A gain control circuit and audio signal processing module for a train broadcast intercom system

Abstract

This invention provides a gain control circuit and audio signal processing module for a train broadcast intercom system, which can stabilize the amplitude of the audio signal within a reasonable range, improving the stability and reliability of the audio signal. The audio gain control chip has an audio signal input port and an audio signal output port. The voltage limiting module includes an operational amplifier chip and a voltage comparator connected to the audio gain control chip. The voltage reference signal Vref output by the audio gain control chip is input to the operational amplifier chip, and the operational amplifier chip outputs a threshold voltage. The input audio signal and the threshold voltage are respectively input to the voltage comparator. The audio gain control chip limits the voltage and reduces noise of the input audio signal according to the output of the voltage comparator, and outputs the limited audio signal from the audio signal output port.

Description

Technical Field

[0001] This utility model relates to the field of rail transit, and in particular to a gain control circuit and audio signal processing module for a train broadcast intercom system. Background Technology

[0002] Currently, the subway train PIS (Public Information System) consists of three subsystems: a train broadcast intercom system, a train passenger information display system, and a video surveillance system. Early subway train PIS systems mostly used analog bus implementations. Later, with the development of network technology, digital broadcast intercom systems based on Ethernet communication emerged. Now, customers have raised higher system requirements, demanding that both digital and analog bus broadcast intercom systems be used concurrently, with the digital broadcast intercom as the primary system and the analog bus broadcast intercom as a secondary (backup) system. This is to ensure that if the Ethernet digital broadcast intercom fails and cannot effectively broadcast, the analog bus broadcast intercom can be activated, thereby improving the overall security of the PIS broadcast intercom system.

[0003] Chinese invention patent CN120223809A discloses a broadcast intercom system for rail transit. This system uses an IMX6Q CPU system for data transmission processing and relies on software algorithms to suppress signal fluctuations. The CPU system can easily handle fluctuations in the amplitude of the input audio signal. However, when using a lower-cost audio signal processing circuit module to process the input audio signal, it is necessary to ensure that the amplitude of the output signal remains stable within a reasonable range to prevent subsequent circuit malfunctions due to excessively strong or weak signals. Utility Model Content

[0004] To address the aforementioned problems, this utility model provides a gain control circuit and audio signal processing module for a train broadcast intercom system, which can stabilize the amplitude of the audio signal within a reasonable range, thereby improving the stability and reliability of the audio signal.

[0005] The technical solution is as follows: a gain control circuit for a train broadcast intercom system, characterized in that:

[0006] Includes: an audio gain control chip, wherein the audio gain control chip has an audio signal input port for inputting audio signals, and the audio gain control chip has an audio signal output port for outputting limited audio signals;

[0007] The voltage limiting module includes an operational amplifier chip and a voltage comparator connected to the audio gain control chip. The voltage reference signal Vref output by the audio gain control chip is input to the operational amplifier chip, and the operational amplifier chip outputs a threshold voltage. The input audio signal and the threshold voltage are respectively input to the voltage comparator. The audio gain control chip limits the voltage and reduces noise of the input audio signal according to the output of the voltage comparator, and outputs the voltage-limited audio signal from the audio signal output port.

[0008] Furthermore, the voltage limiting module includes a first operational amplifier and a second operational amplifier. The port of the audio gain control chip that outputs the voltage reference signal Vref is connected to one of the input terminals of the first operational amplifier. A voltage divider circuit is provided between the first operational amplifier and the second operational amplifier. The voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor. A lower threshold voltage signal V- is output between the first voltage divider resistor and the second voltage divider resistor. An upper threshold voltage signal V+ is output at the output terminal of the second operational amplifier.

[0009] The voltage limiting module also includes a first voltage comparator and a second voltage comparator. The upper threshold voltage signal V+ and the lower threshold voltage signal V- are respectively input to one input terminal of the first voltage comparator and the second voltage comparator. The audio signal is input to the other input terminal of the first voltage comparator and the second voltage comparator. The output terminals of the first voltage comparator and the second voltage comparator are connected to the base of a transistor. The emitter of the transistor is connected to an audio gain control chip. The collector of the transistor is connected to a gain control voltage. The output of the voltage comparator can turn on the transistor so that the gain control voltage is input to the audio gain control chip. The audio gain control chip outputs the voltage-limited audio signal from the audio signal output port.

