A wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration

Abstract

The application discloses a wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration, which comprises a conference host, an infrared receiver, a microphone unit and a communication control module. A digital-analog hybrid FM modulation module modulates the voice signal collected by the microphone to an adjustable multiple resonant oscillator to obtain an FM modulated radio frequency signal, and the infrared driving module drives the infrared light carrying the voice signal to be emitted. The photoelectric conversion module converts the infrared light into a radio frequency electrical signal, and the multi-stage amplification driving module amplifies and automatically gains the radio frequency electrical signal and then controls the output of the RF signal to the conference host. The signal demodulation module restores the audio signal according to the RF signal and outputs the audio signal through the audio output driving module. The digital precise tuning of the digital-analog hybrid FM modulation and demodulation and the multiple resonant oscillator can eliminate the frequency deviation caused by temperature drift and device aging, ensure the 100Hz-20KHz full-band transmission bandwidth and maintain the group delay characteristics, and guarantee the gain stability and consistency of the multi-machine cascade.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of signal processing, and particularly relates to a wireless infrared voice transmission system with adjustable and automatically calibrated carrier frequency. BACKGROUND

[0002] At present, wireless infrared voice transmission systems are usually used in conferences, training, broadcasting and the like to realize audio transmission between a microphone unit and an audio receiving host. According to different modulation modes, the existing systems can be roughly divided into analog FM modulation systems and digital modulation systems. The analog FM modulation system usually adopts a varicap and a center-tapped transformer to construct a frequency modulation and demodulation circuit. This kind of system has a mature structure, but has the following defects: limited audio bandwidth: due to the characteristics of the varicap, the highest audio transmission frequency is usually not more than 10 kHz-12 kHz, and it is difficult to cover the full audio range of 100 Hz-20 kHz; poor frequency stability: the varicap and the center-tapped element need to be manually adjusted to set the carrier, and the carrier frequency is easily shifted and out of tune due to temperature drift and aging, thereby causing transmission interruption.

[0003] Some digital modulation systems usually adopt digital FM, OFDM or QPSK and the like, and complete digital coding, modulation and demodulation through a high-speed DSP or FPGA, so as to realize higher bandwidth and signal-to-noise ratio. However, this kind of scheme also has the following defects: sensitive to group delay and phase distortion: there are sampling, filtering and modulation delays in the digital link, and group delay differences are inevitably generated, which leads to phase distortion of the high-frequency part of the voice and a decrease in the stereophonic positioning sense; high implementation complexity: full-digital modulation and demodulation requires high-power hardware, and ADC, DAC and the like are needed in the front and back ends, so that the system power consumption and cost increase, which is not conducive to portable and low-power consumption scenarios.

[0004] In summary, the traditional analog FM mode cannot meet the bandwidth and frequency stability requirements, and the pure digital modulation mode is also difficult to realize low-delay transmission, and has high cost and high power consumption. Therefore, it is urgent to provide a wireless infrared voice transmission system with adjustable and automatically calibrated carrier frequency to solve the above technical problems. SUMMARY

[0005] Therefore, the present application provides a wireless infrared voice transmission system with adjustable and automatically calibrated carrier frequency, which adopts digital-analog hybrid FM modulation and demodulation technology, and realizes digital precise tuning of the carrier frequency through linearization and dynamic range expansion of a multi-resonant oscillator. The wireless infrared voice transmission system has wide bandwidth and low distortion, and can also realize adjustable and automatically calibrated carrier frequency. The following technical scheme is adopted to realize the wireless infrared voice transmission system.

[0006] The application provides a wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration, which comprises a conference host, an infrared receiver, a plurality of microphone units and a communication control module, wherein the conference host, the infrared receiver and the plurality of microphone units are connected with the communication control module;

[0007] The conference host comprises an RF signal receiving module, a signal demodulation module and an audio output driving module, wherein the RF signal receiving module is connected with the signal demodulation module, and the signal demodulation module is connected with the audio output driving module; the microphone unit comprises a microphone, a digital-analog hybrid FM modulation module and an infrared driving module, wherein the microphone is connected with the digital-analog hybrid FM modulation module, and the digital-analog hybrid FM modulation module is connected with the infrared driving module; and the infrared receiver comprises a photoelectric conversion module and a multi-stage amplification driving module, wherein the photoelectric conversion module is connected with the multi-stage amplification driving module, and the multi-stage amplification driving module is connected with the RF signal receiving module.

[0008] The digital-analog hybrid FM modulation module receives the voice signal collected by the microphone and performs digital-analog hybrid FM modulation to generate an FM modulated radio frequency signal carrying the voice signal; the infrared driving module drives the FM modulated radio frequency signal to be converted into an infrared light signal carrying the FM modulated radio frequency signal and sent to the photoelectric conversion module; the photoelectric conversion module performs photoelectric conversion on the infrared light signal of the FM modulated radio frequency signal to obtain a radio frequency electric signal; the multi-stage amplification driving module amplifies and shapes the radio frequency electric signal and outputs the radio frequency electric signal to the RF signal receiving module to obtain an RF signal; and the signal demodulation module recovers an audio signal from the RF signal and outputs the audio signal through the audio output driving module.

[0009] As a preferred technical solution of the above, the digital-analog hybrid FM modulation module comprises an amplifier, a DAC unit, a summer, a PI controller and an adjustable multi-tuned oscillator, wherein the input end of the amplifier is connected with the microphone, the output end of the amplifier, the DAC unit and the input end of the PI controller are all connected with the summer, the output end of the PI controller is connected with the input end of the adjustable multi-tuned oscillator, the summer is connected with the output end of the adjustable multi-tuned oscillator, and the adjustable multi-tuned oscillator is connected with the infrared driving module.

