Implementation method of analog optocoupler

Abstract

The invention belongs to the technical field of electronic circuits, and particularly relates to an analog optocoupler implementation method which comprises an analog optocoupler simulator circuit which is provided with an LC oscillator, a boost circuit at the TX end, an isolation transformer, a boost circuit at the RX end, a high-voltage-resistant open-drain NMOS output circuit and a voltage-controlled triangular wave generation circuit. A stable alternating current signal is generated through an LC oscillator, then the signal is boosted through a boost circuit at a TX end, the boosted signal is transmitted to an RX end through an isolation transformer, then the boosted signal is boosted again through the boost circuit of the RX end, and finally the signal is converted into a level suitable for subsequent circuit processing through a high-voltage-resistant open-drain NMOS output circuit. The voltage-controlled triangular wave is used for circuit modulation, and the analog optical coupler simulator circuit realizes simulation of functions of a traditional optical coupler through ingenious combination of electronic components. Compared with the prior art, the transmission performance is improved, the power consumption is reduced, and the isolation capability and the anti-electromagnetic interference capability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and more specifically, to a method for realizing a simulated optical coupler. Background Art

[0002] The traditional optocoupler is a commonly used electrical isolation component, which is widely used in signal transmission of electronic equipment. It uses LED (light emitting diode) as the input stage. When the input current passes through the LED, the LED will emit light, and the light emitted by it is transmitted to the photosensitive device at the receiving end through the transparent insulating medium in the middle. The photosensitive device then converts the optical signal into an electrical signal output. This structure has the advantages of electrical isolation and strong anti-interference ability, but it also has some obvious defects.

[0003] First, the transparent insulating medium in traditional optical couplers, such as epoxy resin, will age over time, causing the transparent medium to turn yellow over time, resulting in a decrease in light transmittance, which in turn affects the transmission quality of the optical signal. This aging phenomenon is particularly evident in long-term use or high-temperature environments, causing the transmission performance of the optical coupler to gradually decline, making it unable to meet the needs of some high-reliability application scenarios.

[0004] Secondly, in order to compensate for the decline in transmission performance caused by the aging of transparent media, traditional optocouplers often need to increase the input current to improve the luminous intensity of the LED, thereby enhancing the transmission capacity of the optical signal. However, this will increase the power consumption of the optocoupler, which is not conducive to the development trend of energy saving and consumption reduction and green environmental protection.

[0005] In addition, there are still some technical bottlenecks in the design and manufacturing process of traditional optocouplers. For example, the improvement of performance indicators such as isolation voltage and common-mode transient immunity (CMTI) is limited, and cannot meet the needs of some special application scenarios. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a method for realizing an analog optical coupler which improves transmission performance, reduces power consumption, and improves isolation capability and anti-electromagnetic interference capability.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for realizing a simulated optocoupler includes a simulated optocoupler simulator circuit, wherein the simulated optocoupler simulator circuit is provided with an LC oscillator, a boost circuit at a TX end, an isolation transformer, a boost circuit at an RX end, a high-voltage resistant open-drain NMOS output circuit, and a voltage-controlled triangular wave generating circuit.

[0009] LC oscillator, used to generate high-frequency carrier signal, whose resonant frequency is determined by the coil inductance L and resonant capacitor Ctot of the isolation transformer;

[0010] The boost circuit at the TX end has the same structure as the boost circuit at the RX end. Both the boost circuit at the TX end and the boost circuit at the RX end have input current Iin.

[0011] The boost circuit at the TX end is connected to the LC oscillator to form a current negative feedback loop, which limits the current supplied to the LC oscillator so as to control the oscillation amplitude of the LC oscillator to be linearly related to the input current Iin, and is coupled to the boost circuit receiving end of the RX through the isolation transformer;

[0012] An isolation transformer is used to couple the signal of the boost circuit at the TX end to the boost circuit at the RX end to facilitate electrical isolation;

[0013] The RX boost circuit is used to boost the received signal to a certain voltage and output it by driving the high-voltage open-drain NMOS output circuit;

[0014] A high voltage resistant open drain NMOS output circuit for forming an output current Iout, which is a simulated optocoupler that varies linearly with the input current Iin;

[0015] The voltage-controlled triangle wave generating circuit is used to make the high-frequency carrier wave fluctuate in a small range. The LC oscillator generates the high-frequency carrier wave by resonance, so that the coil inductance of the isolation transformer is L=2Ld.

