FETs on the ASM-1 VCO.

[Joachim Verghese]

> For a vast majority of synth applications,
> there should be no danger to the switch whatsoever.  These switches,
> after all, are integrated versions of the discrete JFETs or MOSFETs
> routinely used in all kinds of discharge applications.

You're right, a lot of the currently available analog switches
can handle peak currents of several hundred milliamps.

> If crosstalk is a concern, individual switches are available in eight-pin
> packages. The MAX319 is one such switch.

I'm having difficulties catching up with all these new Maxim
releases. :-)

> In such cases, you may have to contend with marginal Vgs conditions in
> which the switch can not be fully enhanced.  The nice thing about many
> integrated switches is that they contain the level shifters and other
> goodies to ensure proper enhancement of the output switch, regardless of
> Vds.

A valid point.

> I was a little concerned, though, about possible instabilites in U1A
> resulting from C1's direct connection to its output.

Juergen already answered this more thoroughly than I ever could. :-)

> Have you measured the linearity of this oscillator and R1's relationship
> to linearity?

No, I haven't made any precise measurements yet -- I've so far only
used the oscillator in applications with microcontroller compensated
scaling, but from debugging the scaling code I seem to recall that
the required compensation was rather small. R2 should compensate for
some of the HF-tracking error due to the 1 ms retrace time.

cheers,

-joachim