[0010] The amplifier is used for filtering and linear amplification of the voice signal collected by the microphone and outputting a modulated signal, the DAC unit is used for outputting a carrier setting signal according to a preset carrier reference frequency, the adder is used for summing the modulated signal, the carrier setting signal and the output signal of the adjustable multi-tuned oscillator, and the output signal of the adjustable multi-tuned oscillator is processed by the PI controller to generate a control signal of the adjustable multi-tuned oscillator, the adjustable multi-tuned oscillator generates an FM modulated radio frequency carrier signal according to the control signal and outputs to the infrared drive module, wherein the PI controller is used for generating a compensation signal according to the frequency error between the output signal of the adjustable multi-tuned oscillator and the carrier setting signal, and the compensation signal is used for compensating the temperature drift and power supply fluctuation of the adjustable multi-tuned oscillator and the infrared drive module.

[0011] As a preferred of the above technical solution, the output frequency corresponding to the output signal has an approximate linear corresponding relationship between the reference frequency point and the control signal output by the adder.

[0012] When the control signal changes linearly with time in a period of time, the output frequency of the adjustable multi-tuned oscillator continuously deviates around the reference frequency point to realize phase-continuous FM modulation, wherein the output frequency remains low group delay in the 100Hz-20kHz audio bandwidth.

[0013] As a preferred of the above technical solution, the PI controller generates a control quantity according to the error signal between the controlled quantity and the expected value, and the expression of the PI controller output in continuous form is calculated as:

[0014] (1)

[0015] Wherein, e(t) is the difference between the reference input and the actual output, u(t) is the control quantity, K p is the proportional gain, t represents the time variable, dt represents the differential element of time, K i is the integral gain; the proportional link generates a control action in proportion to the current instantaneous error to affect the response speed and damping characteristics of the system; the integral link time-accumulates the error signal to make the system continuously output an adjustment quantity when there is a non-zero error in the steady state.

[0016] As a preferred of the above technical solution, the digital-analog hybrid FM modulation module further comprises an LFSR unit connected with the DAC unit, and the LFSR unit is connected with the signal demodulation module through the communication control module.

[0017] When the carrier signal corresponding to the carrier reference frequency f ref is converted into a control signal by the DAC unit, the center frequency point of the adjustable multi-tuned oscillator is set;

[0018] The pseudo-random bit stream output by the LFSR unit is mapped by a lookup table and converted into a frequency offset control quantity Δf by another channel DAC unit, which is superimposed with the baseband modulation quantity of the voice signal and the set quantity of the center frequency point in the adder, and a control signal of the adjustable harmonic oscillator is formed through the PI controller, wherein the LFSR unit generates a pseudo-random frequency jitter sequence and an m-sequence preamble uniformly in a digital manner and cooperates with an infrared drive module.

[0019] As a preferred embodiment of the above technical solution, the infrared receiver further comprises an RF band-pass filter module and an RF combining module, the photoelectric conversion module and the RF combining module are connected with the RF band-pass filter module, and the multi-stage amplification driving module is connected with the combining module.

[0020] The RF signal is sequentially processed by the RF band-pass filter module, the RF combining module and the multi-stage amplification driving module to obtain a stable RF signal and output to the conference host, wherein the communication control module comprises a first communication unit and a second communication unit, the conference host and the microphone unit are connected with the first communication unit, and the infrared receiver interacts with the conference host on working state and parameter information through the second communication unit.

[0021] As a preferred embodiment of the above technical solution, the signal demodulation module comprises an FM demodulator and a gain adjustment unit, the gain adjustment unit and the RF signal receiving module are connected with the FM demodulator, and the gain adjustment unit is connected with the audio output driving module.

[0022] The FM demodulator is configured to filter, limit and FM demodulate the RF signal output by the RF signal receiving module to output a line-level audio signal; the conference host interacts with each microphone unit on ChirpIoT data through the first communication unit and transmits a carrier reference signal to the microphone unit in real time to realize automatic carrier calibration.

[0023] As a preferred embodiment of the above technical solution, the multi-stage amplification driving module comprises a plurality of amplifiers connected in series in the RF signal chain and having variable gain, and the multi-stage amplification driving module adjusts the gain of each stage through a common or hierarchical feedback control signal to maintain the output level within a preset range, wherein the multi-stage amplification driving module is configured to compensate for the fluctuations in the received level caused by the microphone distance, directivity and ambient light intensity of the microphone unit.

[0024] As the preferred technical scheme of the above, the microphone unit further comprises a touch display module and a TYPE-C interface module, both of which are connected with the digital-analog hybrid FM modulation module, the touch display module is used for working state display, parameter adjustment and system menu operation, and the TYPE-C interface module is used for realizing battery charging management.

[0025] As the preferred technical scheme of the above, the microphone unit further comprises an audio processing module connected with the microphone, the audio processing module is used for adjusting the gain of different frequency bands to correct the frequency response characteristics of the microphone unit.

[0026] The application provides a wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration, which comprises a conference host, an infrared receiver, a plurality of microphone units and a communication control module. The digital-analog hybrid FM modulation module in the microphone unit modulates the voice signal collected by the microphone to the carrier generated by the adjustable multi-tuned oscillator to obtain an FM modulated radio frequency signal, and the infrared transmitter is driven by the infrared driving module to emit infrared light carrying voice information. The photoelectric conversion module of the infrared receiver converts the infrared light carrying voice information into a radio frequency electrical signal, and the multi-stage amplification driving module amplifies and automatically controls the gain of the radio frequency electrical signal and then outputs the RF signal to the conference host. The signal demodulation module of the conference host recovers the audio signal according to the RF signal and outputs the audio signal through the audio output driving module. The digital precise tuning is realized by using digital-analog hybrid FM modulation and the linearization and dynamic range expansion of the multi-tuned oscillator, the frequency deviation caused by temperature drift and device aging can be eliminated, no physical adjustable device is needed, the transmission bandwidth of 100Hz-20KHz full frequency band is ensured and the group delay characteristics are maintained, the signal-to-noise ratio and coverage stability are improved, and the gain stability and consistency of the cascade of multiple machines are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0028] Figure 1 The structural block diagram of the wireless infrared voice transmission system provided by the application is shown in the figure.

