PWM signal anti-interference circuit and corresponding circuit board

Abstract

The utility model provides a PWM (Pulse Width Modulation) signal anti-interference circuit and a corresponding circuit board, and an optical coupler isolation module can receive a PWM signal output by an FPGA (Field Programmable Gate Array) chip and perform isolation operation on the PWM signal. The signal amplification module is connected with the optocoupler isolation module, and the signal amplification module can carry out voltage amplification operation on the PWM signal, thereby improving the driving capability of the PWM signal. The current limiting module is connected with the signal amplification module, and the current limiting module can transmit the PWM signal to the interface module. And when the current value of the PWM signal is greater than a set value, the current limiting module is in an off state, so that a post-stage circuit and equipment are protected. The interface module is connected with the current limiting module, and the interface module can transmit the PWM signal to a post-stage device. The surge suppression module and the discharge module are both connected with the interface module in parallel, the surge suppression module can perform surge suppression operation on PWM signals, and the discharge module can perform discharge operation on electromagnetic interference of the PWM signals.

Description

Technical Field

[0001] The utility model relates to the technical field of circuits, and in particular to a PWM signal anti-interference circuit and a corresponding circuit board. Background Art

[0002] In modern society, FPGA is widely used in many fields such as communication. Moreover, the signal output by the FPGA chip can be used to drive the subsequent equipment. However, the signal is easily interfered by noise or electromagnetic radiation during the transmission process. Therefore, there is a technical problem that the signal output by the FPGA chip is prone to malfunction due to interference.

[0003] Therefore, it is necessary to provide a PWM signal anti-interference circuit and a corresponding circuit board to solve the above technical problems. Utility Model Content

[0004] The utility model provides a PWM signal anti-interference circuit and a corresponding circuit board, which effectively solves the technical problem that the signal output by the FPGA chip is prone to malfunction due to interference.

[0005] The utility model provides a PWM signal anti-interference circuit, which comprises:

[0006] An optical coupler isolation module, used to receive the PWM signal output by the FPGA chip and perform an isolation operation on the PWM signal;

[0007] A signal amplification module, connected to the optical coupling isolation module, for performing a voltage amplification operation on the PWM signal, thereby improving the driving capability of the PWM signal;

[0008] A current limiting module, connected to the signal amplifying module, for transmitting the PWM signal to the interface module, and when the current value of the PWM signal is greater than a set value, the current limiting module is in a disconnected state, thereby protecting subsequent circuits and devices;

[0009] The interface module is connected to the current limiting module and is used to transmit the PWM signal to the subsequent device, and the PWM signal is used to drive the subsequent device;

[0010] A surge suppression module, connected in parallel with the interface module, and configured to perform surge suppression operation on the PWM signal;

[0011] The discharge module is connected in parallel with the interface module and is used to discharge the electromagnetic interference of the PWM signal. The PWM signal output by the FPGA is output after isolation and amplification, which can improve the driving ability of the signal. The surge suppression module can perform surge suppression on the PWM signal. The discharge module can discharge the electromagnetic interference of the PWM signal, thereby improving the anti-interference ability of the PWM signal and further improving the reliability of the circuit.

[0012] Furthermore, the optocoupler isolation module includes an optocoupler isolation chip, which is used to isolate the PWM signal. The optocoupler isolation chip includes an input pin and an output pin, and the input pin is used to input the PWM signal. The signal amplification module includes a transistor and a PWM power supply, and the transistor is used to perform voltage amplification on the PWM signal. The base of the transistor is connected to the output pin, the emitter of the transistor is connected to the PWM power supply, and the collector of the transistor is used to output the PWM signal.

[0013] Furthermore, the current limiting module includes a resettable fuse, one end of the resettable fuse is connected to the collector of the transistor, and the other end of the resettable fuse is connected to the interface module;

[0014] When the current value of the PWM signal is greater than the set value, the resettable fuse is in an off state; when the current value of the PWM signal is less than or equal to the set value, the resettable fuse is in an on state.

[0015] Furthermore, the surge suppression module includes a transient voltage suppression tube, one end of which is connected between the resettable fuse and the interface module, and the other end of which is grounded.

