[sdiy] Temp comp of OTA and the expo!

[Scott Bernardi]

I thought I saw somewhere that if you use the diode biasing, it cancels 
out the tempco of the gm cell.

Karl Dalen wrote:

>NS once reported that the tempco of the Gm in their LM13700 is 
>-3300ppm C. Since this would then be the very same amount of
>temp drift as in a ordinary exponential converter (-3300ppm/C)
>how would i temp compensate for the "total" temp shifts" properly"
>if a standard PNP exponential converter used as current controll? 
>What if the drift in the expo are e.g -3100ppm and the Gm cell 
>are -3350ppm, how do one actually temp compensate this situation??
>
>And what if they are phusically spaced a bit from each other,
>then the temp drift rate would not be equal, e.g i suspect they 
>start to drift at different time positiuons!!! Urgh!!!
>
>I mean, it would be nice to have a drift free multimode filter
>in resonating mode!
>Any sugestions?? Heating the Gm cell by using the darlington pair
>as heater would perhaps remove the 3300ppm of the Gm cell!!!
>
>Thanks!
>  
>Regards
>KD
>
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-- 
Scott Bernardi
sbernardi at comcast.net