Multi-channel analog signal output module

Abstract

The invention relates to a multi-channel analog signal output module. The multi-channel analog signal output module comprises a main control module, a current output module and a communication multiplexing module, the communication multiplexing module comprises an isolation transmission unit, a modulation-demodulation circuit and a multiplexing switch unit. The multiplexing switch unit is connected with the modulation-demodulation circuit and an output loop of the current output module through a common bus and a plurality of coupling branches; each coupling branch comprises a gating switch assembly and a passive filtering assembly which are connected in series. The gating switch assembly is controlled to be switched on, and the passive filtering assembly is configured to block the analog current signal and allow the frequency shift keying analog signal to pass through. Through a serial connection structure of the gating switch and the filtering assembly, multiplexing of a single modulation-demodulation circuit on multi-path output is realized, hardware cost is reduced, meanwhile, direct-current high voltage is effectively blocked, switching interference is inhibited, and communication stability and module reliability are improved.

Description

Technical Field

[0001] This application relates to the field of industrial automation control, and in particular to a multi-channel analog signal output module. Background Technology

[0002] Currently, analog output modules are widely used in industrial automation control systems (such as DCS) to control field devices such as valve positioners and actuators. With the development of industrial intelligence, the demand for remote monitoring and parameter management of field devices is increasing. Therefore, analog output modules that support the overlay of digital communication protocols (such as the Addressable Remote Sensor High-Speed ​​Channel Protocol, HART) have become the mainstream requirement. They need to overlay digital communication signals while transmitting analog control signals to achieve bidirectional communication.

[0003] In related technologies, analog output modules with digital communication functions typically employ a microcontroller (MCU) architecture combined with a multi-channel digital-to-analog converter (DAC). Specifically, the MCU sends digital commands to the DAC chip via digital buses such as SPI. The DAC chip converts the digital signals into analog voltage or current, which is then output via a driver circuit. Simultaneously, an analog multiplexer is used to poll and switch the communication modem to different output channels.

[0004] However, the aforementioned technologies have drawbacks. Direct switching via analog switches may introduce switching noise, and the complex electromagnetic environment in the field can easily cause crosstalk to the control terminal via the shared bus, potentially affecting communication quality or the accuracy of analog output. Furthermore, traditional DAC chip solutions are costly, and isolation designs for high-density channels are complex. Summary of the Invention

[0005] To address the problems of high signal interference, complex isolation design, and high hardware cost in related technologies, this application provides a multi-channel analog signal output module.

[0006] The multi-channel analog signal output module provided in this application adopts the following technical solution: A multi-channel analog signal output module includes: a main control module, a current output module, and a communication multiplexing module. The main control module outputs pulse-width modulation (PWM) signals, digital communication transmit signals, and channel selection control signals, and is configured to receive digital communication receive signals. The current output module, connected to the main control module, receives the PWM signals and filters and converts them to generate analog signals. The communication multiplexing module includes an isolation transmission unit, a modulation / demodulation circuit, and a multiplexing switch unit. The isolation transmission unit is connected between the main control module and the modulation / demodulation circuit, and electrically isolates and transmits the digital communication transmit and receive signals. The modulation and demodulation circuit is used to modulate the digital communication transmission signal transmitted via the isolation transmission unit into a frequency shift keying (FSK) analog signal and transmit it to the multiplexing switch unit, and demodulate the FFS analog signal from the multiplexing switch unit into a digital communication reception signal and transmit it to the main control module via the isolation transmission unit. The multiplexing switch unit includes a common bus connected to the analog signal terminal of the modulation and demodulation circuit and multiple coupling branches connected between the common bus and the output circuit of the current output module. Each coupling branch includes a gating switch component and a passive filter component connected in series. The control terminal of the gating switch component is connected to the main control module to receive the channel selection control signal to conduct the corresponding coupling branch. The passive filter component is configured to block the analog current signal on the output circuit from entering the common bus and allow the FFS analog signal transmitted via the common bus to pass through.

