CN113572469A - Digital isolator with pseudo-differential structure - Google Patents
Digital isolator with pseudo-differential structure Download PDFInfo
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- CN113572469A CN113572469A CN202110866199.6A CN202110866199A CN113572469A CN 113572469 A CN113572469 A CN 113572469A CN 202110866199 A CN202110866199 A CN 202110866199A CN 113572469 A CN113572469 A CN 113572469A
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Abstract
The invention discloses a digital isolator with a pseudo-differential structure, which comprises: the signal demodulation circuit comprises a signal modulation circuit, a signal demodulation circuit, a common redundancy circuit and an isolation capacitor. The isolation capacitor is connected between the signal modulation circuit and the signal demodulation circuit, the common redundancy circuit comprises a common-mode signal conversion element and a common isolation capacitor, one end of the common-mode signal conversion element is connected with one end of the common isolation capacitor, the other end of the common-mode signal conversion element is connected with the input end of each signal demodulation circuit and used for converting common-mode current into common-mode voltage, and the other end of the common isolation capacitor is grounded. According to the digital isolator provided by the invention, the public redundancy circuit is additionally arranged, each isolation capacitor and the signal modulation circuit form a signal path, the public redundancy circuit and each signal path form a pseudo-differential structure, when the digital isolator has N paths, N +1 isolation capacitors are needed, compared with the traditional method that a full-differential structure is adopted, N-1 capacitors are saved, the area of a chip is further saved, and the reliability of the chip is improved.
Description
Technical Field
The invention relates to the technical field of isolation, in particular to a digital isolator with a pseudo-differential structure.
Background
With the continuous development of science and technology, digital isolators are widely applied to the fields of industry, medical treatment, communication and the like, and with the continuous expansion of the application range of the digital isolators, the performance requirements on the digital isolators are higher and higher. The digital isolator is often used for solving the problem that the control side and the controlled side are not in common ground, and when the reference ground is relatively jittered and common-mode interference is generated, communication failure of the digital isolator can be caused, so that the common-mode transient interference resistance of the digital isolator is an important index for evaluating the digital isolator.
At present, a fully differential structure is the most commonly adopted means for improving the common-mode transient anti-interference capability of the digital isolator. Fig. 1 is a schematic diagram of a digital isolator based on a fully differential structure. As shown in FIG. 1, the digital isolator has a plurality of channels, and the channel 1 is taken as an example for explanation. Isolation capacitors Ciso1 and Ciso2 are connected between the first chip 1 and the second chip 2, and signal input terminals VINN and VINP of a signal demodulation circuit in the second chip 2 are respectively connected with resistors R1 and R2 to form a fully differential structure. When the first chip 1 and the second chip 2 have common-mode transient interference, the fully differential structure acts to reduce the common-mode interference. As can be seen from fig. 1, the digital isolator adopts a fully differential structure, which can improve the common mode transient interference, but each path adopts a fully differential structure, which requires at least 2 capacitors to be connected, and when the digital isolator has N paths, 2N isolation capacitors are required, which is twice as many as the single-end digital isolator, and occupies a large area of the chip.
Therefore, the problem that when the digital isolator adopts a differential structure to improve common-mode transient interference, the isolation capacitor occupies a large area of a chip is a problem to be solved urgently by those skilled in the art.
Disclosure of Invention
The invention aims to provide a digital isolator with a pseudo-differential structure, which reduces the number of isolation capacitors to save the using area of a digital isolator chip and simultaneously keeps the differential structure characteristics of the digital isolator to compensate common-mode current generated by common-mode transient interference.
To solve the above technical problem, the present invention provides a digital isolator with a pseudo-differential structure, comprising: the signal demodulation circuit comprises a signal modulation circuit, a signal demodulation circuit, a common redundancy circuit and an isolation capacitor;
the isolation capacitor is connected between the signal modulation circuit and the signal demodulation circuit;
the common redundancy circuit comprises a common-mode signal conversion element and a common isolation capacitor, one end of the common-mode signal conversion element is connected with one end of the common isolation capacitor, the other end of the common-mode signal conversion element is connected with the input end of each signal demodulation circuit and used for converting common-mode current into common-mode voltage, and the other end of the common isolation capacitor is grounded.
Preferably, the common-mode signal conversion element is a resistor, and correspondingly, one end of the resistor is connected with the common isolation capacitor, and the other end of the resistor is connected with the input end of each signal demodulation circuit.
