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AD8021 is used to amplify weak signals. Why can it be amplified normally?

Hardware design
10월 22, 2020 by Adrian 363

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.

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Sofia 게시 날짜 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.

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Julian 게시 날짜 October 22, 2020

Where did your reference for this circuit come from? For the processing of weak signals, ADI has professional weak signal amplifiers.

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  • Adrian

    Adrian 게시 날짜 October 22, 2020

    This is taken by the teacher from the circuit they have verified before, but the model of JFET is not sure.

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Julian 게시 날짜 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.

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