[0007] By adopting the above technical solution, a physical isolation architecture between the main control logic and field signals was constructed. Specifically, the communication multiplexing module utilizes a coupling branch to connect the modulation and demodulation circuit to the current output circuit via a series structure of a gating switch component and a passive filter component. This structure enables a single modulation and demodulation circuit to multiplex multiple current outputs, reducing hardware costs. Simultaneously, the series connection between the passive filter component and the gating switch helps to block the impact of DC high voltage on the switching devices and the common bus, and suppresses transient interference during switching operations. This facilitates stable coupling of communication signals during channel switching and reduces the impact on the accuracy of analog output.

[0008] Optionally, the multiplexing switch unit further includes a decoder; the input side of the decoder is connected to the main control module to receive the channel selection control signal, and the output side of the decoder is connected to the control terminal of the gating switch assembly in the coupling branch.

[0009] By employing the above technical solution, a decoder is used to logically analyze the channel selection signal. This design reduces the number of I / O pins required by the main control module, helps simplify circuit board wiring complexity, and improves system integration.

[0010] Optionally, the passive filter component is disposed between the current output module and the gating switch component; the passive filter component includes a DC blocking capacitor.

[0011] By adopting the above technical solution, the physical location and specific composition of the filter components were clarified. Placing the DC blocking capacitor before the selection switch (i.e., closer to the current loop) helps isolate the high-voltage DC component in the current loop, allowing the selection switch to primarily handle AC signals. This improves operating conditions during live switching, protects the switch contacts, and also reduces potential interference from DC signals to the modulation and demodulation circuits through the physical path.

[0012] Optionally, the gating switch assembly is a light-controlled solid-state relay; the light-emitting side of the light-controlled solid-state relay is connected to the decoder, and the light-receiving side is connected in series in the coupling branch.

[0013] By adopting the above technical solution, a light-controlled solid-state relay is used to replace the traditional mechanical relay or ordinary analog switch. The light-controlled solid-state relay has the characteristics of being contactless, having no operating noise, low on-resistance, and having built-in opto-isolation, which helps to further reduce electromagnetic noise during channel switching and provides additional electrical isolation protection for the main control logic.

[0014] Optionally, a transmit buffer circuit is further provided between the modulation and demodulation circuit and the common bus; the transmit buffer circuit includes an operational amplifier, and the enable pin of the operational amplifier is connected to the isolated transmission unit to receive a transmit request signal.

[0015] By adopting the above technical solution, a buffering mechanism based on the transmit request signal control is introduced. When no data is being transmitted, the operational amplifier is in a high-impedance state or a disabled state, thereby cutting off the connection path between the modem circuit's transmitting end and the common bus, which helps prevent the modem circuit's own noise floor from affecting the analog current loop.

[0016] Optionally, a receiving filter circuit is further provided between the modulation and demodulation circuit and the common bus; the receiving filter circuit includes cascaded active bandpass filters.

[0017] By adopting the above technical solution, a hardware filtering stage is added to the receiving link. The active bandpass filter can filter out the frequency band specified by the protocol and attenuate common power frequency interference in industrial environments, as well as switching noise that may be generated by the current output module, thereby helping to improve the signal-to-noise ratio and decoding success rate of communication.

[0018] Optionally, the isolation transmission unit is a magnetically coupled digital isolation chip; the magnetically coupled digital isolation chip is configured to isolate the transmission of the digital communication transmit signal, the digital communication receive signal and the transmit request signal.

[0019] By adopting the above technical solution, magnetic coupling isolation technology, which offers faster transmission speeds and more precise timing, was selected, and data transmission and control signals were isolated. This achieves complete electrical isolation between the main control module and the fieldbus, helping to block ground loop interference and improve system safety.

[0020] Optionally, the current output module includes multiple sets of parallel current generation circuits, each current generation circuit including an opto-isolator, a low-pass filter network, and a voltage-to-current converter connected in series; the coupling branch is connected to the output node of the voltage-to-current converter.

