CN212381197U - Digital isolator - Google Patents

Abstract

The utility model provides a digital isolator, which is provided with a signal input module, an isolation capacitor module and a common mode transient disturbance rejection module; the isolation capacitor module is connected with the signal input module and the common-mode transient anti-interference module and is used for transmitting the differential signal processed by the signal input module to the common-mode transient anti-interference module in an isolation manner; the signal input module is a pseudo-differential circuit with impedance matching; the common-mode transient immunity module comprises a high-pass filter circuit and is used for removing the influence on a common-mode signal during CMTI transient and attenuating a low-frequency CMTI signal. Through the digital isolator, the common-mode transient immunity CMTI of the isolator can be effectively improved, meanwhile, the multi-channel common-mode and impedance-matched pseudo-differential circuit can achieve the CMTI effect as good as that of a fully differential circuit, simplify the circuit structure and greatly save the area and power consumption of a chip.

Description

Digital isolator

Technical Field

The utility model relates to a high voltage isolation circuit field especially relates to a digital isolator.

Background

High-voltage capacitor isolation circuits are increasingly applied to signal transmission between chips or systems in different power domains, and can provide electrical isolation of thousands of volts between two or more chips or systems, realize ground isolation between different power domains, and improve the reliability of the chips or systems. The common mode transient immunity CMTI represents the ability of the isolator to withstand rapid changes in the potential difference between its grounds, i.e., without causing bit errors when the common mode changes rapidly. A high CMTI indicates a robust isolated channel. During testing, transient high-voltage pulse is added between two grounds of an isolator chip to serve as a common-mode interference signal, an input end is connected with a high level or a low level, and when high-voltage pulse impact occurs, the condition that an output end signal follows an input end signal and is free from error is ensured; the rising/falling slope of the maximum pulse signal which can be borne at the moment is defined as the transient common mode rejection capability, the unit is KV/us, CMTI is one of the most important parameters for evaluating the performance of the isolator, how to improve the CMTI capability is the key of the design of the isolator, and the isolator in the prior art has the problems of large occupied area and large power consumption.

Therefore, it is desirable to provide an isolator with high common mode transient immunity and low power consumption.

SUMMERY OF THE UTILITY MODEL

In order to solve the above problem, an object of the present invention is to provide a digital isolator, including signal input module, isolation capacitance module and common mode transient immunity module, effectual common mode transient immunity CMTI of improvement isolator simultaneously, can also simplify circuit structure when realizing the CMTI effect as good as the fully differential circuit when adopting the pseudo-differential circuit of the just impedance match of multichannel sharing common mode, saves the area and the consumption of chip in a large number.

In particular, one aspect of the present invention provides a digital isolator having a signal input module, an isolation capacitor module, and a common mode transient immunity module; the isolation capacitor module is connected with the signal input module and the common-mode transient anti-interference module and is used for transmitting the differential signal processed by the signal input module to the common-mode transient anti-interference module in an isolation manner; the signal input module is a pseudo-differential circuit with impedance matching; the common-mode transient immunity module comprises a high-pass filter circuit and is used for removing the influence on a common-mode signal during CMTI transient and attenuating a low-frequency CMTI signal.

Preferably, the high-pass filter circuit is a second-order or multi-order high-pass filter circuit with a common mode clamp.

Preferably, the common mode transient immunity module further comprises a pre-amplifying circuit, and the pre-amplifying circuit adopts multi-stage amplification and is connected in series with a high-pass filter with a common mode arrangement in the middle.

Preferably, the common-mode transient immunity module further comprises a band-stop filter circuit, and the band-stop filter circuit and the high-pass filter circuit jointly suppress the common-mode transient signal.

Preferably, when a plurality of pseudo-differential circuits are present, they share one or more impedance-matched common-mode paths.

Preferably, the reference signal of the common mode path is a direct current common mode signal or a power supply signal or a ground signal of an input terminal.

Preferably, the demodulator to which the digital isolator is connected has an envelope detector and a spur filter.

Preferably, the isolation capacitance module is a series and/or parallel circuit of one or more capacitors.

Preferably, the signal input module is a fully differential circuit.

After the technical scheme is adopted, compared with the prior art, the method has the following beneficial effects:

1. the common-mode transient immunity of the isolator is effectively improved;

2. the circuit structure is simplified, and the area and the power consumption of a chip are greatly saved.

