Digital PDM medium wave transmitter pulse width modulator

Abstract

The utility model discloses a digital PDM medium wave transmitter pulse width modulator. The modulator comprises an audio processing circuit, a power control signal processing circuit, a single-chip microcomputer and a power amplification circuit. An analog-to-digital converter and a pulse width modulation wave generator are integrated in the single-chip microcomputer. The audio processing circuit and the power control signal processing circuit are respectively connected to the analog-to-digital converter; and the pulse width modulation wave generator is connected with the power amplification circuit. The audio processing circuit receives balanced audio signals, processes the balanced audio signals, inputs the processed balanced audio signals to the analog-to-digital converter and converts the processed balanced audio signals into audio digital signals, and the power control signal processing circuit processes received power control signals, inputs the processed power control signals to the analog-to-digital converter and converts the processed power control signals into power control digital signals. The single-chip microcomputer combines the audio digital signal and the power control digital signal according to a set algorithm, converts the audio digital signal and the power control digital signal into a duty ratio value and controls the pulse width modulation wave generator to generate a pulse signal with a corresponding duty ratio, and the power amplification circuit carries out power amplification on the signal so as to meet requirements of post-stage equipment. The pulse width modulator has the advantages that the circuit structure is simple, the integration level is high, and functional parameters are easy to modify and expand.

Description

Technical Field

[0001] The utility model relates to a pulse width modulator, in particular to a digital PDM medium wave transmitter pulse width modulator. Background Art

[0002] In the PDM medium wave transmitter, the role of the pulse width modulator is to generate a constant amplitude width modulated pulse wave whose duty cycle changes with the instantaneous voltage of the audio signal. The traditional pulse width modulator is composed of multiple discrete components, the internally processed signal is an analog signal, and the various functions of the device are realized by hardware circuits. This leads to the problems of large size, complex circuit structure, low reliability of discrete components, and inflexible function expansion of the traditional pulse width modulator. Utility Model Content

[0003] The technical problem to be solved by the utility model is to provide a digital PDM medium wave transmitter pulse width modulator which has simple circuit structure, high integration and easy modification and expansion of functional parameters.

[0004] The utility model solves the above technical problems with the following technical solutions:

[0005] The utility model discloses a digital PDM medium wave transmitter pulse width modulator, comprising an audio processing circuit, a power control signal processing circuit, a single chip microcomputer and a power amplifier circuit;

[0006] The single chip microcomputer is internally integrated with an analog-to-digital converter and a pulse width modulation wave generator;

[0007] The audio processing circuit and the power control signal processing circuit are respectively connected to an analog-to-digital converter;

[0008] The pulse width modulation wave generator is connected to the power amplifier circuit;

[0009] The audio processing circuit receives a balanced audio signal and inputs it into an analog-to-digital converter after processing; the power control signal processing circuit receives a power control signal and inputs it into an analog-to-digital converter after processing; the analog-to-digital converter converts the audio signal and the power control signal into corresponding digital signals respectively; the single-chip microcomputer reads the conversion result of the analog-to-digital converter and combines the audio digital signal with the power control digital signal according to a set algorithm, converts it into a duty cycle value and controls the pulse width modulation wave generator to generate a pulse signal of the corresponding duty cycle; the power amplifier circuit amplifies the power of the signal and outputs it to the outside.

[0010] The audio processing circuit comprises a balanced-unbalanced conversion circuit, a filtering circuit, a signal amplifying circuit and a signal amplitude detection circuit. The balanced-unbalanced conversion circuit receives a balanced audio signal. The output end of the balanced-unbalanced conversion circuit is connected to the input end of the filtering circuit. The output end of the filtering circuit is simultaneously connected to the signal amplifying circuit and the signal amplitude detection circuit. The balanced-unbalanced conversion circuit converts the input balanced audio signal into an unbalanced signal, which is input into the signal amplifying circuit and the signal amplitude detection circuit after passing through the filtering circuit. The signal amplifying circuit amplifies the input audio signal and outputs it to the analog-to-digital converter. The signal amplification coefficient is controlled by the signal amplitude detection circuit.

