JP2018011173A - Digital isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve noise resistance in a digital isolator.SOLUTION: In a digital isolator 100, an insulation transformer 101 is connected between a first circuit 108 by which an input signal VIN is converted into an AC signal and outputted and a second circuit 109 by which an output signal VOUT is generated and outputted, and applies voltage corresponding to the AC signal from the first circuit 108 to the second circuit 109. An insulation capacitor 110 is connected between the first circuit 108 and the second circuit 109 and transmits a ground potential of the first circuit 108 to the second circuit 109. The second circuit 109 detects an inter-ground potential difference that is a difference between the ground potential that is transmitted by the insulation capacitor 110, and a ground potential of the second circuit 109, corrects the voltage applied from the insulation transformer 101 in accordance with the inter-ground potential difference and generates a digital signal corresponding to the corrected voltage as the output signal VOUT.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a digital isolator.

  In a high-voltage power device drive circuit or the like, signal transmission having electrical insulation is widely used for signal transmission between different power supply systems. Conventionally, photocouplers have been used in circuits that require electrical insulation. The photocoupler realizes signal transmission by converting an electrical signal into an optical signal with a light emitting diode in a transmission unit and demodulating the optical signal into an electrical signal with a photodiode in a reception unit.

  In recent years, digital isolators have begun to spread as signal transmission means replacing photocouplers. In a digital isolator, signal transmission is performed via an AC coupling element such as a capacitor or a transformer. A digital isolator has less deterioration over time than a photocoupler, and can be realized in a highly versatile semiconductor process such as a CMOS process. CMOS is an abbreviation for Complementary Metal Oxide Semiconductor. Hereinafter, a case where the AC coupling element is a transformer will be described.

  A transformer is an element in which a primary side coil and a secondary side coil perform signal transmission by magnetic coupling. Transformers have the property that AC signals pass but DC signals do not easily pass. Therefore, when used in signal transmission applications, it is necessary to convert the input signal to an AC signal and input it to the primary coil. There is. A signal input to the primary side coil is transmitted to the secondary side coil by magnetic coupling, and is converted from an AC signal to an output signal in the receiving circuit, thereby realizing signal transmission. Thus, in signal transmission using a transformer, an input signal is converted into an AC signal and input to the primary coil of the transformer, and an AC signal output from the secondary coil of the transformer is used as an output signal. A receiving circuit for conversion is required.

  As a conventional technique, in the technique described in Patent Document 1, a signal is not transmitted in one direction as described above, but an output signal transmitted from the transmission pulse generation circuit to the first transformer and the first reception circuit is fed back. It is fed back from the pulse transmission circuit by the second transformer. Then, the feedback output signal and the input signal are compared by the input / output signal comparison circuit, self-diagnosis is performed from the comparison result, and the diagnosis result is transmitted to the electronic control unit.

JP 2010-10762 A

  In the technique described in Patent Document 1, two transformers are required to compare the input signal and the feedback output signal, and there is a problem that the chip area increases. In addition, when the state is monitored by the self-diagnosis function and a malfunction due to noise inflow is detected, the device can be shifted to a safe state, but it is difficult to use it in an environment where noise constantly occurs. .

  An object of the present invention is to improve noise resistance in a digital isolator.

A digital isolator according to one embodiment of the present invention includes:
A first circuit that receives a digital signal as an input signal, converts the input signal into an AC signal, and outputs the AC signal;
A second circuit for generating and outputting an output signal;
An insulating transformer connected between the first circuit and the second circuit, and applying a voltage corresponding to the AC signal from the first circuit to the second circuit;
An insulating capacitor connected between the first circuit and the second circuit and transmitting a ground potential of the first circuit to the second circuit;
The second circuit detects a ground-to-ground potential difference, which is a difference between the ground potential transmitted by the insulating capacitor and the ground potential of the second circuit, and is applied from the insulating transformer in accordance with the ground-to-ground potential difference. The voltage is corrected, and a digital signal corresponding to the corrected voltage is generated as the output signal.

