency divider 11 to be applied to acoustical ringing signal generator 16.
It is possible to have the rate at which frequency divider 11 is alternately set to the two divisors be determined by the frequency of this a.c. voltage ~hich is detected as a line ringing sig~al. It is, however, alter-natively possible to give frequency divider 12 some addi-tional divisors as will be described in detail with reference to Figs. 3 and 4O Thus, ~req~encies can be ob-tained which are of the same order of magnitude as the frequency o~ the line ringing signal. Instead of` alter-natlng between both divisors at the frequency oi the line ringing signal it i9 possible to alternate between the two extra divisors of frequency divider 12 at ~ rate thus obtained.
Starting from an oscillator frequency of 4Oo~Hz and divisors of divider 11 having the value 432 (= 24 x 18) and 54O (= 3O x 18)~ ringing frequencies o~ 925 Hz and 74O Hz, respectively are obtained. Consequently~ the pitch of the ringing signal changes between these two frequen-cies with a frequency o~ change of~ ~or example~ 25 Hzo The choice of the two additional divisors with a mutual ~LZ~2~3 PHN 'I 0 8 1 1~ -9- 28-8-l984 ratio o* 4:5 has the additional advantage that a ~requenoy ratio is~obtained whioh is known as a ma~or interval whloh has the properties of producing more specifically a pleasan~ sound impression.
Fig~ 3 shows an electronic telephone set which by some changes compared with Fig~ 2 has been made suitable *or supervising the frequency of the line ringi.ng signal on the subsoriber's line. The set circuit diagram o~ Fig.
3 is obtained by adding some elements to the said circuit - lO diagram of Figo 20 The digital tone generator 1 of Fig. 3 comprises a switch 20, ~hich renders the output of frequenoy divider 11 connectable to the input frequency divider 12 this input then being also decoupled ~rom oscil.lator 13.
The adjustable frequency divider 12 is provided with some additional logic circuit elements so that two additional divisors can be real~zed with the adjustable portion 12-1 of this frequency divider9 for exarnple the divi.sors 15 and 12. The originally non-adjustable portion 12-2 o~ fre~
29 quency divider 12 has become adjustable~ by th~ addition of some logic circuit elements to an additional. divisor9 for example 3. Furthermore~ the known generator 1 is exbnded by a comparison circuit 21 for comparing the frequency o~ the line ringing signal on the subscriber line terminals with a lower and an upper frequenc~ whilst an AND-gate 2Z is added ~or the control of switch 15 .
If an aOc. voltage of a sufficiently high ampli-tude is present on terminals 4 then detection Gircuit l4 switches frequency-divider 11 to its addi~onal divisors~
as described above with re~erence to Fig, 2. Detection circuit 14 also adjusts switch 20 to the position sho~n in Fig. 3. As a result thereof the output of frequency divider 11 is connected to the input of frequency divider 12-1 via connecting line 19.
Frequency divider 12-1 is alternat~ly ad.justed to one of the two additional divisors under the control of detection circuit 147 at the same rate as frequency divider 110 The two additional divisors o~ frequency PHN 10 814 -'lO- 28-8-1984 divider 12-1 hav0 been ohosen suoh that the product o~ a,n additional divisor o~ fre~lenoy divider 12-1 and an addi-tional divi~or o~ ~requenoy divider l1 is equal to the product o~ the two other additional divisors. ~his holds ~or the divisors 15 and 24 and the divisors 12 ~nd 30.
By this cho.ice of the di~isors and by the simultaneously alter;nation o~ the divisors~ a signal having one constant ~requency~ denoted the upper limit frequency is produced at the output o~ frequency divider 12-10 ~n the said numerical e:~amples -this limit ~requency is approximately 62 ~zO
Frequency diYider 12-2 is adjusted ~ the additional divisor 3 u;nder the control of detection circui-t 14.