[0011] The power control signal processing circuit comprises a control signal processing circuit, a manual power control potentiometer and a manual / automatic switching switch, wherein the control signal processing circuit and the manual power control potentiometer are respectively connected to the manual / automatic switching switch; the control signal processing circuit steps down the power control voltage signal from the medium wave transmitter to the input voltage range of the analog-to-digital converter, and inputs the signal to the manual / automatic switching switch after filtering; the manual power control potentiometer generates another control voltage signal through a resistor voltage divider and inputs the signal to the manual / automatic switching switch; the manual / automatic switching switch is a single-pole double-throw switch, which can switch the power control signals input by the control signal processing circuit and the manual power control potentiometer and output the signals to the analog-to-digital converter.

[0012] The power amplifier circuit includes a power triode circuit and a pulse signal abnormality detection circuit. The input ends of the power triode circuit and the pulse signal abnormality detection circuit are connected to the output end of the pulse width modulation wave generator, and the output end of the pulse signal abnormality detection circuit is connected to the control end of the power triode circuit. The power triode circuit amplifies the power of the input pulse signal and outputs it to the outside. The pulse signal abnormality detection circuit performs abnormality detection on the input pulse signal, and when no pulse signal input is detected, the power triode circuit is turned off.

[0013] The analog-to-digital converter has a resolution of 12 bits, includes 2 analog input channels, and a voltage detection range of 0-3.3V.

[0014] The pulse width modulation wave generator has a total of 2000 gears, and the generated pulse wave frequency is 72kHz.

[0015] Compared with the prior art, the digital PDM medium wave transmitter pulse width modulator of the utility model has the following beneficial effects:

[0016] 1. The utility model adopts a single-chip microcomputer and its own integrated analog-to-digital converter and pulse width modulation wave generator to replace multiple discrete devices used in traditional pulse width modulators, with high integration and guaranteed working reliability.

[0017] 2. The utility model digitizes the audio signal through an analog-to-digital converter and converts the duty cycle of the output pulse wave through an algorithm. Compared with the existing analog pulse width modulator, it has the advantage of high modulation linearity, and the performance is not affected by the temperature drift, aging and inconsistent component parameter indicators of discrete components.

[0018] 3. The functions of the pulse width modulator of the utility model are mainly realized by software. Compared with the existing pulse width modulator realized by hardware, it has the advantages of simple circuit structure and easy modification and expansion of functional parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The utility model is a structural block diagram of a pulse width modulator of a digital PDM medium wave transmitter.

[0020] Figure 2 yes Figure 1 The structure diagram of the audio processing circuit.

[0021] Figure 3 yes Figure 1 Block diagram of medium power control signal processing circuit.

[0022] Figure 4 yes Figure 1 Medium power amplifier circuit structure diagram. DETAILED DESCRIPTION

[0023] The technical solution of the utility model is described in detail below in conjunction with the accompanying drawings. Those skilled in the art should understand that these implementations are only used to explain the technical principle of the utility model, and are not intended to limit the protection scope of the utility model.

[0024] like Figure 1 As shown, the digital PDM medium wave transmitter pulse width modulator of the utility model includes an audio processing circuit, a power control signal processing circuit, a single chip microcomputer and a power amplifier circuit; an analog-to-digital converter and a pulse width modulation wave generator are integrated inside the single chip microcomputer; the output ends of the audio processing circuit and the power control signal processing circuit are respectively connected to the input end of the analog-to-digital converter; the output end of the pulse width modulation wave generator is connected to the input end of the power amplifier circuit; the audio processing circuit receives the audio signal, and the power control signal processing circuit receives the power control signal. The analog-to-digital converter in the single chip microcomputer collects the audio signal processed by the audio processing circuit and the power control signal processed by the power control signal processing circuit in real time, and converts the audio signal and the power control signal into corresponding digital signals respectively; the single chip microcomputer reads the conversion result of the analog-to-digital converter and combines the audio digital signal with the power control digital signal according to the algorithm set by the software, converts it into a duty cycle value and controls the pulse width modulation wave generator to generate a pulse signal of the corresponding duty cycle; the power amplifier circuit amplifies the power of the signal and outputs it to the outside.