[0016] Furthermore, the discharge module includes a discharge resistor and a discharge capacitor, one end of the discharge resistor is connected between the self-resetting fuse and the interface module, and the other end of the discharge resistor is grounded; one end of the discharge capacitor is connected between the self-resetting fuse and the interface module, and the other end of the discharge capacitor is grounded.

[0017] Furthermore, the PWM signal anti-interference circuit also includes a filter module, one end of the filter module is connected to the current limiting module, and the other end of the filter module is grounded, and the filter module is used to perform a filtering operation on the PWM signal.

[0018] Furthermore, the filtering module includes a first filter capacitor and a second filter capacitor, one end of the first filter capacitor is connected between the self-recovering fuse and the interface module, the other end of the first filter capacitor is grounded, and the second filter capacitor is connected in parallel with the first filter capacitor.

[0019] Furthermore, the PWM signal anti-interference circuit also includes a power supply module and a power isolation module, the power supply module is used to output a power supply voltage, and the power supply voltage is used to power the optocoupler isolation chip. The optocoupler isolation chip also includes a power pin, and the power isolation module includes a +Vi n pin and a VO+ pin. The +Vi n pin is connected to the power supply module, and the VO+ pin is connected to the power pin. The power isolation module is used to isolate the power supply module.

[0020] Furthermore, the optocoupler isolation module also includes a current limiting resistor, one end of the current limiting resistor is connected to the FPGA chip, and the other end of the current limiting resistor is connected to the input pin of the optocoupler isolation chip, and the current limiting resistor is used to perform current limiting operation on the PWM signal.

[0021] A circuit board comprises any one of the above-mentioned PWM signal anti-interference circuits.

[0022] Compared with the prior art, the utility model has the following beneficial effects: the utility model provides a PWM signal anti-interference circuit, which includes an optocoupler isolation module, a signal amplification module, a current limiting module, an interface module and a surge suppression module. The PWM signal output by the FPGA is isolated by the optocoupler isolation module, and the signal amplification module can amplify the PWM signal, which effectively improves the driving ability of the PWM signal. In addition, the surge suppression module can perform surge suppression on the PWM signal, and the discharge module can discharge the electromagnetic interference of the PWM signal. Therefore, the PWM signal will not be interfered by noise or electromagnetic radiation during transmission. The setting of the PWM signal anti-interference circuit improves the anti-interference ability of the PWM signal and enhances the reliability of the circuit. Furthermore, the PWM signal is transmitted through the anti-interference circuit, which can improve the quality of PWM signal transmission and effectively solve the technical problem that the signal output by the FPGA chip is prone to malfunction due to interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. The drawings described below are only drawings corresponding to some embodiments of the utility model.

[0024] Figure 1 This is a circuit diagram of an embodiment of a PWM signal anti-interference circuit of the present utility model.

[0025] Figure 2 The circuit diagram of the power isolation module of an embodiment of the PWM signal anti-interference circuit of the utility model is shown in FIG.

[0026] In the figure, 10, PWM signal anti-interference circuit; 11, optocoupler isolation module; 111, input pin; 112, output pin; 12, signal amplification module; 13, current limiting module; 14, interface module; 15, surge suppression module; 16, discharge module; 161, filter module; 17, power isolation module; 18, power supply module; 19, FPGA chip. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the utility model.

[0028] Directional terms mentioned in the present invention, such as "up", "down", "front", "back", "left", "right", "inside", "outside", "side", "top" and "bottom", are only used for reference to the directions of the drawings. The directional terms used are used to illustrate and understand the present invention, and are not used to limit the present invention.

[0029] The words "first", "second" and the like in the terminology of the present invention are used for descriptive purposes only and should not be understood as indicating or implying relative importance, and should not be construed as limiting the order of precedence.

[0030] In the figures, structurally similar elements are denoted by the same reference numerals.

[0031] Please refer to Figure 1 The utility model provides a PWM signal anti-interference circuit 10. The PWM signal anti-interference circuit 10 is applied to a circuit board, and the PWM signal anti-interference circuit 10 includes an optocoupler isolation module 11, a signal amplification module 12, a current limiting module 13, an interface module 14 and a surge suppression module 15. The optocoupler isolation module 11 can receive the PWM signal output by the FPGA chip 19, and the optocoupler isolation module 11 performs an isolation operation on the PWM signal. The signal amplification module 12 is connected to the optocoupler isolation module 11, and the signal amplification module 12 is used to perform a voltage amplification operation on the PWM signal, thereby improving the driving capability of the PWM signal.

