need help to amplify microvolt AC.

Hi Ahmed,

This need more info, what is the sensor (link to it's datasheet perhaps).

The next question (kind of obvious, but since I don't know the answer so I'm going to ask), have you asked the sensor manufacturer?

What frequency is the signal?

You will need a very low noise amplifier, probably more than one stage.

More information is needed.

What kind of sensor, what frequency range of signals ?

shabaz posted what might be a helpful article:

Building a Measurement Amplifier

MK

I would be more interested in what issue(s) Ahmed has seen.  If it is electrical noise pickup the input impedance may be too high or he may have to put a metal can around the circuit.  If noise is being injected thru the power supply better filtering or separate supplies may be needed.  If the signal you are amplifying is a single known frequency, adding a narrow bandpass filter may help. If the issue is temperature related, thermal insulation may help.  Maybe vibration is a problem.  To go from 100uV to 5V requires a gain of 50,000, so any thing that can cause a shift in the input can be a problem.  In any case, it would be nice to know what problem he is trying to solve.

Stay Well, Gordon

Out of curiosity this is what I see with a 1kHz 100uVp-p signal and the single-stage x 200 amplifier from here:

Building a Measurement Amplifier

I had to string a lot of ferrites on the coax though. It will be nice to put a common-mode choke in the next iteration of the design, but not sure how to do that yet, since the BNC is connected to the enclosure. There are some plastic BNC connectors, so that could be worth experimenting with. I might put the land pattern for a choke on the board, but could be just jumpered across if a plastic connector is not available/used.

The problem-solver:

EDIT: Maybe I should put a land pattern for allowing a twisted-pair cable connector like XLR to be used optionally if BNC is not desired.