[0021] By adopting the above technical solution, an opto-isolator is used to transmit the signal, which is then converted into an analog voltage by a low-pass filter and finally output as current via a voltage-to-current converter. This architecture helps enhance the anti-interference capability between channels, and the coupling branch is connected to the output node, ensuring that the communication signal can be directly superimposed on the final output current loop.

[0022] Optionally, a transient voltage suppression diode is also connected in parallel at the output terminal of the current generation circuit.

[0023] By adopting the above technical solution, transient protection is provided at the output port of the module. When the field cable is induced by a surge or electrostatic discharge, the transient voltage suppression diode can conduct to discharge energy, which helps protect the internal voltage-to-current converter and coupling branch.

[0024] Optionally, the main control module includes a microcontroller and a field-programmable gate array (FPGA); the microcontroller is connected to the isolated transmission unit and is used to run the communication protocol stack; the FPGA is connected to the current output module and is used to generate the pulse width modulation signal.

[0025] By adopting the above technical solution, a dual-core control architecture combining a microcontroller and a field-programmable gate array (FPGA) chip is used. Leveraging the strong parallel processing capabilities of the FPGA chip, multiple high-precision, high-frequency pulse-width modulation (PWM) signals can be generated simultaneously, which improves the synchronization and stability of the current output; while the microcontroller focuses on running the protocol stack and system scheduling. This division of labor and collaboration helps improve the overall response speed and processing power of the module.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. This application sets up a communication multiplexing module and uses a coupling branch containing a series-connected gating switch assembly and a passive filter assembly to connect the modulation and demodulation circuit to each current output module. This design uses the gating switch assembly to realize time-division multiplexing of multiple channels by a single modulation and demodulation circuit, and uses the passive filter assembly connected in series with the gating switch to block DC high voltage and attenuate switching noise. This reduces hardware costs and helps to reduce interference of the multiplexing process on the analog current signal, thereby improving the reliability of the module operation.

[0027] 2. By employing multiple isolation and control methods such as optically controlled solid-state relays, magnetically coupled digital isolation chips, and transmission buffer circuits, potential interference paths are cut off, which helps improve the electromagnetic compatibility of the module in complex industrial environments.

[0028] 3. By using a microcontroller in conjunction with a field-programmable gate array (FPGA) chip and a discrete current generation circuit, multi-channel output is achieved while reducing hardware costs compared to traditional integrated solutions and maintaining the real-time performance of signal processing. Attached Figure Description

[0029] Figure 1 This is a schematic block diagram of the multi-channel analog signal output module according to an embodiment of this application.

[0030] Figure 2 This is a circuit block diagram of the main control module in an embodiment of this application.

[0031] Figure 3 This is a circuit block diagram of the communication multiplexing module according to an embodiment of this application.

[0032] Figure 4 This is a schematic diagram of the current output module according to an embodiment of this application.

[0033] Figure 5 This is a circuit diagram of the current generation circuit according to an embodiment of this application.

[0034] Figure 6 This is a circuit diagram of the modulation / demodulation circuit and conditioning circuit according to an embodiment of this application.

[0035] Figure 7 This is a circuit schematic diagram of the decoder according to an embodiment of this application.

[0036] Figure 8 This is a circuit schematic diagram of the gating switch assembly and the passive filter assembly according to an embodiment of this application.

[0037] Figure 9 This is a circuit schematic diagram of the isolation transmission unit according to an embodiment of this application.

[0038] Figure 10 This is a circuit diagram of the power supply circuit according to an embodiment of this application.

[0039] Explanation of reference numerals in the attached figures: 10. Main control module; 11. Microcontroller; 12. Field-programmable gate array chip; 13. Digital communication interface; 20. Current output module; 21. Current generation circuit; 21a. Opto-isolator; 21b. Low-pass filter network; 21c. Digital-to-analog converter network; 21d. Voltage-to-current converter; 22. Transient voltage suppression diode; 23. Output terminal; 30. Communication multiplexing module; 31. Isolation transmission unit; 32. Modulation and demodulation circuit; 33. Transmit buffer circuit; 34. Receive filter circuit; 35. Multiplexing switch unit; 35a. Decoder; 35b. Gating switch assembly; 35c. Passive filter assembly. Detailed Implementation

[0040] The following is in conjunction with the appendix Figure 1-10 This application will be described in further detail.

