CN102520630B - Automatic power and amplitude modulation factor control circuit and power adjustment method - Google Patents

Abstract

The invention provides an automatic power and amplitude modulation factor control circuit and a power adjustment method. Power modulation equipment comprises a singlechip, a sine wave generation circuit, an analog-to-digital (A/D) conversion circuit, an adjustment circuit, a triangular wave generation circuit, a pulse width modulation (PWM) circuit and an amplifying circuit; an input end of the A/D conversion circuit is connected with an output end of an external power amplification circuit; an output end of the A/D conversion circuit is connected with an input end of the singlechip; an output end of the singlechip is connected with an input end of the adjustment circuit; an output end of the adjustment circuit is connected with an input end of the PWM circuit; an output end of the PWM circuit is connected with an input end of the amplifying circuit; and the output end of the PWM circuit is connected with an input end of the external power amplification circuit. According to the automatic power and amplitude modulation factor control circuit and the power adjustment method, the automatic adjustment of power can be achieved.

Description

Power and amplitude modulation automatic control circuit and power adjustment method

technical field

The invention mainly relates to the field of power adjustment, in particular to an automatic control circuit for power and amplitude modulation and a power adjustment method.

Background technique

In a medium wave transmitter, the output power is proportional to the square of the DC level of the sine wave generated on the PWM board, and the modulation amplitude is a function of the DC level and amplitude of the sine wave. In the original medium-wave transmitter, technicians manually adjust the potentiometer after observing the readings of the power meter on the machine, so as to realize power adjustment. , Artificially adjust the potentiometer, so as to realize the adjustment of the amplitude. This adjustment method requires technical personnel to perform accurate measurement or adjustment after calculation, and non-technical personnel cannot operate.

Contents of the invention

The technical problem solved by the present invention is to provide an automatic power and amplitude modulation control circuit and a power adjustment method, which can solve the technical problem in the prior art that manual adjustment of power and amplitude is required.

In order to solve the above-mentioned technical problems, the present invention provides a power modulation device, including a single-chip microcomputer, a sine wave generating circuit, an analog-to-digital conversion circuit, an adjustment circuit, a triangular wave generating circuit, a pulse width modulation circuit and an amplifying circuit; the analog-to-digital conversion circuit The input end is connected with the output end of the external power amplifier circuit, the output end of the analog-to-digital conversion circuit is connected with the input end of the single-chip microcomputer, and the output end of the single-chip microcomputer is connected with the input end of the adjustment circuit, so The output end of the adjustment circuit is connected to the input end of the pulse width modulation circuit, the output end of the pulse width modulation circuit is connected to the input end of the amplification circuit, and the output end of the pulse width modulation circuit is connected to the external The input end of the power amplifier circuit is connected; the output end of the single-chip microcomputer is also connected with the input end of the sine wave generation circuit; the output end of the sine wave generation circuit is connected with the input end of the adjustment circuit; the The analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the power sampling signal from the power amplifier circuit, and outputs the converted signal to the single-chip microcomputer; the single-chip microcomputer is used to receive the signal from the analog-to-digital conversion circuit, and with the built-in The power reference value is compared, and according to the comparison result, the control adjustment circuit and the sine wave generation circuit; the adjustment circuit is used to receive the sine wave signal from the sine wave generation circuit, and control the sine wave according to the control signal from the single chip microcomputer. The output amplitude of the wave signal; the pulse width modulation forming circuit is used to receive the sine wave signal from the adjustment circuit, and receive the subcarrier signal from the triangular wave generation circuit, and perform pulse width modulation on the sine wave signal; the amplifying The circuit is used to amplify the received signal and output it to an external power amplifier circuit.

Wherein, the adjustment circuit includes a first digital potentiometer, a circuit for adjusting the amplitude of the sine wave, a second digital potentiometer, a circuit for adjusting the DC offset level of the sine wave, the input terminal of the first digital potentiometer, the second digital potentiometer The input terminals of the devices are all connected with the output terminals of the single-chip microcomputer, and the input terminals of the first digital potentiometer and the second digital potentiometer are also connected with the output terminals of the sine wave generating circuit; The output end of the first digital potentiometer and the output end of the second digital potentiometer are both connected to the input end of the pulse width modulation forming circuit.

