WO2008061444A1

WO2008061444A1 - A split-path linear isolation circuit apparatus

Info

Publication number: WO2008061444A1
Application number: PCT/CN2007/003266
Authority: WO
Inventors: Jun Li
Original assignee: Jun Li
Priority date: 2006-11-21
Filing date: 2007-11-19
Publication date: 2008-05-29
Also published as: CN100514071C; CN1963538A

Abstract

A split-path linear isolation circuit apparatus includes a transformer (26), a photoelectric isolation amplifier (102) and a signal combiner (105), and also includes a frequency divider of subtraction type and a time constant adjusting circuit (103). The frequency divider of subtraction type consists of a low-pass filter (100) or a high-pass filter and a subtractor (101), and an input signal is connected together with the input of the low-pass filter (100) or the high-pass filter and one input of the subtractor (101), and the output of the low-pass filter (100) or the high-pass filter is connected with the other input of the subtractor (101). The time constant adjusting circuit (103) is formed of an adjustable resistance (31) and a capacitor (32) connected, and the circuit may adjust the time constant of the photoelectric isolation circuit for compensating for the depressed amplitude-frequency response at the overlapping frequency which is caused by the delay time of the photoelectric isolation circuit longer than that of the transformer.

Description

Sub-line isolation circuit device

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electronic measuring device, and more particularly to a linear shunt (or two-way) isolating circuit having a stable and flat frequency response for electrically isolating electrical signal voltage over a wide frequency range measuring. Background technique

The isolation circuit transmits the electrical signal on the input side to the output side, but the input side and the output side are electrically isolated, or insulated, with only a small capacitance between the input side and the output side.

Isolation circuits improve common-mode rejection ratios during measurement, reduce interference, improve signal quality, isolate dangerous voltages, and protect equipment and personal safety. The isolation circuit also prevents short-circuit accidents caused by common ground between channels when measuring multiple channels simultaneously.

From the signal being processed, the isolation circuit can be divided into digital isolation circuits and linear or analog isolation circuits. The digital isolation circuit only processes high and low level signals, usually 0V and 5V signals, which are switching signals and are technically easy to implement. Linear isolation circuits, commonly referred to as isolation amplifiers, have an output signal that is linear with the input signal and can carry analog signals. Linear isolation circuits with high bandwidth (above several megahertz) are technically difficult to implement.

Since digital isolation is easy to implement, the analog input signal can be first analog-digital converted into a digital signal, then digitally isolated, and then digital-to-analog converted to obtain an analog output signal, which makes it easier to achieve stable high linearity and high. The analog signal isolation of the bandwidth. However, this technical solution has a complicated circuit and a high cost. Although both the input signal and the output signal are analog signals, this method is essentially digital isolation. The object of the invention is a broadband linear isolation circuit.

From the perspective of the medium of signal transmission, the usual methods of isolating the signal are three methods: magnetic field, electric field, and light transmission.

A typical component that transmits a signal with a magnetic field is a transformer. For the isolation of the AC signal, the transformer can be used directly. However, the transformer cannot transmit a DC signal. For a signal with a very low frequency, the excitation reactance becomes small and the transmission effect is not good. To transmit DC and low frequency signals with a transformer, the input signal must be modulated into an AC signal at the input, transmitted by a transformer, and demodulated at the output to obtain an output signal that is linear with the input signal. Typical circuits are AD215 series isolation amplifiers from Analog Devices of the United States. The isolation voltage can be up to 2500Vnn _S , the nonlinearity can reach 0.005 %, and the signal bandwidth can be up to DC-120kHz. After adding modulation and demodulation, the frequency band is not easy to be high.

A typical component that uses a electric field to transmit a signal is a capacitor. Capacitors can only transmit AC signals, and cannot transmit DC signals. For AC signals with lower frequencies, the capacitive reactance becomes large and is not conducive to transmission. To transmit DC and low frequency signals with a capacitor, the input signal must be modulated into an AC signal at the input, which is transmitted by a capacitor and demodulated at the output to obtain an output signal that is linear with the input signal. For good isolation, the capacitance should be low, usually below the number of picofarads. Typical circuits are the IS0124 series from Burr-Brown (now Incorporated to Texas Instruments, USA). The isolation voltage can be up to 1500Vrms, the nonlinearity is 0.01%, and the signal bandwidth can be up to DC-50kHz. After adding modulation and demodulation, the frequency band is not easy to be high.

A typical component for transmitting electrical signals with light is a photocoupler (referred to as an optocoupler). Unlike the above two methods, the optocoupler can directly transmit DC and low frequency signals without being modulated into an AC signal. Early optocouplers were designed primarily for isolated digital signals. To isolate analog signals, peripheral circuits such as op amps were required to operate the LEDs and photocells in the optocoupler in a linear state. This isolation circuit is structurally Divided into non-feedback type and feedback type. The non-feedback type usually consists of two op amps plus an optocoupler with poor linearity. The feedback type is usually composed of two operational amplifiers plus two optocouplers, one of which is used as feedback compensation, and the linearity is improved. Later, a linear optocoupler dedicated to linear isolation was introduced. The structure was to integrate one LED and two photodiodes in one package. One photodiode was used for feedback compensation and the other photodiode was used to transmit signals to the output. side. Typical linear optocouplers are the LOC110 series from CLARE, USA, and the IL300 series from VISHAY, USA. These two optocouplers have a nonlinearity of 0.01% and a bandwidth of DC-200kHz. The Agilent HCNR200/201 linear optocoupler in the United States expands the bandwidth to DC-lMHz.