[0041] This application discloses a multi-channel analog signal output module. This module adopts an architecture that physically isolates the main control logic from the field signals, achieving high-precision analog quantity control and reliable HART digital communication multiplexing. (Refer to...) Figure 1 The module mainly includes a main control module 10, a current output module 20, and a communication multiplexing module 30. The main control module 10 is located on the low-voltage side (logic side); the current output module 20 and the communication multiplexing module 30 are located on the high-voltage side (field side), and the two communicate with each other through an electrical isolation barrier.

[0042] Refer to the specific circuit structure of the main control module 10. Figure 2 As shown, it includes a microcontroller 11 and a field-programmable gate array (FPGA) chip 12 working together. The microcontroller 11 (MCU) acts as the main processor, responsible for running the HART protocol stack, processing upper-layer instructions, and scheduling system tasks. The microcontroller 11 connects to an external host or backplane bus via a digital communication interface 13, and simultaneously receives the demodulated digital communication receive signal (RXD) through an isolated transmission unit 31, and outputs the digital communication transmit signal to be modulated (TXD), a channel selection control signal, and a transmit request signal (RTS). The FPGA chip 12 connects to the microcontroller 11 via a high-speed parallel bus or SPI bus, utilizing its multi-channel parallel processing advantage to generate multiple high-frequency, high-resolution pulse width modulation (PWM) signals according to the instructions of the microcontroller 11. Compared to using only an MCU, using an FPGA to generate PWM signals effectively avoids timing jitter caused by interrupt processing, thereby improving the linearity and stability of subsequent analog outputs.

[0043] The current output module 20 is used to convert the digital PWM signal from the FPGA into an industry-standard 4-20mA analog current signal. (See reference...) Figure 4 and Figure 5 The current output module 20 includes multiple sets of parallel current generation circuits 21 with identical structures and corresponding connected output terminals 23. Taking the first current generation circuit 21 as an example, its signal chain includes a cascaded opto-isolator 21a, a low-pass filter network 21b, a digital-to-analog converter network 21c, and a voltage-to-current converter 21d. The opto-isolator 21a (e.g., Figure 5 U101 (optional high-speed optocoupler) receives the PWM signal output from the FPGA, optically coupling the signal from the logic side to the field side to achieve electrical isolation and cut off ground loop interference. A low-pass filter network 21b is connected to the output side of the opto-isolator 21a and consists of a multi-stage RC filter circuit (including resistors R103, R104 and capacitors C101, C102). Its cutoff frequency is designed to be much lower than the PWM carrier frequency, used to filter out high-frequency switching components in the PWM signal and smoothly restore the duty cycle-changing pulse signal to a DC voltage signal. A digital-to-analog converter network 21c is used to perform amplitude conditioning and reference offset correction on this DC voltage. The voltage-to-current converter 21d uses an operational amplifier U103 in conjunction with a power regulating transistor Q1 and precision sampling resistors R109 and R110 to form a negative feedback constant current source structure. The operational amplifier U103 controls the conduction level of the power transistor Q1 based on the difference between the input voltage and the feedback voltage across the sampling resistor, thereby generating a constant current in the output circuit. In addition, to improve field adaptability, a transient voltage suppression diode 22 is connected in parallel at the output terminal of the current generation circuit 21 (i.e., between the positive and negative terminals of the output terminal 23). Figure 5 (Z104) When the field cable is subjected to lightning surge or electrostatic discharge, the TVS diode quickly conducts the clamping voltage to protect the power transistor Q1 and precision resistor in the subsequent stage from damage.