[0029] Figure 2 The working principle diagram of the wireless infrared voice transmission system provided by the application is shown in the figure.

[0030] Figure 3 The structural block diagram of the digital-analog hybrid FM modulation module provided by the application is shown in the figure.

[0031] Figure 4 The working principle diagram of the digital-analog hybrid FM modulation module provided by the present application is shown in the following figure:

[0032] Figure 5 The control principle diagram of the LFSR unit provided by the present application is shown in the following figure:

[0033] Figure 6 The flow chart of the wireless infrared voice transmission method provided by the present application is shown in the following figure.

[0034] The main element symbols are explained as follows:

[0035] 100-conference host; 110-RF signal receiving module; 120-signal demodulation module; 130-audio output driving module; 200-infrared receiver; 210-optoelectronic conversion module; 220-multistage amplification driving module; 300-microphone unit; 310-microphone; 320-digital-analog hybrid FM modulation module; 321-amplifier; 322-DAC unit; 323-adder; 324-PI controller; 325-adjustable multivibrator; 326-LFSR unit; 330-infrared driving module; 400-communication control module; 410-first communication unit; 420-second communication unit. DETAILED DESCRIPTION

[0036] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0037] In the prior art, the analog FM modulation system mostly uses a varicap and a center-tapped transformer to construct a frequency modulation and demodulation circuit. This kind of system structure is mature, but has the following problems:

[0038] 1. Limited transmission bandwidth: the traditional analog FM system has insufficient high-frequency response, and it is difficult to realize high-fidelity transmission of the full audio band (100Hz~20kHz);

[0039] 2. Poor frequency stability: the varicap and the center-tapped structure are sensitive to temperature and aging, and the frequency needs to be adjusted manually;

[0040] 3. Phase distortion problem of pure digital modulation: although the digital system has bandwidth advantages, the group delay and phase linearity are difficult to guarantee, causing voice distortion, and high-end filter components are required;

[0041] 4. Insufficient frequency adjustability and synchronization: the frequency points of the existing system are fixed, and multi-channel frequency point synchronous adjustment is not supported;

[0042] 5. System anti-interference ability is insufficient: the radio frequency signal of mobile phone, lighting noise, LED light source and so on often causes interference in conference environment;

[0043] 6. Wiring and extension are inconvenient: signal attenuation, delay and consistency are difficult to control in the system of multiple receiver cascade.

[0044] In order to overcome the above shortcomings, the present application aims to provide a wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration. The system uses digital-analog hybrid FM modulation and demodulation technology, and realizes digital precise tuning through linearization and dynamic range expansion of multi-resonant oscillator, so as to achieve the following technical targets:

[0045] (1) Realize the carrier frequency of 2-10MHz range adjustable, step: 20KHz;

[0046] (2) Support automatic frequency calibration (AFC), eliminate the frequency deviation caused by temperature drift and device aging, without physical adjustable devices such as varactor diode and middle week;

[0047] (3) Suppress phase noise through multi-resonant oscillator linearization and dynamic range expansion, ensure voice details and clarity;

[0048] (4) Ensure 100Hz~20kHz full-band transmission bandwidth, while maintaining low group delay characteristics;

[0049] (5) Use multi-stage RF-AGC design and distributed infrared receiving link to improve signal-to-noise ratio and coverage stability;

[0050] (6) Ensure the gain stability and consistency of multiple receiver cascade;

[0051] (7) Integrate intelligent control, human-computer interaction and low-power communication functions, improve system maintainability and intelligent level.

[0052] Referring to Figure 1 and Figure 2 , the present application provides a wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration, which comprises a conference host 100, an infrared receiver 200, a plurality of microphone units 300 and a communication control module 400, the conference host 100, the infrared receiver 200, a plurality of the microphone units 300 are connected with the communication control module 400;

[0053] The conference host 100 includes an RF signal receiving module 110, a signal demodulation module 120 and an audio output driving module 130, the signal demodulation module 120 is connected with the audio output driving module 130, the RF signal receiving module 110 is connected with the signal demodulation module 120, the signal demodulation module is connected with the audio output driving module, the microphone unit 300 includes a microphone 310, a digital-analog hybrid FM modulation module 320 and an infrared driving module 330, the microphone 310 and the infrared driving module 330 are connected with the digital-analog hybrid FM modulation module 320, the infrared receiver 200 includes a photoelectric conversion module 210 and a multi-stage amplification driving module 220, the photoelectric conversion module 210 is connected with the infrared driving module 330, and the multi-stage amplification driving module 220 is connected with the RF signal receiving module 110;

[0054] Wherein, the digital-analog hybrid FM modulation module 320 receives the voice signal collected by the microphone 310 and modulates to the carrier generated by the adjustable multi-tuned oscillator to obtain the FM modulated radio frequency signal, the infrared driving module 330 drives the FM modulated radio frequency signal to obtain the infrared light carrying voice information and sends to the photoelectric conversion module 210, the photoelectric conversion module 210 carries out photoelectric conversion on the infrared light carrying voice information to obtain the radio frequency electric signal, the multi-stage amplification driving module 220 amplifies and shapes the radio frequency electric signal and outputs to the RF signal receiving module 110 to obtain the RF signal, the signal demodulation module 120 recovers the audio signal according to the RF signal and outputs through the audio output driving module 130.