Thus~ a signal having a frequency which is denoted as the lower limit frequency is produced at the,output of ~re-quency divider 12~20 ~n the said numerical examples this limit frequency is approximately 21 Hzo The upper and the lower limit frequencies are ap-plied to comparison circuits 21, as is also the anc. volt-age signal incoming via terminals 4~ If the ~requency o~this a.cO voltage signal is located between the lower and upper limit ~requenoies then the comparison circuit 21 applies a signal which is characteristic o~ this frequency state to AND-gate 22. I~ at the same time the amplitude of the a~c. voltage signal exceeds the threshold value which ~as preset in deteotion circuit 147 then detection circuit 14 applies a signal characterizing this amplitude state to A~D_gate 22. In the presence of these two input signals ~n AND-gate 22 the aOcO voltage is detected as the line ring~ng signal with the proper fre-quenc~ and an adequate amplitudeO In that case AND-gate 22 applies a signal to switch 15. Under the control thereo~
this switch is closed~ ~hich causes the apparatus ringing signal produced by frequency divider 11 to be applied to acoustic ri:nging signal generator 16 It s:hould be noted that the output signal o~
comparison circuit 21 may alternati~ely be applied direct-ly to switc:h 15 with the obJect o~ closing it. In that case ~2~2~313 P~IN 10 814 1 1- 2~3~ 8-1984 no signal is applied ~rom dLetectlon circuit 14 to switch 15 . Then only the frequency o~ the a.o. voltage signal com-ing in via terminals 4 is supervised, Fig. 4 shows an electronic telephone set with which non-r~current brie~ line interruptions for signalling purposes can be adjustedO This said function is 'known as $he call back ~unction.
The said circuit diagram of Fig. 4 is re~ized by omitting switch 15 and acoustic ringing sign~ genera*or 16 from the set shown in Fig. 2 and to add some other elements to the Figure thus obtained. The elements added are an additional keyboard 23 with push-buttons ~or said functions other than the push-button ~one'diall~.L~g~ an additional ciivider 2~, a line interrupt circuit 25 and a switch 26 ~or brief interruptions o~ the subscri'ber line.
Frequency divider 12 is in the form of a series arrange-ment of an adjustable divider 12-1 having additional divisors andL a divider 12-2 having an additional divisor~
The additional divider 24 has a divisor of, ~or example~
the value 2~
The line interrupt circuit 25 is controlled by the divider 24 and by a key of the keyboard 23 9 the key commonly rsf'erred to as the call-back key. The output o~ the line interrupt circuit 25 is connected to switch 26. The conta~t of the call-back key is also co~nected to detection circuit 14.
When the call-back key is operated, the frequency dividers 11 and 12 are adjwsted to the respecti~r~ di~isors 24, 30 and 15~ lZ. It is alternatively possible ~or these ~requency dividers to he adjusted to only one additional divisor~ for example to 30 and 12~ respectively~ which is taken as ths starting point for simplicity o~' the des-cription. Now a signal having a frequency o~ apl)roximate-ly 20 Hz is available at the output o~ ~requenc~ divider 12. This signal ls so divided by ~requency divider 24 that a signal having a frequency of approximately 10 Hz is ob-tained. By operating the call-back key~ line int;arrupt-circuit 25 applies a signal to switch 26~ which signal is ~ 4~3 PHN 10 814 ~12- 28~8~1984 in the form of a pulse having a pulse duration equal to one period o~ th~output signal Or ~reque~cy dl~ider 24~
Switch 26 i9 opened during this pulse~ which cau.ses the subscriber line to be interrupted ror approximabely 001 sO
digital tone generator~lO
The invention relates to an eleotronic telephone set having number selection push-buttons and fl~-ther control elements and comprising a digital tone generator for push-button tone diallin~ incorporating an oscilla tor having a fixed oscillator frequenoy and a :Logic cir-cuit comprising a first frequenoy divider for dividing the oscillator frequency~ the divisors of this frequency divider being adjustable for push button tone dialling under the s~ontrol Or the number selection push--buttons~
l Such a telephone set is disclosed in th~ periodical "IEEE Jou~lal of Solid State Circuits", June 1~77, pages 238 -- 242. The set described in this art:icle gener~tes the tone signals required for push-button tona dialling in accordanoe ~ith the DTMF-system with the aid lS of adjustable frequency dividers as is illustrated more specifically b~ Fig, 6 of the relevant article in the above-mentioned periodical~
In electronic telephone sets it is desirable, in addition to per~orm ~unctions other than the ~?ush-button tone dialling with the aid of electronic circuits 9 pre--ferably mon~lithic integrated circuitsO Such additional~unctions are~ ~or exam~le7 generating an apparatus ring-ing signal~ monitoring the frequency o~ an incoming ~0 voltage in the on-hook state o~ the handset or providin~
a non-recurrent brief interruption of the sub~oriber~s line ~or siignalling purposes 9 the ~unction commonly referred to as the call-back function.
It is customary in an electronic telephone set for these other ~unctions to be performed by separate cir-cuits ~hich are especially in*ended ~or those funct1onsO
Thus, "Nac]rrichtentechnische Zeitschri~t" Vcl. 36 (1983) number 5, pa~e 345 discloses an electronio telephone set for D~ tone dial~lin~ in which an apparatu~ riLngiinB
~;242~3 signal can be produced by a separate ringing circuit which is specially pro-vided for that purpose. A considerable portion of the chip surface of the integrated circu:it of which this ringing circuit forms part ;s occupied by this ringing circuit, which is disadvantageous from a technical and economic point of view.