  In the present invention, the circuit on the reception side corrects the voltage applied from the insulating transformer connected between the transmission side and the reception side according to the potential difference between the grounds on the transmission side and the reception side. For this reason, the noise tolerance in a digital isolator is improved.

FIG. 2 is a circuit diagram illustrating a configuration of a digital isolator according to the first embodiment. FIG. 3 is a circuit diagram illustrating a configuration example of a transmission simulation circuit of the digital isolator according to the first embodiment. FIG. 3 is a circuit diagram illustrating a configuration example of a ground potential difference detection circuit of the digital isolator according to the first embodiment. FIG. 3 is a circuit diagram showing an equivalent circuit of the insulation transformer of the digital isolator according to the first embodiment. FIG. 3 is a waveform diagram showing operation waveforms of the digital isolator according to the first embodiment. FIG. 3 is a waveform diagram showing operation waveforms of the digital isolator according to the first embodiment. FIG. 4 is a circuit diagram showing a configuration of a digital isolator according to a second embodiment. FIG. 4 is a circuit diagram showing a configuration of a digital isolator according to a third embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the part which is the same or it corresponds in each figure. In the description of the embodiments, the description of the same or corresponding parts will be omitted or simplified as appropriate.

Embodiment 1 FIG.
This embodiment will be described with reference to FIGS.

*** Explanation of configuration ***
A configuration of a digital isolator 100 according to the present embodiment will be described with reference to FIG.

  The digital isolator 100 includes a first circuit 108, a second circuit 109, an insulation transformer 101, and an insulation capacitor 110.

  A digital signal is input to the first circuit 108 as the input signal VIN. The first circuit 108 converts the input signal VIN into an AC signal and outputs it. The second circuit 109 generates and outputs an output signal VOUT. The insulating transformer 101 is connected between the first circuit 108 and the second circuit 109. The insulating transformer 101 applies voltages V2P and V2N corresponding to the AC signal from the first circuit 108 to the second circuit 109. The insulating capacitor 110 is also connected between the first circuit 108 and the second circuit 109. The insulating capacitor 110 transmits the ground potential GND1 of the first circuit 108 to the second circuit 109. The second circuit 109 detects a ground potential difference (GND1−GND2) that is a difference between the ground potential GND1 transmitted by the insulating capacitor 110 and the ground potential GND2 of the second circuit 109. The second circuit 109 corrects the voltage V2P applied from the insulating transformer 101 in accordance with the potential difference between grounds (GND1-GND2). Then, the second circuit 109 generates a digital signal corresponding to the corrected voltages V3P and V3N as the output signal VOUT.

  In the present embodiment, the first circuit 108 includes a transmission circuit 102 and a transmission simulation circuit 111. The second circuit 109 includes a receiving circuit 103 and a ground potential difference detection circuit 112. The reception circuit 103 includes a bias setting circuit 104, a balun circuit 105, a differential amplifier circuit 106, and a comparison circuit 107.

  The transmission circuit 102 converts the input signal VIN into an AC signal and inputs the AC signal to the primary coil of the insulating transformer 101 that is an AC coupling element. The receiving circuit 103 converts the voltages V2P and V2N generated in the secondary coil of the insulating transformer 101 into an output signal VOUT. The bias setting circuit 104 supplies a reference voltage VB of an input signal to the receiving circuit 103. The balun circuit 105 performs differential conversion on the voltage V2P with reference to the reference voltage VB. The differential amplifier circuit 106 amplifies and outputs the differential signals V3P and V3N transmitted from the balun circuit 105. The comparison circuit 107 compares the output voltage V4 of the differential amplifier circuit 106 with the reference voltages VR1 and VR2 of the bias setting circuit 104, and outputs an output signal VOUT. The transmission simulation circuit 111 connects the ground of the first circuit 108 and the insulation capacitor 110 that transmits the variation between the insulation potentials of the second circuit 109 that is electrically insulated from the first circuit 108. The ground potential difference detection circuit 112 detects a difference between the ground potential GND 1 transmitted from the insulating capacitor 110 and the ground potential GND 2 of the second circuit 109.