[0055] In the embodiment, the infrared receiver 200 further comprises an RF band-pass filter module and an RF combining module, the photoelectric conversion module 210 and the RF combining module are connected with the RF band-pass filter module, and the multi-stage amplification driving module 220 is connected with the combining module; the radio frequency electrical signal is sequentially processed by the RF band-pass filter module, the RF combining module and the multi-stage amplification driving module 220 to obtain a stable RF signal and output to the conference host 100, wherein the communication control module 400 comprises a first communication unit 410 and a second communication unit 420, the conference host 100 and the microphone unit 300 are connected with the first communication unit 410, the infrared receiver 200 interacts with the conference host 100 for working state and parameter information through the second communication unit 420, the first communication unit 410 is a ChirpIoT link, and the second communication unit 420 is network communication. In other words, the conference host 100 and the microphone unit 300 communicate by using ChirpIoT communication, and the conference host 100 and the infrared receiver 200 communicate by using network communication; the microphone unit 300 and the infrared receiver 200 use infrared transmission, and the transmission is one-way transmission from the microphone unit 300 to the infrared receiver 200.

[0056] The signal demodulation module 120 comprises an FM demodulator and a gain adjustment unit, the gain adjustment unit and the RF signal receiving module 110 are connected with the FM demodulator, and the gain adjustment unit is connected with the audio output driving module 130; wherein the FM demodulator is used for conditioning and FM demodulating the RF signal output by the RF signal receiving module 110 to output a line-level audio signal; the conference host 100 performs ChirpIoT data interaction with each microphone unit 300 through the first communication unit 410, and transmits a carrier reference signal to the microphone unit 300 in real time to realize automatic carrier calibration.

[0057] It should be noted that the multi-stage amplification driving module 220 includes a plurality of amplifiers connected in series in the radio frequency signal chain and having variable gain, the multi-stage amplification driving module 220 adjusts the gain of each stage through a common or hierarchical feedback control signal to maintain the output level within a preset range, wherein the multi-stage amplification driving module 220 is used to compensate for the fluctuations in the received level caused by the microphone distance, directivity and ambient light intensity of the microphone unit 300. The microphone unit 300 also includes a touch display module and a TYPE-C interface module (not shown), both of which are connected to the digital-analog hybrid FM modulation module 320, the touch display module is used for working state display, parameter adjustment and system menu operation, and the TYPE-C interface module is used for battery charging management. The microphone unit 300 also includes an audio processing module connected to the microphone 310, which is used to adjust the gain of different frequency bands to correct the frequency response characteristics of the microphone unit 300.

[0058] Among them, the digital-analog hybrid FM modulation module 320 adopts an adjustable multivibrator as a carrier source, discards the traditional variable capacitance tube and intermediate cycle structure, realizes FM modulation and decoupling through digital and analog collaborative control, adopts multivibrator (adjustable multivibrator 325) linearization and dynamic range expansion technology, realizes the digital precise tuning of carrier frequency, reduces nonlinear error and effectively suppresses phase noise, so as to ensure the details and clarity of voice signal, the digital-analog hybrid FM modulation module 320 not only retains the low group delay and phase continuity of analog FM, but also avoids the distortion and delay of pure digital modulation, to realize 100Hz~20kHz wideband high-fidelity voice transmission. The audio receiving host (conference host 100) can synchronously issue the carrier frequency point to a plurality of microphone units 300 in real time, realizing the inter-channel synchronization setting and independent setting.

[0059] The communication control module includes a ChirpIoT wireless communication unit (first communication unit), which works in the ISM (433MHz, 868MHz, 915MHz) frequency band, and is used to establish a low-power control data link between the conference host and multiple microphone units, to realize remote configuration and interaction of carrier reference frequency, microphone parameters and working state information. The application introduces a ChirpIoT low-power wireless communication method working in the ISM frequency band in the control data channel, so that the parameter configuration, state monitoring and carrier reference information between the conference host and multiple microphone units are all completed through independent low-frequency spread spectrum links. On the one hand, the reliability of the control link can be maintained in multi-room, large-scene and complex electromagnetic environments; on the other hand, thanks to the low path loss of the ISM frequency band and the low transmission power design of the system itself, the energy consumption of the microphone unit control link can be significantly reduced, and long-lasting work can be realized with the built-in battery. At the same time, the control link and the infrared audio link are completely isolated in frequency band, and no additional audio noise or crosstalk is introduced.

[0060] It should be understood that by setting the conference host 100, the infrared receiver 200, the multiple microphone units 300 and the communication control module 400, the digital-analog hybrid FM modulation module 320 in the microphone unit 300 modulates the voice signal collected by the microphone 310 to the carrier generated by the adjustable multi-tuned oscillator 325 to obtain an FM modulated radio frequency signal, which is driven by the infrared driver module 330 to emit infrared light carrying the voice signal; the photoelectric conversion module 210 of the infrared receiver 200 converts the infrared light carrying the voice signal into a radio frequency electrical signal, and the multi-stage amplification and drive module 220 amplifies and automatically controls the gain of the radio frequency electrical signal and then outputs the RF signal to the conference host 100. The signal demodulation module 120 of the conference host 100 restores the audio signal according to the RF signal and outputs it through the audio output drive module 130. The use of digital-analog hybrid FM modulation and the linearization and dynamic range expansion of the multi-tuned oscillator realizes digital precise tuning, which can eliminate the frequency offset caused by temperature drift and device aging, does not require physical adjustable devices, ensures 100Hz~20KHz full-band transmission bandwidth and maintains group delay characteristics, improves signal-to-noise ratio and coverage stability, and guarantees the gain stability and consistency of multi-machine cascading, has human-computer interaction and low-power communication functions, and also improves system maintainability and intelligent level.

[0061] Optionally, the digital-analog hybrid FM modulation module 320 comprises an amplifier 321 connected with the microphone 310, a DAC unit 322, an adder 323, a PI controller 324 and an adjustable multi-tuned oscillator 325, an output terminal of the amplifier 321, an input terminal of the DAC unit 322 and an input terminal of the PI controller 324 are all connected with an input terminal of the adder 323, an output terminal of the PI controller 324 is connected with an input terminal of the adjustable multi-tuned oscillator 325, the adder 323 is connected with an output terminal of the adjustable multi-tuned oscillator 325, and the adjustable multi-tuned oscillator 325 is connected with the infrared drive module 330.