[0010] Furthermore, the audio gain control chip is model SA571, the operational amplifier chip is model LM358D, and the voltage comparator is model LM358.

[0011] An audio signal processing module for a train broadcast intercom system includes: the aforementioned gain control circuit, wherein one audio signal input port of the audio gain control chip is used to input an audio signal, and the other audio signal input port is connected to a microphone via a first operational amplifier module; one audio signal output port of the audio gain control chip is connected to a second operational amplifier module to output a digital artificial broadcast audio signal, and the other audio signal output port is connected to a third operational amplifier module to output an analog artificial broadcast audio signal.

[0012] A digital spectrum intercom processing module, comprising a digital audio processing chip, wherein the input terminal of the digital audio processing chip is connected to a microphone, and the output terminal of the digital audio processing chip outputs a digital intercom audio signal;

[0013] An analog spectrum intercom processing module includes an analog audio processing chip. The audio signal output port of the audio gain control chip is connected to the fourth operational amplifier module and then to the audio signal input port of the analog audio processing chip. The audio signal output port of the analog audio processing chip outputs an analog intercom audio signal.

[0014] Furthermore, the analog audio processing chip has at least two audio signal output ports. One audio signal output port is connected to a fifth operational amplifier module, which is connected to the intercom bus. The other audio signal output port is connected to a sixth operational amplifier module, which is connected to the intercom microphone. The fifth operational amplifier module and the sixth operational amplifier module are respectively used to adjust the magnitude of the analog intercom audio signal output by the analog audio processing chip.

[0015] Furthermore, it also includes a power supply module for supplying power.

[0016] Furthermore, the power supply module includes a DC-DC power chip, which can convert the input DC12V power supply into DC3.3V power supply. The DC12V power supply powers the audio gain control chip and the first, second, third, fourth, fifth, and sixth operational amplifier modules, while the DC3.3V power supply powers the digital audio processing chip and the analog audio processing chip.

[0017] This utility model discloses a gain control circuit for a train broadcast intercom system. Through an audio gain control chip and a voltage limiting module, it can perform voltage limiting and noise reduction processing on the input audio signal. When the amplitude of the audio signal exceeds the preset range, the gain control mechanism is triggered to stabilize the amplitude of the output signal within a reasonable range. This can effectively solve the problem of low-cost audio signal processing circuit modules when processing fluctuating audio signals, improve the stability and reliability of audio signals, reduce distortion and noise caused by excessive signal fluctuations, and make the communication between drivers and passengers, and between drivers, clearer and more stable, thus improving the call quality. Attached Figure Description

[0018] Figure 1 This is a block diagram of a gain control circuit for a train broadcast intercom system, as shown in the embodiment.

[0019] Figure 2This is a circuit diagram of an audio gain control chip and a voltage comparator for a gain control circuit used in a train broadcast intercom system, as shown in the embodiment.

[0020] Figure 3 This is a circuit schematic diagram of an operational amplifier chip used in a gain control circuit for a train broadcast intercom system, as shown in the embodiment.

[0021] Figure 4 This is a block diagram of an audio signal processing module for a train broadcast intercom system, as shown in the embodiment. Detailed Implementation

[0022] See Figure 1 , 2 3. A gain control circuit for a train broadcast intercom system according to the present invention includes: an audio gain control chip 101, the audio gain control chip 101 having an audio signal input port for inputting audio signals, and the audio gain control chip 101 also having an audio signal output port for outputting limited audio signals.

[0023] The voltage limiting module 102 includes an operational amplifier chip and a voltage comparator connected to the audio gain control chip. The voltage reference signal Vref output by the audio gain control chip is input to the operational amplifier chip, and the operational amplifier chip outputs a threshold voltage. The audio signal and the threshold voltage are respectively input to the voltage comparator. The audio gain control chip limits the voltage and reduces noise of the input audio signal according to the output of the voltage comparator, and outputs the limited audio signal from the audio signal output port.