Wherein, the amplitude of the output sine wave signal is adjusted by adjusting the resistance value of the first digital potentiometer.

Wherein, the second digital potentiometer adjusts the offset level of the output sine wave signal by adjusting the change of the resistance value.

Wherein, the pulse width modulation forming circuit includes an automatic power and amplitude modulation automatic control circuit and a high-speed comparator, and the automatic power and amplitude modulation automatic control circuit is connected with the high-speed comparator to provide an adjustable DC level , the DC level and the audio amplification signal are superimposed and output to the inverting input of the high-speed comparator; the positive input of the high-speed comparator receives the subcarrier signal from the triangular wave generation circuit; the output of the high-speed comparator The terminal is connected with the amplifying circuit, and is used for outputting a pulse signal to the amplifying circuit.

In order to solve the above technical problems, the present invention also provides a power adjustment method, including the following steps:

Step 1: Carry out AD sampling on the output signal, and calculate the power and amplitude modulation of the sampling signal;

Step 2: Compare the power and amplitude of the signal with the built-in preset value to judge whether it is within the error range, if yes, return to step 1; if not, go to step 3;

Step 3: Calculate the DC level and amplitude value of the sine wave corresponding to the current actual power and modulation amplitude;

Step 4: Calculate the sine wave DC level and amplitude modulation value corresponding to the difference;

Step 5: Change the resistance value of the digital potentiometer, thereby changing the corresponding sine wave DC level and amplitude value, and return to step 1.

Wherein, the AD sampling time is to read a sampling signal every 2s.

Adopting the above-mentioned technical scheme, compared with the technical problem in the prior art that the power and amplitude cannot be automatically adjusted, the beneficial effect of the present invention is: since the standard power and amplitude modulation values are set in the single-chip microcomputer, by sampling the output signal, Compare the sampling signal with the amplitude modulation value, and use the comparison result as a benchmark for adjusting the output power. The single-chip microcomputer controls the sine wave generation circuit and the digital potentiometer, and controls the output sine wave power and modulation amplitude through the adjustment of the resistance value of the digital potentiometer. , so as to realize automatic power adjustment and overcome the problem of low efficiency of manual adjustment.

Description of drawings

Fig. 1 is the structural diagram of power and amplitude modulation automatic control circuit provided by the present invention;

Fig. 2 is the specific structural diagram of a kind of embodiment of the power and amplitude modulation automatic control circuit provided by the present invention;

Fig. 3 is a flowchart of the power adjustment method provided by the present invention;

Fig. 4 is the relationship diagram of sine wave DC level, amplitude and modulation amplitude provided by the present invention;

Fig. 5 is a schematic diagram of the automatic adjustment of output power provided by the present invention;

Fig. 6 is a schematic diagram of the automatic adjustment of the modulation degree provided by the present invention;

7 is a schematic diagram of a pulse width modulation forming circuit provided by the present invention;

FIG. 8 is a schematic diagram of the pulse width modulation circuit provided by the present invention.

Detailed ways

In order to describe the technical content, structural features, achieved goals and effects of the present invention in detail, the following will be described in detail in conjunction with the embodiments and accompanying drawings.

