The wide-band amplifier whose gain can be controlled automatically is mainly based on AT89S51 single-chip microcomputer as the main controller, which is composed of front-end amplifier circuit, programmable gain amplifier circuit, power amplifier circuit, PWM gain control circuit, peak detection circuit, display module, etc. The system can preset and compare the output voltage through the storage and reading function of the single chip microcomputer, and realize the linear change of the total gain in the broadband range of 0dB ~ 40dB, so that the gain can be controlled automatically. The voltage controlled gain device is used to adjust the step size of 4dB. In the design, low noise and wide-band chips are used to solve the problem that the bandwidth decreases sharply with the increase of gain and the slew rate is insufficient. The system has the functions of wide controllable bandwidth, noise suppression, stable output signal, automatic gain control and digital program control.<BR>
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