I would like to ask, when the differential input signal is small, the amplification factor of AD623 drops sharply?

hf12345

I would like to ask, when the differential input signal is small, the amplification factor of AD623 drops sharply? [Copy link]

 

I would like to ask you, the above figure is the measured data of the ad623 instrument amplifier. I originally wanted to get a 160x gain (gain resistor 0.62k), but it was not actually achieved, about 140. The problem now is that when the differential input signal is small, especially below 1 millivolt, the gain drops sharply. What is the reason? The front-end circuit is a pressure sensor based on a Wheatstone bridge. The bridge voltage is 2.97V. When there is no pressure, the bridge output is 0 millivolt, that is, the differential input is 0 millivolt.

cruelfox

When asking questions, please post the complete circuit diagram.

maychang

Did you use a single power supply? Please post the complete electrical schematic.

hf12345

cruelfox posted on 2018-9-4 18:23 When asking questions, you should post the complete circuit diagram.

It has been posted, please help me check it out

hf12345

maychang posted on 2018-9-4 18:24 Did you use a single power supply? Please post the complete electrical schematic.

The circuit diagram has been posted. The reference terminal of ad623 is directly grounded. Does this mean a single power supply?

cruelfox

I checked the AD623 manual and found that REF can be connected to -Vs, so I don't see the problem. What is the power supply voltage? How big is the resistance connected to the input? Is the information provided complete?

hf12345

cruelfox posted on 2018-9-4 20:03 I looked at the AD623 manual and found that REF can be connected to -Vs. So I haven't found any problems. What is the power supply voltage? How big is the resistor connected to the input? Information provided...

The power supply voltage is provided by the voltage regulator chip, 2.97v, and there is no resistor connected to the input.

cruelfox

hf12345 posted on 2018-9-4 20:11 The power supply voltage is provided by the voltage regulator chip, 2.97v, and there is no resistor connected to the input

Can the power supply voltage be so low?

hf12345

cruelfox posted on 2018-9-4 20:59 Can the power supply voltage be so low?

Yes, no problem. The 2.97V voltage regulator provided by the tps73230 voltage regulator chip. You think the power supply is too low, where will the problem occur?

hf12345

cruelfox posted on 2018-9-4 20:59 Can the power supply voltage be so low?

However, I found that my ad623 can no longer output a higher value after it reaches 1.5v. It cannot reach the power supply voltage. I wonder if this has anything to do with the voltage of 2.97v being too low? I remember that if ad623 wants to output full power, it seems to have a requirement for the common mode input voltage. It must reach 2v to output full power? My current common mode input voltage is only about 2.97/2=1.48v

cruelfox

The indicators given in the data sheet are under 5V power supply. Increase the power supply voltage to see if there is any change.