Fast VCOs/V->F converters

[Arthur Harrison]

Karl H. wrote:
>
>I've been thinking about doing a wavetable oscillator project lately, and
>like several others people have remarked, getting a fast enough VCO to
>drive it is difficult.
>
>However, I've just looked through my favorite Linear Technology appnote
>(AN14 - Designs for High Performance V-to-F converters), and the "Fast
>Response 1Hz->2.5MHz V->F converter" design looks promising. Now, how do
>we convert this from a V->F to a I->F converter (so we can use a regular
>expo. converter)? Anybody with more analog design experience that me care
>to comment?

An I to V converter could be an operational amplifier (signal fed to 
the summing node).  Perhaps the exponential function may be 
implemented directly in this stage's feedback loop.

There are some Ananlog Devices VCOs, too, that might have a large
enough range.

>If it can be made to work, it can provide 20Hz-20kHz bandwidth with a 64
>byte wavetable with speed to spare, also fast response ensures you can use
>FM on it as well. Linearity of the V-F itself is spec'ed to 0.05%.

Sounds good to me!

-Art