[0032] Please refer to Figure 1The optocoupler isolation module 11 includes an optocoupler isolation chip U601, and the model of the optocoupler isolation chip U601 is HCPL2601. The optocoupler isolation chip U601 is used to isolate the PWM signal, and the optocoupler isolation chip U601 includes an input pin 111 and an output pin 112. The input pin 111 is used to input the PWM signal, and the signal amplification module 12 includes a transistor Q601 and a PWM power supply PWM_VCC. The transistor Q601 is used to perform a voltage amplification operation on the PWM signal, and the base of the transistor Q601 is connected to the output pin 112. The emitter of the transistor Q601 is connected to the PWM power supply PWM_VCC, and the collector of the transistor Q601 is used to output the PWM signal.

[0033] Please refer to Figure 1 and Figure 2 , the PWM signal anti-interference circuit 10 also includes a power supply module 18 and a power isolation module 17. The power supply module 18 is used to output a power supply voltage, and the power supply voltage is used to power the optocoupler isolation chip U601. The optocoupler isolation chip U601 also includes a power pin PWM_5V, and the power isolation module 17 includes a power isolation chip MD601, and the model of the power isolation chip MD601 is B0505S. The power isolation chip MD601 includes a +Vi n pin and a VO+ pin, and the +Vi n pin is connected to the power supply module 18. The VO+ pin is connected to the power pin PWM_5V, and the power isolation chip MD601 is used for the power supply module 18 to perform an isolation operation. Therefore, the setting of the power isolation chip MD601 can prevent the voltage value of the power supply voltage from being too large to damage the optocoupler isolation chip U601. The power isolation chip MD601 also includes a GND pin and a VO- pin, and the GND pin and the VO- pin are both grounded.

[0034] Please refer to Figure 1 and Figure 2 The power isolation module 17 also includes a first resistor R608, a first capacitor C601, a second capacitor C602, a third capacitor C605, and a fourth capacitor C606. One end of the first capacitor C601 is connected to the +Vi n pin, the other end of the first capacitor C601 is grounded, and the second capacitor C602 is connected in parallel with the first capacitor C601. One end of the first resistor R608 is connected to the VO+ pin, and the other end of the first resistor R608 is grounded. One end of the third capacitor C605 is connected to the VO+ pin, the other end of the third capacitor C605 is grounded, and the fourth capacitor C606 is connected in parallel with the third capacitor C605.

[0035] Please refer to Figure 1, the signal amplification module 12 is provided with a PWM power supply PWM_VCC, and the optocoupler isolation chip U601 can isolate the PWM power supply PWM_VCC from the FPGA chip 19, thereby preventing the PWM power supply PWM_VCC from outputting an excessive voltage to damage the FPGA chip 19. Therefore, the setting of the optocoupler isolation chip U601 can effectively protect the FPGA chip 19. In addition, the optocoupler isolation chip U601 has good electrical insulation and anti-interference functions, which is conducive to improving the anti-interference ability of the PWM signal during transmission. Through the electrical-optical-electrical conversion of the optocoupler isolation chip U601, the optocoupler isolation module 11 can isolate and process the PWM signal. The power supply can be isolated through the power isolation chip MD601, thereby realizing the full isolation design of the PWM signal and the power supply. After the PWM signal passes through the three-stage tube, the signal is amplified, thereby improving the driving ability of the PWM signal. In addition, the PWM power supply PWM_VCC can be a 24V or 5V power supply. Users can select a suitable power supply according to their needs to meet different application products, thereby improving product competitiveness.

