[sdiy] ARP VCO PNP-NPN exponential pair matching

[Ian Fritz]

At 11:05 PM 6/7/2008, Paul Schreiber wrote:
>If you want to track 1V/Oct accurately, then yes.

Remember that in an expo converter one transistor provides the expo 
response and the other is for temperature compensation.

The purpose of transistor matching is to ensure that the exponential 
prefactors cancel, in order to avoid temperature drift from this potential 
source.  It has nothing to do with tracking, which depends on the 
characteristics (log conformance)  of the anti-logging transistor.

Ian