Signal transmission circuit for analog optocoupler

Abstract

The present invention provides a signal transmission circuit simulating an optocoupler, the signal transmission circuit comprising a reverse voltage protection module, a voltage clamping module and an isolation transmission module connected in sequence, the reverse voltage protection module being connected to the positive electrode of a power supply to transmit a current signal to the voltage clamping module; the voltage clamping module comprising a positive temperature coefficient branch and a negative temperature coefficient branch connected in series, the output voltage of the voltage clamping module being the sum of the positive temperature coefficient voltage at both ends of the positive temperature coefficient branch and the negative temperature coefficient voltage at both ends of the negative temperature coefficient branch. A reverse voltage protection module is first set to prevent the voltage at the negative electrode of the power supply from being higher than the positive electrode of the power supply, which is equivalent to simulating the reverse bias cutoff characteristic of the optocoupler. Moreover, by adjusting the parameters in the positive temperature coefficient branch and the negative temperature coefficient branch, the output voltage of the voltage clamping module can be made close to the zero temperature coefficient, thereby improving the accuracy and delay of the output voltage.

Description

Technical Field

[0001] The invention relates to the field of isolation drive chips, in particular to a signal sending circuit simulating an optical coupler. Background Art

[0002] In the prior art, when transmitting signals, an optocoupler can be used for signal transmission. For example, when current flows from the anode to the cathode, the LED lamp of the optocoupler can be illuminated, so that the phototransistor on the other side of the optocoupler receives the light signal, thereby isolating the signal on the left side and transmitting it to the right side.

[0003] However, the optical coupler has light attenuation during signal transmission, and the current conversion ratio will change with time and temperature, thus affecting the delay and accuracy of the output signal. In addition, the optical coupler transmission is relatively slow and is not suitable for high-speed systems. In addition, the common mode rejection ratio of the optical coupler is poor, which is prone to produce erroneous pulses.

[0004] Therefore, a signal transmission circuit that simulates an optocoupler and has higher efficiency must be designed. Summary of the invention

[0005] To solve one of the above problems, the present invention provides a signal sending circuit of an analog optocoupler, wherein the signal sending circuit comprises a reverse voltage protection module, a voltage clamping module and an isolation transmission module connected in sequence, wherein the reverse voltage protection module is connected to the positive pole of a power supply to transmit a current signal to the voltage clamping module; the voltage clamping module comprises a positive temperature coefficient branch and a negative temperature coefficient branch connected in series, and the output voltage of the voltage clamping module is the sum of a positive temperature coefficient voltage at both ends of the positive temperature coefficient branch and a negative temperature coefficient voltage at both ends of the negative temperature coefficient branch.

[0006] As a further improvement of the present invention, the negative temperature coefficient branch includes a first triode and a second triode, the bases of the first triode and the second triode are interconnected, the emitters are both connected to the negative pole of the power supply, and the base and collector of the first triode are connected to each other.

[0007] As a further improvement of the present invention, the area of ​​the second transistor is N times that of the first transistor, wherein N>1.

[0008] As a further improvement of the present invention, the positive temperature coefficient branch includes a first resistor, one end of the first resistor is connected to the output end of the reverse voltage protection module, and the other end is connected in series with the negative temperature coefficient branch; the negative temperature coefficient branch also includes a second resistor, and the emitter of the second transistor is connected to the negative pole of the power supply through the second resistor.

[0009] As a further improvement of the present invention, the negative temperature coefficient branch also includes a first MOSFET and a second MOSFET, the gates of the first MOSFET and the second MOSFET are connected to each other and to the base of the first triode; the first resistor is connected to the input ends of the first MOSFET and the second MOSFET, and the output ends of the first MOSFET and the second MOSFET are respectively connected to the collectors of the first triode and the second triode.

[0010] As a further improvement of the present invention, the first MOS tube and the second MOS tube are both PMOS tubes and have the same threshold voltage.