Preferably, the digital isolator further comprises a filter, the filter comprising a first filter and a second filter;
the first filter is connected between the common mode signal conversion element and the signal demodulation circuit, and the second filter is connected between the isolation capacitor and the signal demodulation circuit.
Preferably, the digital isolator further comprises an alternating current coupling circuit;
the input end of the alternating current coupling circuit is connected with the common-mode signal conversion element and the isolation capacitor, and the output end of the alternating current coupling circuit is connected with the input end of the signal demodulation circuit.
Preferably, the digital isolator further comprises a glitch filtering circuit;
the burr filtering circuit is connected with the output end of the signal demodulation circuit.
Preferably, the filter includes a resistor and a capacitor, and correspondingly, the first filter includes a first resistor and a first capacitor, and the second filter includes a second resistor and a second capacitor;
one end of the first capacitor is connected with the first resistor, the other end of the first capacitor is connected with the input end of the signal demodulation circuit, the common end of the first capacitor and the first resistor is connected with the common-mode signal conversion element, and the free end of the first resistor is grounded;
one end of the second capacitor is connected with the second resistor, the other end of the second capacitor is connected with the input end of the signal demodulation circuit, the common end of the second capacitor and the second resistor is connected with the isolation capacitor, and the free end of the second resistor is grounded.
Preferably, the first resistor and the second resistor have the same resistance.
Preferably, the capacitance values of the first and second capacitors are the same.
Preferably, the common isolation capacitance has the same capacitance value as the isolation capacitance.
Preferably, two common isolation capacitors are connected between the common mode signal conversion element and ground, and two isolation capacitors are connected between each of the signal modulation circuits and the signal demodulation circuit.
The invention provides a digital isolator with a pseudo-differential structure, which comprises: the signal demodulation circuit comprises a signal modulation circuit, a signal demodulation circuit, a common redundancy circuit and an isolation capacitor. The isolation capacitor is connected between the signal modulation circuit and the signal demodulation circuit, the common redundancy circuit comprises a common-mode signal conversion element and a common isolation capacitor, one end of the common-mode signal conversion element is connected with one end of the common isolation capacitor, the other end of the common-mode signal conversion element is connected with the input end of each signal demodulation circuit and used for converting common-mode current into common-mode voltage, and the other end of the common isolation capacitor is grounded. When the digital isolator adopts a fully differential structure, a differential structure formed between the signal modulation circuit and the signal demodulation circuit at least needs to be connected with 2 capacitors, when the digital isolator has N channels, 2N isolation capacitors are needed, the number of the isolation capacitors is twice that of a single-end digital isolator, and a large amount of area of a chip is occupied.
Drawings
In order to illustrate the embodiments of the present invention more clearly, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained by those skilled in the art without inventive effort.
FIG. 1 is a schematic diagram of a digital isolator based on a fully differential structure;
FIG. 2 is a waveform diagram of the digital isolator based on the fully differential structure of FIG. 1;
FIG. 3 is a schematic diagram of a digital isolator according to the present invention;
FIG. 4 is a schematic diagram of a pseudo-differential structure-based digital isolator;
FIG. 5 is a waveform diagram of the pseudo-differential architecture based digital isolator of FIG. 4;
the reference numbers are as follows: 1 is a first chip, 2 is a first chip, 3 is a common redundancy circuit, 4 is a first filter, and 5 is a second filter.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative work belong to the protection scope of the present invention.
The core of the invention is to provide a digital isolator with a pseudo-differential structure, which reduces the number of isolation capacitors to save the chip use area of the digital isolator and simultaneously still keeps the differential structure of the digital isolator to compensate the characteristic of common-mode current generated by common-mode transient interference.