[0016] The present invention is further configured as follows: the angular frequency of the resonance is , is the total input capacitance, and the quality factor of the isolation transformer coil inductance is Q , For a resistor, the resistance .

[0017] The present invention is further configured as follows: a negative resistor -Rp is connected in parallel to the resistor Rp, and the negative resistor -Rp adopts a fully differential cross-coupling structure, and the fully differential cross-coupling structure adopts a PMOS cross-coupling structure or an NMOS cross-coupling structure. The admittance gm of the fully differential cross-coupling structure is doubled, and the negative resistance -Rp of the LC oscillator is obtained = , negative resistance -Rp= , then Rp ,in is the admittance of the PMOS cross-coupled structure, is the admittance of the NMOS cross-coupled structure.

[0018] The present invention is further configured as follows: the admittance gm , K is the process coefficient, which is used to describe or quantify the influence of process factors on circuit performance, Iosc is the oscillation current, where K= is the carrier mobility, Cox is the gate oxide capacitance per unit area, wp is the power loop, LP is the low-pass filter, for PMOS cross-coupling structure The width-to-length ratio of a negative resistor.

[0019] The present invention is further configured as follows: the amplitude Vo of the LC oscillator is equal to Iosc Rp= Iosc Q, RP is a potentiometer, is the circuit angular frequency.

[0020] The present invention is further configured as follows: The inductance L and Q value of the isolation transformer are determined, the amplitude Vo of the LC oscillator is proportional to Iosc, the input current Iin = Iosc + Iboost + Ir, the input current Iin is the total input current, Ir is a fixed current, and Iboost is the open-drain output current of the boost circuit at the TX end.

[0021] The present invention is further configured as follows: the output end of the LC oscillator is a high-frequency oscillation signal of TX_indp and TX_indn, the resonant capacitor Ctot is the total equivalent capacitance between TX_indp and TX_indn, TX_indp is the positive or non-inverting signal of the differential signal, TX_indn is the negative or inverting signal of the differential signal, one path of the capacitor is coupled to Couple_p and Couple_N, Couple_p is the coupling circuit of TX_indp, Couple_N is the coupling circuit of TX_indn, and the boost circuit at the TX end is boosted to Vbst_tx, Iboost= (Vbst_tx-Vth) , where is the process coefficient of MN4, Vbst_tx is a voltage signal or a transmission parameter used for transmission, and Vth is the threshold voltage of MN4.

[0022] The present invention is further configured as follows: the amplitude of the LC oscillator and the output current Iboost to get the output current losc, Substituting losc into the input current Iin = Iosc + Iboost + Irr, we can get Iin = losc+lr,

[0023] The RX boost circuit receives the voltage at the receiving end and boosts it to Vbst_rx through the RX boost circuit. The output current lout= Iosc, input current Iin=β Iout, It is the ratio of input current Iin to output current Iout.

[0024] By adopting the above technical solution, the beneficial effects of the present invention are:

[0025] First, a stable AC signal is generated through an LC oscillator, and then the signal is boosted through the boost circuit at the TX end. The boosted signal is transmitted to the receiving end of the RX boost circuit through an isolation transformer, and then boosted again by the RX boost circuit. Finally, the signal is converted to a level suitable for subsequent circuit processing through a high-voltage open-drain NMOS output circuit. At the same time, the voltage-controlled triangular wave generating circuit can generate a triangular wave signal for circuit modulation. During the debugging process, the performance of the circuit can be optimized by adjusting the parameters of each component.

[0026] The analog optocoupler simulator circuit simulates the functions of traditional optocouplers through a clever combination of electronic components, and overcomes the problems of performance degradation and excessive power consumption caused by medium aging, thereby improving transmission performance, reducing power consumption, and improving isolation and anti-electromagnetic interference capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a circuit diagram of an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the circuit of the LC oscillator of the present invention;

[0029] Figure 3 It is a circuit diagram of the on-off keying OOK of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0031] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0032] like Figure 1 As shown, the implementation method of the simulated optocoupler includes a simulated optocoupler simulator circuit, wherein the simulated optocoupler simulator circuit is provided with an LC oscillator, a boost circuit at the TX end, an isolation transformer, a boost circuit at the RX end, a high-voltage resistant open-drain NMOS output circuit, and a voltage-controlled triangle wave generating circuit.