[0024] Specifically, in one embodiment of this utility model, the voltage limiting module includes a first operational amplifier U3A and a second operational amplifier U3B. The 8th port of the audio gain control chip output voltage reference signal Vref is connected to the 3rd port of the input terminal of the first operational amplifier U3A. A voltage divider circuit is provided between the first operational amplifier and the second operational amplifier. The voltage divider circuit includes a first voltage divider resistor R9 and a second voltage divider resistor R10. The 1st port of the output terminal of the first operational amplifier U3A is connected to the 2nd port of the input terminal. The 1st port of the output terminal of the first operational amplifier U3A is connected to one end of the first voltage divider resistor R9. The 1st port of the output terminal of the first operational amplifier U3A is connected to the 5th port of the second operational amplifier U3B. A resistor R24 ​​is connected between the first voltage divider resistor R9 and the second voltage divider resistor R10 and then connected to the 6th port of the second operational amplifier U3B. The lower threshold voltage signal V- is output between the first voltage divider resistor R9 and the second voltage divider resistor R10. The upper threshold voltage signal V+ is output at the 7th port of the output terminal of the second operational amplifier.

[0025] The voltage limiting module also includes a first voltage comparator U2A and a second voltage comparator U2B. The upper threshold voltage signal V+ is input to port 7 of the first voltage comparator U2A, and the lower threshold voltage signal V- is input to port 4 of the second voltage comparator U2B. The audio signal is input to port 6 of the first voltage comparator U2A and port 5 of the second voltage comparator U2B. Port 1 of the first voltage comparator U2A and port 2 of the second voltage comparator U2B are connected to the base of transistor Q1. The emitter of transistor Q1 is connected to the audio gain control chip, and the collector of transistor Q1 is connected to the gain control voltage. The output of the voltage comparator can turn on the transistor so that the gain control voltage is input to the audio gain control chip. The audio gain control chip outputs the voltage-limited audio signal from the audio signal output port.

[0026] For low-cost hardware audio processing modules, the gain control circuit provided in this embodiment, by setting an audio gain control chip and a voltage limiting module, can perform voltage limiting and noise reduction processing on the input audio signal, stabilizing the amplitude of the audio signal within a certain range. This can effectively solve the problem of excessively large or small audio signal amplitude, and improve the stability of the audio signal and call quality.

[0027] The embodiment achieves real-time compression of the input audio signal amplitude without CPU intervention. Through the collaborative work of a pure hardware voltage limiting module and an audio gain control chip, the input audio signal with large fluctuations is stably controlled within a reasonable range for output. This ensures that subsequent circuits receive a stable audio signal, avoiding malfunctions caused by excessively strong or weak signals, and guaranteeing the stable operation of the train broadcast intercom system. This ensures clear voice broadcasts and normal intercom functions. Compared to CPU systems using the IMX6Q, the gain control circuit provided in the embodiment significantly reduces hardware costs, which is beneficial for the product's market promotion.

[0028] See Figure 2 , 3 In practice, the audio gain control chip is model SA571, the first operational amplifier U3A and the second operational amplifier U3B are model LM358D, the first voltage comparator U2A and the second voltage comparator U2B are model LM358, the audio gain control chip SA571 outputs a 1.8V voltage reference Vref signal from pin 8 (THD signal), the first operational amplifier U3A is an emitter follower circuit, and pin 1 also outputs a 1.8V voltage, R9 and R10 are voltage divider circuits, and after voltage division, the lower threshold voltage signal V- is 0.7V. According to the principle of virtual short and virtual open of operational amplifiers, the voltage of pins 5 and 6 of the second operational amplifier U3B is 1.8V, the output voltage V+ from pin 7 is 2.9V, and the upper threshold voltage signal V+ is...