USA Patent 4,070,551 discloses a telephone set in which a variety of tone signals are generated in response to commands received. These tone signals are obtained with the aid of a tone generator in which a fixed oscillator frequency is divided so as to obtain the desired tone frequencies.
Generating these tone signals is also effected by means of a separate circuit which is specially provided for that purpose, so that a separate oscillator and a separate frequency dividing circuit are necessary. This requires many components or, when implemented by integrated circuit techniques a large portion of the available chip surface or even a separate integrated circuit.
It is an object of the invention to provide an elec-tronic telephone set of the type set forth in the opening paragraph in which cl number of func-tions other than the tone push-button selection can be realized in a way which in the event of monolithic integration occupies only a small additional sur-face area of the integrated circuit.
According to the invention, there is provided in an electronic telephone set having line terminals, number selection push-buttons, digital tone generator means having an oscillator having a fixed oscillator frequency and logic circuit means connected to said oscillator and comprising first frequency divider means for dividing said oscillator frequency by one of a plurality of divisors selectable under control of said number selection push-buttons, a plurality of further control elements, and means for externally ~;~242~3 -2a-generating a control signal, the improvement comprlsing: detection means for detecting sai.d externally generated control signal and generating in response thereto a frequency control signal; additional frequency divider means; and means for interconnecting said additional frequency divider means between said first frequency divider means and a selected one of said further control elements in response to said frequency control signal.
Because of these simple additions the digital tone generator which was originally intended to generate DTMF tones can now also be used for generating different tones or generating desired time interva.ls in dependence on detected commands from the '~2~42~3 PHN 10 814 -3- 2~-8-198 subscriber line or from the further control element~
"Further control elements" must~ ~or axample, be under-stood to mean an additional push-button ~or the oall-baok ~unction or the hook contact of the telephone set.
A ~urther embodiment o~ the telephone set in accordance with the in~ention suitabla ~or gene~ating a ringing signal for the acoustic ringing arrang~ment of the telephone set is characterized in that the det~ction oir~
cuit is arranged for detecting on the subscriber line terminals an a.c. voltage having an amplitude which exoeeds a predetermined threshold value and that the lo~ic circuit comprises a first switch Por coupling the output o~ the frequency divider to the acoustic ringing signa7 generator of the telephone set under *he control of at least the detection circuit. These measures have the advantage that in this way one gets the choice of apparatus ringing signals other than the cutomary a.c. voltage o~ ~or example, 25 H~ on the subscriber~s lines, so th.at the sound produced by the ringing signal generator can be ZO given a spectral composition ~hich can be heard better and is more ag~eable to the car than the customary elec-tromechanical bells. Moreover~ the apparatus r~nging signal generated by the telephone set is independent o~
the frequency of the line ringing signal used ~or ringing ~5 on the subscriber line9 which increases the -fields of app~ication o~ this telephone setO
It s:hould bs noted that ~rom the periodical "Review Or the Electrical Communication Laboratories"
Vol. 22 9 No ~ 3 - 4, March/April 1974, an electronic telephone sa* i8 known in which the DTMF t~e generator is used to generate in the on-hook condition Or the hand-set a 1336 :Hz apparatus ringing signal which pulsates at the ~requency of the re¢eived line ringing signal, in res-pon3e to the line ringing signal on tha subs¢riber line.
This apparatus ringing signal is however not obtained with the aid o~ a digital tone generator compriqing a frequency divider h~v:~ng an add~tional divisor~ but by switching-on an RC-oscillator which is normally intended ~or DTMF tone ~224~g3 selec-tion. The dual-purpose use of the frequency dividers of the digital tone generator is consequently n.ot known from this periodical.
A further embodiment of the telephone set acoording to the invention is parti¢ularly suitable for ~upervising the frequency of aOcO voltages on the subscriber line in the on-h.ook condition of the handsetO In thi.s embodiment the logic circuit ~urther comprises a seoond frequency divider for dividing the oscillator frequency~ the divisor of this second frequency divider being adjusta~le under the control of the push-buttons, and a third frequency divider having a divisor required for push-button tone~
dïalling~ the input of this third frequency divider being connected to the OUtpllt of the second ~requenc~ divider.
