thermistor III

Rene Schmitz uzs159 at
Sat Jan 10 11:27:56 CET 1998

At 10:34 09.01.1998 +0100, you wrote:
>Using the said NTC from my last mail "thermistor II" with parallel res
>1950 Ohm (for adjusting "steepness") and serial res 3900 Ohm (for
>adjusting resistance "offset") as uper leg and 100 Ohm as lower leg
>gives about five times smaller temperature error of the exponentiator
>current over a temp range from 10C to 90C chip temperature.  This
>includes 2% error of NTC curve, and 5DEG mismatch of NTC and actuall
>chip temp. An ideal matched pair is assumed, and other sources of error
>are neglected.

I have the feeling that 5deg mismatch is far too pessimistic,
unless you got a large heat source near your exponentiator. If one 
epoxies the NTC (assumed a not too bulky one is used) directly to 
the chip the temperature mismatch won't be that high.

>I'm really thinking about compensating my exp/lin VCA with such
>devices (expo as well as log circuitry).

I'll try it on a VCO, and if its suitable there, its definately 
suitable for filters and vcas too.


=(uzs159 at
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