We are now ready to use AD8021 to amplify weak signals. The amplifying circuit is roughly as shown in the figure below. First, you need to select a suitable N-JFET. In the multism test, 2N5521 can achieve the function, but I don’t know why it can be amplified normally. Some people want to choose a SMD packaged N-JFET. How to choose? Thank you.
Sofia postato su October 22, 2020
Without adding there will be a lot of noise, only the DC signal is amplified, and the AC is not well amplified.
Julian postato su October 22, 2020
Where did your reference for this circuit come from? For the processing of weak signals, ADI has professional weak signal amplifiers.
Adrian postato su October 22, 2020
This is taken by the teacher from the circuit they have verified before, but the model of JFET is not sure.
Julian postato su October 22, 2020
The principle of your circuit is to amplify high gain through N-JFET, and the amplified signal enters the op amp through the DC blocking capacitor. You have to understand that the most important thing is that the gain of the N-JFET is relatively large, and ordinary op amps can’t do this, but your circuit is not the best. It is only viewed by simulation. Simulation is only a principle verification. The actual circuit noise will be very large. , I guess it is difficult for your circuit to achieve the target you want. I suggest you go to the ADI official website to choose a small signal amplifier that suits you.