[0062] The amplifier 321 is configured to filter and linearly amplify the voice signal collected by the microphone 310 and output a modulation signal, the DAC unit 322 is configured to output a carrier setting signal according to a preset carrier reference frequency, the adder 323 is configured to sum the modulation signal, the carrier setting signal and an output signal of the adjustable multi-tuned oscillator 325, and the output signal of the adjustable multi-tuned oscillator 325 is processed by the PI controller 324 to generate a control signal of the adjustable multi-tuned oscillator 325, the adjustable multi-tuned oscillator 325 generates an FM modulated radio frequency carrier signal according to the control signal and outputs the FM modulated radio frequency carrier signal to the infrared drive module 330, wherein the PI controller 324 is configured to generate a compensation signal according to a frequency error between the output signal of the adjustable multi-tuned oscillator 325 and the carrier setting signal, and the compensation signal is used to compensate for temperature drift and power supply fluctuation of the adjustable multi-tuned oscillator 325 and the infrared drive module 330.

[0063] In the embodiment, as shown in Figure 3 and Figure 4 The output frequency corresponding to the output signal has a linear corresponding relationship between the reference frequency and the control signal output by the adder 323.

[0064] When the control signal changes linearly over time within a period of time, the output frequency of the adjustable multi-tuned oscillator 325 continuously deviates around the reference frequency to realize continuous FM modulation of the phase, and the output frequency remains low group delay within the 100Hz-20kHz audio bandwidth.

[0065] The PI controller 324 generates a control quantity according to an error signal between a controlled quantity and an expected value, and the expression of the output of the PI controller 324 in a continuous form is as follows:

[0066] (1)

[0067] Wherein, e(t) is the difference between the reference input and the actual output, u(t) is the control quantity, K pKt is a proportional gain, t is a time variable, dt is a differential element of time i The integral gain; the proportional element generates a control action in proportion to the current instantaneous error to affect the response speed and damping characteristics of the system; the integral element time accumulates the error signal to make the system output adjustment in the presence of non-zero error at steady state, thereby significantly improving the low-frequency gain, eliminating the static error, and achieving zero steady-state error tracking. In other words, the proportional-integral PI (Proportional-Integral) controller is a kind of linear feedback controller that is most widely used in engineering practice. Its role is to generate control quantity in real time according to the error signal between the controlled quantity and the expected value, in order to suppress disturbance, improve the steady-state accuracy and dynamic response performance of the system.

[0068] In the adjustable multi-tuned oscillator control loop designed by the application, the PI controller 324 takes the frequency error between the oscillator (adjustable multi-tuned oscillator) output frequency (or voltage, current sampling value equivalent to it) and the digital control DAC set value as input, adjusts the control signal to drive the oscillator operating point, so that the carrier center frequency is locked around the reference value, and slow disturbances such as temperature drift and power supply fluctuation are compensated; thanks to the closed-loop characteristics of PI control, the system can obtain higher frequency stability and smaller steady-state frequency deviation under the premise of ensuring phase margin, providing a stable basis for subsequent FM modulation and infrared transmission.

[0069] It should be noted that the digital-analog hybrid FM modulation module 320 further comprises an LFSR unit 326 connected with the DAC unit 322, and the LFSR unit 326 is connected with the signal demodulation module 120 through the communication control module 400;

[0070] When the carrier signal corresponds to the carrier reference frequency f ref The center frequency point of the adjustable multi-tuned oscillator 325 is set when the carrier signal is converted into a control signal by the DAC unit 322;

[0071] The pseudo-random bit stream output by the LFSR unit 326 is mapped by another channel DAC unit 322 to convert the frequency offset control quantity Δf, and the baseband modulation quantity of the voice signal and the set quantity of the center frequency point are superimposed in the adder 323, and the control signal of the adjustable multi-tuned oscillator 325 is formed through the PI controller 324, wherein the LFSR unit 326 generates a pseudo-random frequency jitter sequence and an m-sequence preamble in a digital manner, and cooperates with the infrared drive module 330, and the embodiment is aimed at a digital-analog hybrid FM infrared voice transmission link with a working frequency band of 2-10MHz. Figure 5The system introduces a single linear feedback shift register (LFSR) core at the transmitting end to generate pseudo-random frequency dithering sequences and m-sequence preambles in a digital manner without changing the existing voice FM modulation / demodulation architecture, and cooperates with the AFC closed loop at the transmitting end.

[0072] Specifically, during voice transmission, the carrier is pseudo-randomly dithered at a small amplitude, so that the instantaneous frequency is distributed within a small bandwidth around the carrier reference frequency f ref The LFSR generates predefined m-sequence preambles according to the same sequence, and different microphone units are allocated with mutually independent frequency sequences, so that the same frequency crosstalk is suppressed and reliable frame synchronization is achieved when multiple devices share a frequency band. The LFSR (Linear Feedback Shift Register) is a sequence generator based on shift register and linear feedback logic. By selecting a specific feedback polynomial, the LFSR can generate a pseudo-random sequence with a long period and statistical characteristics close to white noise with minimal hardware overhead. In the system, a single LFSR is used to generate pseudo-random dithering sequences and m-sequence preambles.

[0073] Pseudo-random frequency dithering refers to applying a controlled amplitude and statistically random frequency perturbation around the carrier center frequency, so that the instantaneous frequency is distributed within a small bandwidth. The purpose is not to change the service modulation itself, but to expand the energy originally concentrated in a single frequency point in the frequency domain, thereby reducing the EMI peak observed on the spectrum analyzer and alleviating narrowband interference on other systems. The m-sequence preamble is a maximum length sequence generated by the LFSR, which has good autocorrelation and cross-correlation characteristics. Sending a segment of m-sequence as the "preamble" of the frame can achieve high-reliability frame header positioning and synchronization through correlation detection in the conference host, and is used to identify different devices or different channel configurations. The system uses the LFSR to generate the m-sequence preamble to enhance the detection reliability of the control frame in a low signal-to-noise ratio and multipath environment.