Drawings

Fig. 1 is a schematic structural diagram of a digital isolator according to a preferred embodiment of the present invention;

FIG. 2 is a graph of transient behavior during CMTI suppression in accordance with a preferred embodiment of the present invention;

fig. 3 is an amplitude-frequency characteristic diagram in accordance with a preferred embodiment of the present invention;

fig. 4 is a schematic circuit diagram of a digital isolator in a modulation scheme according to a preferred embodiment of the present invention.

Detailed Description

The advantages of the present invention will be further explained with reference to the accompanying drawings and specific embodiments.

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the exemplary embodiments below are not intended to represent all implementations consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present disclosure, as detailed in the appended claims.

The terminology used in the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used in this disclosure and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present disclosure. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context.

In the following description, suffixes such as "module", "part", or "unit" used to indicate elements are used only for the convenience of description of the present invention, and have no specific meaning in itself. Thus, "module" and "component" may be used in a mixture.

Referring to fig. 1, a digital isolator according to a preferred embodiment of the present invention has a signal input module, an isolation capacitor module, and a common mode transient immunity module.

Keep apart the electric capacity module and be connected with signal input module and common mode transient state immunity module, the utility model discloses an among the digital isolator, signal input module is located the TX end of signal, and common mode transient state immunity module is located the RX end of signal, keeps apart the electric capacity module and keeps apart the transmission to the common mode transient state immunity module of RX end with the difference signal that TX end process signal input module handled.

The utility model discloses do not restrict the implementation of keeping apart the electric capacity module, keep apart the electric capacity module and only do the utility model discloses the signal transmission passageway of digital isolator, any circuit that can realize signal isolation transmission is all in the utility model discloses an in the protection range, if, keep apart the series connection and/parallel circuit that the electric capacity module adopted one or more electric capacity.

In order to obtain better CMTI effect, the utility model discloses the TX end adopts signal input module to carry out differential processing to the signal, and signal input module can adopt fully differential circuit or pseudo-differential circuit all can, all be in the utility model discloses a protection range.

By adopting the fully differential circuit, better common-mode interference resistance can be realized, the common-mode noise of signals received by the receiving end can be almost completely offset, and the CMTI circuit has better CMTI effect and is suitable for long-distance transmission. However, there is a problem in that the fully differential circuit needs to convert each single-ended signal differentially and output two signals, one in phase with the original signal and one in anti-phase with the original signal, that is, for each signal to be transmitted, a positive phase path and a negative phase path are required. If a plurality of signals need to be transmitted, if N, 2 times, that is, 2N paths are needed for signal transmission, and the requirements for the circuit arrangement and the wiring area are higher when the signal transmission requirement is large, which is not beneficial to saving the chip area.

Therefore, as an improvement to the above technical solution, in a preferred embodiment, the signal input module of the TX end of the present invention adopts a pseudo-differential circuit architecture. Preferably an impedance matched pseudo-differential circuit. The CMTI is the rapid change of the potential difference between two sides of the isolator, through the pseudo-differential circuit, the common mode change brought by the CMTI on all the paths sharing the ground can be detected only by one path of impedance matching common mode path, and other paths can share the common mode signal as a reference source to carry out the difference. That is, when there is multi-channel signal transmission, all the paths can detect the common mode change caused by CMTI on all the paths only by sharing one common mode path, so as to suppress the common mode interference, and the required path is N +1 at this time, so that the chip area and the power consumption can be effectively saved. And by setting the common-mode path impedance matching, the CMTI effect as good as that of a fully differential circuit can be realized.

The utility model discloses well common mode transient state immunity module that is located the RX end receives isolation capacitance module transmission signal for to the influence of common mode signal, decay low frequency CMTI signal when getting rid of the CMTI transient. The common mode transient immunity module comprises a high-pass filter circuit, preferably a second-order or multi-order high-pass filter circuit with a common mode clamp, and inhibits common mode signals with lower frequency and low frequency jitter on the ground. The utility model provides a high pass filter circuit can cut through reasonable design low frequency to the frequency and attenuate the low frequency disturbance, through high pass filter suppression direct current signal simultaneously, resets common mode signal through the common mode clamp and realizes getting rid of the influence that the common mode point drift that the preceding stage mismatch caused. The utility model discloses in, do not restrict high pass filter circuit's order among the common mode transient state immunity module, high pass filter circuit's order can be the second order also can be multistage, all is the utility model discloses an within the protection scope, multistage high pass filter helps improving the band gap border precipitous degree of wave filter.