[0025] like Figure 2 As shown, the audio processing circuit includes a balanced-unbalanced conversion circuit, a filtering circuit, a signal amplification circuit and a signal amplitude detection circuit; the balanced-unbalanced conversion circuit receives a balanced audio signal, the output end of the balanced-unbalanced conversion circuit is connected to the input end of the filtering circuit, and the output end of the filtering circuit is simultaneously connected to the signal amplification circuit and the signal amplitude detection circuit. The balanced-unbalanced conversion circuit converts the input balanced audio signal into an unbalanced signal, which is input to the signal amplification circuit and the signal amplitude detection circuit after passing through the filtering circuit; the signal amplification circuit amplifies the input audio signal and outputs it to the analog-to-digital converter, the signal amplification coefficient is controlled by the signal amplitude detection circuit, and the audio signal voltage output to the analog-to-digital converter is controlled within the range of 0.2 to 3.1V, and the DC bias voltage is 1.65V; the signal amplitude detection circuit performs amplitude detection on the input audio signal, and when the signal amplitude is less than the threshold, the amplification coefficient of the signal amplification circuit is set to 1 times, and when the signal amplitude is greater than or equal to the threshold, the amplification coefficient of the signal amplification circuit is set to 0.6 times, so as to realize the function of suppressing the audio signal from exceeding the limit.

[0026] like Figure 3 As shown, the power control signal processing circuit includes a control signal processing circuit, a power manual control potentiometer and a manual / automatic switching switch; the control signal processing circuit and the power manual control potentiometer are respectively connected to the two switching ends of the manual / automatic switching switch, and the common end of the manual / automatic switching switch is connected to the analog-to-digital converter. The control signal processing circuit uses an adjustable resistor, which can be adjusted according to actual conditions to reduce the power control signal from the main controller of the medium wave transmitter to a range of 1.5V to 2V, and input it to the manual / automatic switching switch after filtering; the power manual control potentiometer generates a voltage signal of 1.5V to 2V through a resistor voltage divider and inputs it to the manual / automatic switching switch; the manual / automatic switching switch is a single-pole double-throw switch, which can switch the power control signal input by the control signal processing circuit and the power manual control potentiometer and output it to the analog-to-digital converter.

[0027] like Figure 4 As shown, the power amplifier circuit includes a power triode circuit and a pulse signal abnormality detection circuit, the input ends of the power triode circuit and the pulse signal abnormality detection circuit are connected to the output end of the pulse width modulation wave generator, and the output end of the pulse signal abnormality detection circuit is connected to the control end of the power triode circuit; the power triode circuit amplifies the power of the input pulse signal and outputs it to the outside; the pulse signal abnormality detection circuit performs abnormality detection on the input pulse signal, and when no pulse signal input is detected, the power triode circuit is turned off.

[0028] In order to improve the sampling quality of audio signals and power control signals, the utility model adopts an analog-to-digital converter with a resolution of 12 bits and a sampling rate of 72kHz, including 2 analog input channels, and a voltage detection range of 0-3.3V. The audio signal is converted by the analog-to-digital converter to obtain an audio digital signal in the range of ±1800; the power control signal is converted by the analog-to-digital converter to obtain a power control digital signal in the range of 0 to 730.

[0029] In order to reduce the distortion of the transmitter, the pulse width modulation wave generator of the utility model can adopt a pulse width modulation wave generator with 2000 gears, and the frequency of the generated pulse wave is 72kHz.

[0030] The utility model converts the above audio signal and power control signal into a duty cycle value ranging from 0 to 2000 through an algorithm, and the specific process is as follows:

[0031] 1. Calculate the audio-free duty cycle based on the power control signal mute , the formula is as follows:

[0032]

[0033] Among them, duty mute_max V is the duty cycle value corresponding to the rated power of the transmitter without audio frequency. ctrl_max is the maximum value of the power control signal, which is 730, V ctrl is the power control signal currently collected.

[0034] 2. Calculate the audio positive peak duty cycle duty based on the power control signal pp , the formula is as follows:

[0035]

[0036] Among them, duty max is the maximum duty cycle value allowed by the adapted transmitter, V ctrl_max is the maximum value of the power control signal, which is 730, V ctrl is the power control signal currently collected.

[0037] 3. Calculate the audio duty cycle conversion coefficient a based on the no-audio duty cycle and the audio positive peak duty cycle vd , the formula is as follows:

[0038]

[0039] Where V voice_pmax It is the maximum positive peak value of the audio signal, and its value is 1800.