[0011] As a further improvement of the present invention, the output voltage Vclamp of the voltage clamping module is:

[0012]

[0013] Among them, △V be is the Vbe voltage difference between the second transistor and the first transistor, R1 is the first resistor, R2 is the second resistor, V1be is the voltage difference between the base and the emitter of the first transistor, and Vth is the threshold voltage of the first MOS tube.

[0014] As a further improvement of the present invention, the voltage clamping module also includes a loop gain branch, which includes a third resistor and a third transistor; the base of the third transistor is connected to the collector of the second transistor, the emitter is connected to the negative pole of the power supply, and the collector is connected to the positive pole of the power supply through the third resistor.

[0015] As a further improvement of the present invention, the loop gain branch also includes a third MOS tube, the third MOS tube is a PMOS, the gate of the third MOS tube is connected between the third resistor and the collector of the third transistor, the source of the third MOS tube is connected to the positive electrode of the power supply, and the drain is connected to the negative electrode of the power supply.

[0016] As a further improvement of the present invention, the reverse voltage protection module includes a fourth MOS tube, the fourth MOS tube is a PMOS tube, the gate of the fourth MOS tube is connected to the negative electrode of the power supply, the source is connected to the positive electrode of the power supply, and the drain is connected to the voltage clamping module.

[0017] Compared with the prior art, in the present invention, a reverse voltage protection module is first set to prevent the voltage of the negative electrode of the power supply from being higher than the positive electrode of the power supply, which is equivalent to simulating the reverse bias cutoff characteristics of the optocoupler. In addition, the voltage clamping module can start working according to the transmitted current signal, and can clamp the output voltage at a suitable size for subsequent transmission. In addition, the voltage clamping module includes a positive temperature coefficient branch and a negative temperature coefficient branch. The positive temperature coefficient branch generates a positive temperature coefficient voltage, and the negative temperature coefficient generates a negative temperature coefficient voltage. Therefore, by adjusting the parameters in the positive temperature coefficient branch and the negative temperature coefficient branch, the output voltage of the voltage clamping module can be made close to the zero temperature coefficient, thereby improving the accuracy and delay of the output voltage. Finally, the output voltage is transmitted to the subsequent receiving circuit through the isolation transmission module. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of a signal sending circuit simulating an optical coupler of the present invention;

[0019] Figure 2 The circuit diagram of the signal sending circuit of the simulated optocoupler of the present invention. Specific embodiments

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] like Figure 1 to Figure 2 The figure shows a signal sending circuit for simulating an optocoupler, wherein the signal sending circuit comprises a reverse voltage protection module 1, a voltage clamping module 2 and an isolation transmission module 3 connected in sequence, wherein the reverse voltage protection module 1 is connected to the positive pole of the power supply to transmit the current signal to the voltage clamping module 2; the voltage clamping module 2 comprises a positive temperature coefficient branch and a negative temperature coefficient branch connected in series, and the output voltage Vclamp of the voltage clamping module 2 is the sum of the positive temperature coefficient voltage at both ends of the positive temperature coefficient branch and the negative temperature coefficient voltage at both ends of the negative temperature coefficient branch.

[0022] In the present invention, in the signal transmission circuit, a reverse voltage protection module 1 is first set to prevent the voltage of the negative electrode of the power supply from being higher than the positive electrode of the power supply, which is equivalent to simulating the reverse bias cutoff characteristics of the optocoupler. In addition, the voltage clamping module 2 can start working according to the transmitted current signal, and can clamp the output voltage Vclamp to a suitable size for subsequent transmission. In addition, the voltage clamping module 2 includes a positive temperature coefficient branch and a negative temperature coefficient branch. The positive temperature coefficient branch generates a positive temperature coefficient voltage, and the negative temperature coefficient generates a negative temperature coefficient voltage. Therefore, by adjusting the parameters in the positive temperature coefficient branch and the negative temperature coefficient branch, the output voltage Vclamp of the voltage clamping module 2 can be made close to the zero temperature coefficient, thereby improving the accuracy and delay of the output voltage Vclamp. Finally, the output voltage Vclamp is transmitted through the isolation transmission module 3.