There is also a literature on the linear isolation circuit of the DC-4MHZ bandwidth.

As can be seen from the above description, off-the-shelf single mode linear isolation circuits can operate in the DC to several MHz band. For higher bandwidth (such as DC to tens of megahertz or hundreds of megahertz) signals, the above circuit cannot achieve linear isolation transfer.

Note that the above circuit can achieve linear isolation of signals from DC to hundreds of kilohertz, and can be directly realized from low frequency (several kilohertz) to high frequency (tens of megahertz or hundreds of megahertz) with a transformer or capacitor. Linear isolation of the AC signal, if combined, can achieve linear isolation from DC to hundreds of megahertz bandwidth. This is called a shunt (or two-way) linear isolation circuit. It consists of a DC to low frequency channel (referred to as low path) and a low frequency to high frequency channel (referred to as high path).

Since the circuit of the modulation and demodulation method is complicated and has a large delay, the low path generally uses linear photoelectric isolation. High-speed transformers are easier to implement than capacitors.

In order to achieve the separation of the route, the input signal must first be decomposed into two parts: the low path and the high path. Then, the optical isolation channel and the transformer channel are respectively isolated, and finally the signals of the two channels are added to obtain the input signal. The output signal in a linear relationship. There are two difficulties in this approach.

The first difficulty is to break the signal into two parts, the low road and the high road. Traditionally, a crossover composed of a low pass filter and a high pass filter is used to decompose the input signal into low and high paths. However, after adding the output signals of the two filters, the input signal cannot be restored as it is. In the vicinity of the overlapping frequency of the high-low-pass filter, there are bumps or pits in the amplitude-frequency response, and the phase-frequency response of the whole circuit is not linear. Therefore, the output signal has a poor square wave response and cannot be used for wideband signal measurement. To this end, complex compensation and regulation circuits need to be added to improve the system's amplitude-frequency response and phase-frequency response. This results in a high cost, complicated debugging, and poor stability of the broadband isolation circuit. Typical products are the A6902B, an early product from Tektronix, USA.

The second difficulty is that the delays of the low and high isolation channels are inconsistent. The high channel is isolated by the transformer to process the low frequency to high frequency signals with low delay. The low channel is optically isolated to process the signal from DC to low frequency with long delay. Even if the first difficulty does not exist, the delay between the low and high paths will still cause the synthesized output signal to not restore the input signal. The phenomenon is that the top of the square wave responds to the top of the front edge. To this end, a delay circuit needs to be added to the high path, as described in the paper "Electrical Measurement and Instrumentation", No. 6, 2004, "Design of Dual-Channel Wideband Isolation Amplifier". The delay circuit also increases the circuit cost and stability, and has side effects such as uneven amplitude frequency response and nonlinear phase response.

In order to overcome the above difficulties, Chinese patent ZL 96101007.X proposes a broadband double-track isolation circuit that uses the output signal of the photoelectric isolation circuit to zero-flux the transformer in the DC to low frequency range. However, the transformer in this method is more complicated, and when the low-channel and high-path signal amplitudes are not well matched, DC magnetic flux may appear in the transformer core, which may cause the core to be saturated or magnetized, and further, its photoelectric isolation circuit Common mode rejection at high frequencies is relatively low. Disclosure of invention

In view of the above problems, the present invention provides a simple split-line isolation circuit device, which can eliminate complicated frequency compensation adjustment and delay compensation adjustment, has wide signal measurement bandwidth, low total cost, and high reliability. Accurate and reliable response over a wide range of signal measurement frequencies; this simplified, split-line isolation circuit arrangement maintains stable frequency and impulse response with simple frequency response compensation adjustments The high path is added to the delay circuit, and there is no need to zero-transform the transformer in the DC to low frequency band. This kind of distributed isolation circuit device has only a small amplitude response drift over a wide temperature range.

The above technical problem of the present invention is mainly solved by the following technical solutions: A shunt isolation circuit device comprising a transformer circuit, an opto-isolation circuit and a signal combination circuit, characterized in that it further comprises the following circuits:

(1) a subtraction type divider circuit that decomposes the broadband input signal voltage into a DC to low frequency portion and a low frequency to a high frequency portion;

(2) A time constant adjustment circuit is to adjust the time constant of the photoelectric isolation circuit so that the high frequency response of the photoelectric isolation circuit is appropriately raised relative to the low frequency to compensate for the low path caused by the long delay time of the photoelectric isolation circuit than the transformer. The amplitude-frequency response at the intersection of the high roads is not flat;

The high-channel signal outputted by the subtraction type divider circuit is connected to the transformer circuit, and the transformer circuit is connected to the signal combination circuit;

The low path signal outputted by the subtraction type divider circuit is coupled to the opto-isolation circuit, and the opto-isolation circuit is coupled to the time constant adjustment circuit.