In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 2 is a waveform diagram of the digital isolator based on the fully differential structure in fig. 1. Digital isolators are often used to deal with the problem of non-common ground on the control and controlled sides, which causes common mode glitches when the two sides are dithered with respect to ground, resulting in a failure of the digital isolator to communicate. As shown in fig. 1, a fully differential structure is usually adopted to improve common mode transient interference of a digital isolator, and the digital isolator has a plurality of channels, which is described by taking a channel 1 as an example. Isolation capacitors Ciso1 and Ciso2 are connected between the first chip 1 and the second chip 2, and signal input terminals VINN and VINP of a signal demodulation circuit in the second chip 2 are respectively connected with resistors R1 and R2 to form a fully differential structure. When the first chip 1 and the second chip 2 have common-mode transient interference, the fully differential structure acts to reduce the common-mode interference, and as shown in fig. 2, the digital isolator adopts the differential structure to significantly improve the common-mode transient interference at the stages of T3-T4 and T5-T6. Therefore, the digital isolator adopts a fully differential structure, although common-mode transient interference can be improved, each passage adopts a fully differential structure and at least 2 capacitors need to be connected, when the digital isolator has N passages, 2N isolation capacitors are needed, the number of the isolation capacitors is twice that of the single-end digital isolator, and a large amount of area of a chip is occupied.
Fig. 3 is a schematic structural diagram of a digital isolator according to the present invention. In order to solve the problem that the isolation capacitor occupies a large area of a chip, the invention provides a digital isolator with a pseudo-differential structure, as shown in fig. 3, each signal modulation circuit is connected with an isolation capacitor to form a signal path, a common redundancy circuit 3 is added in the digital isolator, and the common redundancy circuit 3 comprises a common isolation capacitor CISO0And the common redundancy channel VREF and each signal path form a pseudo-differential structure, when the digital isolator is subjected to common-mode interference, the common redundancy channel VREF feeds the common-mode interference back to each signal path, meanwhile, the signal path formed by the isolation capacitor and the signal modulation circuit carries modulated high-frequency signals and a small part of high-frequency common-mode transient interference signals, and for the signal demodulation circuit, pseudo-differential signals are received. The pseudo-differential structure formed by sharing a common redundancy channel VREF by each signal path reserves the characteristics of a fully differential structure and can still improveCommon mode transient interference of stages T3-T4 and T5-T6. As can be seen from fig. 3, each signal path shares a common redundancy channel VREF to form a pseudo-differential structure, and when the digital isolator has N signal paths, N +1 isolation capacitors are required, which reduces N-1 isolation capacitors compared with a fully-differential structure, and reduces the number of isolation capacitors, thereby saving the chip area of the digital isolator. It should be noted that the common mode signal conversion element in the common redundancy circuit 3 may be any one of a resistor, an operational amplifier, a current mirror, and the like, and the present invention is not limited thereto.
The common mode range of circuit input of the general fully differential structure is limited, when the common mode voltage input by the signal demodulation circuit exceeds the common mode range, the communication failure of the output end DOUT _1 can occur, in order to avoid the possibility of the communication failure of the digital isolator, the digital isolator provided by the invention is additionally provided with a common redundancy circuit 3, a filter is additionally arranged outside a pseudo-differential structure formed by the digital isolator and a signal modulation circuit, the filter is connected between a common mode signal conversion element and the signal demodulation circuit in a common redundancy channel VREF, and a filter is arranged in each signal path and connected between an isolation capacitor and the signal demodulation circuit. Therefore, the pseudo-differential structure formed by the public redundancy circuit 3 and the signal modulation circuit is added, so that the area of a chip is saved, the characteristic of a full-differential structure is kept, communication failure caused when common-mode voltage input by the signal demodulation circuit exceeds a common-mode range is avoided, partial signal distortion caused by a signal path and a public redundancy channel VREF is avoided, and the common-mode transient anti-interference capability of the digital isolator is further enhanced.
In a specific embodiment, in order to further ensure normal transmission of signals, an alternating current coupling circuit is additionally arranged in the digital isolator, and an input end of the alternating current coupling circuit is connected with a common mode signal conversion element in the common redundancy circuit 3 and an isolation capacitor in a signal path, so that transient distortion caused by common mode interference components can be avoided.
In addition, in order to avoid the signal demodulation failure of the signal demodulation circuit, a burr filtering circuit is added in the digital isolator, and the burr filtering circuit is connected with the output end of the signal demodulation circuit and used for filtering the signal which is demodulated by the signal demodulation circuit failure so as to ensure the normal transmission of the signal of the digital isolator.
Note that, in order not to destroy the pseudo differential structure formed by the common redundant circuit 3 and the signal modulation circuit, the capacitance values of the common isolation capacitor in the common redundant channel VREF and the isolation capacitor in the signal path are set to be compatible. In addition, the number of the common isolation capacitor in the common redundancy channel VREF and the isolation capacitor in the signal path may be one, two or more, which is not limited in the present invention.