  A configuration example of the transmission simulation circuit 111 will be described with reference to FIG.

  In the example of FIG. 2, the transmission simulation circuit 111 includes a high potential side output dummy switch 113, a low potential side output dummy switch 114, a high potential side control dummy inverting element 115, and a low potential side control dummy inverting element 116. Have. Each of the high potential side output dummy switch 113 and the low potential side output dummy switch 114 is a MOSFET. MOSFET is an abbreviation for Metal-Oxide-Semiconductor Field-Effect Transistor. The transmission simulation circuit 111 is configured to simulate the output stage of the transmission circuit 102.

  In the present embodiment, the transmission circuit 102 outputs an AC signal to the insulating transformer 101 when the input signal VIN is input. At this time, the fluctuation of the ground potential GND1 of the first circuit 108 is transmitted from the transmission circuit 102 to the second circuit 109 via the insulating transformer 101. The transmission simulation circuit 111 applies a voltage VD1 corresponding to the fluctuation of the ground potential GND1 of the first circuit 108 transmitted from the transmission circuit 102 to the second circuit 109 via the insulation transformer 101 to the insulation capacitor 110.

  A configuration example of the ground potential difference detection circuit 112 will be described with reference to FIG.

  In the example of FIG. 3, the ground potential difference detection circuit 112 includes an adjustment circuit 117 including an adjustment capacitor connected to the ground of the second circuit 109, an analog-digital converter 118, and a control logic circuit 119. The ground potential difference detection circuit 112 detects the potential fluctuation of the ground potential GND1 with respect to the ground potential GND2 input from the output voltage VD2 of the insulation capacitor 110 by the adjustment circuit 117, and samples the analog-digital converter 118 to monitor the fluctuation. Processing is performed by the control logic circuit 119 to control the bias setting circuit 104.

  In the present embodiment, when the voltages V2P and V2N from the insulating transformer 101 are applied, the receiving circuit 103 corrects the applied voltage V2P according to the reference voltage VB. When an analog signal corresponding to the voltage VD2 output from the insulation capacitor 110 is input, the analog-to-digital converter 118 converts the analog signal into an analog-digital signal, and outputs the analog-to-ground potential difference (GND1-GND2) detection signal. . The control logic circuit 119 controls the reference voltage VB of the receiving circuit 103 in accordance with the value of the detection signal output from the analog / digital converter 118.

  In the present embodiment, the bias setting circuit 104 generates a voltage corresponding to the potential difference between grounds (GND1-GND2) as a reference voltage VB for correcting the voltage V2P applied from the insulating transformer 101.

  An equivalent circuit of the insulating transformer 101 will be described with reference to FIG.

  FIG. 4 shows a simplified equivalent circuit of the insulating transformer 101. The equivalent circuit of the insulating transformer 101 may be expressed as a distributed constant by a large number of inductors, resistors, and capacitors, but here it is expressed by a parasitic capacitor 120 and an inductor 121 for simplicity.

*** Explanation of operation ***
The operation of the digital isolator 100 according to the present embodiment will be described with reference to FIGS. 5 and 6 in addition to FIGS. The operation of the digital isolator 100 corresponds to the signal transmission method according to the present embodiment.

  The operation of the main path for signal transmission in the digital isolator 100 will be described.

  When the input signal VIN is input to the transmission circuit 102, the transmission circuit 102 converts the rising edge and the falling edge of the input signal VIN into a pulsed signal V1P and outputs it to the isolation transformer 101. The signal V1P input to the insulating transformer 101 is applied to the primary coil of the insulating transformer 101, and generates a voltage V2P to the secondary coil by magnetic coupling action. The output voltage V2P of the isolation transformer 101 is input to the balun circuit 105 corresponding to the input stage of the receiving circuit 103, is distributed to the differential signals V3P and V3N, and is input to the differential amplifier circuit 106. In the differential amplifier circuit 106, the voltage V3P is half-wave rectified to the plus side with respect to the reference voltage VB, the voltage V3N is half-wave rectified to the minus side, and these signals are amplified and output in a single phase. The output signal V4 is compared with the positive threshold voltage VR1 and the negative threshold voltage VR2 by the comparison circuit 107, and the output signal VOUT is output.