[0074] Specifically, the conference host synchronously issues the bidding frequency points to multiple microphone units in real time, realizing synchronous and independent settings among channels. The microphone units output control signals through digital-to-analog converters (DAC units), which can realize arbitrary frequency selection within the range of 2-10 MHz, i.e., realizing the functions of arbitrary carrier frequency adjustment and multi-channel synchronization. For example, Figure 5As shown, in Adaptive Carrier Frequency and Spectrum Shaping Control (AFC), the transmitter uses a single LFSR to generate a pseudo-random sequence, which is then mapped to a DAC microstep control quantity via a lookup table to drive an adjustable multivibrator. Figure 5 (multivibrator in f) ref Small-amplitude pseudo-random frequency jitter is performed within the +Δf range. During power-on or reconnection, the microphone unit sends an m-sequence preamble, and the conference host obtains the frequency offset and initial timing value through relevant detection and feeds it back to the controller (PI controller) to achieve rapid acquisition and automatic correction of carrier deviation. During operation, the system detects the instantaneous frequency and long-term average frequency offset of the received signal in real time, and adaptively corrects the DAC (digital-to-analog converter) control signal through digital frequency measurement and AFC algorithm, so that the carrier center frequency is locked near the target value for a long time, maintaining frequency consistency without manual adjustment of the intermediate frequency transformer.

[0075] It should be noted that, in Figure 5 In the carrier frequency adaptation and spectrum shaping control block diagram, the receiver is equipped with a correlator to perform cross-correlation calculations on the demodulated control frame baseband signal and the m-sequence preamble generated by the local LFSR unit. The correlator calculates the correlation output by sliding multiplication and summation of the received sequence and the local reference sequence on the time axis, resulting in a significant main peak at the preamble alignment position. When the main peak of the correlation output exceeds a preset threshold, the correlator outputs a preamble detection flag and the corresponding frame start position, achieving reliable acquisition and time synchronization of the control frame. The link quality can be estimated through the main peak amplitude and sidelobe ratio. The preamble detection result of the correlator serves as the trigger condition for the carrier frequency adaptation and spectrum shaping control logic. Only when the preamble detection is successful and subsequent error checking passes can the carrier reference frequency, jitter parameters, and other information carried in the control frame be used to update the target frequency point and LFSR jitter configuration of the AFC loop on the conference host side. This ensures the stability of the control link and the reliability of carrier frequency adaptive adjustment even in complex electromagnetic environments.

[0076] Specifically, spectrum shaping is achieved by separating the bandwidth and amplitude of the voice (baseband) signal and the dithering control signal (control signal). The frequency offset of pseudo-random dithering is limited to a range far below the FM modulation level and changes slowly in a step-by-step manner, ensuring that the carrier frequency only produces narrowband widening within the service bandwidth without introducing perceptible audio quality degradation, eliminating the need for additional distortion compensation. This mechanism widens the carrier spectrum and reduces EMI peak values ​​at single frequencies, while also suppressing crosstalk between multiple devices operating at the same frequency in conjunction with multi-channel planning. The same LFSR core (unit) is also reused for scrambling code and cyclic redundancy check sequence generation, reducing hardware resource consumption and improving the reliability of preamble detection and error detection capabilities of control frames. This ensures the stability and reliability of the control link during long-term operation and in complex electromagnetic environments, thus achieving the function of adaptive carrier control (AFC).

[0077] Specifically, the infrared receiver is connected to the conference host in a "hand-in-hand" manner through a common six-type network cable, up to six receivers can be connected, meeting the coverage needs of the general conference scene; low-noise RF pre-amplification, RF combiner, multi-stage AGC and automatic limiting design are adopted to ensure continuous and stable signal transmission and improve the signal-to-noise ratio, that is, to constitute a distributed infrared receiving and multi-stage RF-AGC link. The audio front end of the microphone unit has independent adjustable functions of acoustic sensitivity, gain, equalization (EQ) and low-cut filtering, which can be flexibly matched according to the sound field environment; the anti-radio frequency interference circuit and filter network are added, which can effectively suppress the radio frequency pulse envelope interference of GSM, LTE and 5G, and significantly suppress the pop and cross talk, that is, to realize the functions of high-fidelity audio front end and anti-radio frequency interference.

[0078] The microphone unit is equipped with a 2.8-inch touch screen (touch display module) for working state display, parameter adjustment and system menu operation, TYPE-C interface (module) for battery charging management, ChirpIoT low-power wireless chip (ISM frequency band) for control data communication, supporting multi-room ID differentiation, remote parameter configuration and encrypted communication, improving system intelligence and maintainability, to realize intelligent control and human-computer interaction.

[0079] Referring again to Figure 2 , the system is composed of a conference host, an infrared receiver and a microphone unit. The conference host mainly completes the functions of radio frequency signal reception, demodulation and audio output, and internally includes: an RF signal receiving module, an RF shunt module, an FM demodulator, a gain adjustment module, an audio signal output driving module and a communication control module. On the one hand, it processes and FM demodulates the RF signal from the infrared receiver, and outputs a line-level audio signal; on the other hand, it performs ChirpIoT data interaction through the first communication unit and each microphone unit, and simultaneously transmits a carrier reference signal to the microphone unit in real time for carrier automatic calibration;