The invention provides a digital isolator, comprising: the signal demodulation circuit comprises a signal modulation circuit, a signal demodulation circuit, a common redundancy circuit and an isolation capacitor. The isolation capacitor is connected between the signal modulation circuit and the signal demodulation circuit, the common redundancy circuit comprises a common-mode signal conversion element and a common isolation capacitor, one end of the common-mode signal conversion element is connected with one end of the common isolation capacitor, the other end of the common-mode signal conversion element is connected with the input end of each signal demodulation circuit and used for converting common-mode current into common-mode voltage, and the other end of the common isolation capacitor is grounded. When the digital isolator adopts a fully differential structure, a differential structure formed by the signal modulation circuit and the signal demodulation circuit at least needs to be connected with 2 capacitors, when the digital isolator has N channels, 2N isolation capacitors are needed, the number of the isolation capacitors is twice that of a single-end digital isolator, and a large amount of area of a chip is occupied.
In a specific embodiment, from the viewpoint of cost, the common mode signal conversion element is provided as a resistor, one end of the common isolation capacitor is connected to the resistor, the other end is grounded, and the other end of the resistor is connected to the input terminal of the signal demodulation circuit.
In the digital isolator provided by this embodiment, the common-mode signal conversion element is set as a resistor, the common redundancy circuit is a simplest structure, when the digital isolator is subjected to the common-mode transient interference, the resistor converts the common-mode current into the common-mode voltage, and the common-mode voltage and the signal received by the signal modulation circuit form a pseudo-differential signal, so that the characteristic of a fully-differential structure is retained for the common-mode interference signal, and the interference of the common-mode transient to the digital isolator is improved.
In a specific embodiment, the digital isolation provided by the invention adds the pseudo-differential structure formed by the common redundancy circuit 3 and the signal modulation circuit, so that the number of isolation capacitors is reduced, the characteristics of a fully differential structure are kept, and the common-mode interference resistance of the digital isolator is enhanced. In order to improve the signal distortion of the digital isolator in a short time, the digital isolator provided by the invention is additionally provided with a first filter 4 and a second filter 5, wherein the first filter 4 is connected between the common-mode signal conversion element and the signal demodulation circuit, and the second filter 5 is connected between the isolation capacitor and the signal demodulation circuit.
The digital isolator provided by the embodiment is additionally provided with the filter, so that partial distortion of signals in a short time caused when the digital isolator is subjected to common-mode transient interference in the signal transmission process can be avoided, normal transmission of the signals is ensured, and communication failure of the digital isolator caused by signal distortion is avoided.
Based on the above embodiment, in order to ensure the reliability of the transmission signal and ensure the normal communication of the digital isolator, an ac coupling circuit is added in the digital isolator, and the input end of the ac coupling circuit is connected with the common mode signal conversion element in the common redundancy circuit 3 and the isolation capacitor in the signal path.
The digital isolator provided by the embodiment is additionally provided with the alternating current coupling circuit, transient distortion caused by common-mode interference components can be avoided on the basis of adding the filter to avoid transient signal distortion, and the common-mode transient anti-interference capability of the digital isolator is further enhanced.
In a specific embodiment, a possibility of demodulation failure may occur in the process of demodulating the received high-frequency signal into a low-frequency signal by the signal demodulation circuit, thereby causing a signal transmission failure. In order to avoid the signal demodulation failure of the signal demodulation circuit, a burr filtering circuit is added in the digital isolator, and the burr filtering circuit is connected with the output end of the signal demodulation circuit and used for filtering the signal which is demodulated by the signal demodulation circuit failure so as to ensure the normal transmission of the signal of the digital isolator.
The digital isolator provided by the embodiment is additionally provided with the burr filtering circuit, when the signal demodulation circuit receives a high-frequency signal transmitted by a previous-level system, the high-frequency signal is demodulated into a low-frequency signal and transmitted to a next-level system, if the signal demodulation circuit fails to demodulate the high-frequency signal, the signal is transmitted to the burr filtering circuit, the burr filtering circuit filters the signal with failed demodulation, normal transmission of the signal is ensured, and the signal transmission reliability of the digital isolator is further improved.