[0023] like Figure 2 As shown, the negative temperature coefficient branch includes a first transistor Q1 and a second transistor Q2, the bases of the first transistor Q1 and the second transistor Q2 are interconnected, the emitters are both connected to the negative electrode of the power supply, and the base and collector of the first transistor Q1 are connected to each other.

[0024] It is known that the voltage Vbe between the base and emitter of a transistor has a temperature coefficient and decreases with increasing temperature, i.e., a negative temperature coefficient. Therefore, in this embodiment of the present invention, the voltage V1be between the base and emitter of the first transistor Q1 has a negative temperature coefficient, and the voltage V2be between the base and emitter of the second transistor Q2 also has a negative temperature coefficient. Moreover, since the bases of the two are interconnected, the base voltages of the first transistor Q1 and the second transistor Q2 are equal.

[0025] Furthermore, the area of ​​the second transistor Q2 is N times that of the first transistor Q1, where N>1. The difference in Vbe between the two transistors with interconnected bases, i.e., △Vbe, also has a temperature coefficient, and increases with increasing temperature, i.e., a positive temperature coefficient. Since only when the area of ​​the second transistor Q2 is N times that of the first transistor Q1 and N>1, △Vbe=VT*ln(N), where VT is a positive temperature coefficient, △Vbe is positively correlated with temperature. Therefore, through the above characteristics, a positive temperature coefficient branch can be designed.

[0026] Specifically, the positive temperature coefficient branch includes a first resistor R1, one end of the first resistor R1 is connected to the output end of the reverse voltage protection module 1, and the other end is connected in series with the negative temperature coefficient branch; the negative temperature coefficient branch also includes a second resistor R2, and the emitter of the second transistor Q2 is connected to the negative pole of the power supply through the second resistor R2.

[0027] Therefore, since the emitter of the second transistor Q2 is connected to the negative electrode of the power supply through the second resistor R2, the positive temperature coefficient voltage Vtep+ of the positive temperature coefficient branch is:

[0028]

[0029] Thus, in the negative temperature coefficient branch, the negative temperature coefficient voltage Vtep- is:

[0030] V tep- =V 1be ;

[0031] Wherein, V1be is the voltage between the base and the emitter of the first transistor Q1. Since the base and the collector of the first transistor Q1 are interconnected, V1be is also the voltage between the collector and the emitter of the first transistor Q1.

[0032] In addition, in fact, in the present invention, the negative temperature coefficient branch also includes a first MOSFET M1 and a second MOSFET M2, the gates of the first MOSFET M1 and the second MOSFET M2 are connected to each other and to the base of the first transistor Q1, and the output ends of the first MOSFET M1 and the second MOSFET M2 are respectively connected to the collectors of the first transistor Q1 and the second transistor Q2.

[0033] Therefore, the first resistor R1 is not directly connected to the transistor, but is connected to the first transistor Q1 and the second transistor Q2 respectively through the first MOSFET M1 and the second MOSFET M2, so that a negative temperature coefficient branch that can adjust the negative temperature coefficient is further added to the voltage clamping module 2 to make the output voltage Vclamp of the voltage clamping module 2 more reasonable.

[0034] Specifically, the first MOS tube M1 and the second MOS tube M2 are both PMOS tubes, and have the same threshold voltage. Therefore, the source of the first MOS tube M1 and the second MOS tube M2 is connected to the first resistor R1, and the drain is connected to the collector of the first transistor Q1 and the second transistor Q2 respectively. Since the threshold voltage Vth of the first MOS tube M1 and the second MOS tube M2 is also a negative temperature coefficient, therefore, in this specific implementation, the negative temperature coefficient voltage Vtep- is actually:

[0035] V tep- =V 1be +V th ;

[0036] Wherein, Vth is the threshold voltage of the first MOSFET M1 and the second MOSFET M2.