After the input signal is decomposed into a high path and a low path by the subtraction type frequency divider, if the two signals are directly added together, the input signal can be restored as it is. The sum of the output signals of the subtracted divider and the input signal has a flat amplitude response, a linear phase response, and an accurate impulse response. One of the low pass filters (or The above characteristics remain when the parameters of the high-pass filter are in error or the parameters drift with temperature. This frequency divider requires no adjustment and has stable performance. After the high and low signal are respectively separated by transformer and optoelectronic isolation, if the transformer and the opto-isolated circuit have sufficient linearity and overcome the delay time difference between the transformer and the opto-isolated circuit, the sum of the isolated signals still has the above characteristics. . In addition to the need to adjust the amplitude of the isolated high and low signal to match, no additional adjustments are required, and no transformer flux zeroing circuit is required. The first difficulty described above is overcome by the subtractive divider described.

By reasonably setting or adjusting the time constant of the RC circuit in the opto-isolated circuit, the high-frequency response of the opto-isolated circuit can be appropriately increased relative to the low frequency, and the low-path and the delay time of the opto-isolated circuit longer than the transformer can be compensated. The amplitude and frequency response of the sum signal of the high path is not flat. This method eliminates the need for adding a delay circuit to the high path, eliminating the need for complicated adjustments and providing stable performance. Through this method, the second difficulty described above is overcome.

The function of the time constant adjustment circuit can set the time constant of the opto-isolated circuit by adjusting the product of the capacitance and resistance in the opto-isolated circuit or the product of the capacitance and resistance in the time constant adjustment circuit. Therefore, the high-frequency response of the photoelectric isolation circuit is appropriately raised relative to the low frequency, and the amplitude-frequency response of the low-channel and high-circuit overlapping frequencies caused by the compensation of the optical isolation circuit is longer than that of the transformer circuit, and the optical isolation circuit is When a flat-topped square wave with a frequency of ΙΟΟΚΗζ is input, the leading edge of the output waveform has an overshoot.

Advantageously, said subtractive divider circuit is comprised of a low pass filter and a subtractor, said wideband input signal voltage being simultaneously coupled to an input of the low pass filter and an input of the subtractor, and low The output of the pass filter is connected to the other input of the subtractor. The subtraction type divider is composed of a low pass filter and a subtractor, and the input signal is simultaneously connected to the input of the low pass filter and an input of the subtractor, and the output of the low pass filter and the subtractor The other input is connected. The output of the low-pass filter is a signal from DC to low frequency, that is, a low-channel signal. In the output signal of the subtractor, the signal from DC to low frequency band has been subtracted, leaving the low-frequency to high-band signal, so that High road signal.

Advantageously, said subtractive frequency divider comprises a high pass filter and a subtractor, said wideband input signal voltage being simultaneously coupled to an input of the high pass filter and an input of the subtractor, and the high pass filter The output is connected to the other input of the subtractor. The subtraction type frequency divider may also be composed of a high pass filter and a subtractor, and the input signal is simultaneously connected to the input end of the high pass filter and an input end of the subtractor, and the output end of the high pass filter and the subtractor The other input is connected. The output of the high-pass filter is the signal from the low frequency to the high frequency band, that is, the high-channel signal. In the output signal of the subtractor, the signal from the low-frequency to high-frequency band has been subtracted, leaving the DC to the low-band signal, thus obtaining the low path. signal.

Preferably, the low pass filter employs a Sallen-Key circuit topology, and the approximation algorithm is a fourth order Bessel approximation with a -3 dB cutoff frequency between 30 kHz and 200 kHz.

Preferably, after the input signal passes through the low pass filter, DC and low frequency components are obtained at the output of the low pass filter, and the input signal and the low path signal are sent to the subtractor for subtraction, and at the output of the subtractor, The complete input signal is subtracted from its DC and low frequency components, leaving only the low to high frequency components.

Preferably, the time constant adjustment circuit is formed by connecting an adjustable resistor and a capacitor, and the circuit is to adjust a time constant of the photoelectric isolation circuit, so that two sets of resistances in the photoelectric isolation circuit are multiplied by a capacitance and a time constant adjustment circuit. The resistance of the multiplied by the capacitance, the resistance multiplied by the capacitance of the three product values of the sum of about 220

Preferably, the photoelectric isolation circuit has two groups, and a single-ended to double-ended conversion circuit is provided between the subtractive frequency dividing circuit and the photoelectric isolation circuit, and the single-ended to double-ended conversion The output of the circuit is a pair of differential signals of opposite polarities, and the pair of differential signals respectively serve as input ends of two sets of photoelectric isolation circuits; the output ends of the two sets of photoelectric isolation circuits are connected at the input end of the differential amplifier, The output of the differential amplifier is connected to a time constant adjustment circuit; the subtraction circuit and the change A single-ended to double-ended conversion circuit is provided between the voltage regulator circuits. The drive circuit and the drive and receive are changed to differential drive and differential receive. The opto-isolated circuit adds a completely identical set of circuits. It also uses differential drive and differential receive to increase the common mode rejection ratio, especially at high frequencies. Common mode rejection ratio.

Preferably, the transformer is a transmission line transformer.

After the input signal is decomposed into a high path and a low path by the subtraction type frequency divider, if the two signals are directly added together, the input signal can be restored as it is. The sum of the output signals of the subtracted divider and the input signal has a flat amplitude response, a linear phase response, and an accurate impulse response. This frequency divider requires no adjustment and has stable performance.

