How to measure noise of preamp circuit???

So i have designed a basic preamp circuit with an op amp and National Semiconductor evaluation board. Im trying to measure the noise that the circuit creates. Im having some trouble doing this properly.

Im using a very high bandwidth op amp (1.5Ghz) connected in non inverting configuration. Ive also got a capacitor on the feedback resistor to roll the gain off at 20Mhz.

Ive got a spec that I am trying to see weather i meet or not. aprox 60uV

Ive quite a bit of test equipment availbale but ive come to a dead end. I tried shorting the input and measuring the output with a Boonton RF voltmeter. But this device only goes down to a 200uV accuracy. So Measuring 60uV is impossible.

Any ideas? Whats the standard way of MEASURING noise? Not calculating it....

Thanks!

Ethan

an osilliscope would probaly be required

3lectrokid said:

an osilliscope would probaly be required

Click to expand...

Oscilloscopes do not have enough resolution to complete the measurement im trying to do. Lowest voltage devision even on any analogs are 50mv per dev. Im measuring MICRO volts uV so this will not work...

Thanks for your response though

Ethan

If the circuit has enough gain you can use a spectrum analyser or equivalent with ADC on output feeding a FFT computation. The noise performance can be dependent on sourcing impedance and therefore somewhat dependent on application. For op amps it is usually expressed in nV of equivalent input noise voltage per square root hz. This would be used to compute the equivalent output noise voltage but the spectral response is likely a function of frequency.

Do you have a low noise, high gain, 20MHz amp at the op amp's output to get the noise into a more measurable range? Of course you need to take the noise of the added amp into account but that should be small for a reasonably low noise amp.

Have a look at this app note.

**broken link removed**