[0044] The communication multiplexing module 30 is designed to achieve time-division multiplexing of multiple channels using a single modulation and demodulation resource. (Refer to...) Figure 3 The communication multiplexing module 30 includes an isolation transmission unit 31, a modulation and demodulation circuit 32, a signal conditioning stage including a transmit buffer circuit 33 and a receive filter circuit 34, and a multiplexing switch unit 35.

[0045] Reference Figure 9The isolation transmission unit 31 uses a high-speed magnetically coupled digital isolation chip E9 (e.g., π142E61). This chip is connected between the digital ground (GND_D) of the main control module 10 and the analog ground (GND_A) of the communication multiplexing module 30. It is responsible not only for isolating and transmitting TXD and RXD data signals, but also for transmitting the critical control signal RTS (transmit request). Compared with traditional optocouplers, the magnetically coupled isolation scheme has lower transmission delay and lower pulse width distortion, can support higher baud rates, and maintains the accuracy of HART signal timing.

[0046] Reference Figure 6 The modulation and demodulation circuit 32 uses a low-power HART modulation and demodulation chip U2 (such as AD5700) as its core, and is externally connected to a 3.6864MHz crystal oscillator XT5 and resonant capacitors C8 and C10 to provide a precise clock. Chip U2 is responsible for physical layer protocol conversion: in the transmission direction, it modulates the digital TXD signal sent by the microcontroller 11 into a frequency shift keying (FSK) analog signal conforming to the Bell 202 standard (logic 1 corresponds to 1200Hz, logic 0 corresponds to 2200Hz); in the reception direction, it demodulates the analog FSK signal back to the digital RXD signal.

[0047] To address impedance matching and noise interference issues caused by multiplexing, a dedicated conditioning circuit is added between the modulation / demodulation circuit 32 and the common bus. The transmit buffer circuit 33, located between the output terminal HART_OUT of chip U2 and the common bus, consists of operational amplifier D1 and control transistor N3. Operational amplifier D1 is configured as a voltage follower or non-inverting amplifier to enhance signal driving capability. The base of transistor N3 is controlled by the transmit request signal HT_RTS from the isolated transmission unit 31. When HT_RTS is valid (e.g., low level), transistor N3 conducts, the enable terminal of the operational amplifier is activated, and the modulated FSK signal is injected into the common bus with low impedance; when HT_RTS is invalid, the operational amplifier enters a high-impedance (off) state, completely cutting off the transmit path. This "transmit enable" mechanism is crucial, preventing the noise floor of the modulation / demodulation circuit in the idle state from coupling to the common bus, thereby avoiding minor disturbances to the high-precision 4-20mA analog output. The receiving filter circuit 34 is located between the common bus and the input terminal ADC_IP of chip U2. It is an active bandpass filter composed of resistors R12, R8, R13 and capacitors C6 and C7. Its passband range is set to cover the frequency band from 1200Hz to 2200Hz. It can effectively filter out 50Hz / 60Hz power frequency interference and PWM ripple that may remain in the current output module, which is beneficial for the demodulator to accurately extract the FSK signal in harsh electromagnetic environments.

[0048] The multiplexing switch unit 35 enables physical switching from the common bus to each current output channel. (Refer to...) Figure 3 , Figure 7 and Figure 8 This unit consists of a decoder 35a, a gating switch assembly 35b, and a passive filter assembly 35c. The decoder 35a uses a 3-8 line decoder chip D3 (e.g., 74HC138). Its input terminals A0-A2 are connected to the control signals of the microcontroller 11, and its output terminals Y0-Y7 are connected to the control terminals of each channel gating switch assembly. The gating switch assembly 35b uses a photo-controlled solid-state relay (PhotoMOS, e.g., E1 to E8). Compared to traditional mechanical relays, it has no contact wear and no operational jitter; compared to ordinary analog switches, it has extremely high turn-off impedance and input-output isolation characteristics. The passive filter assembly 35c is specifically embodied as a DC blocking capacitor (e.g., C41, 2.2uF). Each coupling branch adopts a topology of "photo-controlled solid-state relay in series with DC blocking capacitor," with one end connected to the common bus and the other end connected to the output node of the corresponding channel voltage-to-current converter 21d.