[0036] Please refer to Figure 1 , the optocoupler isolation module 11 also includes a current limiting resistor R601. One end of the current limiting resistor R601 is connected to the FPGA chip 19, and the other end of the current limiting resistor R601 is connected to the input pin 111 of the optocoupler isolation chip U601. The current limiting resistor R601 is used to perform current limiting operation on the PWM signal. Therefore, even if the current of the PWM signal is large, the PWM signal will not damage the optocoupler isolation chip U601. The optocoupler isolation module 11 also includes a second resistor R602, one end of the second resistor R602 is connected to the VO+ pin, and the other end of the second resistor R602 is connected to the optocoupler isolation chip U601. Moreover, the signal amplification module 12 also includes a third resistor R603, a fourth resistor R604, and a fifth resistor R606. One end of the third resistor R603 is connected to the base of the transistor Q601, and the other end of the third resistor R603 is connected to the output pin 112 of the optocoupler isolation chip U601. One end of the fourth resistor R604 is connected to the emitter of the transistor Q601, and the other end of the fourth resistor R604 is connected to the output pin 112 of the optocoupler isolation chip U601. One end of the fifth resistor R606 is connected to the collector of the transistor Q601, and the other end of the fifth resistor R606 is grounded.

[0037] Please refer to Figure 1, the current limiting module 13 is connected to the signal amplification module 12, and the current limiting module 13 is used to transmit the PWM signal to the interface module 14. Moreover, when the current value of the PWM signal is greater than the set value, the current limiting module 13 is in a disconnected state, thereby protecting the circuits and equipment of the subsequent stage. The current limiting module 13 includes a resettable fuse, one end of which is connected to the collector of the transistor Q601, and the other end of the resettable fuse is connected to the interface module 14. Among them, the resettable fuse includes a first resettable fuse F601 and a second resettable fuse F602. When the current value of the PWM signal is greater than the set value, the resettable fuse is in a disconnected state. When the current value of the PWM signal is less than or equal to the set value, the resettable fuse is in a conducting state. Moreover, the PWM signal anti-interference circuit 10 is provided with a resettable fuse. Therefore, when the current in the circuit exceeds the set value, the resettable fuse will quickly cut off the circuit, which can effectively prevent the circuit components from being damaged by large currents. After the fault is eliminated, the resettable fuse will automatically reset and resume normal working state. Furthermore, the resettable fuse does not require manual replacement or on-site maintenance, which can reduce circuit maintenance costs and improve equipment reliability.

[0038] Please refer to Figure 1 , the interface module 14 is connected to the current limiting module 13. The interface module 14 is used to transmit the PWM signal to the subsequent device, and the PWM signal is used to drive the subsequent device. Among them, the interface module 14 includes an interface J601, and the interface J601 includes a first connection terminal J6011, a second connection terminal J6012, a third connection terminal J6013, and a fourth connection terminal J6014. The first connection terminal J6011 is connected to the current limiting module 13, and the first connection terminal J6011 can transmit the PWM signal to the subsequent device. The second connection terminal J6012 is connected to the third connection terminal J6013, and the third connection terminal J6013 is grounded. The fourth connection terminal J6014 is used to connect an external power supply (not shown in the figure) and a PWM power supply PWM_VCC, so that the external power supply can output a voltage to the PWM power supply PWM_VCC. The interface module 14 also includes a diode D604, the positive electrode of the diode D604 is connected to the external power supply, and the negative electrode of the diode D604 is connected to the PWM power supply PWM_VCC, and the diode can prevent the voltage of the PWM power supply PWM_VCC from being reversely output to the external power supply. The PWM signal anti-interference circuit 10 also includes a sixth resistor R610, one end of which is connected to the first self-recovery fuse F601 of the current limiting module 13, and the other end of which is connected to the first connection terminal J6011.

[0039] Please refer to Figure 1, the surge suppression module 15 is connected in parallel with the interface module 14, and the surge suppression module 15 can perform surge suppression operation on the PWM signal. The surge suppression module 15 includes a transient voltage suppression tube, one end of which is connected between the self-recovery fuse and the first connection terminal J6011 of the interface module 14, and the other end of the transient voltage suppression tube is grounded. Among them, the transient voltage suppression tube includes a first transient voltage suppression tube D603 and a second transient voltage suppression tube D602. When a surge voltage appears instantly in the PWM signal anti-interference circuit 10, the transient voltage suppression tube can quickly perform a Zener breakdown operation, and the transient voltage suppression tube can change from a high-resistance state to a low-resistance state. Thus, the transient voltage suppression tube can shunt and clamp the surge voltage, thereby protecting the components in the circuit from being damaged by the instantaneous surge voltage.