Referring to fig. 2, in order to show the transient characteristic diagram of CMTI suppression according to a preferred embodiment of the present invention, it can be seen from the transient characteristic in the diagram that a VCM signal of several kilovolts becomes a V1 signal of several kilovolts after passing through an isolation capacitor module, and becomes a V2 signal having small spikes only at the edge of the VCM signal change after passing through a high pass filter circuit (the common mode level of the V2 signal is set by VR). Preferably, the high-pass filter circuit of the common-mode transient immunity module is followed by a differential amplifier to remove the small spike of the V2 signal.

Through the common mode transient immunity module, the signal enters the demodulator at the RX end for final demodulation, and in the demodulator, part of the high-frequency signal converted from the common mode to the differential mode due to mismatch can be removed through various filtering forms (such as a glitch filter or a low-pass filter). Referring to fig. 3, in order to obtain an amplitude-frequency characteristic diagram according to a preferred embodiment of the present invention, it can be seen from fig. 3 that the CMTI signal can be attenuated to the maximum extent without affecting the amplification of the carrier signal as long as the cut-off frequency is designed reasonably.

Based on the above embodiments, in a preferred embodiment, when the signal input module at the TX end adopts a pseudo-differential circuit, the common-mode transient immunity module at the RX end adopts a second-order or multi-order high-pass filter with a common-mode clamp, and the second-order or multi-order high-pass filter provides good impedance matching for the pseudo-differential structure, thereby achieving a CMTI effect as good as that of a fully differential circuit, and greatly saving the area and power consumption of the circuit by sharing a common-mode path.

When adopting pseudo-differential circuit, above-mentioned multichannel signal sharing common mode passageway all the way is the utility model discloses an optimal technical scheme is not only technical scheme. The utility model discloses be not restricted to the quantity and the sharing condition of common mode route in the pseudo-differential circuit, both can be as above multichannel (including two the tunnel) sharing common mode all the way, also can every signal all the way set up the common mode change that own common mode route detection CMTI brought, also can the multichannel common mode of multichannel sharing, the part sharing is all the way promptly, other sharing or branch use the multichannel, all are in the utility model discloses an within the protection scope. Preferably, when there are multiple pseudo-differential circuits, as described above, the multiple pseudo-differential circuits share one or more impedance-matched common-mode paths.

In the above embodiment, the input signal of the common mode path is the dc common mode voltage of one circuit, the power supply of the TX end, the ground or other internal reference potentials that can reflect the common mode change can be selected, and the selection of other potentials can also be understood as the deformation of the technical solution, which is also within the protection scope of the present invention.

In a preferred embodiment, the common-mode transient immunity module at the RX end further includes a pre-amplifier circuit, the pre-amplifier circuit is connected to the high-pass filter circuit, and receives a signal after the common-mode signal is substantially suppressed after the high-pass filter process, the pre-amplifier circuit is disposed at the front end of the demodulator, and as a pre-process before demodulation, the pre-amplifier circuit employs multi-stage amplification and connects a high-pass filter with a common-mode setting in the middle in series, so as to further improve the common-mode rejection and remove the mismatch influence. Referring to fig. 3, the signal output after passing through the pre-amplification circuit is V3, the amplitude-frequency characteristic of which is shown in the figure, and by additionally arranging the pre-amplification circuit, it is possible to provide good gain for the carrier signal while further attenuating the common mode signal and removing the mismatch of the previous stage.

In a preferred embodiment, the common-mode transient immunity module at the RX end further includes a band-stop filter circuit, and the band-stop filter circuit and the high-pass filter circuit jointly suppress the common-mode transient signal to obtain a better CMTI effect.

It should be noted that the utility model discloses a digital isolator is applicable to multiple modulation-demodulation framework, can use OOK modulation or marginal modulation or also other modulations if TX partial modulation, and RX's demodulation can be envelope detection or other demodulation methods, all can adopt the utility model discloses a digital isolator arranges in order to obtain better CMTI effect or save circuit space, the utility model discloses do not restrict the type of the modulation-demodulation framework that is suitable for, as long as adopt the utility model discloses a digital isolator all is within the protection band.