FIG. 4 is a schematic diagram of a pseudo-differential structure-based digital isolator. In a specific embodiment, the filter is configured as a first-order passive filter, which includes a resistor and a capacitor, from the viewpoint of cost, power consumption, structural complexity, and operational reliability. As shown in fig. 4, taking the signal path VSIG1 as an example, the first filter 4 includes a first resistor R1 and a first capacitor C1, and the second filter 5 includes a second resistor R2 and a second capacitor C2. One end of the first capacitor C1 is connected with the first resistor R1, the other end is connected with the input end of the ac coupling circuit, the common end of the first capacitor C1 and the first resistor R1 is connected with the resistor R, and the free end of the first resistor R1 is grounded. One end of a second capacitor C2 is connected with the second resistor R2, the other end is connected with the input end of the signal demodulation circuit, and the common end of the second capacitor C2 and the second resistor R2 and the isolation capacitor CISO1The free end of the second resistor R2 is connected to ground. FIG. 5 is a waveform diagram of the pseudo-differential structure based digital isolator of FIG. 4. Referring to FIG. 5, also taking signal path VSIG1 as an example for explanation, during the phases T7-T8 and T9-T10, common mode interference occurs while signal transmission is performed, and the common redundancy channel VREF and the signal path VSIG1 are in short timePart of signal distortion occurs, but due to the filtering characteristics of the first filter 4 and the second filter 5, the first resistor R1 and the second resistor R2 absorb most of the low-frequency and medium-frequency current in the common-mode interference, and a small part of the high-frequency component is transmitted to the rear-stage alternating-current coupling circuit through the filters, meanwhile, the high-frequency modulation signal in the signal path can smoothly pass through the first capacitor C1 and the second capacitor C2, and the common-mode interference of the same component of a small part of the common redundant channel is transmitted to the alternating-current coupling circuit. Therefore, the waveforms of the common redundancy channel VREF and the signal path VSIG1 are substantially consistent with the common mode interference which does not occur in the stages of T7-T8 and T9-T10. Therefore, the common-mode input range of the signal demodulation circuit of the second chip 2 only deviates from the set common-mode voltage for a short time, and the risk of communication failure caused by the limited input common-mode range of the traditional fully differential circuit is avoided.
The digital isolator provided by the embodiment is configured as a first-order passive filter, the filter includes a resistor and a capacitor, correspondingly, the first filter includes a first resistor R1 and a first capacitor C1, and the second filter includes a second resistor R2 and a second capacitor C2. When the digital isolator generates common-mode transient interference, if the common redundancy channel VREF and the signal path generate partial signal distortion within a short time, the first filter and the second filter can filter signals, the influence of the signal distortion on communication is eliminated, the risk of communication failure is avoided, and further the common-mode transient interference resistance of the digital isolator is improved.
On the basis of the above embodiment, in order to ensure the signal strength transmitted by the digital isolator, the resistance values of the first resistor R1 and the second resistor R2 are set to be the same, and the capacitance values of the first capacitor C1 and the second capacitor C2 are set to be the same.
In the digital isolator provided by the embodiment, the resistances of the first resistor R1 and the second resistor R2 are set to be the same, and the capacitances of the first capacitor C1 and the second capacitor C2 are set to be the same, when the digital isolator generates common-mode transient interference, the first resistor R1 and the first capacitor C1 of the first filter and the second resistor R2 and the second capacitor C2 of the second filter signals, so that the common redundancy channel VREF and a signal path are prevented from generating partial signal distortion within a short time, the strength of transmitted signals is ensured, and the reliability of signal transmission of the digital isolator is improved.
In an embodiment, consider if the common isolation capacitance CISO0And an isolation capacitor CISO1The capacitance values of the capacitors (C) are different, the pseudo-differential structure of the digital isolator can be damaged, and the possibility of communication failure is increased, so that the common isolation capacitor C is usedISO0And an isolation capacitor CISO1The capacitance values of (a) are set to be the same.
In the digital isolator provided by this embodiment, the common isolation capacitor C is usedISO0And an isolation capacitor CISO1The capacitance values are set to be the same, so that the pseudo-differential structure of the digital isolator cannot be damaged, the strength of a transmission signal is ensured, the normal transmission of the signal is ensured, and the common-mode transient anti-interference capability of the digital isolator is further enhanced.
In a specific embodiment, from the viewpoint of high voltage resistance, two common isolation capacitors are connected between the common mode signal conversion element and the ground, and two isolation capacitors are connected between each signal modulation circuit and the signal demodulation circuit. It should be noted that, the capacitance values of the common isolation capacitor and the isolation capacitor are set to be the same without destroying the pseudo-differential structure.