[0040] 4. According to the current audio signal and the audio duty conversion coefficient, calculate the duty cycle corresponding to the current audio signal. The formula is as follows:

[0041] duty=a vd ·V voice +duty mute

[0042] The utility model discloses a digital PDM medium wave transmitter pulse width modulator, which has the advantages of simple circuit structure, high integration, and easy modification and expansion of functional parameters, and solves the problems of complex circuit structure, low reliability and low flexibility of functional expansion of existing analog pulse width modulators based on discrete components.

Claims

1. A digital PDM medium wave transmitter pulse width modulator, characterized in that: It includes an audio processing circuit, a power control signal processing circuit, a single chip microcomputer and a power amplifier circuit; The single chip microcomputer is internally integrated with an analog-to-digital converter and a pulse width modulation wave generator; The audio processing circuit and the power control signal processing circuit are respectively connected to an analog-to-digital converter; The pulse width modulation wave generator is connected to the power amplifier circuit; The audio processing circuit receives the balanced audio signal and inputs it into the analog-to-digital converter after processing; the power control signal processing circuit receives the power control signal and inputs it into the analog-to-digital converter after processing; The analog-to-digital converter converts the audio signal and the power control signal into corresponding digital signals respectively; the single-chip microcomputer reads the conversion result of the analog-to-digital converter and combines the audio digital signal with the power control digital signal according to the set algorithm, converts it into a duty cycle value and controls the pulse width modulation wave generator to generate a pulse signal with a corresponding duty cycle; the power amplifier circuit amplifies the power of the signal and outputs it externally.

2. The digital PDM medium wave transmitter pulse width modulator according to claim 1, characterized in that: The audio processing circuit comprises a balanced-unbalanced conversion circuit, a filtering circuit, a signal amplifying circuit and a signal amplitude detection circuit. The balanced-unbalanced conversion circuit receives a balanced audio signal. The output end of the balanced-unbalanced conversion circuit is connected to the input end of the filtering circuit. The output end of the filtering circuit is simultaneously connected to the signal amplifying circuit and the signal amplitude detection circuit. The balanced-unbalanced conversion circuit converts the input balanced audio signal into an unbalanced signal, which is input into the signal amplifying circuit and the signal amplitude detection circuit after passing through the filtering circuit. The signal amplifying circuit amplifies the input audio signal and outputs it to the analog-to-digital converter. The signal amplification coefficient is controlled by the signal amplitude detection circuit.

3. The digital PDM medium wave transmitter pulse width modulator according to claim 1 or 2, characterized in that: The power control signal processing circuit comprises a control signal processing circuit, a manual power control potentiometer and a manual / automatic switching switch, wherein the control signal processing circuit and the manual power control potentiometer are respectively connected to the manual / automatic switching switch; the control signal processing circuit steps down the power control voltage signal from the medium wave transmitter to the input voltage range of the analog-to-digital converter, and inputs the signal to the manual / automatic switching switch after filtering; the manual power control potentiometer generates another control voltage signal through a resistor voltage divider and inputs the signal to the manual / automatic switching switch; the manual / automatic switching switch is a single-pole double-throw switch, which can switch the power control signals input by the control signal processing circuit and the manual power control potentiometer and output the signals to the analog-to-digital converter.

4. The digital PDM medium wave transmitter pulse width modulator according to claim 1 or 2, characterized in that: The power amplifier circuit includes a power triode circuit and a pulse signal abnormality detection circuit. The input ends of the power triode circuit and the pulse signal abnormality detection circuit are connected to the output end of the pulse width modulation wave generator, and the output end of the pulse signal abnormality detection circuit is connected to the control end of the power triode circuit. The power triode circuit amplifies the power of the input pulse signal and outputs it to the outside. The pulse signal abnormality detection circuit performs abnormality detection on the input pulse signal, and when no pulse signal input is detected, the power triode circuit is turned off.

5. The digital PDM medium wave transmitter pulse width modulator according to claim 1, characterized in that: The analog-to-digital converter has a resolution of 12 bits, includes 2 analog input channels, and a voltage detection range of 0-3.3V.

6. The digital PDM medium wave transmitter pulse width modulator according to claim 1, characterized in that: The pulse width modulation wave generator has a total of 2000 gears, and the generated pulse wave frequency is 72kHz.

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