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From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: Current to voltage converter for AC only ?
Date: Fri, 27 Sep 2002 18:56:04 GMT
NNTP-Posting-Date: Fri, 27 Sep 2002 11:56:04 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Steve Parus wrote:
> I need to measure the current noise of a device which has a DC voltage
> applied to it. DC current level is milliamps, desired bandwidth is
> 0.1 Hz to 100 kHz. Am trying to convert the current to a voltage and
> digitize by computer. Increasing an op amp i-V convertere's gain to
> magnify the AC noise component has limits of the DC output of the amp.
> One idea is to use a AC-coupled voltage amplifer after the i-V
> converter to magnify the AC portion only. Are there alternatives ?
> Because the device's resistance may change, I'm using a conventional
> op amp current to voltage converter so the device sees virtual ground
> when connected to the inverting input.
The standard method for measuring the approximate noise of a device is
to measure the noise at the output with zero signal at the input, then
connect a noise source at the input and adjust the source level until
the output noise has doubled.
The noise level of the source will be approximately equal to that of
Viable from low audio to microwave.
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