RE(2): matched expo source / sink idea

[Haible Juergen]

	>A couple thoughts.  The current through Q4 is the base current of
Q1, 
	>typically a very small amount of current.  The Vbe of Q1 and Q4
will
	>therefore be very different,  to fix that you should source some
current
	>into the collector/base of Q4 by adding a resistor to +15V.   

All right, I've changed the circuit a little:
http://home.debitel.net/user/jhaible/jh_expo_source_sink.gif

Collector of Q4 goes to +15V now.
I've also removed the CA3096 suggestion for the transistors.
I think when I try this on the breadboard, I'm going to use a
2SC3381 / 2SA1349 combination. Maybe the two pairs don't 
even have to be at the same temperature for 1st order temperature
compensation, as Q1 compensates Q2, and Q4 compensates Q3. (?)
Both pairs should be in thermal contact with the tempco resistor,
of course, for 2nd order compensation.

JH.