[0049] This series structure provides dual protection: First, the DC blocking capacitor C41 prevents the DC voltage of up to 24V in the current output circuit from entering the common bus and subsequent low-voltage circuits, allowing only the AC FSK signal to pass through; second, the photoelectric solid-state relay E1 provides a controllable access point. When communication with the Nth channel is required, the microcontroller 11 selects the corresponding photoelectric solid-state relay through the decoder, turning it on. At this time, the FSK voltage signal generated by the modulation and demodulation circuit 32 passes through the common bus, the turned-on relay, and the DC blocking capacitor, and is finally superimposed as current on the 4-20mA loop of the Nth channel (or the current signal is extracted from the loop). Due to the good linearity and low on-resistance of the photoelectric solid-state relay, combined with the DC blocking capacitor, the integrity of the signal coupling is maintained.

[0050] In addition, the module is equipped with a highly reliable power supply circuit (see reference). Figure 10 After the external 24V loop power supply LOOPA+ is input, it first undergoes overcurrent protection via fuse F1, reverse voltage is blocked by a reverse connection protection diode, and high-energy surges are absorbed by a high-power TVS diode Z2. The pre-processed power supply is converted into a clean 3.3V voltage (3.3V_A) by an LDO regulator chip U1 (such as L78L33). This 3.3V power supply uses independent wiring and is equipped with multiple decoupling capacitors (C19, C22) to specifically power the secondary side of the modem circuit 32, the isolation transmission unit 31, and the light-controlled solid-state relay, thus preventing digital circuit switching noise from interfering with the analog signal link through the power line.

[0051] After the module is powered on and initialized, the microcontroller 11 in the main control module 10 configures the system parameters, and the field-programmable gate array chip 12 (FPGA) continuously generates high-precision pulse width modulation (PWM) signals through multi-channel parallel logic. These PWM signals are isolated by the opto-isolator 21a in the current output module 20, smoothed by the low-pass filter network 21b, and converted by the voltage-to-current converter 21d to generate standard 4-20mA analog control current on each output channel to drive field devices. When the microcontroller 11 receives a HART digital communication command for a specific channel (e.g., channel 1), it outputs the corresponding channel selection control signal according to the command. After being decoded by the decoder 35a, this signal only drives the gating switch component 35b (e.g., optically controlled solid-state relay E1) in the coupling branch of channel 1 to conduct, thereby connecting the current output circuit of channel 1 to the common bus through the passive filter component 35c (e.g., DC blocking capacitor C41), while other channels remain physically disconnected. If data transmission is performed, the microcontroller 11 outputs a digital transmit signal (TXD) and a valid transmit request signal (RTS). When the RTS signal is enabled, the modem circuit 32 modulates the TXD into a frequency shift keying (FSK) analog signal and drives it to the common bus via the transmit buffer circuit 33. This signal then passes through the activated gating switch assembly and the passive filter assembly and is superimposed onto the current loop of channel 1. If data reception is performed, the FSK response signal superimposed on the current loop of channel 1 is filtered by the passive filter assembly to remove the DC component. It then enters the common bus through the activated gating switch assembly, is filtered by the receive filter circuit 34, and demodulated by the modem circuit 32 into a digital receive signal (RXD). Finally, it is transmitted back to the microcontroller 11 via the isolation transmission unit 31. After the communication task is completed, the microcontroller 11 controls the gating switch assembly to open, restoring the channel to a pure analog signal output state. This achieves efficient, isolated, and low-interference communication multiplexing of multiple analog output channels using a single modem circuit.

