[Guangdong University of Technology] Simple transistor amplifier

1. Design tasks

Design a transistor amplifier device.

2. Topic requirements

The external signal output frequency is 1kHZ and the peak-to-peak sinusoidal voltage ui is 20mV, which can achieve the following functions:

1.Basic requirements

(1) The amplifier can output a sinusoidal voltage uo without obvious distortion.

(2) Measurement shows its input and output resistance.

(3) Draw the waveform diagram.

(4) Display the gain of the amplifier and draw the amplitude-frequency characteristic curve.

2. Play part

(1) It can output the distorted voltage at the top and draw the waveform diagram.

(2) It can output the voltage with bottom distortion and draw the waveform diagram.

(3) When the amplifier outputs distortion-free voltage and two distortion voltages, the peak-to-peak value is not less than 2V.

(4) The measurement shows the approximate value of the distortion-free voltage and the "total harmonic distortion" of the two distortion voltages.

Introduction to the work: This design uses a transistor (NPN) two-stage common emitter amplifier circuit and a Class B power amplifier circuit. By changing the resistance value of RA to change the level of the static operating point Q, the waveforms of cut-off distortion and saturation distortion are obtained. By adjusting RB The resistance value changes the transistor amplification factor to obtain a waveform with a peak-to-peak value greater than 2V. The acquisition part uses STM32F103 for control operations, uses the ADC peripheral of the microcontroller to accurately collect voltage waveforms, and then uses the DMA peripheral to open a direct data transmission path for RAM and I/O devices, which can greatly improve the efficiency of the CPU. Configuring a timer to trigger AD conversion can control the sampling frequency. After collecting the waveform, you can clearly see the waveform data by displaying it on the TFTLCD screen. Introduce the DSP library and use fast Fourier transform to measure and calculate the total harmonic distortion. Use a timer to regularly output a specific sampling frequency. The number of sampling points is 1024. The sampled data is used for FFT on the microcontroller to obtain the modulus values ​​of different frequencies. . When the input of a linear amplifier is a sinusoidal signal, its nonlinear distortion is manifested as harmonic components in the output signal, which requires the fifth harmonic. Therefore, according to the 1kHz signal of the signal source, 1kHz, 2kHz, 3kHz, and 4kHz need to be collected. , 5kHz amplitudes are U01, U02, U03, U04, and U05 respectively. THD can be calculated according to the formula. After measuring the frequency and voltage gain, the amplitude-frequency characteristic curve can be drawn.