Please refer to Fig. 1, the present invention provides a kind of power and amplitude modulation automatic control circuit, comprise single-chip microcomputer, sine wave generation circuit, analog-to-digital conversion circuit, adjustment circuit, triangular wave generation circuit, pulse width modulation circuit, amplifying circuit; The input end of the conversion circuit is connected to the output end of the external power amplifier circuit, the output end of the analog-to-digital conversion circuit is connected to the input end of the single-chip microcomputer, and the output end of the single-chip microcomputer is connected to the input end of the adjustment circuit. connected, the output terminal of the adjustment circuit is connected with the input terminal of the pulse width modulation circuit, the output terminal of the pulse width modulation circuit is connected with the input terminal of the amplification circuit, and the output terminal of the pulse width modulation circuit end is connected with the input end of the external power amplifier circuit; the output end of the single-chip microcomputer is also connected with the input end of the sine wave generation circuit; the output end of the sine wave generation circuit is connected with the input end of the adjustment circuit connected; the analog-to-digital conversion circuit is used to carry out analog-to-digital conversion to the power sampling signal from the power amplifier circuit, and outputs the converted signal to the single-chip microcomputer; the single-chip microcomputer is used to receive the signal from the analog-to-digital conversion circuit, and communicate with The built-in power reference value is compared, and the adjustment circuit and the sine wave generation circuit are controlled according to the comparison result; the adjustment circuit is used to receive the sine wave signal from the sine wave generation circuit, and control the The output amplitude of the sine wave signal; the pulse width modulation forming circuit is used to receive the sine wave signal from the adjustment circuit, and receive the subcarrier signal from the triangular wave generation circuit, and perform pulse width modulation on the sine wave signal; The amplifier circuit is used to amplify the received signal and output it to an external power amplifier circuit.

Please refer to Figure 2, the adjustment circuit includes a first digital potentiometer, a circuit for adjusting the amplitude of the sine wave, a second digital potentiometer, a circuit for adjusting the DC offset level of the sine wave, the input terminal of the first digital potentiometer, the second The input terminals of the two digital potentiometers are all connected with the output terminals of the single-chip microcomputer, and the input terminals of the first digital potentiometer and the second digital potentiometer are also connected with the output terminals of the sine wave generating circuit ; The output end of the first digital potentiometer and the output end of the second digital potentiometer are both connected to the input end of the pulse width modulation forming circuit.

In this embodiment, the amplitude of the output sine wave signal is adjusted by adjusting the resistance value of the first digital potentiometer. The second digital potentiometer adjusts the offset level of the output sine wave signal by adjusting the change of the resistance value.

Further, the pulse width modulation forming circuit includes an automatic power and amplitude modulation automatic control circuit and a high-speed comparator, and the automatic power and amplitude modulation automatic control circuit is connected with the high-speed comparator to provide adjustable direct current flat, the DC level and the audio amplification signal are superimposed and output to the inverting input of the high-speed comparator; the positive input of the high-speed comparator receives the subcarrier signal from the triangular wave generation circuit; the high-speed comparator The output end is connected with the amplifying circuit, and is used for outputting a pulse signal to the amplifying circuit.

In this embodiment, the working method of the sine wave generating circuit is: the single-chip microcomputer reads the sine wave sampling value stored in the memory every 61.5us, and the sampling value is subjected to D/A conversion (digital-to-analog conversion) to generate a corresponding Trapezoidal waveform, the trapezoidal waveform is amplified and filtered to obtain a 1020Hz sine wave.

The working mode of the triangular wave generation circuit is: a subcarrier signal is required in the pulse width modulation circuit, and a high frequency triangular wave comparison signal is provided for the pulse width modulation forming circuit. Triangular wave generation requires a hysteresis comparator and an integrator. In the case of a single power supply, the closed-loop circuit of the conventional triangular wave oscillation circuit cannot work normally, but as shown in Figure 6, it can generate a symmetrical and stable triangular wave. The working principle is: the high and low levels output by the comparator control the turn-on and turn-off of the MOSFET switch, and in the case of the turn-on and turn-off of the MOSFET switch, it is limited by the reference level, and the capacitors of the integrator are respectively charged with the same current Charge and discharge, so the integrator can output a triangular wave with the same slope of the rising part and the falling part. The triangular wave is then used as the input of the hysteresis comparator to generate high and low levels to control the turn-on and turn-off of the MOSFET switch.

After the single-chip microcomputer judges the modulation range of the sampling, it controls the digital potentiometer to make its resistance change accordingly, thereby controlling the output range of the sine wave and achieving the purpose of automatically adjusting the modulation degree.