The digital isolator provided by the embodiment sets the number of the common isolation capacitors between the common mode signal conversion element and the ground and the number of the isolation capacitors between each signal modulation circuit and each signal demodulation circuit to two, so that the strength of signal transmission can be ensured, the voltage withstanding degree of a common redundancy channel VREF and a signal path can be ensured, and the reliability of the digital isolator is improved.
In order to make those skilled in the art better understand the technical solution of the present invention, the following will be described in further detail with reference to the schematic diagram of the pseudo-differential structure-based digital isolator shown in fig. 4 and the waveform diagram of the pseudo-differential structure-based digital isolator shown in fig. 4 and shown in fig. 5. The following description will be described in detail with reference to the signal path VSIG1 as an example.
As shown in FIG. 4, the digital isolator includes a plurality of signal paths, and the common redundancy circuit 3 includesCommon isolation capacitor CISO0The first filter 4 comprises a first resistor R1 and a first capacitor C1, one end of the first capacitor C1 is connected with the first resistor R1, the other end of the first capacitor C1 is connected with the input end of the alternating current coupling circuit, the common end of the first capacitor C1 and the first resistor R1 is connected with the resistor R, the free end of the first resistor R2 is grounded, and the common isolation capacitor C is connected with the resistor RISO0One end of the second resistor is connected with the resistor R, and the other end of the second resistor is grounded to form a common redundancy channel VREF. Isolation capacitor CISO1One end of the second resistor R2 is connected to the signal modulation circuit, the other end is connected to the common end of the second resistor R2 and the second capacitor C2 in the second filter 5, the free end of the second capacitor is connected to the input end of the ac coupling circuit, and the free end of the second resistor R2 is grounded to form a signal path VSIG 1. Signal path VSIG1 forms a pseudo-differential structure with common redundancy channel VREF.
The digital isolator adopts a fully differential structure, and mainly aims to solve the problem of common-mode transient interference generated by the first chip 1 and the second chip 2 in an unconventional mode, as shown in fig. 1, when the digital isolator adopts the fully differential structure, the differential structure formed between the signal modulation circuit and the signal demodulation circuit at least needs to be connected with 2 capacitors, when N channels exist, 2N isolation capacitors are needed, the number of the isolation capacitors is twice that of the single-end digital isolator, if the voltage withstanding degree of the circuit is considered, each channel needs to be connected with 4 isolation capacitors, correspondingly, when N channels exist, 4N isolation capacitors are needed, and a large amount of area of the chip is occupied. In order to solve the problem, the invention provides a digital isolator with a pseudo-differential structure, a plurality of signal paths shown in fig. 1 can adopt a single-ended form as shown in fig. 4, a common redundancy channel VREF is added, a common mode interference component is extracted and is superposed in each path of digital isolator, a common redundancy circuit 3 is added, the use of isolation capacitors can be obviously reduced, and further the chip area is saved, when the digital isolator has N signal paths, N +1 isolation capacitors are needed, compared with the traditional full-differential scheme, N-1 capacitors are saved, and the small area and the low cost of a chip are realized.
In addition, the digital isolator provided by the invention is additionally provided with the filter and the alternating current coupling circuit, so that the amplitude of a transmitted signal is ensured while the digital isolator absorbs common-mode transient interference, the gain requirement of the digital isolator on the demodulation circuit is obviously reduced, the reliability of a system is improved, the requirement of the signal demodulation circuit on the amplification factor of the signal is reduced, the power consumption of the system is saved, and the problem that the amplitude of a signal at the input end of the signal demodulation circuit is limited when the traditional digital isolator generates common-mode interference, so that the amplitude of an effective signal input when a digital signal normally works is smaller is solved.
As shown in FIG. 4, a common isolation capacitor CISO0The filter is a first-order filter of the common redundancy channel VREF, a first resistor R1 and a first capacitor C1 form a second-order filter of the common redundancy channel VREF, and an isolation capacitor CISO1The first order filter constituting the signal path and the second filter 5 constituting the second order filter of the signal path. When the digital isolator is subjected to common-mode transient interference, the common redundancy channel VREF feeds back the common-mode interference to the signal demodulation circuit of each signal path. The signal path is an isolation channel used for transmitting signals, carries high-frequency signals modulated by the signal modulation circuit and a small part of high-frequency common-mode transient interference signals, and for the signal demodulation circuit, pseudo differential signals are received.
