Controllable amplifier mainly includes amplifier and filter. In the amplifier part, the resistance of feedback resistor is changed by analog switch CD405 1, thus the voltage gain of the amplifier is changed. The adjustable step of gain from 10dB to 60dB is 10dB. In the filtering part, the microcontroller AT89S5 1 is used to program the programmable filter chip MAX262, which can simultaneously perform second-order low-pass, Qualcomm, band-pass, band-stop and all-pass filtering on two input signals. The center frequency of the filter can be adjusted by 64 steps in the frequency range of 15 kHz ~ 50 kHz, and its q value can be adjusted by128th step in the range of 0.5 ~ 64.

Adjustable amplifier mainly includes amplifier and filter. Through the analog switch CD405 1, the amplifier changes the feedback resistance value, and then changes the voltage gain of the amplifier. The adjustable step of gain from 10dB to 60dB is 10dB. In the filtering part, the single chip microcomputer AT89S5 1 is used to realize the program control of the programmable filter chip MAX262. It can simultaneously realize the second-stage low-pass, Qualcomm, band-pass, band-stop and all-pass filtering processing for two input signals. The center frequency of the filter is between15khz and 50khz; In this frequency range, 64 levels of program control adjustment are realized, and its Q value can be adjusted at 128 level in the range of 0.5~64.