VCO from Harris 8038 ic? or Exar xr2206 ?

[Martin Czech]

> Kip,
> 
>     The 8038 has possibilities.  There's a better one, MAX38.
> Unfortunately, these chips were intended to be used with a resistor for
> frequency control.  It may be possible to use it by feeding a current
> source into one of the terminals where the resistor is attached.  I
> haven't looked at the schematic for a long time.  The nice thing about it
> is that it generates a Sine if I'm not mistaken.  The not so nice thing is
> 
> that it has no sawtooth, although you could get one with a little work
> from the triangle.  Maybe some others have experience with this chip.
> 
> Gene Zumchak (I'm new on the list)
> 
> 
Just poping in:

I did an VCLFO with XR2206 ages ago.
Worked of 10 Octaves, since I feed a current into the chip
internal mirror.
AFAIK all these devices have an internal current mirror/polarity
mirror for their triangle generation, so you can always feed
a current. 

I'd prefer the XR2205, if any, it seems to have the lowest THD for
the sine. Unfortunately you can only switch between tri and sine.
You can achieve a crippled saw by the pwm option (see data sheet).

But really: don't use them. Following the ca3080 app. note
oscillator is still the best choice. You can hack it, modify it,
everything you want. You can also add an discrete diode sine
waveshaper, much better then those on-chip things (of course you
have to trim/select).

m.c.