Among them, please refer to Figure 5 and Figure 6. The working method of adjusting the sine wave amplitude circuit and adjusting the sine wave DC offset level circuit is: through an MCU decision to judge the output power and the detection value of the modulation degree from data collection, and send out the adjustment Information, adjust the SPWM circuit in real time, so that the pulse width modulation signal driving the audio pulse width modulation power amplifier can realize closed-loop automatic adjustment, which also realizes automatic modulation of power and modulation degree. Specifically, the single-chip microcomputer first samples the output power and compares it with the power reference value. According to the comparison result, the digital potentiometer is controlled to change its resistance accordingly, so that the offset level of the sine wave increases or decreases. In order to realize the automatic adjustment of the output power. In the same way, after the single-chip microcomputer judges the modulation amplitude of the sampling, it controls the digital potentiometer to make its resistance change accordingly, thereby controlling the output amplitude of the sine wave and achieving the purpose of automatically adjusting the modulation degree.

Please refer to Figure 7 and Figure 8, the working principle of the pulse width modulation forming circuit is: pulse width modulation is to use the audio sine wave to modulate the triangular wave, so as to obtain a pulse train with the same amplitude and varying pulse width. The sine wave and triangular wave are sent to the comparator for comparison, so that a pulse train with modulated pulse width is obtained from the output terminal of the comparator. The pulse width of this pulse train varies with the audio frequency, so it carries audio information. In this scheme, high-speed comparator LT1715 is used to realize pulse width modulation. The audio signal is superimposed with an adjustable DC level and sent to the inverting input of LT1715 (pin 3), and the subcarrier signal (100KHz) is sent to the non-inverting input of LT1715, so that a width is obtained at the output of LT1715 A TTL pulse signal that varies with the amplitude of the audio signal. By adjusting the DC level of the automatic power and amplitude modulation automatic control circuit output to the inverting input of the comparator, the DC level of the audio signal can be adjusted to change the output pulse width, and finally the automatic adjustment of the output power of the carrier power amplifier is realized.

Referring to Fig. 3, the present invention also provides a power adjustment method, including the following steps:

Step 1: Carry out AD sampling on the output signal, and calculate the power and amplitude modulation of the sampling signal;

Step 2: Compare the power and amplitude of the signal with the built-in preset value to judge whether it is within the error range, if yes, return to step 1; if not, go to step 3;

Step 3: Calculate the DC level and amplitude value of the sine wave corresponding to the current actual power and modulation amplitude;

Step 4: Calculate the sine wave DC level and amplitude modulation value corresponding to the difference;

Step 5: Change the resistance value of the digital potentiometer, thereby changing the corresponding sine wave DC level and amplitude value, and return to step 1.

Further, the AD sampling time in step 1 is to read a sampling signal every 2s.

Please refer to Fig. 4, the present invention adopts this method, and the basic calculation principle that it adopts is:

1) Control the output power by adjusting the DC level of the sine wave

2) Control the modulation amplitude by adjusting the amplitude of the sine wave

3) Because changing the output power will change the modulation range, but changing the modulation range will not change the output power, so adjust the power first, and then adjust the modulation range each time you adjust

4) The square of the DC level of the sine wave is proportional to the output power

The amplitude range of the triangular wave is [0V, 5V], so any signal compared with the triangular wave, the difference between it and the lowest level of the triangular wave (that is, 0V) will be amplified in the same proportion after being modulated by the power amplifier (class D power amplifier principle), and This difference is obviously its level value. That is to say, if a signal with a level value of 1V is amplified to 10V after being modulated by a power amplifier, then a signal with a level value of 2V will be amplified to 40V, so the output power will be the original 22 times.