This embodi.ment of the telephone set according to the in-vention is characterized in that - the logic circuit comprises a second switch for connect-ing the input o~ the second frequency divider l;o the output of the first frequenc~ divider under the control of the detection circuit~
- the second frequency divider is adJustable under the rontrol of the detection oircuit to at least one additional divisor for establishing an upper limit frequency;
~ the third. frequency divider is adjustable under -the control of the detection circuit to a second divisor ~or establishing a lower cut-off frequency~
- the digital tone generator comprises a comparison cir-cuit for comparing the frequency of the a.cO vo~ge with the lower limit fraquency and with the upper limit ~re-30 queno~y - and that the first switch couples the first frequency divider to the aooustic ringing signal generator of the telephone set under the control of the comparison circuit output si&~lal.
The upper and lower limit frequencies can be chosen such that i.nterfering voltages~ for example owing to induction ~y ~ectrlc rail transport, do not result in the ringing devic~ of the telephone set belng activated.
~ Zz ~ ~3 P~ 10 814 ~5~ 28-8-1984 A ~lrther embodiment of ~he telephone set ac¢ord-ing to the invention i9 also suita~le for the oall-back function. To that end this telephone set is characterized in that it compr:ises a third s~itch ~or interrupting the sub scriber~s ;line) - the digital tone generator comprises a line in-terrupt circuit for controlling the third switchg the digital tone generator also comprises 2 ~ourth frequency <livider whose input is connected to the output of the third frequency divider andwhose output is oonnec-t~
ed to the input of the line interrupt circuit.
- and that under the control of the detection circuit and in dependence on the activation of one of the further control elements o~ the telephone set the line interrupt circuit applies a pulse to the third switch for interrupt-ing the subscriber's line, the pulse duration of this pulse being equal to the period of the output 6ignal of the fourth frequency divider.
The invention will now be described in greater detail by ~tay of example with reference to the accom-panying Fig~1res~ corresponding components in the dif~erent Figures having been given the same reference numeralsO
Herein:
Figo 1 shows an electxonic telephone set as it is known from the prior art 9 Fig. 2 shows an electronic telephone set according to the invention comprising a digital to~e generator ~uitable for generating an apparatus ringing signal, Figu 3 shows an electronic telephone set a¢cording to the invention comprising a digital tone generator suitable for supervising the frequsncy of tha :Line ringing signal and Fig. 4 shows an electronic telephone set according to the invention comprising a digital tone generator suitable fc>r the call-back functionO
~ he prior art telephone set shown in Figo 1 com-prise~ a digital tone genera ~r 1 for generating dialling ~ 2 ~ 3 P.HN 10 814 -6- ~8~8-1984 tones ~or push-button tone dialling in accord~lc0 wi-th the DTMF-systemO This tone generator is connec1;ed to the subscriber line terminals 4 ~ia a switoh 2 and the hook contaots 3, ~he acoustic ringing signal genera~or 5 of` the telephone set is provided between the subscriber line t3rminals 4 and behind the hook contact 3 seen from the telephone set. In Fi~. 1, this acoustic ringing signal generator is constituted by a ringing capacitor and an electro-mechanical bell. A dif~erent~ also kno~m manner o~
ringing is e~fec-ted with a separate ringing signal circuit which appli.es a ringing signal to an electroacoustic transducer~ for example a loudspeaker.
In one o~ the wires o~ the subscribers line a recti~ier circuit 27 is provided between the acoustic ringing signal generator 5 and one of the hook contac~O
~his rectifier circuit renders the telephone set insensi tive to polarity changes o~ the voltage on subscriber line terminals 4.
The logic circuit 1 is ~ormed by an osci.llator 13 having a fixed oscilla-tor frequency of, for example~
400 kHz, two~requencr dividers 11 and 12 having an adjustable divisor, two digital-to-analog converters 6 and ~, an a.dder circuit 8 and a keyboard 9. The .~ixed oscillator ~requency is divided by each o~ the two ~re quency dividers 11 and 12 under the control o~ the ke~board 9 to obtain two ~requencies ~rom the DTMF-system. The two ~requencies ara added together after con~ersion by a D/A-converter and applied to the subscriber line.
I~ none o~ the push-buttons of the keyboard 9 i.s activated9 switch 2 is opened A Any speech signals are transmitted to and from a speech circui*, not shown~ via a speech transmission line 10.
Each of the two frequency dividers 11 and 12 is constituted by a series arrangement of a divider having a ~ariable divisor and a divider having a fixed d.ivisor.