[0080] The microphone unit is responsible for voice acquisition and infrared emission, and also undertakes local control and state reporting functions, and internally includes: a microphone, an acoustic sensitivity / gain / EQ / low-cut independent adjustable module, an anti-interference circuit, a carrier synchronization and linearization control module, an AFC controller, a digital-analog hybrid modulation module, an infrared driving module, a touch display and a TYPE-C interface, and a ChirpIoT communication module (communication control module). The voice signal collected is sent to the digital-analog hybrid FM modulation link (digital-analog hybrid FM modulation module) after front-end conditioning, and then the infrared driving module drives the infrared emission diode array to radiate to the space; at the same time, the microphone unit performs parameter configuration, state feedback and control instruction interaction with the conference host through the ChirpIoT communication module;

[0081] The infrared receiver completes the conversion of the spatial infrared signal to the radio frequency signal and the front-end amplification. The infrared receiver internally comprises an infrared photoelectric conversion module, an RF preamplification module, an RF band-pass filtering module, an RF combining module, a multi-stage RF-AGC and amplification driving module (multi-stage amplification driving module), and a second communication unit. The received modulated infrared light is first converted into a radio frequency electrical signal through photoelectric conversion, and then sequentially passes through band-pass filtering, combining, and multi-stage AGC amplification to improve the signal-to-noise ratio and suppress interference, and finally is output to the conference host in the form of a stable RF signal; at the same time, the infrared receiver interacts with the conference host through a network link (second communication unit) to exchange working state and parameter information.

[0082] In a feasible embodiment, referring to Figure 6 The application further provides a wireless infrared voice transmission method, comprising the following steps:

[0083] S1: The microphone unit collects the speaker's voice, which is sent to a digital-analog hybrid FM modulation link after being conditioned by front-end sensitivity / gain / EQ / low-cut, etc. modules; the modulated radio frequency carrier excites an infrared emitting diode array through an infrared driving module to radiate to the receiving end in the form of modulated infrared light;

[0084] S2: The infrared receiver photoelectrically converts the information-bearing infrared light in space to obtain a radio frequency electrical signal; the signal is output to the RF signal receiving module of the conference host after being amplified by the RF preamplifier, band-pass filtered, combined by the RF, and shaped by the multi-stage AGC;

[0085] S3: The conference host sends the received RF signal to the FM demodulator after being amplified and filtered again, restores the audio signal, drives the subsequent power amplifier or recording and broadcasting system after gain adjustment and power amplification, and realizes the output of the conference voice.

[0086] Among them, the host transmits the carrier reference to each microphone unit in real time and issues control instructions through the internal carrier reference source and the ChirpIoT communication module, and the AFC controller (carrier frequency adaptive and spectrum shaping control) and the carrier synchronization module in the microphone unit perform carrier automatic calibration and linearization compensation accordingly, thereby ensuring the transmission stability and spectral consistency in the multi-microphone scene. FM modulation (Frequency Modulation) refers to a kind of angle modulation mode for representing the amplitude of the baseband signal by changing the instantaneous frequency of the carrier. After the voice signal is pre-emphasized and amplitude-limited, the high-frequency carrier is proportionally offset around the center frequency, and the instantaneous value of the baseband signal corresponds to the frequency offset size of the carrier.

[0087] Multi-Stage Automatic Gain Control (AGC) amplification refers to a kind of automatic gain control structure in which multiple amplifiers with variable gain are connected in series in a signal chain, and the gain of each stage is automatically adjusted by a common or hierarchical feedback control signal to maintain the output level within a preset range; the system generates a control quantity by detecting the signal amplitude of the intermediate stage or the output end and comparing it with the reference level, dynamically reduces or increases the gain of each stage to compensate for the fluctuations in the received level caused by changes in the microphone distance, direction and ambient light intensity; by using multi-stage cascading, the total gain can be guaranteed while the amplification factor is dispersed, avoiding single-stage saturation distortion and self-excitation problems, and improving the linearity and dynamic range of the entire receiving link.

[0088] Equalization & Low-Cut Filter is an audio processing module that finely adjusts the gain of different frequency bands to correct the frequency response characteristics of the microphone and improve voice clarity and subjective listening experience. The low-cut filter reduces the low-frequency components below a certain cutoff frequency.

[0089] It should be noted that phase continuity means that the carrier phase φ(t) of the adjustable multi-tuned oscillator changes continuously with time during modulation, without sudden changes or phase jumps; when the control signal changes smoothly, the frequency only slowly shifts around the center frequency point, and the corresponding phase trajectory is a continuously differentiable curve, which can avoid phase jumps caused by sudden frequency switching or oscillator restart, reduce spectral expansion and sidelobe overflow, avoid hearing pops, noise clicks and other distortions in audio, and also facilitate demodulation and locking at the receiving end. Group delay is the negative derivative of the system phase with respect to the angular frequency, representing the effective time delay experienced by the signal envelope or modulation information passing through the system. "Small group delay" means that the modulation link (amplifier + PI + oscillator + transmitter) introduces a short total delay to the voice baseband, which is beneficial to reducing the end-to-end voice delay and ensuring real-time performance in conference scenarios; on the other hand, it means that the group delay changes little within the working frequency band, and the system phase characteristic is approximately linear, so that the modulation signal will not produce obvious waveform distortion due to different propagation times of frequency components, thereby maintaining voice clarity and intelligibility.

[0090] In all examples shown and described herein, any specific values should be interpreted as merely exemplary and not as a limitation, and thus other examples of the example embodiments can have different values.