Fig. 4 is a schematic circuit diagram of a digital isolator in a modulation scheme according to a preferred embodiment of the present invention. Fig. 4 shows a circuit embodiment of a digital isolator for improving CMTI according to the present invention, in which the isolator includes a signal input module composed of a pseudo-differential circuit, a common mode transient immunity module composed of a multi-step high-pass filter circuit and a pre-amplifier circuit, and an isolation capacitor module.

In the embodiment of the isolator, firstly, a signal is modulated and then transmitted through a PA, and meanwhile, a power supply VDD (which may also be a ground or other internal direct-current voltage reference point) at a TX end is also transmitted through the PA to implement impedance matching, which is a key for implementing common-mode signal matching of signal transmission and common-mode path transmission. Preferably, the output stage of the PA and the high-pass filter behind the isolation capacitor have better impedance matching.

As described in the above embodiments, the common mode signal transmitted by the common mode channel can be shared in multiple ways, i.e. one common mode channel is used for multiple signal channels, so as to reduce the power consumption and area of the circuit. The high-pass filter circuit adopts a common-mode clamped multi-order high-pass filter circuit and is used for inhibiting the influence on a common-mode signal during CMTI transient and attenuating a low-frequency CMTI signal. The pre-amplifying circuit adopts a high-pass filter which is amplified in multiple stages and arranged in a common mode in the middle series band so as to improve common mode rejection and remove the influence of mismatch.

The pre-amplified signal enters a demodulator consisting of an envelope detector and a spur filter to recover the input signal. The envelope detector is used for removing a carrier and demodulating a signal, and the burr eliminating circuit at the later stage is used for removing error codes, noise and phase loss caused by high-frequency noise and carrier modulation, so that a better CMTI (CMTI) effect is achieved.

The above-mentioned digital isolator based on a certain modulation architecture is only an example for explaining how to implement the architecture, and the digital isolator of the present invention is applicable to various modulation architectures, and is not limited to this embodiment.

Through the utility model discloses a digital isolator adopts the high pass filter circuit who takes the common mode clamp and can restrain the common mode signal effectively with signal input module, improves the CMTI effect, simultaneously, adopts impedance matching's pseudo-differential circuit can further save the consumption and the area of circuit when guaranteeing better CMTI effect, has great meaning to the chip design.

It should be noted that the embodiments of the present invention have better practicability and are not intended to limit the present invention in any way, and any person skilled in the art may change or modify the technical contents disclosed above to equivalent effective embodiments, but all the modifications or equivalent changes and modifications made to the above embodiments according to the technical spirit of the present invention still fall within the scope of the technical solution of the present invention.

Claims (9)

1. A digital isolator is characterized by comprising a signal input module, an isolation capacitor module and a common-mode transient disturbance rejection module;

the isolation capacitor module is connected with the signal input module and the common-mode transient anti-interference module and is used for transmitting the differential signal processed by the signal input module to the common-mode transient anti-interference module in an isolation manner;

the signal input module is a pseudo-differential circuit with impedance matching;

the common-mode transient immunity module comprises a high-pass filter circuit and is used for removing the influence on a common-mode signal during CMTI transient and attenuating a low-frequency CMTI signal.

2. The digital isolator of claim 1, wherein the high pass filter circuit is a second or multiple order high pass filter circuit with common mode clamping.

3. The digital isolator of claim 1, wherein the common mode transient immunity module further comprises a pre-amplification circuit that employs multi-stage amplification and a high pass filter in a middle series band common mode arrangement.

4. The digital isolator of claim 1, wherein the common mode transient immunity module further comprises a band-reject filter circuit that together with the high-pass filter circuit rejects common mode transient signals.

5. The digital isolator of claim 1, wherein when a plurality of pseudo-differential circuits are present, the plurality of pseudo-differential circuits share one or more impedance-matched common-mode paths.

6. The digital isolator according to claim 5, wherein the reference signal of the common mode path is a DC common mode signal or a power signal or a ground signal of an input terminal.

7. The digital isolator according to any of claims 1-6, wherein the demodulator to which the digital isolator is connected has an envelope detector and a glitch filter.

8. The digital isolator of any of claims 1-6, wherein the isolation capacitance module is a series and/or parallel circuit of one or more capacitors.

9. The digital isolator of any of claims 1-4, wherein the signal input module is a fully differential circuit.

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