How to improve the anti-interference (radiation) ability of operational amplifiers

sfcsdc

How to improve the anti-interference (radiation) ability of operational amplifiers [Copy link]

I use ADA4528 to amplify the signal 300 times, the characteristics are as follows: The normal amplified signal waveform is as follows: But when making a call around the device, the signal will be interfered I have checked the power supply of the op amp, and it is basically not interfered and very stable; It should be that the radiation is coupled into the input of the op amp and amplified 300 times. I would like to ask you: Is there any way to solve this phenomenon? In addition to paying attention to PCB layout and structural shielding, what suppression measures can be added in the schematic design stage?

maychang

"But when you make a call near the device, the signal will be interfered with." Are you using a mobile phone? This phenomenon will not occur with a landline phone.

sfcsdc

maychang posted on 2019-4-16 10:11 "But when you make a call near the device, the signal will be interfered with." Are you using a mobile phone? A wired phone will not produce this phenomenon.

Yes, it is a mobile phone

maychang

sfcsdc posted on 2019-4-16 10:21 Yes, it is a mobile phone

For this phenomenon, it is best to put your entire device in a closed metal box. The electrical connection between the box cover and the box body must be good. Add low-pass filtering to each input and output line (including the power line). It is very troublesome.

sfcsdc

maychang posted on 2019-4-16 10:25 For this phenomenon, it is best to put your entire device in a closed metal box, and the electrical connection between the box cover and the box body must be good. Each input and output line (including the power...

Yes, but now it is not a conduction problem, it is caused by radiation. How can I improve the radiation resistance of the op amp input (non-PCB design method)?

maychang

sfcsdc posted on 2019-4-16 10:34 Yes, but now it is not a conduction problem, but radiation. How can I improve the anti-radiation ability of the op amp input (non-PCB design method...

Metal shell shielding and low-pass filtering of each input and output line are the ways to reduce radiation interference.

sfcsdc

maychang posted on 2019-4-16 10:53 Metal shell shielding and low-pass filtering of input and output lines are the ways to reduce radiation interference.

Oh, this signal is not from the outside, but generated by the sensor. Do I need to add filtering between the sensor and the op amp?

maychang

sfcsdc posted on 2019-4-16 11:00 Oh, this signal is not from the outside, but generated by the sensor. Do I need to add filtering between the sensor and the op amp?

"This signal is not from the outside, but generated by the sensor." It is possible. Especially when the connection line between the sensor and your device is long. If so, using a twisted pair cable between the sensor and your device may have some effect, and adding common mode filtering and low-pass filtering to the op amp input may also have an effect. Low-pass filtering cannot affect the normal signal transmission of the sensor.

chunyang

Countermeasures: 1. Since the coupled external RF interference is often common mode, improving common mode rejection is a more effective method. The circuit is designed to be a differential signal input mode, the signal frequency is not high, and even an instrument amplifier can be used. 2. Adding an LC low-pass filter is more effective in conjunction with differential signal transmission. 3. For high-speed, high-impedance input circuits, consider using a shielding cover.

yanshiwen

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