By reasonably setting or adjusting the time constant of the RC circuit in the opto-isolated circuit, the high-frequency response of the opto-isolated circuit can be appropriately increased relative to the low frequency, and the low-path and the delay time of the opto-isolated circuit longer than the transformer can be compensated. The amplitude and frequency response of the sum signal of the high path is not flat. This method eliminates the need for adding a delay circuit to the high path, eliminating the need for complicated adjustments and providing stable performance.

The transformer circuit and the opto-isolated circuit use differential drive and differential reception to increase the common mode rejection ratio, especially at high frequencies.

DRAWINGS

Figure 1 is a circuit diagram of the present invention showing a preferred shunt isolation amplifier;

Figure 2 is a plot of the amplitude-frequency response of the sum of the low, high, and the sum of the subtracted divider of Figure 1. Figure 3 is the square wave response of the low and high of the subtracted divider of Figure 1. Waveform

Figure 4 is a waveform of the input end and the output end of the signal combining circuit of Figure 1;

Figure 5 is a step response waveform of the circuit of Figure 1;

Figure 6 is a 100 kHz square wave response waveform of the photoelectric isolation circuit of Figure 1;

7A, 7B and 7C are diagrams showing the resistance of the time constant adjustment circuit of Fig. 1 at different values, Fig. 1 10 kHz square wave response waveform of the circuit;

Figure 8 is a circuit diagram of another embodiment of the present invention showing a differential mode shunt isolation amplifier. Best way to implement the invention

The technical solutions of the present invention will be further specifically described below by way of embodiments and with reference to the accompanying drawings. Example 1

As shown in Figure 1, each component in the figure is connected by electronic components in the dotted line. The device of the present invention is a split-path isolation circuit device 200 (hereinafter referred to as device 200). The low-pass filter 100 (hereinafter referred to as filter 100), the subtractor 101, the transformer 26, and the linear optical isolation circuit 102 (hereinafter referred to as optocoupler) The circuit 102), the time constant adjustment circuit 103 (hereinafter referred to as the circuit 103), the low path gain adjustment circuit 104 (hereinafter referred to as the circuit 104), and the signal combination circuit 105 (hereinafter referred to as the combiner 105) are composed. The signal under test 70 is coupled to the input 71 of the device 200. Input 71 of device 200 is coupled to input 72 of filter 100 and positive input 74 of subtractor 101. The output 73 of the filter 100 is connected to both the negative input 75 of the subtractor 101 and to the input 77 of the optocoupler circuit 102. The output 78 of the optocoupler circuit 102 is coupled to the circuit 103. The output 82 of the circuit 103 is coupled to the input of the circuit 104, and the output 83 of the circuit 104 is coupled to the negative input 79 of the combiner 105. The output of combiner 105 is also the output 81 of device 200. The output 76 of the subtractor 101 is connected to the primary of the transformer 26, and the secondary of the transformer 26 is connected to the positive input 80 of the combiner 105. The terminal of the output terminal 76 of the transformer 26 primary connection subtractor 101 is the same name as the terminal of the positive input terminal 105 of the secondary connection combiner 105.

In FIG. 1, insulating isolation layer 204 separates device 200 into input side 202 and output side 203. The input side 202 and the output side 203 are insulated, and there is only a small value between the two. On the input side The grounding point 65 has a grounding point 66 on the output side. The grounding voltage 65 and the grounding point 66 are insulated, and there is only a small value between the two. The circuitry on input side 202 and the circuitry on output side 203 should be powered by isolated power supplies. The insulating isolation layer 204 may be formed of an air gap, a vacuum layer, or some other form of electrical insulator. In this embodiment, the insulating spacer 204 is composed of insulation between the windings of the transformer 26, insulation of the optocoupler circuit 102, and an insulating layer between the input side and the output side power supply.

The transformer 26, the optocoupler circuit 102, the transformer in the power supply, and other parasitic capacitances together cause a total capacitance of about 50 picofarads across the isolation layer 204, which is sufficient to minimize external ground current.

In the filter 100, the input terminal 72 is connected to the resistor 11, the resistor 11 is connected to the resistor 12 and the capacitor 15, and the resistor 12 is connected to the capacitor 16 and the positive input terminal of the operational amplifier 19. The capacitor 15 is connected to the output terminal of the operational amplifier 19, and the capacitor is connected. 16 is in turn connected to ground point 65. The negative input of operational amplifier 19 is connected to its output. The output of the operational amplifier 19 is connected to the resistor 13, the resistor 13 is connected to the resistor 14 and the capacitor 17, and the resistor 14 is connected to the capacitor 18 and the positive input terminal of the operational amplifier 20. The capacitor 17 is connected to the output of the operational amplifier 20, and the capacitor 18 is connected. Connected to ground point 65. The negative input of operational amplifier 20 is connected to its output. The output of operational amplifier 20 is also the output 73 of filter 100. The low pass filter 100 preferably uses a Sallen-Key circuit topology, and the approximation algorithm is preferably a fourth order Bessd approximation with a -3 dB cutoff frequency preferably at 30 kHz. Other types of low-pass filters, such as MFB topologies, Butterworth approximations, cutoff frequencies for other values, such as values between 30kHz and 200kHz, are also acceptable. The op amps 19 and 20 are best selected from Analog Devices' AD8039.

