Block diagram of CS-80 VCO chip online

[Paul Perry]

At 01:12 AM 7/10/00 GMT, Bjorn Julin wrote:

>Well, talking about that some people are looking into
>application notes, this looks wery similary to the XR4151/LM331!!
>
There is a fascinating history of VCOs in "Analog Circuit Design:
 Art, Science, and Personalities"(ed. Jim Williams), where Bob Pease who 
designed the LM311 shows its history.. right back to a circuit from 1967,
from SWEDEN, of all places! What a coincidence BJ! (Maybe an uncle?)

Incidentally, the 'magic' in this ckt (consisting of an opamp and a UJT)
was that on each output pulse, a precise amount of charge was fed back to 
discharge the integrating capacitor.
Pease points out that the RC1451 VCO (1970) was the first IC VFO, but was
timer based like the 555. And, consequently, not very linear or temp stable.

Pease is rather disparaging in his comments on the unknown hero from Sweden,
saying "apparently the Swedish engineers had stumbled onto this crude but
functional circuit". Well, I don't know whether it was 'stumbled' on or not.
I do know somebody didn't bother patenting it, and some US companies made a
lot of money from it!

What I do know, is that this story gives an interesting insight to the whole
question of 'original circuit design'. It is quite likely that the Swedish
designer just connected the reset cap into the circuit without realising that 
it wouldn't TOTALLY discharge the integrator, which was the key to the 
linearity. What Pease deserves full credit for, is understanding how it
worked, and being able to improve it so much as to take it into another 
level altogether. Including throwing out the UJT. 

So can we say Pease invented this VCO core?
No more than we can say Edison invented trhe light bulb, or Ford the auto.

paul perry melb aust