[0029] The upper threshold voltage signal V+ is input to port 7 of the first voltage comparator U2A, and the lower threshold voltage signal V- is input to port 4 of the second voltage comparator U2B. When the audio signal PA_TALK_IN input to the audio gain control chip SA571 is greater than 2.9V or less than 0.7V, transistor Q1 turns on, and the RECTCAP voltage at pin 1 of the audio gain control chip SA571 is the gain control voltage AVCC12. The audio gain control chip SA571 starts gain control, and pin 7 of the audio gain control chip outputs a 2.2Vp-p audio signal. That is, when the PA_TALK_IN signal is 6Vp-p, SA571 outputs a 2.2Vp-p signal, thereby realizing gain control for the input signal.

[0030] See Figure 4 In an embodiment of this utility model, an audio signal processing module for a train broadcast intercom system is also provided, comprising:

[0031] The aforementioned gain control circuit 1 has one audio signal input port of the audio gain control chip used to input audio signals, and the other audio signal input port is connected to the first operational amplifier module 2 and then to the microphone 3. One audio signal output port of the audio gain control chip is connected to the second operational amplifier module 4 and then outputs a digital artificial broadcast audio signal, and the other audio signal output port is connected to the third operational amplifier module 5 and then outputs an analog artificial broadcast audio signal.

[0032] The digital spectrum intercom processing module 6 includes a digital audio processing chip. The input of the digital audio processing chip is connected to the microphone 3, and the output of the digital audio processing chip outputs a digital intercom audio signal.

[0033] The analog spectrum intercom processing module 7 includes an analog audio processing chip. The audio signal output port of the audio gain control chip is connected to the fourth operational amplifier module 8 and then connected to the audio signal input port of the analog audio processing chip. The audio signal output port of the analog audio processing chip outputs an analog intercom audio signal.

[0034] In this embodiment, the analog audio processing chip has at least two audio signal output ports. One audio signal output port is connected to the fifth operational amplifier module 9, which is connected to the intercom bus. The other audio signal output port is connected to the sixth operational amplifier module 10, which is connected to the intercom microphone. The fifth operational amplifier module 9 and the sixth operational amplifier module 10 are respectively used to adjust the magnitude of the analog intercom audio signal output by the analog audio processing chip.

[0035] In this embodiment, a power supply module 11 is also included for power supply. The power supply module includes a DC-DC power chip. In this embodiment, the DC-DC power chip is model TPS5430DDA. The DC-DC power chip can convert the input DC12V power supply into DC3.3V power supply. The DC12V power supply powers the audio gain control chip and the first, second, third, fourth, fifth, and sixth operational amplifier modules. The DC3.3V power supply powers the digital audio processing chip and the analog audio processing chip.

[0036] In this embodiment, the digital audio processing chip is model PNC201, the analog audio processing chip is model ML7037-003TB, and the operational amplifier module is model SE5532AD. The microphone input audio signal is 100mVp-p, which is output as a 3.3V digital carrier audio signal after passing through the PNC201 digital intercom audio processing chip. The microphone input audio signal is 100mVp-p, which is amplified 60 times by the operational amplifier module and output as a 6Vp-p signal. After being subjected to voltage limiting and noise reduction processing by the audio gain control circuit, it outputs a 2.2Vp-p signal. After being amplified 0.5 times by the operational amplifier module, it outputs a 1.1Vp-p audio signal to the analog audio processing chip ML7037-003TB. After signal processing by the ML7037-003TB, it is amplified 2 times by the operational amplifier module and outputs a 2.2Vp-p audio signal.

[0037] The audio signal processing module for the train broadcast intercom system in this embodiment performs voltage limiting and noise reduction processing on the input audio signal through an audio gain control circuit. This stabilizes the amplitude of the audio signal, reduces distortion and noise caused by excessive signal fluctuations, and makes communication between drivers and passengers, as well as between drivers, clearer and more stable, thus improving call quality. Under the gain control of the audio gain control chip, the audio signal processing module can precisely adjust the amplitude and reduce noise of the audio signal, reducing echo. Combined with digital spectrum intercom processing modules and analog spectrum intercom processing modules, it can also achieve compatibility between analog and digital lines. It can adapt to broadcast intercom systems using different technical solutions in different types and periods of rail transit projects. In the renovation of older trains, it can directly replace the original power amplifier front end without upgrading the control host. The gain control circuit, as a preprocessing module, can work collaboratively with existing digital systems, sharing the CPU load.