[0037] Therefore, combining the negative temperature coefficient branch and the positive temperature coefficient branch, the output voltage Vclamp of the voltage clamping module 2 is:

[0038]

[0039] Thus, by adjusting the first resistor R1, the second resistor R2, the first MOS tube M1 and the second MOS tube M2, the output voltage Vclamp of the voltage clamping module 2 can have a lower temperature coefficient, and even in an ideal case, it can be adjusted to a zero temperature coefficient, thereby providing a clamped output voltage Vclamp with a low temperature coefficient. Therefore, using the signal transmission circuit in the present invention to simulate the optocoupler can solve the problem that the optocoupler varies greatly with temperature, and expand the application scenarios.

[0040] The voltage clamping module 2 in this specific embodiment of the present invention is connected to the reverse voltage protection module 1 and receives the current signal transmitted by the reverse voltage protection module 1, so that the voltage clamping module 2 works. The voltage clamping module 2 can output the clamped output voltage Vclamp in the working state. And because the voltage clamping module 2 includes a positive temperature coefficient branch and a negative temperature coefficient branch, the output voltage Vclamp of the voltage clamping module 2 is the sum of the positive temperature coefficient voltage and the negative temperature coefficient voltage. Therefore, the output voltage Vclamp of the voltage clamping module 2 can be as zero temperature coefficient as possible, reducing the influence of temperature on the output voltage Vclamp.

[0041] The voltage clamping module 2 also includes a loop gain branch, which includes a third resistor R3 and a third transistor Q3; the base of the third transistor Q3 is connected to the collector of the second transistor Q2, the emitter is connected to the negative pole of the power supply, and the collector is connected to the positive pole of the power supply through the third resistor R3.

[0042] Furthermore, the loop gain branch also includes a third MOS tube M3, which is a PMOS tube. The gate of the third MOS tube M3 is connected between the third resistor R3 and the collector of the third transistor Q3, and the source of the third MOS tube M3 is connected to the positive electrode of the power supply, and the drain is connected to the negative electrode of the power supply.

[0043] Therefore, the third resistor R3, the third triode Q3 and the third MOS tube M3 provide loop gain. Moreover, since the third MOS tube M3 can also absorb a part of the current after being turned on, the voltage clamping module 2 can provide a high-precision clamping voltage when the current signal output by the reverse voltage protection module 1 is within a certain range, and power the subsequent isolation transmission module 3. Moreover, since the loop bandwidth is fast and the establishment time is short, high-speed signal transmission can be achieved.

[0044] The output voltage Vclamp after passing through the loop gain branch is then transmitted to the subsequent signal receiving circuit through the isolation transmission module 3 .

[0045] In addition, the reverse voltage protection module 1 includes a fourth MOS tube M4, which is a PMOS tube, the gate of the fourth MOS tube M4 is connected to the negative electrode of the power supply, the source is connected to the positive electrode of the power supply, and the drain is connected to the voltage clamping module 2. Since the characteristic of the PMOS tube is low-level conduction, the fourth MOS tube M4 will only be turned on when the negative electrode of the power supply is connected to a low level, so as to transmit the current of the positive electrode of the power supply to the voltage clamping module 2. If the voltage of the negative electrode of the power supply is higher than the voltage of the positive electrode of the power supply, the fourth MOS tube M4 is turned off, and no current is generated inside the fourth MOS tube M4. Thus, the fourth MOS tube M4 can simulate the reverse bias cutoff characteristics of the optocoupler.

[0046] In summary, the present invention provides a signal transmission circuit for simulating an optocoupler, wherein the reverse bias cutoff characteristic of the optocoupler can be simulated by setting a reverse voltage protection module 1. When the voltage of the positive electrode of the power supply is higher than the voltage of the negative electrode of the power supply, a current will flow through the fourth MOS tube M4 of the reverse voltage protection module 1, and the current signal will be transmitted to the voltage clamping module 2.