In the subtractor 101, the positive input terminal 74 is connected to the resistor 1, the negative input terminal 75 is connected to the resistor 3, and the resistor 1 is connected to the resistor 2 and the positive input terminal of the operational amplifier 5, and the resistor 3 is connected to the resistor 4 and the operational amplifier. The negative input terminal of 5 is connected, the other end of the resistor 2 is connected to the grounding point 65, and the resistor 4 is operated again. The output of amplifier 5 is connected, and the output of operational amplifier 5 is also the output 76 of subtractor 101. The subtractor 101 is actually a differential amplifier having a magnification of 1:1, which is used here as a subtractor. The operational amplifier 5 is preferably AD8055 from Analog Devices.

After the input signal 70 passes through the low pass filter 100, the DC and low frequency components, i.e., the low pass signal, are obtained at the output 73 of the low pass filter 100. The input signal 70 and the low path signal are again sent to the subtractor 101 for subtraction. In the signal at the output 76 of the subtractor 101, the complete input signal 70 is subtracted from its DC and low frequency components, leaving only the low frequency. To the high frequency component, this is the high road signal. This splits the input signal 70 into two parts, a low signal and a high signal. When the circuit delay is short enough, if the signal at the output 76 of the low pass filter 100 is added to the signal at the output 76 of the subtractor 101, the input signal 70 can be recovered without distortion. That is, the low-channel and high-path signals obtained by the subtraction type frequency divider, the sum of the two can restore the input signal 70 as it is, or the subtraction type frequency divider, the sum of the low-channel and high-path signals and the input signal There is a flat amplitude response and linear phase response between 70, and an accurate impulse response. This feature is basically independent of ambient temperature and component parameter errors.

In FIG. 2, curve 150 is the amplitude-frequency response of low-pass filter 100, that is, the low-path signal amplitude-frequency response; curve 151 is the amplitude-frequency response of the signal of output 76 of subtractor 101 with respect to input signal 70, that is, The high path signal amplitude response; and curve 152 is the amplitude frequency response of the sum of the low and high path signals relative to the input signal 70. Curve 150 has the fastest roll-off of -24dB/octave, while curve 151 has the fastest roll-off of -6dB/octave. The high-frequency signal amplitude-frequency response curve obtained by the subtraction has a convexity at the overlapping frequency. When the low-pass filter 100 is a fourth-order Bessd filter with a -3dB cutoff frequency of 30 kHz, the peak of the protrusion appears at 35 kHz, and its value It is 1.52 times the input signal. Nevertheless, since the sum of the low signal and the high signal is vector added, the sum signal curve 152 is still close to a straight line.

In FIG. 3, the waveform 153 is the waveform of the input signal 70, which is a 10 kHz square wave, and the waveform 154 is The waveform of the output 73 of the filter 100, the waveform 155 is the waveform of the output 76 of the subtractor 101. This figure visually shows how the subtracted divider divides a square wave pulse into two parts, low and high.

In the optocoupler circuit 102, on the input side, the input terminal 77 is connected to the positive input terminal of the operational amplifier 21, and the negative input terminal of the operational amplifier 21 is connected to the resistor 22, the capacitor 24, and the photodiode 62 in the photocoupler 25. The output of the amplifier 21 is connected to a resistor 23 and a capacitor 24. The resistor 23 is in turn connected to a light-emitting diode 64 in the photocoupler 25. The resistor 22 is in turn connected to a bias voltage -Vref1. On the output side, the negative input terminal of the operational amplifier 28 is connected to the resistor 29, the capacitor 30 and the photodiode 63 in the photocoupler 25. The positive input terminal is connected to the bias voltage +Vref2, and the output terminal thereof is connected to the resistor 29 and the capacitor 30. The output of operational amplifier 28 is also the output 78 of optocoupler circuit 102.

The photocoupler 25 is a linear isolation dedicated optocoupler that is internally packaged with a light emitting diode 64 and two matched photodiodes 62 and 63, a photodiode 62 for feedback, and a photodiode 63 for isolating the coupled signal. Agilent's HCNR201 is preferred for this optocoupler. The bias voltage -Vrefl enables the optocoupler circuit 102 to transmit a bipolar signal. If the optocoupler selects HCNR201 and the resistor 22 takes 15kQ, -Vrefl can take -0.4V, and -Vrefl can be generated by the voltage reference circuit. After -Vrefl is determined, +Vref2 is adjusted so that when the voltage at the input terminal 77 is 0, the voltage at the output terminal 78 is also 0, and +Vref2 is generated by the voltage reference circuit adjusting the voltage. The operational amplifiers 21 and 28 are preferably AD8038 from Analog Devices. The resistor 23 is 150 Ω. The selection of the resistor 22 is determined by the signal amplitude of the input terminal 77 and the maximum photocurrent of the photodiode 62. The recommended value is 15 kΩ. The recommended value for capacitor 24 at this time is 4.7 pF. The value of resistor 29 is equal to the value of resistor 22 multiplied by the desired gain of aperture circuit 102, where the gain of optocoupler circuit 102 is taken as 0.5, so the value of resistor 29 is 7.5 kQ. Capacitor 30 can take 10 pF. Under the above component parameters, in the amplitude-frequency response of the optocoupler circuit 102, the high frequency is boosted relative to the low frequency. In the circuit 104, the negative input terminal of the operational amplifier 35 is connected to the resistor 33 and the adjustable resistor 34, and the adjustable resistor 34 is connected to the output terminal of the operational amplifier 35. Its gain is about 2 times. This part of the circuit is used to adjust the amplitude of the low signal to match the high signal. The operational amplifier 35 is preferably AD8038 from Analog Devices.