When an oscillator frequency o~, ~or example~ 400~Iz is used, the fixed divider o~ frequency divider 11 ha~ a divisor o~, for example, 18 and the ~ixed divid.er o~
:~Z242~3 PHN 10 814 -7- 28~8-1984 ~requenoy clivider 12 then has a di~isor o~ ~or example~
14. By sli~htly extending the logio cirouits ~orming the said ~requency di~iders it is possible to oause the digital tone generator to perform Pun¢tions o*her than generating dialling -tonesO
Figure 2 shows an eIectronic telephone se-t which~
by slightly extending the logic circuits of the digital tone generator can be made suitable ~or detect~ng a line ringing sigrnal on the terminals 4 and generating an apparatus ringing signal in dependence thereona The telephone ~;et shown in Figure 2 is formed by the set shown in Figur0 1 to which a pluralit~ of elements haYe been added and ~rom which the con~entional rin~ing signal generator 5 ha~:been omitted.
In ~ig~re 2, the tone generator 1 compr:ises a detection circuit 14 ~or deteoting -the line ringing signal on the te:~linals 4O To that end the detection circuit 14 comprises a connecting line 18; whi:~h~ in the on-hook condition o~ the handset is connected to the terminals 4O The adj~lstable ~requency divider 11 has some additional logic switc:hiDg elements-so that two extra divisors can be realizedL by means o~ the adjustable portion o~ this ~requency dLivider~ ~or example the divisors 24 ~nd 3O~
So~ in oom~)lnation with the ~ixed portion~ havlng the 25 divisor 18, Or frequenc~ diYider 11, the divisors 432 and 54O are obtainedO
In addition,:the telephone set shown in Figo 2 com-prises an acoustic ringring signal generator 16 ~or produc ingr the acoustic ringing signal and a switch 15 ~or applying the electric ringing signal to ringing signal generator 16O Ringring signal generator 16 is ~d by ringlng supply 29 which converts the line ringing signal rectified by recti~ier clrcuit 27 into supply energy ~or the acoustic ringing signal generator 16.
A capacitor 31 used ~or smoothing the rl~cti~ied, pulsating ~oltage is provided at the input of ringing supply 29. A Zener diode 3O which together with resistor 28 constitutes the overvoltage protection in the on-hoo~
~22~ 3 condition of the handqet is arranged in parallel w-lth capacitor 31. Capaoitor 17 which together with resistor 28 forms a serie~ arrangement has for its ob~ect; to provide the customary separation of direct curre~nt and alternating current in the on-hook condition. I~ the on-hook condition of the handset tone generator 1 is also powered by ringing supply 29 in a manner not shown in the Figure.
Detection circuit 14 compares the amplitude of an aOcO voltage signal on the terminals 4 with a predeter-mined threshold value in the circuit. If the amplitude of the aOoO voltage exceeds this threshold valu~ then frequency divider 11 is alternately set to one of the two extra di~isors by means of a control signalv At the same time~ switch 15 is closed under the control of de-tection circuit 14~ causing ~he apparatus ringillg signal produced by oscillator 13 and frequency divider 11 to be applied to acoustical ringing signal generator 16.
It is possible to have the rate at which frequency divider 11 is alternately set to the two divisors be determined by the frequency of this a.c. voltage ~hich is detected as a line ringing sig~al. It is, however, alter-natively possible to give frequency divider 12 some addi-tional divisors as will be described in detail with reference to Figs. 3 and 4O Thus, ~req~encies can be ob-tained which are of the same order of magnitude as the frequency o~ the line ringing signal. Instead of` alter-natlng between both divisors at the frequency oi the line ringing signal it i9 possible to alternate between the two extra divisors of frequency divider 12 at ~ rate thus obtained.
Starting from an oscillator frequency of 4Oo~Hz and divisors of divider 11 having the value 432 (= 24 x 18) and 54O (= 3O x 18)~ ringing frequencies o~ 925 Hz and 74O Hz, respectively are obtained. Consequently~ the pitch of the ringing signal changes between these two frequen-cies with a frequency o~ change of~ ~or example~ 25 Hzo The choice of the two additional divisors with a mutual ~LZ~2~3 PHN 'I 0 8 1 1~ -9- 28-8-l984 ratio o* 4:5 has the additional advantage that a ~requenoy ratio is~obtained whioh is known as a ma~or interval whloh has the properties of producing more specifically a pleasan~ sound impression.
Fig~ 3 shows an electronic telephone set which by some changes compared with Fig~ 2 has been made suitable *or supervising the frequency of the line ringi.ng signal on the subsoriber's line. The set circuit diagram o~ Fig.
3 is obtained by adding some elements to the said circuit - lO diagram of Figo 20 The digital tone generator 1 of Fig. 3 comprises a switch 20, ~hich renders the output of frequenoy divider 11 connectable to the input frequency divider 12 this input then being also decoupled ~rom oscil.lator 13.