[0033] LC oscillator is used to generate high-frequency carrier signal and stable AC signal as the basic signal source of the circuit. Its resonant frequency is determined by the coil inductance L and resonant capacitor Ctot of the isolation transformer.

[0034] The boost circuit at the TX end performs voltage boost processing on the signal generated by the LC oscillator to improve the driving capability of the signal. The boost circuit at the TX end has the same structure as the boost circuit at the RX end. Both the boost circuit at the TX end and the boost circuit at the RX end have input current Iin.

[0035] The boost circuit at the TX end is connected to the LC oscillator to form a current negative feedback loop, which limits the current supplied to the LC oscillator so as to control the oscillation amplitude of the LC oscillator to be linearly related to the input current Iin, and is coupled to the boost circuit receiving end of the RX through the isolation transformer;

[0036] An isolation transformer is used to couple the signal of the boost circuit at the TX end to the boost circuit at the RX end, so as to facilitate electrical isolation and transmit the boosted signal to ensure the safety of the circuit;

[0037] The RX boost circuit is used to boost the received signal to a certain voltage and output it by driving the high-voltage open-drain NMOS output circuit. The RX boost circuit receiving end boosts the signal again to compensate for the attenuation of the signal during transmission.

[0038] The high-voltage resistant open-drain NMOS output circuit is used to form an output current Iout, which changes linearly with the input current Iin. The analog optocoupler converts the received signal into a level suitable for subsequent circuit processing, while ensuring that the circuit can withstand higher voltages.

[0039] The voltage-controlled triangle wave generating circuit is used to make the high-frequency carrier wave fluctuate in a small range. The LC oscillator uses resonance to generate the high-frequency carrier wave.

[0040] By adding a simple voltage-controlled triangle wave generator circuit to generate a triangle wave signal as a modulation signal of the circuit, the flexibility and adaptability of the circuit are enhanced, thereby reducing the electromagnetic interference EMI of the circuit. The isolation capability of the circuit mainly depends on the transformer, and the CMTI of the circuit mainly depends on the fully differential circuit.

[0041] like Figure 2 As shown in Figure 1, (a) is the series resistance of the LC oscillator and the coil inductance L of the isolation transformer and the equivalent circuit, and (b) is the actual LC oscillator, the coil inductance L of the isolation transformer and the equivalent circuit. (c) is the series resistance and equivalent circuit of the actual LC oscillator, the coil inductance L and Rp of the isolation transformer, and the parallel resistance and equivalent circuit.

[0042] The main principle of the overall analog optocoupler simulator circuit is that the oscillator mainly uses LC resonance to generate a high-frequency carrier, so that the coil inductance of the isolation transformer is L=2Ld, and the resonant capacitance is Ctot, which is the total equivalent capacitance between TX_indp and TX_indn, so the angular frequency of the resonance is ,in Represents the total input capacitance, and the quality factor of the isolation transformer coil inductance is Q , For a resistor, the resistance Due to the existence of Rp, there will be energy loss in the resonant network, so a negative resistor -Rp must be connected in parallel with the positive resistor to compensate for the energy loss of the resistor.

[0043] Commonly used resistor-Rp pairs include PMOS cross-coupling structure and NMOS cross-coupling structure negative resistance. In the analog optocoupler simulator circuit, PMOS cross-coupling structure and NMOS cross-coupling structure negative resistance are used, and then a fully differential cross-coupling structure is used. Compared with only using PMOS cross-coupling structure or only using NMOS cross-coupling structure, the fully differential cross-coupling structure doubles the admittance gm, so for low Q inductors, this structure can also maintain good oscillation.