[0040] Please refer to Figure 1 , the discharge module 16 is connected in parallel with the interface module 14, and the discharge module 16 can discharge the electromagnetic interference of the PWM signal. The discharge module 16 includes a discharge resistor R661 and a discharge capacitor C660, one end of the discharge resistor R661 is connected between the self-recovery fuse and the first connection terminal J6011 of the interface module 14, and the other end of the discharge resistor R661 is grounded. One end of the discharge capacitor C660 is connected between the self-recovery fuse and the first connection terminal J6011 of the interface module 14, and the other end of the discharge capacitor C660 is grounded. Therefore, the discharge module 16 is arranged near the interface module 14, which can improve the anti-electromagnetic interference capability of the circuit of the utility model.

[0041] Please refer to Figure 1 , one end of the filter module 161 is connected to the current limiting module 13, and the other end of the filter module 161 is grounded. The filter module 161 is used to filter the PWM signal, and the filter module 161 includes a first filter capacitor C603 and a second filter capacitor C604. One end of the first filter capacitor C603 is connected between the self-recovery fuse and the interface module 14, the other end of the first filter capacitor C603 is grounded, and the second filter capacitor is connected in parallel with the first filter capacitor C603. Because the filter module 161 can filter the PWM signal, the filter module 161 can remove interference components in the PWM signal, such as electromagnetic interference, etc., thereby improving the quality and reliability of the PWM signal.

[0042] The working principle of the utility model is as follows: when the PWM signal anti-interference circuit 10 is working, first, the FPGA chip 19 outputs a PWM signal. In order to avoid the current of the PWM signal being too large, the current limiting resistor R601 can perform a current limiting operation on the PWM signal. At the same time, the power supply module 18 outputs a power supply voltage, and the power supply voltage can power the optocoupler isolation chip U601. In order to avoid the voltage value of the power supply voltage being too large to damage the optocoupler isolation chip U601, the power isolation module 17 can perform an isolation operation on the power supply module 18. In addition, the optocoupler isolation module 11 performs an isolation operation on the PWM signal. Then, the signal amplification module 12 receives the PWM signal, and the PWM power supply PWM_VCC outputs a voltage to the transistor. Thus, the transistor of the signal amplification module 12 performs a voltage amplification operation on the PWM signal, thereby improving the driving ability of the PWM signal. Subsequently, the PWM signal passes through the current limiting module 13. If the current value of the PWM signal is greater than the set value, the self-recovery fuse is in a disconnected state; if the current value of the PWM signal is less than or equal to the set value, the self-recovery fuse is in a conducting state. Therefore, the resettable fuse prevents the circuit elements from being damaged by the high-current PWM signal. In addition, in order to perform surge suppression operation on the PWM signal, the surge suppression module 15 is provided with a transient voltage suppression tube. In order to discharge the electromagnetic interference of the PWM signal, the discharge module 16 is provided with a discharge resistor R661 and a discharge capacitor C660. In order to filter the PWM signal, the filter module 161 is provided with a first filter capacitor C603 and a second filter capacitor C604. Then, the current limiting module 13 transmits the PWM signal to the interface module 14. The first connection terminal J6011 of the interface module 14 can transmit the PWM signal to the subsequent device, and the PWM signal is used to drive the subsequent device.

[0043] The utility model provides a PWM signal anti-interference circuit, which includes an optocoupler isolation module, a signal amplification module, a current limiting module, an interface module and a surge suppression module. The PWM signal output by the FPGA is isolated by the optocoupler isolation module, and the signal amplification module can amplify the PWM signal, which effectively improves the driving ability of the PWM signal. In addition, the surge suppression module can perform surge suppression on the PWM signal, and the discharge module can discharge the electromagnetic interference of the PWM signal. Therefore, the PWM signal will not be interfered by noise or electromagnetic radiation during transmission. The setting of the PWM signal anti-interference circuit improves the anti-interference ability of the PWM signal and enhances the reliability of the circuit. Furthermore, the PWM signal is transmitted through the anti-interference circuit, which can improve the quality of PWM signal transmission and effectively solve the technical problem that the signal output by the FPGA chip is prone to malfunction due to interference.