The adjustable frequency divider 12 is provided with some additional logic circuit elements so that two additional divisors can be real~zed with the adjustable portion 12-1 of this frequency divider9 for exarnple the divi.sors 15 and 12. The originally non-adjustable portion 12-2 o~ fre~
29 quency divider 12 has become adjustable~ by th~ addition of some logic circuit elements to an additional. divisor9 for example 3. Furthermore~ the known generator 1 is exbnded by a comparison circuit 21 for comparing the frequency o~ the line ringing signal on the subscriber line terminals with a lower and an upper frequenc~ whilst an AND-gate 2Z is added ~or the control of switch 15 .
If an aOc. voltage of a sufficiently high ampli-tude is present on terminals 4 then detection Gircuit l4 switches frequency-divider 11 to its addi~onal divisors~
as described above with re~erence to Fig, 2. Detection circuit 14 also adjusts switch 20 to the position sho~n in Fig. 3. As a result thereof the output of frequency divider 11 is connected to the input of frequency divider 12-1 via connecting line 19.
Frequency divider 12-1 is alternat~ly ad.justed to one of the two additional divisors under the control of detection circuit 147 at the same rate as frequency divider 110 The two additional divisors o~ frequency PHN 10 814 -'lO- 28-8-1984 divider 12-1 hav0 been ohosen suoh that the product o~ a,n additional divisor o~ fre~lenoy divider 12-1 and an addi-tional divi~or o~ ~requenoy divider l1 is equal to the product o~ the two other additional divisors. ~his holds ~or the divisors 15 and 24 and the divisors 12 ~nd 30.
By this cho.ice of the di~isors and by the simultaneously alter;nation o~ the divisors~ a signal having one constant ~requency~ denoted the upper limit frequency is produced at the output o~ frequency divider 12-10 ~n the said numerical e:~amples -this limit ~requency is approximately 62 ~zO
Frequency diYider 12-2 is adjusted ~ the additional divisor 3 u;nder the control of detection circui-t 14.
Thus~ a signal having a frequency which is denoted as the lower limit frequency is produced at the,output of ~re-quency divider 12~20 ~n the said numerical examples this limit frequency is approximately 21 Hzo The upper and the lower limit frequencies are ap-plied to comparison circuits 21, as is also the anc. volt-age signal incoming via terminals 4~ If the ~requency o~this a.cO voltage signal is located between the lower and upper limit ~requenoies then the comparison circuit 21 applies a signal which is characteristic o~ this frequency state to AND-gate 22. I~ at the same time the amplitude of the a~c. voltage signal exceeds the threshold value which ~as preset in deteotion circuit 147 then detection circuit 14 applies a signal characterizing this amplitude state to A~D_gate 22. In the presence of these two input signals ~n AND-gate 22 the aOcO voltage is detected as the line ring~ng signal with the proper fre-quenc~ and an adequate amplitudeO In that case AND-gate 22 applies a signal to switch 15. Under the control thereo~
this switch is closed~ ~hich causes the apparatus ringing signal produced by frequency divider 11 to be applied to acoustic ri:nging signal generator 16 It s:hould be noted that the output signal o~
comparison circuit 21 may alternati~ely be applied direct-ly to switc:h 15 with the obJect o~ closing it. In that case ~2~2~313 P~IN 10 814 1 1- 2~3~ 8-1984 no signal is applied ~rom dLetectlon circuit 14 to switch 15 . Then only the frequency o~ the a.o. voltage signal com-ing in via terminals 4 is supervised, Fig. 4 shows an electronic telephone set with which non-r~current brie~ line interruptions for signalling purposes can be adjustedO This said function is 'known as $he call back ~unction.
The said circuit diagram of Fig. 4 is re~ized by omitting switch 15 and acoustic ringing sign~ genera*or 16 from the set shown in Fig. 2 and to add some other elements to the Figure thus obtained. The elements added are an additional keyboard 23 with push-buttons ~or said functions other than the push-button ~one'diall~.L~g~ an additional ciivider 2~, a line interrupt circuit 25 and a switch 26 ~or brief interruptions o~ the subscri'ber line.
Frequency divider 12 is in the form of a series arrange-ment of an adjustable divider 12-1 having additional divisors andL a divider 12-2 having an additional divisor~
The additional divider 24 has a divisor of, ~or example~
the value 2~
The line interrupt circuit 25 is controlled by the divider 24 and by a key of the keyboard 23 9 the key commonly rsf'erred to as the call-back key. The output o~ the line interrupt circuit 25 is connected to switch 26. The conta~t of the call-back key is also co~nected to detection circuit 14.