[0091] It should be noted that similar reference numbers and letters represent similar items in the following drawings, and thus once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0092] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration, characterized in that, The wireless infrared voice transmission system includes a conference host, an infrared receiver, multiple microphone units, and a communication control module. The conference host, the infrared receiver, and the multiple microphone units are all connected to the communication control module. The conference host includes an RF signal receiving module, a signal demodulation module, and an audio output driver module. The RF signal receiving module is connected to the signal demodulation module, and the signal demodulation module is connected to the audio output driver module. The microphone unit includes a microphone, a hybrid digital-analog FM modulation module, and an infrared driver module. The microphone is connected to the hybrid digital-analog FM modulation module, and the hybrid digital-analog FM modulation module is connected to the infrared driver module. The infrared receiver includes a photoelectric conversion module and a multi-stage amplification driver module. The photoelectric conversion module is connected to the multi-stage amplification driver module, and the multi-stage amplification driver module is connected to the RF signal receiving module. The system comprises: a mixed-signal FM modulation module receiving the voice signal collected by the microphone and performing mixed-signal FM modulation to generate an FM modulated radio frequency signal carrying the voice signal; an infrared driving module driving the FM modulated radio frequency signal to convert it into an infrared light signal carrying the FM modulated radio frequency signal and sending it to the photoelectric conversion module; the photoelectric conversion module performing photoelectric conversion on the infrared light signal of the FM modulated radio frequency signal to obtain a radio frequency electrical signal; a multi-stage amplification driving module amplifying and shaping the radio frequency electrical signal and outputting it to the RF signal receiving module to obtain an RF signal; and a signal demodulation module recovering the audio signal from the RF signal and outputting it through the audio output driving module. The mixed-signal FM modulation module includes an amplifier, a DAC unit, an adder, a PI controller, and an adjustable multivibrator. The amplifier is connected to the microphone. The input terminals of the amplifier, the DAC unit, and the PI controller are all connected to the adder. The output terminal of the PI controller is connected to the input terminal of the adjustable multivibrator. The adder is connected to the output terminal of the adjustable multivibrator. The adjustable multivibrator is connected to the infrared driving module. The amplifier is used to filter and linearly amplify the voice signal acquired by the microphone and output a modulation signal. The DAC unit is used to output a carrier setting signal according to a preset carrier reference frequency. The adder is used to sum the modulation signal, the carrier setting signal and the output signal of the adjustable multivibrator, and process them through the PI controller to generate a control signal for the adjustable multivibrator. The adjustable multivibrator generates an FM modulated radio frequency carrier signal according to the control signal and outputs it to the infrared drive module. The PI controller is used to generate a compensation signal based on the frequency error between the output signal of the adjustable multivibrator and the carrier setting signal. The compensation signal is used to compensate for the temperature drift and power supply fluctuation of the adjustable multivibrator and the infrared drive module.

2. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 1, characterized in that, The output frequency corresponding to the output signal has a linear correspondence between the reference frequency and the control signal output by the adder. When the control signal changes linearly with time over a period of time, the output frequency of the adjustable multivibrator continuously shifts near the reference frequency point to achieve phase-continuous FM modulation, wherein the output frequency maintains low group delay within the 100Hz to 20kHz audio bandwidth.

3. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 2, characterized in that, The PI controller generates a control quantity based on the error signal between the controlled variable and the desired value. The expression for the continuous form PI controller output is as follows: （1） wherein, is the difference between the reference input and the actual output, is the control variable, is the proportional gain, is the integral gain; the proportional element generates a control action proportional to the current instantaneous error in order to influence the response speed and the damping behavior of the system; the integral element accumulates the error signal over time and makes the system output a non-zero error in steady state.

4. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 3, characterized in that, The mixed digital-analog FM modulation module further includes an LFSR unit connected to the DAC unit, and the LFSR unit is connected to the signal demodulation module through the communication control module; When the carrier signal corresponds to the carrier reference frequency When the signal is converted from a control signal by the DAC unit, the center frequency of the adjustable multivibrator is set. The pseudo-random bitstream output by the LFSR unit is converted into a frequency offset control quantity by another channel DAC unit after being mapped by a lookup table. The baseband modulation amount of the voice signal and the set amount of the center frequency are superimposed on the adder, and the control signal of the adjustable multivibrator is formed by the PI controller. The LFSR unit generates pseudo-random dithering sequence and m-sequence preamble digitally and works in conjunction with the infrared drive module.

5. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 1, characterized in that, The infrared receiver also includes an RF bandpass filter module and an RF combiner module. The photoelectric conversion module and the RF combiner module are both connected to the RF bandpass filter module, and the multi-stage amplification driver module is connected to the combiner module. The radio frequency signal is sequentially amplified and processed by the RF bandpass filter module, the RF combiner module, and the multi-stage amplification and drive module to obtain a stable RF signal, which is then output to the conference host. The communication control module includes a first communication unit and a second communication unit. The conference host and the microphone unit are both connected to the first communication unit. The infrared receiver interacts with the conference host to exchange working status and parameter information through the second communication unit.

6. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 5, characterized in that, The signal demodulation module includes an FM demodulator and a gain adjustment unit. The gain adjustment unit and the RF signal receiving module are both connected to the FM demodulator, and the gain adjustment unit is connected to the audio output driver module. The FM demodulator is used to filter, limit, and demodulate the RF signal output by the RF signal receiving module to output a line-level audio signal. The conference host interacts with each microphone unit through the first communication unit to perform ChirpIoT data interaction and transmits carrier reference signals to the microphone units in real time to achieve automatic carrier calibration.

7. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 1, characterized in that, The multi-stage amplification driving module includes multiple amplifiers connected in series in the radio frequency signal chain and having variable gain. The multi-stage amplification driving module adjusts the gain of each stage through common or hierarchical feedback control signals to maintain the output level within a preset range. The multi-stage amplification driving module is used to compensate for the received level fluctuations caused by changes in microphone distance, directivity, and ambient light intensity of the microphone unit.

8. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 7, characterized in that, The microphone unit also includes a touch display module and a TYPE-C interface module. Both the touch display module and the TYPE-C interface module are connected to the hybrid digital-analog FM modulation module. The touch display module is used for displaying the working status, adjusting parameters, and operating the system menu. The TYPE-C interface module is used for battery charging management.

9. The wireless infrared voice transmission system with adjustable carrier frequency and automatic calibration according to claim 7, characterized in that, The microphone unit also includes an audio processing module connected to the microphone, which is used to adjust the gain of different frequency bands to correct the frequency response characteristics of the microphone unit.

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