5) The modulation amplitude is directly related to the DC level and amplitude of the sine wave:

amplitude $m=\frac{\mathrm{vpp}}{2\×\mathrm{Vdc}}\×100\%---\left(1\right)$

amplitude $m=\frac{A\max -A\min }{A\max +A\min }\×100\%---\left(2\right),$

Also obtained from Figure 4: $A\max =(\mathrm{Vdc}+\frac{1}{2}\mathrm{Vpp})\×2,$ $A\min =(\mathrm{Vdc}-\frac{1}{2}\mathrm{Vpp})\×2,$ Substitute into formula (2), get formula (1). Vpp and Vdc are proportionally amplified after being modulated by the power amplifier, so it is sufficient to consider their values before being amplified.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (4)

1. power and an AM depth automatic control circuit, is characterized in that: comprise that single-chip microcomputer, sine wave generation circuit, analog to digital conversion circuit, Circuit tuning, circuit for generating triangular wave, width modulation form circuit and amplifying circuit;

The input end of analog-digital conversion circuit as described is connected with the output terminal of external power amplifier circuit, the output terminal of analog-digital conversion circuit as described is connected with the input end of described single-chip microcomputer, the output terminal of described single-chip microcomputer is connected with the first input end of described Circuit tuning, the output terminal of described Circuit tuning is connected with the input end that described width modulation forms circuit, described width modulation forms the output terminal of circuit and the input end of described amplifying circuit is connected, and the output terminal of described amplifying circuit is connected with the input end of external power amplifier circuit;

The output terminal of described single-chip microcomputer is also connected with the input end of described sine wave generation circuit; The output terminal of described sine wave generation circuit is connected with the second input end of described Circuit tuning;

Analog-digital conversion circuit as described is used for the power sampled signal from power amplifier to carry out analog to digital conversion, and the signal after conversion is outputed to single-chip microcomputer; Described single-chip microcomputer is used for receiving the signal from analog-digital conversion circuit as described, and compares with built-in power reference value, according to comparison result, controls Circuit tuning and sine wave generation circuit; Described Circuit tuning is used for receiving the sine wave signal from sine wave generation circuit, and according to the control signal from single-chip microcomputer, controls the output amplitude of described sine wave signal; Described width modulation forms circuit for receiving the sine wave signal of self-adjusting circuit, and receives the subcarrier signal from circuit for generating triangular wave, and described sine wave signal is carried out to width modulation; Described amplifying circuit is for amplifying the signal receiving and outputing to external power amplifier circuit;

Described Circuit tuning comprises the first digital regulation resistance, adjusts sinusoidal wave amplitude circuit, the second digital regulation resistance, adjust sinusoidal wave direct current offset level circuit, the first input end of the first input end of described the first digital regulation resistance, the second digital regulation resistance is all connected with the output terminal of described single-chip microcomputer, and the second input end of described the first digital regulation resistance, the second input end of the second digital regulation resistance are connected with the output terminal of described sine wave generation circuit; The output terminal of the output terminal of described the first digital regulation resistance, the second digital regulation resistance is all connected with the input end of described width modulation formation circuit;

Described width modulation forms circuit and comprises automated power Circuit tuning and high-speed comparator, described automated power Circuit tuning is connected with described high-speed comparator, in order to adjustable DC level to be provided, after superposeing, described DC level and audio amplification signal output to the inverting input of high-speed comparator; The positive input of described high-speed comparator receives the subcarrier signal from circuit for generating triangular wave; The output terminal of described high-speed comparator is connected with described amplifying circuit, for to described amplifying circuit output pulse signal.

2. power according to claim 1 and AM depth automatic control circuit, is characterized in that: described the first digital regulation resistance, by adjusting the variation of resistance, is adjusted the amplitude of the sine wave signal of output.

3. power according to claim 1 and AM depth automatic control circuit, is characterized in that: described the second digital regulation resistance, by adjusting the variation of resistance, is adjusted the offset level of the sine wave signal of output.

4. a power regulating method, the power based on claim 1-3 any one and AM depth automatic control circuit, is characterized in that, comprises the following steps:

Step 1: the output signal of external power amplifier is carried out to AD sampling, the power of calculating sampling signal, AM depth;

Step 2: the power of described signal, AM depth are compared with built-in power reference value, AM depth reference value, judge whether in error range, if so, return to step 1; If not, forward step 3 to;

Step 3: calculate current real power and AM depth corresponding sinusoidal wave DC level and range value;

Step 4: sinusoidal wave DC level and range value that calculated difference is corresponding;

Step 5: change the resistance value of digital regulation resistance, thereby change corresponding sinusoidal wave DC level and range value, return to step 1.

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