[sdiy] Help with Timing Capacitor types.

[Dave Manley]

Ian Fritz wrote:
> As I showed a couple of years ago, there is a much simpler way. This 
> is to add a bit of dc offset at the base of the converter transistor.  
> Just takes a trimpot and a resistor.   This gives an adjustment that 
> may be used to eliminate all linear temperature drifts, i.e., the 
> correction is adjustable.  The old, old, servo loop method makes a 
> fixed compensation and requires an opamp and several resistors.
>
> I'm surprised that none of the early designers seems to have used this 
> simpler method.  Although I developed it on my own, by studying the 
> tempco math in detail, I later found a similar circuit in one of the 
> app notes for matched pairs.
>
>   Ian
>
> http://home.comcast.net/~ijfritz/sy_cir7.htm
> (discussion in paragraph above the last figure)
>
> http://home.comcast.net/~ijfritz/sy_cir9.htm
> (R13 and R14)
One reason I would guess this method isn't widely used is the 
calibration procedure requires temperature cycling the DUT.  In a 
manufacturing environment this would be cost prohibitive because of the 
increased test time.

-Dave