First of all, the diode does not amplify the function of the transistor can work in the linear amplification area, play the role of amplifying the input signal, as for why the signal is amplified, it is because the input signal is very weak, the post-stage circuit can not be processed, after linear amplification, the amplitude of the signal increases, the post-stage circuit can carry out the next step of its operation, such as: The analog sensor will have an output after detecting the signal, and the output can be analyzed and displayed by the digital system after AD (analog-to-digital conversion), but the output signal of the sensor is often weak, and after being amplified by the op amp or the transistor, it can be converted into a digital quantity with AD, so the accuracy is higher