The transformer 26 is a wideband transformer whose operating frequency is such that it can effectively pass all the high-channel signals. The curve 151 of Fig. 2 shows that the minimum operating frequency needs to extend below 1 kHz, and the highest operating frequency needs to be in the entire sub-route isolation circuit device. 200 above the expected maximum operating frequency. Also, the insulation withstand voltage between the primary and secondary of the transformer should satisfy the desired insulation withstand voltage requirements of the entire distributed isolation circuit device 200. The capacitance between the primary and secondary should be as small as possible to reduce the AC leakage current between the input side 202 and the output side 203 of the device 200. In this embodiment, the transformer 26 employs a transmission line transformer to achieve a better frequency response. Other forms of transformers are also available. The transformer core is preferably an A10-T12 X6X4C toroidal core from ACME Electronics of China. The wire is preferably a three-layer insulated wire of TEX-E 0. 2mm from the Furukawa Electric Industrial Co., Ltd. of Japan. Use this wire to make a twisted pair of about 1 twisted per centimeter, and evenly wind 22 turns on the core, and lead four lead wires. The primary and secondary can pass the 9kV-minute withstand voltage test. Its operating frequency can be above 100MHz. The capacitance between the primary and secondary is approximately 25pF. The resistor 27 is used as a terminating resistor, and when the above transformer is used, its value is 136 Ω.

In the combiner 105, the positive input terminal 80 is connected to the resistor 6, the negative input terminal 79 is connected to the resistor 8, and the resistor 6 is connected to the resistor 7 and the positive input terminal of the operational amplifier 10. The resistor 8 is connected to the resistor 9 and the operational amplifier. The negative input terminal of 10 is connected, the other end of the resistor 7 is connected to the grounding point 66, and the resistor 9 is connected to the output terminal of the operational amplifier 10, and the output terminal of the operational amplifier 10 is also the output terminal 81 of the device 200. The combiner 105 is actually a differential amplifier with a magnification of 1:1, which is used to complete the low The sum of the road signal and the high road signal. The signal at the output 78 of the optical circuit 102 is inverted from the signal at the input 77, so that the signal at the output 83 of the circuit 104 and the signal at the input 77 of the optocoupler circuit 102 are also inverted, connecting it to At the negative input of the combiner 105, the addition of the low signal and the high signal is achieved. The operational amplifier 10 is preferably an AD8055 from Analog Devices.

The gain of the adjustment circuit 104 changes the amplitude of the low path signal to match the high path signal, and the adjustment circuit 103 boosts the low frequency signal high frequency response appropriately at the output of the combiner 105, that is, the output of the device 200. Terminal 81 obtains a signal that is in a strictly linear relationship with input signal 70. The waveforms at various points of the combiner 105 are shown in FIG. Waveform 156 is the waveform that inverts the signal at the negative input 79 of combiner 105, waveform 157 is the waveform at the positive input 80 of combiner 105, and waveform 158 is the waveform output from the combiner, which is also the output waveform of device 200. The visible output waveform 158 faithfully restores the input waveform 153 as compared to the input waveform 153 of FIG. A good square wave response illustrates the device 200 having a flat amplitude response, a linear phase response, and an accurate impulse response. The waveform in Figure 5 is a square wave rising edge waveform measured at the output 81 of the device 200 with a rise time of the input signal 70 itself of about 1.5 ns. The rise time of this waveform is about 3.5 ns, which illustrates Device 200 has a -3 dB bandwidth in excess of 100 MHz.

Obviously, the gain of the low signal can also be fixed, and the gain adjustment circuit can be added to the high path to match the low signal by adjusting the gain of the high signal.

The circuit 103 is formed by connecting an adjustable resistor 31 and a capacitor 32. The purpose of adding the circuit 103 is to adjust the time constant of the photoelectric isolation circuit, multiplying the resistance 22 by the sum of the capacitance products 24, the resistance 29 multiplied by the capacitance 30, the resistance 31 multiplied by the capacitance 32 (referred to as the photoelectric isolation circuit time) The constant) is about 220 kQ-pF, and the ultimate goal is to make the high-frequency response of the opto-isolated circuit be properly raised relative to the low-frequency, to compensate for the low- and high-path intersection caused by the long delay time of the opto-isolated circuit. Stacking frequency The amplitude frequency response at the location is concave. The result of the adjustment is such that the opto-isolated circuit has a square wave response as in the shape of Figure 6. The waveform of FIG. 6 is a waveform obtained at the output 82 of the circuit 103 after inputting a flat-top square wave having a frequency of 100 kHz and an amplitude of 360 mV at the input terminal 77 of the optocoupler circuit 102, and the square wave front has an overshoot. It is the result of the high frequency being raised relative to the low frequency. In this way, it is possible to compensate for the amplitude-frequency response sag at the overlapping frequency due to the sum of the final high- and low-path signals due to the delay time of the opto-isolated circuit. 7A, 7B and 7C show the square wave response of the apparatus 200 when the input signal 70 is a flat top square wave having a frequency of 10 kHz, the resistance 31 is adjusted, and the time constant of the optical isolation circuit is changed. When the resistance 31 is small, the time constant of the photoelectric isolation circuit is small, and the high frequency is increased too much, the output waveform is as shown in FIG. 7A, and the square wave is convex at the top; when the resistance 31 is large, the time constant of the photoelectric isolation circuit is large and high. When the frequency boost is insufficient, the output waveform is as shown in Fig. 7B, and the top of the square wave is concave; and when the resistor 31 is suitable, the time constant of the photoelectric isolation circuit is appropriate, and when the high frequency is suitable, the output waveform is as shown in Fig. 7C, and the square wave is flat at the top. .

