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AD8221 oscillation problem

Question asked by SNZ on May 13, 2014
Latest reply on May 13, 2014 by harryh

Hi,

 

I have oscillation problem in ADD8221 circuit, here is the circuit info:

 

1 Supply : +15V, -15 V

2 Input signal, for test: 1.5KHZ, 5 Vp-p

3 AD8221 gain set to 1

4 This will work in a circuit range from 10V to -10V in put signal, to get the same level output voltage.

5 The picture shows example of output 1.5KHZ , 5V p-p, of same specification input values (Pic: TEK00016)  (This means circuit is functioning as expected)

6The problem is , even the circuit is working in a range from 10V to -10V, but even 1 mV is important as this a part of measurement system.

7 In the pic (TEK00015) attached, I disconnected the inputs and shorted them, what I got is   45mV p-p oscillation.

8 The power supply is clean (noise of about 5 mV) and it is not correlated with the oscillation shown in the pic.

9 Also, attached the simple circuit diagram, the output wires is about 1ft long and remotely grounded with AD8221 ground.(Pic: ggg)

 

The circuit is a part of a bigger one having similar noise problem, I built a small board of just the AD8221 circuit and I got the same oscillation which shown in pic.

 

 

 

Any idea why this?

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