When the call-back key is operated, the frequency dividers 11 and 12 are adjwsted to the respecti~r~ di~isors 24, 30 and 15~ lZ. It is alternatively possible ~or these ~requency dividers to he adjusted to only one additional divisor~ for example to 30 and 12~ respectively~ which is taken as ths starting point for simplicity o~' the des-cription. Now a signal having a frequency o~ apl)roximate-ly 20 Hz is available at the output o~ ~requenc~ divider 12. This signal ls so divided by ~requency divider 24 that a signal having a frequency of approximately 10 Hz is ob-tained. By operating the call-back key~ line int;arrupt-circuit 25 applies a signal to switch 26~ which signal is ~ 4~3 PHN 10 814 ~12- 28~8~1984 in the form of a pulse having a pulse duration equal to one period o~ th~output signal Or ~reque~cy dl~ider 24~
Switch 26 i9 opened during this pulse~ which cau.ses the subscriber line to be interrupted ror approximabely 001 sO
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an electronic telephone set having line terminals, number selec-tion push-buttons, digital tone generator means having an oscillator having a fixed oscillator frequency and logic circuit means connected to said oscil-lator and comprising a first frequency divider means for dividing said oscil-lator frequency by one of a plurality of divisors selectable under control of said number selection push-buttons, a plurality of further control elements, and means for externally generating a control signal, the improvement com-prising: detection means for detecting said externally generated control signal and generating in response thereto a frequency control signal; addi-tional frequency divider means; and means for interconnecting said additional frequency divider means between said first frequency divider means and a selected one of said further control elements in response to said frequency control signal.
2. An electronic telephone set as set forth in claim 1, wherein said externally generated control signal is a line ring signal having an amplitude exceeding a predetermined threshold value; wherein said electronic telephone set further has an acoustic ringing signal generator, said acoustic ringing signal generator constituting said selected one of said further control elements; and wherein said interconnecting means comprises means for connect-ing said additional frequency divider means to said acoustic ringing signal generator.
3. An electronic telephone set as set forth in claim 2, wherein said additional frequency divider means comprises means for alternately dividing said oscillator frequency at a given rate by a first or a second additional divisor.
4. An electronic telephone set as set forth in claim 3, wherein said signal on said line terminals is an AC signal having a predetermined fre-quency; and wherein said given rate corresponds to said predetermined fre-quency.
5. An electronic telephone set as set forth in claim 2, wherein said interconnecting means comprises means for creating an upper and lower limit frequency signal in response to said frequency control signal; wherein said line ring signal has a predetermined frequency; wherein said telephone set further has means for comparing said predetermined frequency to said upper and lower limit frequencies and generating a comparator output signal when said predetermined frequency is between said lower and upper limit frequen-cies; and wherein said interconnecting means couples said first frequency divider means to said acoustic ringing signal generator means under control of said comparison output signal.
6. An electronic telephone set as set forth in claim 5, wherein said electronic telephone set further has second frequency divider means having a second frequency divider input and second frequency divider output, and third frequency divider means having a third frequency divider input connected to said frequency divider output; wherein said interconnecting means further comprises a second switch for connecting said second frequency divider input to said first frequency divider means; wherein said additional frequency divider means comprises means for creating at least one additional division for said second frequency divider means thereby creating said upper limit frequency signal and a second divisor for said third frequency divider means, thereby establishing said lower limit frequency signal.
7. An electronic telephone set as set forth in claim 1, said set further having interrupter switch means for interrupting the subscriber line, and a line interrupter circuit for controlling said interrupt means, said line interrupter circuit constituting said selected one of said further control elements.
