[sdiy] Buchla-Bergfotron VCO

[Ian Fritz]

Hello --

Can anyone tell me why the 5.1k resistors are even there?  It seems to me 
they just cause common-mode and offset problems.

In my triangle VCO I just fix the top of the mirrors at 2V (to keep 
everything out of saturation).  With an accurate and *symmetrical* current 
mirror the waveform symmetry at high frequency is fine.

Any triangle VCO will eventually fail at low frequency because of the input 
bias current of the integrator.  To see where the errors are significant, 
just look up the bias current  and compare it to the control current vs 
frequency.  An easy enough calculation.  This bias error is easily 
compensated with the usual offset trimming technique.

   Ian