Help me with measuring ripple of a low noise power supply

[rauol]

op37 preamplifier

:? I want to measure Ripple of a very low noise power supply, may be around 100 to 200 micro volt. i am facing problem with low signal measurement. the scope which i use has a 2milli volt minimum scale, but even with the probe inputs shorted it is showing a noise of 1 miili volt.

what do you elektrodians recommend.

i am planing to built an amplifier using OP37 with DC blocking at its input with a gain of around 10, then may be ii will be able to measure low signal levels.

Regards

 

[jiangwp]

Re: Preamplifier

when designing a PLL , we measure the phase noise of VCO .

we first to do the FFT of output wave.

May be you also can do the FFT of power supply to measure the noist floor.So you

can evaluate the ripple of the power supply.

 

[abhigopal]

Preamplifier

maybe an instrumentation amplifier may help.. Not sure though

 

[IanP]

Re: Preamplifier

OP37 seems to be good choice for this application although you may have some small problems with internal noise. For this level (µV) you will have to "silience" the power supply by usong LC filters on both supply lines including GND and shield the IC by using a metal cage. (see also MAX437)

 

[Borber]

Re: Preamplifier

If you know the frequency of the ripple you can limit the bandwidth of the measured signal by using low pass filter. You should use low noise amplifier in front of filter.

 

[vdaniel]

Re: Preamplifier

The choice of the best preamplifier strongly depends on the cirquit impedance. If it is low then op37 is a good choice, if it is high most dominant bacame the current noses and you should use an amplifier with a small input curren. There are very nice Design Note in the Linear Technology site about OpAmp noises.

Varuzhan