variable gain amplifier

Shown above is a variable gain amplifier. It is used in amplifier circuits with fixed input signal and controllable output signal amplitude. The main body of this circuit is an operational amplifier. The gain of the amplifier is changed by changing the feedback amount of the negative feedback circuit. In the figure, a double-gate field effect transistor PIX429D negative feedback control device with a base control terminal is used, and the control voltage is between -10~-2 Changing between V can cause the output to change between 220 mV~2.2 V.