[sdiy] Henry Walmsley's page

[Ian Fritz]

At 01:40 PM 12/23/2009, mark verbos wrote:
>What is the actual difference between a VCO and a Voltage to Frequency
>converter? I have heard them mentioned, but it has never made sense to
>me. I need a square wave  oscillator that goes up to around 500kHz for
>a project I'm planning. This may be the solution.

V/F converters are a kind of VCO.  Often described as having a linear 
response to input voltage, they are generally easy to use with standard 
expo current sources.  They work on the charge balance principle, which you 
can read up on in the datasheets/app notes.  They are highly accurate 
because the control current keeps flowing during the switching process, so 
there is no dead time.

Their main drawback for synths is that the main output is a narrow 
pulse.  (There is also a low-amplitude Saw which has been used 
occassionally).  So if you need a true square wave, then you need to run at 
twice the frequency.  You can check the data sheets for the high 
performance devices to see if any will work up to the frequency you need. (GL)

   Ian