[0047] Furthermore, the voltage clamping module 2 can clamp the output voltage Vclamp to ensure the stability of the output voltage Vclamp; and the voltage clamping module 2 includes a positive temperature coefficient branch and a negative temperature coefficient branch connected in series, so that the output voltage Vclamp is the sum of the positive temperature coefficient voltage and the negative temperature coefficient voltage, and the output voltage Vclamp has a lower temperature coefficient;

[0048] Furthermore, the voltage clamping module 2 also includes a loop gain branch, which can be quickly adjusted through the loop, and the third MOS tube M3 therein also has current absorption capability, so that high-speed and high-precision voltage clamping can be achieved within a certain input current range;

[0049] Finally, the reverse voltage protection module 1 and the voltage clamping module 2 can provide stable power supply for the subsequent isolation transmission module 3, and realize the signal transmission effect of the optocoupler. Compared with the traditional optocoupler, the influence of the temperature coefficient is minimized, the accuracy of signal transmission is increased, and the delay is also low. It can also be suitable for high-speed systems and has low common-mode interference.

[0050] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0051] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A signal transmission circuit simulating an optocoupler, characterized in that: The signal sending circuit comprises a reverse voltage protection module, a voltage clamping module and an isolation transmission module which are connected in sequence, wherein the reverse voltage protection module is connected to the positive electrode of the power supply to transmit the current signal to the voltage clamping module; the voltage clamping module comprises a positive temperature coefficient branch and a negative temperature coefficient branch which are connected in series, and the output voltage of the voltage clamping module is the sum of the positive temperature coefficient voltage at both ends of the positive temperature coefficient branch and the negative temperature coefficient voltage at both ends of the negative temperature coefficient branch; The negative temperature coefficient branch comprises a first triode and a second triode, the bases of the first triode and the second triode are interconnected, the emitters are both connected to the negative electrode of the power supply, and the base and collector of the first triode are connected to each other; The positive temperature coefficient branch includes a first resistor, one end of which is connected to the output end of the reverse voltage protection module; the negative temperature coefficient branch also includes a first MOSFET and a second MOSFET, the gates of the first MOSFET and the second MOSFET are connected to each other and to the base of the first triode; the other end of the first resistor is connected to the input end of the first MOSFET and the second MOSFET, and the output ends of the first MOSFET and the second MOSFET are respectively connected to the collectors of the first triode and the second triode.

2. The signal transmission circuit according to claim 1, characterized in that: The area of ​​the second transistor is N times that of the first transistor, where N>1.

3. The signal transmission circuit according to claim 2, characterized in that: The negative temperature coefficient branch further includes a second resistor, and the emitter of the second transistor is connected to the negative electrode of the power supply through the second resistor.

4. The signal transmission circuit according to claim 3, characterized in that: The output voltage Vclamp of the voltage clamp module is: Among them, △Vbe is the Vbe voltage difference between the second transistor and the first transistor, R1 is the first resistor, R2 is the second resistor, V1be is the voltage difference between the base and the emitter of the first transistor, and Vth is the threshold voltage of the first MOS tube.

5. The signal transmission circuit according to claim 1, characterized in that: The first MOS tube and the second MOS tube are both PMOS tubes and have the same threshold voltage.

6. The signal transmission circuit according to claim 1, characterized in that: The voltage clamping module also includes a loop gain branch, which includes a third resistor and a third transistor; the base of the third transistor is connected to the collector of the second transistor, the emitter is connected to the negative pole of the power supply, and the collector is connected to the positive pole of the power supply through the third resistor.

7. The signal transmission circuit according to claim 6, characterized in that: The loop gain branch also includes a third MOS tube, which is a PMOS tube. The gate of the third MOS tube is connected between the third resistor and the collector of the third transistor. The source of the third MOS tube is connected to the positive electrode of the power supply, and the drain is connected to the negative electrode of the power supply.

8. The signal transmission circuit according to claim 1, characterized in that: The reverse voltage protection module includes a fourth MOS tube, which is a PMOS tube. The gate of the fourth MOS tube is connected to the negative electrode of the power supply, the source is connected to the positive electrode of the power supply, and the drain is connected to the voltage clamping module.

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