  FIG. 5 shows operation waveforms in the present embodiment. When an external input signal VIN is input to the transmission circuit 102, a positive pulse signal V1P is output to the isolation transformer 101 in synchronization with the rising edge. Further, a negative pulse signal V1N is output to the insulating transformer 101 at the timing of the falling edge. The polarity of the pulse output to the insulation transformer 101 is controlled by the direction of the current applied to the primary coil of the insulation transformer 101. When a current flows from the terminal POS of the transmission circuit 102 to the terminal NEG, a positive pulse is output to the insulation transformer 101, and when a current flows from the terminal NEG to the terminal POS, a negative pulse is output. The input signal V1P to the primary side coil in the insulation transformer 101 generates a signal to the secondary side coil by magnetic coupling action, and a pulse signal V2P is output as the output of the insulation transformer 101. The output signal V2P of the insulation transformer 101 is a positive / negative pulse signal based on the ground potential GND2. Since the differential amplifier circuit 106 has an input voltage range in which stable operation is possible, a reference voltage VB that satisfies the input voltage range of the differential amplifier circuit 106 is added by the bias setting circuit 104, and the balun circuit Differential signals V3P and V3N are output from 105. The differential signals V3P and V3N are input to the differential amplifier circuit 106, and an amplified signal V4 is output. The amplitude of the output voltage V2P of the insulation transformer 101 varies depending on the amount of change in the current to the primary coil in the signal change, the coupling coefficient indicating the strength of magnetic coupling of the insulation transformer 101, and the like. When the amplitude is small, it may not be detected by comparison with the reference voltages VR1 and VR2 set in advance by the comparison circuit 107. Therefore, the differential amplifier circuit 106 amplifies the voltage difference between the differential signals V3P and V3N. Thus, a sufficient amplitude is secured at the input V4 to the comparison circuit 107. The output signal V4 of the differential amplifier circuit 106 is input to the comparison circuit 107, compared with reference voltages VR1 and VR2 set in advance by the bias setting circuit 104, and the comparison result is output as the output signal VOUT.

  The above is the description of the operation of the main signal path by the insulating transformer 101 that generates the output signal VOUT from the input signal VIN.

  FIG. 6 shows operation waveforms in the present embodiment under the driving environment of the power element. The power element is connected before the output VOUT of the second circuit 109 with the ground potential GND2 as a reference, and controls the motor by turning on / off. In the driving environment of the power element, a large current flows to the ground of the second circuit 109 at the timing when the power element is turned on, so that the ground potential GND2 with respect to the ground potential GND1 varies greatly. Considering the ground potential GND2 as a reference, this is equivalent to a change in the ground potential GND1. Therefore, the variation of the ground potential GND1 is superimposed on the main signal path through the parasitic capacitor 120 of the insulating transformer 101, and the voltage V2P varies in synchronization with the variation of the ground potential GND1.

  As described above, since the differential amplifier circuit 106 has an input voltage range in which stable operation is possible, the voltages V3P and V3N are out of the input voltage range due to the influence of potential fluctuations, and differential amplification is performed. The stable operation of the circuit 106 is impaired. Therefore, when the comparison circuit 107 compares the signal V4 amplified by the differential amplifier circuit 106 with the reference voltages VR1 and VR2, the magnitude relationship between the signal V4 and the reference voltages VR1 and VR2 is not inverted at the intended timing, and the output signal VOUT has a waveform different from that of the input signal VIN.

  Therefore, in the present embodiment, the potential fluctuation is detected by the transmission simulation circuit 111 disposed in the first circuit 108, the insulating capacitor 110, and the ground potential difference detection circuit 112 disposed in the second circuit 109, and the voltages V3P and V3N are detected. Is provided in a correction path for adjusting the reference voltage VB generated by the bias setting circuit 104 so that the voltage falls within the input voltage range of the differential amplifier circuit 106.