In this way, the delay time of the opto-isolated circuit is more effectively overcome than the low-channel and high-path and the signal frequency response unevenness caused by the length of the transformer channel, eliminating complicated compensation circuits and cumbersome adjustment, and eliminating A delay circuit is added to the transformer channel to obtain a good frequency response.

After the other circuit component parameters are determined, the optimal time constant of the required opto-isolated circuit is also determined, so the value of the resistor 31 is also determined. In actual production, it is only necessary to adjust the optimum value of the resistor 31 on the first sample. Subsequent products can directly replace the resistor 31 with a fixed resistor similar to this optimum value, eliminating the need to adjust the time constant of each product, resulting in improved production efficiency.

Circuitry 103 can also be provided at input 77 of the opto-isolated circuit.

The adjustment of the low path signal gain and the adjustment of the time constant of the opto-isolated circuit can also be realized by the regulating resistor 22, the resistor 29, the capacitor 24 and the capacitor 30. For example, by adjusting the resistor 22, the resistor 29 The value of the low-channel signal is adjusted to match the high-path signal, and the values of the capacitor 24 and the capacitor 30 are adjusted so that the time constant of the photoelectric isolation circuit is appropriate to obtain a square wave response as shown in FIG. 7C. Thus, circuit 103 and circuit 104 can be omitted. The disadvantage of this method is that the time constant of the opto-isolated circuit also changes when the gain is adjusted. Another method is to set the gain adjustment circuit to the high path, adjust the resistor 22, the resistor 29, the capacitor 24 and the capacitor 30 to achieve a suitable time constant of the photoelectric isolation circuit, and then adjust the amplitude of the high signal to match the low path. .

Example 2:

Figure 8 shows an embodiment of the differential form. In Fig. 8, the low pass filter 100, the subtractor 101, the transformer 26, the optocoupler circuit 102, the time constant adjustment circuit 103, the low path gain adjustment circuit 104, and the signal combination circuit 105 are the same as the embodiment shown in Fig. 1. I will not repeat them here. The difference is that the drive and reception of the transformer are changed to differential drive and differential reception. The opto-isolated circuit adds a completely identical circuit to the optocoupler circuit 102, that is, the optocoupler circuit 108, which also uses differential drive and differential reception. This increases the common mode rejection ratio, especially the common mode rejection ratio at high frequencies.

The low path signal of the output terminal 73 of the low pass filter 100 is sent to the subtractor 101, and is also sent to the single-ended to double-ended conversion circuit 106 to convert the signal into a pair of differential signals of equal magnitude and opposite polarity, and then, The positive polarity signal is sent to the optocoupler circuit 102, and the negative polarity signal is sent to the optocoupler circuit 108. At the output of the optocoupler circuit, differential amplifier 110 converts the pair of equal-sized, opposite-polarity differential signals into a single-ended signal and then to circuit 103.

The high path signal of the output terminal 76 of the subtractor 101 is first sent to the single-ended to double-ended conversion circuit 107, and the signal is converted into a pair of differential signals of equal magnitude and opposite polarity, and then respectively connected to the two primary poles of the transformer 26. Terminal. The secondary two terminals of the transformer are respectively connected to the two input terminals of the differential amplifier 109, and the differential signal outputted by the transformer is converted into a single-ended signal, and then sent to the positive of the signal combiner 105. Input.

The output of optocoupler circuits 102 and 108 no longer requires a DC bias circuit. The DC offset voltages at the outputs of optocoupler circuits 102 and 108 are canceled out in differential amplifier 110. The output of differential amplifier 110 has no large DC offset voltage, only a small DC offset due to asymmetry in circuit parameters. You can fix this DC offset by first fixing -Vrefl and then fine-tuning -Vref2. The differential form of the opto-isolated circuit reduces the DC offset and temperature drift while increasing the common-mode rejection ratio.

In the single-ended to double-ended conversion circuit 106, the output 73 of the filter 100 is connected to the positive input terminal of the operational amplifier 40 and the resistor 43. The negative input terminal of the operational amplifier 40 is connected to its output terminal, and the resistor 43 is connected to the operational amplifier 41. The negative input terminal is connected to the resistor 42, and the resistor 42 is connected to the output terminal of the operational amplifier 41. The positive input terminal of the operational amplifier 41 is connected to the ground point 65. The output of operational amplifier 40 is coupled to input 77 of optocoupler circuit 102; the output of operational amplifier 41 is coupled to input terminal 84 of aperture circuit 108. The op amps 40 and 41 are preferably AD8039 from Analog Devices.