[0044] It can be concluded that the negative resistance of the LC oscillator -Rp= , negative resistance -Rp= , in order to maintain oscillation, Rp must be satisfied ,in is the admittance of the PMOS cross-coupled structure, is the admittance of the NMOS cross-coupled structure. Considering some design margins, we make Rp In this way, the circuit can fully offset the influence of the inductor parasitic resistance, and the circuit can also achieve stable high-frequency oscillation under lower input current conditions.

[0045] Admittance gm , K is the process coefficient, which is used to describe or quantify the influence of process factors on circuit performance, Iosc is the oscillation current, where K= is the carrier mobility, Cox is the gate oxide capacitance per unit area, wp is the power loop, LP is the low-pass filter, is the width-to-length ratio of the negative resistor in the PMOS cross-coupling structure.

[0046] The amplitude of the LC oscillator Vo = Iosc Rp= Iosc Q, RP is a potentiometer, is the circuit angular frequency. When the circuit angular frequency The inductance L and Q value of the transformer are determined, and the amplitude Vo of the oscillator is proportional to Iosc.

[0047] Input current Iin= Iosc+Iboost+Ir, input current Iin is the total input current, Ir is a fixed current, and Iboost is the open-drain output current of the boost circuit at the TX end.

[0048] The output end of the LC oscillator is the high-frequency oscillation signal of TX_indp and TX_indn, the resonant capacitor Ctot is the total equivalent capacitance between TX_indp and TX_indn, TX_indp is the positive or non-inverting signal of the transmitted differential signal, and TX_indn is the negative or inverting signal of the transmitted differential signal.

[0049] One of the capacitors of TX_indp and TX_indn is coupled to Couple_p and Couple_N.

[0050] The boost circuit at the TX end boosts the voltage to Vbst_tx, making the output current Iboost = (Vbst_tx-Vth), where Couple_p is the coupling circuit of TX_indp, and Couple_N is the coupling circuit of TX_indn, where is the process coefficient of MN4, Vbst_tx is a voltage signal or a transmission parameter used for transmission, and Vth is the threshold voltage of MN4.

[0051] The amplitude of the LC oscillator Combined with the formula of output current Iboost, the output current is obtained losc, Substituting losc into the input current Iin = Iosc + Iboost + Irr, we can get Iin = losc+lr ,

[0052] Similarly, the RX boost circuit receives the voltage at the receiving end and boosts it to Vbst_rx through the RX boost circuit. The final output current lout = Iosc, so the input current Iin==β Iout, It is the ratio of input current Iin to output current Iout.

[0053] There are also on-off keying OOK modulation and demodulation waveforms in the circuit, such as Figure 3 As shown,

[0054] IF_INPUT is the total input current, the on-off keying OOK modulation waveform is a high-frequency LC oscillation carrier, VOUT is the open-drain output voltage waveform, and the circuit can ultimately achieve an isolation withstand voltage level of 3.75KVrms, a surge capability of 10KV, a maximum withstand voltage of 80V at the output, and a temperature range of -40°C to 125°C. The CTR performance varies according to different models, meeting application scenarios under different load conditions, and has high reliability and stability.

[0055] First, a stable AC signal is generated through an LC oscillator, and then the signal is boosted by the boost circuit at the TX end. The boosted signal is transmitted to the RX end through an isolation transformer, and then boosted again by the boost circuit of RX. Finally, the signal is converted into a level suitable for subsequent circuit processing through a high-voltage open-drain NMOS output circuit. At the same time, the voltage-controlled triangular wave generating circuit can generate a triangular wave signal for circuit modulation. During the debugging process, the performance of the circuit can be optimized by adjusting the parameters of each component.