8. A digital tone generator for use in an electronic telephone set having number selection push-buttons and a plurality of further control elements, the tone generator comprising an oscillator having a fixed oscil-lator frequency, logic circuit means connected to said oscillator and compris-ing first frequency divider means and additional frequency divider means, the first frequency divider means being arranged to divide the oscillator fre-quency by one of a plurality of divisors selectable under control of the number selection push-buttons, means for connecting said additional frequency divider means between said first frequency divider means and a selected one of the further control elements in response to a frequency control signal, and detection means for detecting an externally generated control signal and generating in response thereto the frequency control signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8303701A NL8303701A (en) | 1983-10-27 | 1983-10-27 | DTMF TELEPHONE WITH MULTIPLE USE OF THE DIGITAL TONE GENERATOR LOGIC. |
| NL8303701 | 1983-10-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1224293A true CA1224293A (en) | 1987-07-14 |
Family
ID=19842625
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000466175A Expired CA1224293A (en) | 1983-10-27 | 1984-10-24 | Dtmf-telephone set with multiple use of the logic of the digital tone generator |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4571462A (en) |
| EP (1) | EP0143481B1 (en) |
| JP (1) | JPS60111558A (en) |
| CA (1) | CA1224293A (en) |
| DE (1) | DE3475862D1 (en) |
| NL (1) | NL8303701A (en) |
| SG (1) | SG50790G (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3504243A1 (en) * | 1985-02-08 | 1986-08-14 | Philips Patentverwaltung Gmbh, 2000 Hamburg | METHOD AND CIRCUIT ARRANGEMENT FOR GENERATING AN ACOUSTIC CALL SIGNAL IN SUBSCRIBER TERMINALS OF TELECOMMUNICATION SYSTEMS |
| US4669110A (en) * | 1985-10-25 | 1987-05-26 | Itt Corporation | Call progress tone system |
| US4914694A (en) * | 1988-04-11 | 1990-04-03 | Eidak Corporation | Modifying a television signal to inhibit recording/reproduction |
| JPH0226167A (en) * | 1988-07-15 | 1990-01-29 | Mitsubishi Electric Corp | Compact electronic equipment |
| US5208852A (en) * | 1988-09-27 | 1993-05-04 | Seiko Epson Corporation | Sound generation circuit |
| US4879743A (en) * | 1988-10-03 | 1989-11-07 | American Telephone And Telegraph Company | PBX and adjunct using multi-frequency tones for communication therebetween |
| JP2560660Y2 (en) * | 1991-03-29 | 1998-01-26 | 村田機械株式会社 | Wireless telephone |
| NL9200320A (en) * | 1992-02-20 | 1993-09-16 | Ericsson Radio Systems Bv | CHAIN FOR LINKING A TELEPHONE AND CALLS FROM A PERSONAL CALL SYSTEM. |
| US5459784A (en) * | 1992-09-28 | 1995-10-17 | Comsat Corporation | Dual-tone multifrequency (DTMF) signalling transparency for low-data-rate vocoders |
| US5583933A (en) * | 1994-08-05 | 1996-12-10 | Mark; Andrew R. | Method and apparatus for the secure communication of data |
| US5907597A (en) * | 1994-08-05 | 1999-05-25 | Smart Tone Authentication, Inc. | Method and system for the secure communication of data |
| US5848149A (en) * | 1995-05-26 | 1998-12-08 | Lucent Technologies Inc. | Subscriber line interface and power circuit |
| CN1404679A (en) * | 2000-12-13 | 2003-03-19 | 皇家菲利浦电子有限公司 | Electroacoustic apparatus having ringing signal generation means capable of producing a subjective bass perception |
| JP2003169128A (en) | 2001-12-03 | 2003-06-13 | Matsushita Electric Ind Co Ltd | Telephone set and private branch exchange |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4061886A (en) * | 1975-09-29 | 1977-12-06 | Mostek Corporation | Dual tone multiple frequency generator |
| GB1521127A (en) * | 1975-10-02 | 1978-08-16 | Standard Telephones Cables Ltd | Telecommunication systems |
| DE2924752C2 (en) * | 1979-06-20 | 1984-02-02 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Tone generator for generating signaling frequencies in a DTMF telephone set |
| FR2513051B1 (en) * | 1981-06-03 | 1985-06-07 | Constr Telephoniques | CIRCUIT FOR GENERATING CALIBRATED LOOP OPENINGS FOR MULTI-FREQUENCY DIALING TELEPHONE SET |
| US4503288A (en) * | 1981-08-31 | 1985-03-05 | Novation, Inc. | Intelligent telephone |
-
1983
- 1983-10-27 NL NL8303701A patent/NL8303701A/en not_active Application Discontinuation
-
1984
- 1984-10-18 EP EP84201509A patent/EP0143481B1/en not_active Expired
- 1984-10-18 DE DE8484201509T patent/DE3475862D1/en not_active Expired
- 1984-10-22 US US06/663,603 patent/US4571462A/en not_active Expired - Fee Related
- 1984-10-24 CA CA000466175A patent/CA1224293A/en not_active Expired
- 1984-10-24 JP JP59222299A patent/JPS60111558A/en active Granted
-
1990
- 1990-07-04 SG SG50790A patent/SG50790G/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60111558A (en) | 1985-06-18 |
| DE3475862D1 (en) | 1989-02-02 |
| NL8303701A (en) | 1985-05-17 |
| SG50790G (en) | 1990-08-31 |
| US4571462A (en) | 1986-02-18 |
| EP0143481B1 (en) | 1988-12-28 |
| EP0143481A1 (en) | 1985-06-05 |
| JPH0453140B2 (en) | 1992-08-25 |
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| MKEX | Expiry |