At 08:34 PM 2/17/01 -0700, you wrote:
>Yes, and an 800 PPM/K spec.

An 800PPM/K *typical* spec (no maximum). Of course you could always
just change the temperature by a bit if it's off by 1%. ;-)

>If your application allows it, you might want to look at using a
>multiplying
>DAC for your tuning function. You basically get a high precision R/2R
>network
>and better tempcos. The downside is that you have to intialize them at
>powerup.

He wants to use it as a rheostat, though. I don't see how that could
work. There are plenty of solutions for voltage dividers, few for
absolute resistance and fewer still for accurate absolute resistance.

Putting PWM modulated analog switch of low on-resistance in series with
a precision resistor would have a chance, as you just suggested, given
high enough PWM frequency, low charge injection in the switch, and
so on. If several "resistors" have to track in tandem, it might work ok.

Best regards,

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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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