[0038] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.

[0039] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A gain control circuit for a train broadcast intercom system, characterized in that: include: An audio gain control chip, wherein the audio gain control chip has an audio signal input port for inputting an audio signal, and an audio signal output port for outputting a limited audio signal; The voltage limiting module includes an operational amplifier chip and a voltage comparator connected to the audio gain control chip. The voltage reference signal Vref output by the audio gain control chip is input to the operational amplifier chip, and the operational amplifier chip outputs a threshold voltage. The input audio signal and the threshold voltage are respectively input to the voltage comparator. The audio gain control chip limits the voltage and reduces noise of the input audio signal according to the output of the voltage comparator, and outputs the voltage-limited audio signal from the audio signal output port.

2. A gain control circuit for a train broadcast intercom system as defined in claim 1, wherein: The voltage limiting module includes a first operational amplifier and a second operational amplifier. The port of the audio gain control chip that outputs the voltage reference signal Vref is connected to one of the input terminals of the first operational amplifier. A voltage divider circuit is provided between the first operational amplifier and the second operational amplifier. The voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor. The lower threshold voltage signal V- is output between the first voltage divider resistor and the second voltage divider resistor. The output terminal of the second operational amplifier outputs the upper threshold voltage signal V+. The voltage limiting module also includes a first voltage comparator and a second voltage comparator. The upper threshold voltage signal V+ and the lower threshold voltage signal V- are respectively input to one input terminal of the first voltage comparator and the second voltage comparator. The audio signal is input to the other input terminal of the first voltage comparator and the second voltage comparator. The output terminals of the first voltage comparator and the second voltage comparator are connected to the base of a transistor. The emitter of the transistor is connected to an audio gain control chip. The collector of the transistor is connected to a gain control voltage. The output of the voltage comparator can turn on the transistor so that the gain control voltage is input to the audio gain control chip. The audio gain control chip outputs the voltage-limited audio signal from the audio signal output port.

3. A gain control circuit for a train broadcast intercom system as defined in claim 2, wherein: The audio gain control chip is model SA571, the operational amplifier chip is model LM358D, and the voltage comparator is model LM358.

4. An audio signal processing module for a train broadcast intercom system, characterized by: include: The gain control circuit according to any one of claims 1 to 3, wherein one audio signal input port of the audio gain control chip is used to input an audio signal, and the other audio signal input port is connected to a microphone after connecting to a first operational amplifier module; one audio signal output port of the audio gain control chip is connected to a second operational amplifier module to output a digital artificial broadcast audio signal, and the other audio signal output port is connected to a third operational amplifier module to output an analog artificial broadcast audio signal. A digital spectrum intercom processing module, comprising a digital audio processing chip, wherein the input terminal of the digital audio processing chip is connected to a microphone, and the output terminal of the digital audio processing chip outputs a digital intercom audio signal; An analog spectrum intercom processing module includes an analog audio processing chip. The audio signal output port of the audio gain control chip is connected to the fourth operational amplifier module and then to the audio signal input port of the analog audio processing chip. The audio signal output port of the analog audio processing chip outputs an analog intercom audio signal.

5. The audio signal processing module for a train broadcast intercom system of claim 4, wherein: The analog audio processing chip has at least two audio signal output ports. One audio signal output port is connected to a fifth operational amplifier module, which is connected to an intercom bus. The other audio signal output port is connected to a sixth operational amplifier module, which is connected to an intercom microphone. The fifth and sixth operational amplifier modules are used to adjust the magnitude of the analog intercom audio signal output by the analog audio processing chip.

6. The audio signal processing module for a train broadcast intercom system of claim 4, wherein: It also includes a power supply module for supplying power.

7. The audio signal processing module for a train broadcast intercom system of claim 6, wherein: The power supply module includes a DC-DC power chip, which can convert the input DC12V power supply into DC3.3V power supply. The DC12V power supply powers the audio gain control chip and the first, second, third, fourth, fifth, and sixth operational amplifier modules, while the DC3.3V power supply powers the digital audio processing chip and the analog audio processing chip.

Images