[0052] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A multi-channel analog signal output module, characterized in that, include: The main control module (10) is used to output pulse width modulation signals, digital communication transmission signals and channel selection control signals, and to receive digital communication reception signals; The current output module (20) is connected to the main control module (10) and is used to filter and convert the pulse width modulation signal to generate an analog signal. The communication multiplexing module (30) includes an isolation transmission unit (31), a modulation and demodulation circuit (32), and a multiplexing switch unit (35). The isolation transmission unit (31) is connected between the main control module (10) and the modulation and demodulation circuit (32) and is used to electrically isolate and transmit the digital communication transmission signal and the digital communication reception signal. The modulation and demodulation circuit (32) is used to modulate the digital communication transmission signal transmitted through the isolation transmission unit (31) into a frequency shift keying analog signal and transmit it to the multiplexing switch unit (35). It is also used to demodulate the frequency shift keying analog signal from the multiplexing switch unit (35) into a digital communication reception signal and transmit it through the isolation transmission unit (31). The signal is transmitted to the main control module (10); the multiplexing switch unit (35) includes a common bus connected to the analog signal terminal of the modulation and demodulation circuit (32) and multiple coupling branches connected between the common bus and the output circuit of the current output module (20). Each coupling branch includes a gating switch component (35b) and a passive filter component (35c) connected in series. The control terminal of the gating switch component (35b) is connected to the main control module (10) to receive the channel selection control signal and thus turn on the corresponding coupling branch. The passive filter component (35c) is configured to block the analog current signal on the output circuit from entering the common bus and allow the frequency shift keying analog signal to pass through.

2. The multi-channel analog signal output module according to claim 1, characterized in that, The multiplexing switch unit (35) further includes a decoder (35a); the input side of the decoder (35a) is connected to the main control module (10) to receive the channel selection control signal, and the output side of the decoder (35a) is connected to the control terminal of the gating switch assembly (35b) in the coupling branch.

3. The multi-channel analog signal output module according to claim 1, characterized in that, The passive filter component (35c) is disposed between the current output module (20) and the gating switch component (35b); the passive filter component (35c) includes a DC blocking capacitor.

4. The multi-channel analog signal output module according to claim 2, characterized in that, The gating switch assembly (35b) is a light-controlled solid-state relay; the light-emitting side of the light-controlled solid-state relay is connected to the decoder (35a), and the light-receiving side is connected in series in the coupling branch.

5. The multi-channel analog signal output module according to claim 1, characterized in that, A transmit buffer circuit (33) is also provided between the modulation and demodulation circuit (32) and the common bus; the transmit buffer circuit (33) includes an operational amplifier, and the enable pin of the operational amplifier is connected to the isolated transmission unit (31) to receive a transmit request signal.

6. The multi-channel analog signal output module according to claim 1, characterized in that, A receiving filter circuit (34) is also provided between the modulation and demodulation circuit (32) and the common bus; the receiving filter circuit (34) includes cascaded active bandpass filters.

7. The multi-channel analog signal output module according to claim 5, characterized in that, The isolation transmission unit (31) is a magnetically coupled digital isolation chip; the magnetically coupled digital isolation chip is configured to isolate the transmission of the digital communication transmission signal, the digital communication reception signal and the transmission request signal.

8. The multi-channel analog signal output module according to claim 1, characterized in that, The current output module (20) includes multiple sets of parallel current generation circuits (21), each current generation circuit (21) including an opto-isolator (21a), a low-pass filter network (21b), and a voltage-to-current converter (21d) connected in series; the coupling branch is connected to the output node of the voltage-to-current converter (21d).

9. The multi-channel analog signal output module according to claim 8, characterized in that, The output terminal of the current generation circuit (21) is also provided with a transient voltage suppression diode (22) connected in parallel.

10. The multi-channel analog signal output module according to claim 1, characterized in that, The main control module (10) includes a microcontroller (11) and a field-programmable gate array (12); the microcontroller (11) is connected to the isolation transmission unit (31) and is used to receive the digital communication receiving signal and output the digital communication sending signal and the channel selection control signal; the field-programmable gate array (12) is connected to the current output module (20) and is used to output the pulse width modulation signal.

Images