  An example of potential fluctuation detection and control will be described using the configuration example of the transmission simulation circuit 111 shown in FIG. 2 and the configuration example of the ground potential difference detection circuit 112 shown in FIG.

  As described above, the transmission simulation circuit 111 is configured to simulate the output stage of the transmission circuit 102. This is because the parasitic capacitor 120 in the insulating transformer 101 simulates the timing and waveform of transmission from the first circuit 108 to the second circuit 109. First, the potential fluctuation transmitted from the ground of the first circuit 108 is transmitted through the parasitic capacitance between the source or back gate and drain of the low potential side output dummy switch 114 or the like. The potential fluctuation is transmitted through the insulating capacitor 110 as the voltage VD2. Since the voltage VD2 is divided by the resistance of the insulating capacitor 110 and the resistance of the adjustment circuit 117, the adjustment circuit 117 can adjust the amplitude of the voltage VD2. Voltage fluctuation is detected by periodically taking in the voltage VD2 by the analog-digital converter 118. The setting is changed by the control logic circuit 119 that adjusts the value of the reference voltage VB of the bias setting circuit 104 and the output impedance of the reference voltage VB according to the detected slope of the voltage fluctuation. Specifically, when voltage fluctuation to the positive side occurs, the reference voltage VB is adjusted to the negative side. On the contrary, when the voltage fluctuation to the minus side occurs, the reference voltage VB is adjusted to the plus side. In addition, when the amplitude fluctuation is large, the responsiveness can be improved by lowering the output impedance.

  With the above operation, according to the present embodiment, it is possible to improve resistance to noise generated between different ground potentials, and in a motor driving device that drives a power element with a large current, signal transmission between insulating potentials can be performed. realizable.

*** Explanation of the effect of the embodiment ***
In the present embodiment, the voltage V2P applied from the insulating transformer 101 connected between the transmission side and the reception side is determined by the circuit on the reception side according to the potential difference (GND1-GND2) between the transmission side and the reception side. Correct. For this reason, the noise tolerance in the digital isolator 100 is improved.

  According to the present embodiment, a mechanism for detecting a different ground potential difference between the transmission circuit 102 and the reception circuit 103 is provided, and correction is made to the reference voltage VB of the reception circuit 103 when noise between different ground potentials is mixed. Thus, it is possible to supply the digital isolator 100 that suppresses the influence of noise mixing and enables signal transmission between the insulation potentials.

  In this embodiment, the transmission simulation circuit 111 arranged in the first circuit 108, the insulation capacitor 110, and the ground potential difference detection circuit 112 arranged in the second circuit 109 detect the potential fluctuation, and the voltages V3P and V3N are different. By providing a correction path for adjusting the reference voltage VB generated by the bias setting circuit 104 so as to be within the input voltage range of the dynamic amplifier circuit 106, it is possible to improve resistance to noise generated between different ground potentials. It becomes.

  According to the present embodiment, it is possible to improve the signal transmission resistance against noise generated between different ground potentials in the digital isolator semiconductor device.

*** Other configurations ***
In the present embodiment, the digital isolator 100 is applied to a motor drive device that drives a power element with a large current, but the digital isolator 100 may be applied to other devices.

Embodiment 2. FIG.
The difference between the present embodiment and the first embodiment will be mainly described with reference to FIG.

  The configuration of the digital isolator 100 according to the present embodiment will be described with reference to FIG.

  In the present embodiment, the receiving circuit 103 of the second circuit 109 has a termination resistor circuit 122 instead of the balun circuit 105. That is, the input stage of the receiving circuit 103 to which the voltages V2P and V2N are applied is a termination resistor circuit 122. The termination resistor circuit 122 inputs the differential signals V3P and V3N directly to the differential amplifier circuit 106.

  In this embodiment, the reception circuit 103 includes a demodulation circuit 123 instead of the comparison circuit 107. The signals V4P and V4N amplified by the differential amplifier circuit 106 are input to the demodulation circuit 123, and an output signal VOUT is output from the demodulation circuit 123.