[0056] The analog optocoupler simulator circuit simulates the functions of traditional optocouplers through a clever combination of electronic components, and overcomes the problems of performance degradation and excessive power consumption caused by medium aging, thereby improving transmission performance, reducing power consumption, and improving isolation and anti-electromagnetic interference capabilities.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for implementing a simulated optocoupler, characterized in that: It includes an analog optocoupler simulator circuit, which is equipped with an LC oscillator, a boost circuit at the TX end, an isolation transformer, a boost circuit at the RX end, a high-voltage open-drain NMOS output circuit, and a voltage-controlled triangle wave generating circuit. LC oscillator, used to generate high-frequency carrier signal, whose resonant frequency is determined by the coil inductance L and resonant capacitor Ctot of the isolation transformer; The boost circuit at the TX end has the same structure as the boost circuit at the RX end. Both the boost circuit at the TX end and the boost circuit at the RX end have input current Iin. The boost circuit at the TX end is connected to the LC oscillator to form a current negative feedback loop, which limits the current supplied to the LC oscillator so as to control the oscillation amplitude of the LC oscillator to be linearly related to the input current Iin, and is coupled to the boost circuit receiving end of the RX through the isolation transformer; An isolation transformer is used to couple the signal of the boost circuit at the TX end to the boost circuit at the RX end to facilitate electrical isolation; The RX boost circuit is used to boost the received signal to a certain voltage and output it by driving the high-voltage open-drain NMOS output circuit; A high voltage resistant open drain NMOS output circuit for forming an output current Iout, which is a simulated optocoupler that varies linearly with the input current Iin; The voltage-controlled triangle wave generating circuit is used to make the high-frequency carrier wave fluctuate in a small range. The LC oscillator generates the high-frequency carrier wave by resonance, so that the coil inductance of the isolation transformer is L=2Ld.

2. The method for realizing a simulated optocoupler according to claim 1, characterized in that: The angular frequency of the resonance is , is the total input capacitance, and the quality factor of the isolation transformer coil inductance is Q , For resistor, we get resistance .

3. The method for implementing a simulated optocoupler according to claim 2, characterized in that: The resistor Rp is connected in parallel with a negative resistor -Rp. The negative resistor -Rp adopts a fully differential cross-coupling structure. The fully differential cross-coupling structure adopts a PMOS cross-coupling structure or an NMOS cross-coupling structure. The admittance gm of the fully differential cross-coupling structure is doubled, and the negative resistance -Rp of the LC oscillator is obtained = , negative resistance -Rp= , then Rp ,in is the admittance of the PMOS cross-coupled structure, is the admittance of the NMOS cross-coupled structure.

4. The method for realizing a simulated optocoupler according to claim 3, characterized in that: The admittance gm , K is the process coefficient, which is used to describe or quantify the influence of process factors on circuit performance, Iosc is the oscillation current, where K= is the carrier mobility, Cox is the gate oxide capacitance per unit area, wp is the power loop, LP is the low-pass filter, is the width-to-length ratio of the negative resistor in the PMOS cross-coupling structure.

5. The method for realizing a simulated optocoupler according to claim 4, characterized in that: The amplitude of the LC oscillator Vo = Iosc Rp= Iosc Q, RP is a potentiometer, is the circuit angular frequency.

6. The method for realizing a simulated optocoupler according to claim 5, characterized in that: Said Determined, and the inductance L and Q value of the isolation transformer are determined, the amplitude Vo of the LC oscillator is proportional to Iosc, Input current Iin= Iosc+Iboost+Ir, input current Iin is the total input current, Ir is a fixed current, and Iboost is the open-drain output current of the boost circuit at the TX end.

7. The method for realizing a simulated optocoupler according to claim 6, characterized in that: The output end of the LC oscillator is the high-frequency oscillation signal of TX_indp and TX_indn, and the resonant capacitor Ctot is the total equivalent capacitance between TX_indp and TX_indn. TX_indp is the positive or non-inverting signal of the differential signal, and TX_indn is the negative or inverting signal of the differential signal. One of the capacitors is coupled to Couple_p and Couple_N. Couple_p is the coupling circuit of TX_indp, and Couple_N is the coupling circuit of TX_indn. The boost circuit at the TX end is boosted to Vbst_tx, and Iboost= (Vbst_tx-Vth) , where is the process coefficient of MN4, Vbst_tx is a voltage signal or a transmission parameter used for transmission, and Vth is the threshold voltage of MN4.

8. The method for realizing a simulated optocoupler according to claim 7, characterized in that: The amplitude of the LC oscillator and the output current Iboost to get the output current losc, Substituting losc into the input current Iin = Iosc + Iboost + Irr, we can get Iin = losc+lr , The RX boost circuit receives the voltage at the receiving end and boosts it to Vbst_rx through the RX boost circuit. The output current lout= Iosc, input current Iin=β Iout, It is the ratio of input current Iin to output current Iout.

Images