From: Spehro Pefhany
Subject: Re: Voltage Controlled Resistor?
X-Newsreader: Forte Agent 1.92/32.572
Date: Wed, 11 Dec 2002 17:53:08 GMT
NNTP-Posting-Date: Wed, 11 Dec 2002 12:53:08 EST
On 11 Dec 2002 08:59:39 -0800, the renowned Winfield Hill
>> What's a good way of doing a precision VCR?
>> I thought it was easy, but have been doodling
>> on paper for half a day now. I could have
>> sworn it could be done without a multiplier.
>> Must be going senile.........
>> The spec; Vcontrol= 0-10V, Rout= 0-1k, over
>> the range 0-10v or 0-10mA. 15-0-15 available.
> You can make 2-quadrant voltage-controlled resistors
> with a programmable transconductance amplifier (OTA)
> such as an LM13700. These are not very expensive and
> a 20:1 range is practical. OK, an OTA is a type of
> multiplier. So what's wrong with using a multiplier?
> Hmm, do you only need single-quadrant operation? You
> could program a simple active resistor with an EEPOT.
*Precision* 0-1K (0.1-0.01 Ohm accuracy? ) would not be
very easy with a digital pot, directly anyway.
I did some work on this in terms of calibrator design
some years ago, can't recall the conclusions at the
moment, but it's certainly not insoluble.
Might have used a multiplying DAC and some circuitry.
"it's the network..." "The Journey is the reward"
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