  In the differential transmission type digital isolator 100 according to the present embodiment, the resistance to noise generated between different grounds can be improved by adjusting the reference voltage VB using the correction path, as in the first embodiment. Is possible.

Embodiment 3 FIG.
In the present embodiment, differences from the second embodiment will be mainly described with reference to FIG.

  The configuration of the digital isolator 100 according to the present embodiment will be described with reference to FIG.

  In the present embodiment, the insulating transformer 101 is composed of two pairs of coils instead of one pair of coils. In the present embodiment, the reference voltage VB is input to the intermediate node of the isolation transformer 101.

  In the present embodiment, the receiving circuit 103 of the second circuit 109 does not have the termination resistor circuit 122. That is, the input stage of the receiving circuit 103 to which the voltages V2P and V2N are applied is a differential amplifier circuit 106. The signals V4P and V4N amplified by the differential amplifier circuit 106 are input to the demodulation circuit 123, and an output signal VOUT is output from the demodulation circuit 123.

  In the differential transmission type digital isolator 100 according to the present embodiment, the resistance to noise generated between different grounds can be improved by adjusting the reference voltage VB using the correction path, as in the second embodiment. Is possible.

  As mentioned above, although embodiment of this invention was described, you may implement combining 2 or more embodiment among these embodiments. Alternatively, among these embodiments, one embodiment or a combination of two or more embodiments may be partially implemented. In addition, this invention is not limited to these embodiment, A various change is possible as needed.

  DESCRIPTION OF SYMBOLS 100 Digital isolator, 101 Insulation transformer, 102 Transmission circuit, 103 Reception circuit, 104 Bias setting circuit, 105 Balun circuit, 106 Differential amplifier circuit, 107 Comparison circuit, 108 1st circuit, 109 2nd circuit, 110 Insulation capacitor, 111 Transmission simulation circuit, 112 Ground potential difference detection circuit, 113 High potential side output dummy switch, 114 Low potential side output dummy switch, 115 High potential side control dummy inversion element, 116 Low potential side control dummy inversion element, 117 Adjustment circuit, 118 Analog Digital converter, 119 control logic circuit, 120 parasitic capacitor, 121 inductor, 122 termination resistor circuit, 123 demodulation circuit.

Claims (4)

A first circuit that receives a digital signal as an input signal, converts the input signal into an AC signal, and outputs the AC signal;
A second circuit for generating and outputting an output signal;
An insulating transformer connected between the first circuit and the second circuit, and applying a voltage corresponding to the AC signal from the first circuit to the second circuit;
An insulating capacitor connected between the first circuit and the second circuit and transmitting a ground potential of the first circuit to the second circuit;
The second circuit detects a ground-to-ground potential difference, which is a difference between the ground potential transmitted by the insulating capacitor and the ground potential of the second circuit, and is applied from the insulating transformer in accordance with the ground-to-ground potential difference. A digital isolator that corrects a voltage and generates a digital signal corresponding to the corrected voltage as the output signal. The first circuit includes:
A transmission circuit that receives the input signal and outputs the AC signal to the isolation transformer;
The transmission simulation circuit according to claim 1, further comprising: a transmission simulation circuit that applies a voltage according to a change in ground potential of the first circuit transmitted from the transmission circuit to the second circuit via the insulation transformer. Digital isolator. The second circuit includes:
A receiving circuit for applying a voltage from the isolation transformer and correcting the applied voltage in accordance with a reference voltage;
An analog signal corresponding to the voltage output from the insulating capacitor is input, the analog signal is converted from analog to digital, and output as a detection signal of the potential difference between grounds; and
The digital isolator according to claim 1, further comprising a control logic circuit that controls a reference voltage of the receiving circuit in accordance with a value of a detection signal output from the analog-digital converter. The second circuit includes:
3. The digital isolator according to claim 1, further comprising a bias setting circuit that generates a voltage corresponding to the potential difference between the grounds as a reference voltage for correcting a voltage applied from the insulating transformer. 4.

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