SV: Re: [sdiy] Upper frequency limit for VCO

[karl dalen]

--- Tony Clark <clark at andrews.edu> skrev:

> > Does anyone know what the upper frequency limit for the 
> > integrator-with-reset VCO is?  I want to divide it down to mix footages.
> 
>    Typically up to 20kHz.  Depends quite greatly on the type of parts 
> used.  The useable upper frequency limit is often determined by the size 
> of the integrating cap and the discharge circuitry.  The smaller the cap, 
> the higher the frequency, sometimes upwards of 40kHz, but of course it 
> suffers on the low end.
>    However, if you plan to divide it down, then that may be the route to 
> take.  Of course, great care must be taken at higher frequencies to 
> eliminate any board leakage, stray capacitance, wives peering over
> shoulders, etc.

I wouldent say that there is a "typical" limit, my bench saw ramp VCO
here runs about 43Mhz at the moment, razor sharp saw, i investigating
the AD8033 80Mhz device but i think i will try out some 450Mhz current
OP amps for fun! Guess expo heting will be a chore, perhaps a pll loop 
will be better to stabilize it! Things start to get a bit silly at 
these frequencies its all RF and with that comes RF design routines.
Starts to be easier with a DSS.

Anyhow you can get exellent 1-2Mhz saw osc's with perfect scale
tracking,(as in line with Tony says) you need to use modern
OP amps and comparators, forget TL072 and LM311 etc in this 
higher freq applications. 

Check archives and you will find 4046 saw
based VCO up to several mega hertz.

Reg
KD