When there is no common mode transient interference between GND1 and GND2, if the input terminal DIN _1 of the signal modulation circuit does not receive an input signal, the input signal VSIG of the first chip 1 is equal to VREF, as shown in fig. 5, which corresponds to a time before T1 in the diagram. If input DIN _1 of the signal conditioning circuit receives an input signal, VSIG superimposes a high frequency modulation signal on VREF, corresponding to stages T1-T2 in FIG. 5.
When the digital isolator is subjected to common-mode transient interference, at the stages of T3-T4 and T5-T6 in fig. 5, the first resistor R1 and the second resistor R2 in the second chip 2 absorb most of the medium-low frequency energy in the common-mode interference, and the generated voltage is V ═ VCMTI/(T4-T3)*CISO0,1R1,2, wherein VCMTIIs a common mode transient voltage, CISO0,1Is a common isolation capacitor CISO0Or an isolation capacitor CISO1The capacitance value R1,2 is the resistance value of the first resistor R1 or the second resistor R2. It should be noted that, in the following description,common isolation capacitor CISO0An isolation capacitor CISO1The capacitance values of the first resistor R1 and the second resistor R2 are equal. A small part of high-frequency components are transmitted to the signal demodulation circuit through the first capacitor C1 and the second capacitor C2, the signal path VSIG1 and the common redundancy channel VREF form a pseudo-differential structure, and the characteristics of the differential circuit are reserved for interference signals, so that the differential signals received by the input end of the signal demodulation circuit are still zero, and the common-mode transient anti-interference capability of the digital isolator is improved.
As shown in fig. 2, although the differential structure significantly improves the common mode interference at the stages T3-T4 and T5-T6, at the stage T7-T8, the reference ground at both sides of the first chip 1 and the second chip 2 changes Δ V within Δ T time, so that the common mode interference is improved by the isolation capacitor CISO1,2The second chip 2 is fed with a common-mode current Δ I ═ Δ V/# Δ T ═CISO1,2In which C isISO1,2The capacitance value of the isolation capacitor in fig. 2 causes the common mode of the input signals VINN and VINP of the signal demodulation circuit to significantly increase Δ I × R1,2, where R1,2 is the resistance value of the resistor R1 or R2 in the differential circuit in fig. 2, and the input common mode range of the circuit in the fully differential structure is usually limited, so that the signal demodulation circuit of the second chip 2 has a risk of input saturation or output voltage range reduction due to the excessively high input common mode range in the stages T7 to T8, and thus communication failure occurs on the output DOUT _ 1.
Similarly, this scheme is in the time period T9-T10, since the isolation capacitor will sink the common mode current Δ I ═ Δ V/Δ T × C from the second chip 2ISO1,2Therefore, the common-mode voltage of the input signals VINN and VINP becomes smaller by Δ I × R1,2, which may cause the risk of overvoltage of the signal demodulation circuit of the second chip 2, thereby affecting the long-term reliability of the chip, or exceeding the common-mode input range of the demodulation circuit, resulting in communication failure.
In order to solve the problem of communication failure in the stages of T7-T8 and T9-T10, the digital isolator provided by the invention is additionally provided with a filter, common-mode interference occurs while signals are transmitted, a first resistor R1 and a first capacitor C1 in a first filter 4 and a second resistor R2 and a second capacitor C2 in a second filter 5 act, and signal distortion control in a signal path VSIG1 and a common redundancy channel VREF occurs in a short time. The first resistor R1 and the second resistor R2 absorb most of the low-frequency and medium-frequency current in the common-mode interference, a small part of high-frequency components are transmitted to the rear-stage AC coupling circuit, meanwhile, a high-frequency modulation signal in the signal path VSIG1 is smoothly transmitted to the rear-stage AC coupling circuit through the first capacitor C1 and the second capacitor C2, and a small part of common-mode interference of the same components as the common redundancy channel is also transmitted to the rear-stage AC coupling circuit, so that the waveform of the signal path VSIG1 and the common redundancy channel VREF is basically consistent with the common-mode interference which does not occur in the whole stages of T7-T8 and T9-T10. In addition, the common-mode input range of the signal demodulation circuit of the second chip 2 deviates from the set common-mode voltage for a short time, and communication failures of the traditional fully differential circuit in stages T7-T8 and T9-T10 are avoided.
