possible tempco with KTY81

Ian Fritz ijfritz at earthlink.net
Fri Nov 19 04:49:00 CET 1999


Rene --

Hmm... I don't think so. I believe the fractional pitch error is the
same as the fractional resistance error, comparing the resistance to the
ideal case. Of course this is much smaller than the error you would get
without compensation. 

An example from your table: 

Consider three cases -- (a) your R1 (KTY + 1350) (b) your ideal R2 = C*T
and (c) uncompensated R3 = 2340 fixed.  Look at T = -20.

R1 = 2019
R2 = 1987
R3 = 2340

R1 compared to ideal R2: error = 2019/1987 - 1 = .016 (1.6%)
R3 compared to ideal R2: error = 2340/1987 - 1 = .178 (17.8%)

The deviation of KTY + 1350 from the ideal is 1.6% (not 1.6% of 17.8%).

On a per-degree basis the R1 error averages to 1.6%/45 = .035%/K. 
And for the uncompensated (R3) case 17.8%/45 = .39%/K, about as
expected.

I may not have understood how you did your calculations, as I can't get
col 4 from cols 2 and 3.

  Ian


Rene Schmitz wrote:
> 
> >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%.



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