possible tempco with KTY81

Rene Schmitz uzs159 at uni-bonn.de
Thu Nov 18 17:41:32 CET 1999


At 19:34 17.11.99 -0700, Ian Fritz wrote:
>Rene --
>
>Looks pretty good. I've seen this with thermistor compensation schemes
>before -- you get a small, non-monotonic error over some fairly small T
>range, then rapid increases outside that range. The way I see your data
>is that between 10 and 40C you have a total deviation of about 0.1%,
>which roughly averages out to about 30 ppm/K. It's hard to measure this
>small a change! And, as you say, other sources of drift will be more
>important.

I even forgot to mention the typical drift of metal film resistors, which
can be 
50-100ppm.

>I don't understand what you mean by the error being the error of the
>compensation. I think a 1% deviation from the ideal R(T) translates
>directly to a 1% pitch error.

Wouldn't that be the case for a linear VCO only?

Assumed we have no compensation at all, we find the VCO to go down in pitch
0.33% per degree. Now ideally we chose the gain so that this gets
compensated. In the ideal case of a TC resistor, we raise the gain by 0.33%
per degree. Now with the KTY I think we make an error of 1% of that 0.33%
per degree. That means 3.3*10^-4%.

Bye
 René



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