Tri 2 Sin

[Martin Czech]

A while ago I asked for the circuit for tri 2 sin conversions that
employs multiple difference amps. No response.

I was just cooling down a wafer to -40C (wait, wait, wait...) when an
old Analog databook came into sight, and there in the chapter AD639
sin/cos/tan Coverter I found the following reference: 

IEEE Journal of Solid State Circuits Vol SC17, No 6, p. 1179. 

Now I rushed into the library and got it. It's by Barry Gilbert and
describes exactly the above mentioned method for precision tri 2 sin
conversion. Of course it makes use of specific aspects of integration,
ie. transistor matching und equal temparature on chip etc. but it could
well be that the principles of operation will also w be good enough for
a discrete circuit. The author proposes that a  4 npn  diff amp makes a
resonable good converter.

Any comments ?

m.c.