Temp-Co resistors

A.S.P. ms20 at zebu.serv.net
Tue Jan 9 02:14:08 CET 1996

On Mon, 8 Jan 1996, Haible_Juergen#Tel2743 wrote:

> >I used to put two 1K tempco resistors in series, available from Farnell
> >Electronic Components, order number 143-584. For new designs you could
> >use one 1K tempco and lower the value of the other divider resistor to
> >achieve the desired 18 mV/oct scaling.
> That's the way to go, for sure.
> Anyway, I have seen the 2k tempcos mostly in designs where the
> 2k is in the feedback loop of the input summer, and the
> "other" resistor(s) are the 100k summing resistors from the 1V/8ve
> inputs - so You might need an extra opamp stage in that case.
> Or maybe You build a low impedance voltage divider (say, with two
> 330 Ohm MF resistors) at the opamp's output and derive the feedback
> signal from the half output voltage point. Then the summing node sees
> only one half of the current it would get from the 1k tempco, just as if You
> were using a 2k tempco.

This makes good sense.  What I've done is halved the 100K summing 
resistors.  I don't know if this is going to work, but I'll probably find 
out tomorrow when I fire up the first one of these modules.


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