The internal circuit of the single-ended to double-ended conversion circuit 107 is identical to the single-ended to double-ended conversion circuit 106. The output 76 of the subtractor 101 is coupled to the positive input of the operational amplifier 36 and to the resistor 39. The output of the operational amplifier 36 is connected to one terminal of the primary of the transformer 26, and the output of the operational amplifier 37 is connected to the other terminal of the primary of the transformer 26.

The internal circuits of the differential amplifiers 109 and 110 and the subtractor 101 and the combiner 105 may be the same.

The terminal of the positive input of the transformer 26 secondary differential amplifier 109 is the same name as the terminal of the output of the primary operational amplifier 36.

In the optocoupler circuit 108, the resistor 46 can be adjustable. Adjusting the value of the resistor 46 allows the optocoupler circuit 108 to be matched with the optocoupler circuit 102 to increase the common mode rejection ratio of the entire circuit. Obviously, you can The resistor 23 is adjusted to match the optocoupler circuit 102 with the optocoupler circuit 108 to increase the common mode rejection ratio of the entire circuit.

It will be apparent to those skilled in the art that certain aspects of the invention may be practiced in other embodiments.

The preferred embodiment above lists some preferred component types and values, but it will be apparent that some amplifiers, transformers, optocouplers, and components of various types and values may be modified, added, or removed to accommodate a variety of specific applications. need.

Also, the invention described above is implemented in discrete components, however, some of the amplifiers, components, and subsystems may be fabricated as components of an integrated circuit, hybrid circuits, or multi-chip modules.

Additionally, although the preferred embodiment describes manually adjusting the associated components to match low path gain to high path, optocoupler channel time constants, and two optocoupler circuits, manual or automatic, analog or digital. Parameter adjustments can also be used on any of the active circuit components of the present invention.

The specific embodiments described herein are merely illustrative of the concepts of the invention. The invention can also be used in relation to signal isolation, not just electrical signal measuring equipment. A person skilled in the art can make various modifications or additions to the specific embodiments described or replace them in a similar manner, without departing from the spirit of the invention or beyond the appended claims. The scope of the definition.

Claims

Rights request

1. A shunt isolation circuit device comprising a transformer circuit, an opto-isolated circuit and a signal combining circuit, characterized in that it further comprises the following circuit.

(2) A time constant adjustment circuit (103) is to adjust the time constant of the photoelectric isolation circuit, so that the high frequency response of the photoelectric isolation circuit is appropriately raised relative to the low frequency to compensate for the longer delay time of the optical isolation circuit than the transformer. The amplitude-frequency response at the intersection of the low and high roads is not flat;

2. The shunt isolation circuit device according to claim 1, wherein: said subtractive frequency divider circuit comprises a low pass filter (100) and a subtractor (101), said wideband input signal The voltage is simultaneously connected to the input of the low pass filter and to the input of the subtractor, and the output of the low pass filter is connected to the other input of the subtractor.

3. The shunt isolation circuit device according to claim 1, wherein: said subtractive frequency divider comprises a high pass filter and a subtractor, said wideband input signal voltage being simultaneously connected to a high pass filter The input is connected to one input of the subtractor, and the output of the high pass filter is connected to the other input of the subtractor.

4. The shunt isolation circuit device according to claim 2, wherein: said low pass filter adopts a Sallen-Key circuit topology, and the approximation algorithm is a fourth-order Bezier approximation, and the -3dB cutoff frequency is from 30 kHz to 200 kHz. between.

5. A shunt isolation circuit device according to claim 1 or 2 or 4, characterized in that the input signal (70) passes through the low pass filter (100) and is at the output of the low pass filter (100) (73) The DC and low frequency components are obtained, and the input signal (70) and the low signal are sent to the subtractor (101) for subtraction. In the signal at the output (76) of the subtractor (101), the complete input signal (70) is subtracted from its DC and low frequency components, leaving only the low to high frequency components.

6. The shunt isolation circuit device according to claim 1, wherein said time constant adjustment circuit (103) is formed by connecting an adjustable resistor (31) and a capacitor (32), the circuit is Adjust the time constant of the opto-isolated circuit, multiplying the resistance (22) by the capacitance (24), the resistance (29) multiplied by the capacitance (30), and the resistance (31) multiplied by the capacitance (32). The sum of the three product values is about 220 kQ. * pF.

7. The shunt isolation circuit device according to claim 1, wherein: said photoelectric isolation circuit has two groups, and said single subtraction type frequency dividing circuit and said photoelectric isolation circuit are provided with a single The end-to-double-ended conversion circuit (106), the output of the single-ended to double-ended conversion circuit is a pair of differential signals of opposite polarities, and the pair of differential signals respectively serve as input terminals of two sets of optical isolation circuits;

The output ends of the two sets of photoelectric isolation circuits are connected to the input end of the differential amplifier (110), and the output end of the differential amplifier (110) is connected to the time constant adjustment circuit; the high output of the subtraction type frequency dividing circuit is A single-ended to double-ended conversion circuit (107) is provided between the transformer circuits.

8. The sub-route circuit device according to claim 1, wherein: said transformer is a transmission line transformer.