The input end of the alternating current coupling circuit is connected with a first capacitor C1 in a public redundancy channel VREF and a second capacitor C2 in a signal path VSIG1, and the output end of the alternating current coupling circuit is connected with the input ends VINN and VINP of the signal demodulation circuit, so that transient distortion caused by high-frequency components in the stages of T7-T8 and T9-T10 in common-mode interference is further weakened, and the common-mode transient anti-interference capability of the digital isolator is enhanced.
The burr filtering circuit is connected with the output end of the signal demodulation circuit, if very transient signal demodulation failure caused by circuit mismatch, network limited bandwidth and the like exists in the stages of T7-T8 and T9-T10, the burr filtering circuit can filter the signal which is failed in demodulation, and the common-mode transient anti-jamming capability of the digital isolator is further improved.
Therefore, the digital isolator provided by the invention changes a single-ended digital isolator into a pseudo-differential structure by adding a common redundant channel, retains the advantage of strong anti-interference capability of a fully-differential circuit, obviously reduces the number of isolation capacitors, saves the area of a chip and reduces the cost. In addition, an alternating current coupling circuit, a pass filter and a burr filtering circuit are additionally arranged in the second chip, and the common mode range of the input signals is controlled within a reasonable range, so that the risk of communication failure caused by overlarge common mode fluctuation of a traditional fully differential structure is avoided, and the transient anti-interference capability of the common mode is obviously enhanced.
The digital isolator with the pseudo-differential structure provided by the invention is described in detail above. The embodiments are described in a progressive manner in the specification, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
It is further noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Claims (10)
1. A digital isolator with a pseudo-differential structure, comprising: the signal demodulation circuit comprises a signal modulation circuit, a signal demodulation circuit, a common redundancy circuit and an isolation capacitor;
the isolation capacitor is connected between the signal modulation circuit and the signal demodulation circuit;
the common redundancy circuit comprises a common-mode signal conversion element and a common isolation capacitor, one end of the common-mode signal conversion element is connected with one end of the common isolation capacitor, the other end of the common-mode signal conversion element is connected with the input end of each signal demodulation circuit and used for converting common-mode current into common-mode voltage, and the other end of the common isolation capacitor is grounded.
2. The digital isolator according to claim 1, wherein the common mode signal converting element is a resistor, and correspondingly, one end of the resistor is connected to the common isolation capacitor, and the other end of the resistor is connected to the input end of each signal demodulating circuit.
3. The digital isolator of claim 1, further comprising a filter comprising a first filter and a second filter;
the first filter is connected between the common mode signal conversion element and the signal demodulation circuit, and the second filter is connected between the isolation capacitor and the signal demodulation circuit.
4. The digital isolator of claim 1, further comprising an ac coupling circuit;
the input end of the alternating current coupling circuit is connected with the common-mode signal conversion element and the isolation capacitor, and the output end of the alternating current coupling circuit is connected with the input end of the signal demodulation circuit.
5. The digital isolator according to claim 1, further comprising a glitch filtering circuit;
the burr filtering circuit is connected with the output end of the signal demodulation circuit.
6. The digital isolator according to claim 3, wherein the filter comprises a resistor and a capacitor, and correspondingly, the first filter comprises a first resistor and a first capacitor, and the second filter comprises a second resistor and a second capacitor;
one end of the first capacitor is connected with the first resistor, the other end of the first capacitor is connected with the input end of the signal demodulation circuit, the common end of the first capacitor and the first resistor is connected with the common-mode signal conversion element, and the free end of the first resistor is grounded;
one end of the second capacitor is connected with the second resistor, the other end of the second capacitor is connected with the input end of the signal demodulation circuit, the common end of the second capacitor and the second resistor is connected with the isolation capacitor, and the free end of the second resistor is grounded.
7. The digital isolator of claim 6, wherein the first resistor and the second resistor have the same resistance.
8. The digital isolator of claim 6, wherein the capacitance values of the first and second capacitors are the same.
9. The digital isolator according to any of claims 1-8, wherein the common isolation capacitance has the same capacitance value as the isolation capacitance.
10. The digital isolator according to claim 1, wherein two of said common isolation capacitors are connected between said common mode signal converting element and ground, and two of said isolation capacitors are connected between each of said signal modulating circuit and said signal demodulating circuit.
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