[0044] In summary, although the present invention has been disclosed as above in terms of preferred embodiments, the above preferred embodiments are not intended to limit the present invention. A person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined in the claims.

Claims

1. A PWM signal anti-interference circuit, characterized in that: It includes, An optical coupler isolation module, used to receive the PWM signal output by the FPGA chip and perform an isolation operation on the PWM signal; A signal amplification module, connected to the optical coupling isolation module, for performing a voltage amplification operation on the PWM signal, thereby improving the driving capability of the PWM signal; A current limiting module, connected to the signal amplifying module, for transmitting the PWM signal to the interface module, and when the current value of the PWM signal is greater than a set value, the current limiting module is in a disconnected state, thereby protecting subsequent circuits and devices; The interface module is connected to the current limiting module and is used to transmit the PWM signal to the subsequent device, and the PWM signal is used to drive the subsequent device; A surge suppression module, connected in parallel with the interface module, and configured to perform surge suppression operation on the PWM signal; The discharge module is connected in parallel with the interface module and is used for performing a discharge operation on the electromagnetic interference of the PWM signal.

2. The PWM signal anti-interference circuit according to claim 1, characterized in that: The optocoupler isolation module includes an optocoupler isolation chip, which is used to isolate the PWM signal. The optocoupler isolation chip includes an input pin and an output pin, and the input pin is used to input the PWM signal. The signal amplification module includes a transistor and a PWM power supply, and the transistor is used to perform voltage amplification on the PWM signal. The base of the transistor is connected to the output pin, the emitter of the transistor is connected to the PWM power supply, and the collector of the transistor is used to output the PWM signal.

3. The PWM signal anti-interference circuit according to claim 2, characterized in that: The current limiting module includes a resettable fuse, one end of the resettable fuse is connected to the collector of the transistor, and the other end of the resettable fuse is connected to the interface module; When the current value of the PWM signal is greater than the set value, the resettable fuse is in an off state; when the current value of the PWM signal is less than or equal to the set value, the resettable fuse is in an on state.

4. The PWM signal anti-interference circuit according to claim 3, characterized in that: The surge suppression module comprises a transient voltage suppression tube, one end of which is connected between the self-recovery fuse and the interface module, and the other end of which is grounded.

5. The PWM signal anti-interference circuit according to claim 3, characterized in that: The discharge module includes a discharge resistor and a discharge capacitor, one end of the discharge resistor is connected between the self-recovery fuse and the interface module, and the other end of the discharge resistor is grounded; one end of the discharge capacitor is connected between the self-recovery fuse and the interface module, and the other end of the discharge capacitor is grounded.

6. The PWM signal anti-interference circuit according to claim 3, characterized in that: The PWM signal anti-interference circuit further includes a filter module, one end of which is connected to the current limiting module, and the other end of which is grounded, and the filter module is used to perform a filtering operation on the PWM signal.

7. The PWM signal anti-interference circuit according to claim 6, characterized in that: The filter module includes a first filter capacitor and a second filter capacitor, one end of the first filter capacitor is connected between the self-recovery fuse and the interface module, the other end of the first filter capacitor is grounded, and the second filter capacitor is connected in parallel with the first filter capacitor.

8. The PWM signal anti-interference circuit according to claim 2, characterized in that: The PWM signal anti-interference circuit also includes a power supply module and a power isolation module. The power supply module is used to output a power supply voltage, and the power supply voltage is used to power the optocoupler isolation chip. The optocoupler isolation chip also includes a power pin. The power isolation module includes a +Vin pin and a VO+ pin. The +Vin pin is connected to the power supply module, and the VO+ pin is connected to the power pin. The power isolation module is used to isolate the power supply module.

9. The PWM signal anti-interference circuit according to claim 2, characterized in that: The optocoupler isolation module also includes a current limiting resistor, one end of which is connected to the FPGA chip, and the other end of which is connected to the input pin of the optocoupler isolation chip. The current limiting resistor is used to perform current limiting operation on the PWM signal.

10. A circuit board, characterized in that: It includes the PWM signal anti-interference circuit described in any one of claims 1-9.

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