[sdiy] Decoupling caps?

[Neil Johnson]

Charlie,

> I am designing a PCB for the ASM-1 VCO.  I am limited in board space and
> want to make a single sided board so I can press-n-peel.

I've done a small, double-sided VCO, with a similar design to the ASM-1
VCO.  It all fits on a 2"x2" PCB, so I do agree that small is possible!

See here:
	http://www.njohnson.co.uk/msm.html

Tony Clark wrote:
> The other thing that MAY need to be decoupled is the power to the
> exponential converter (1M resistor tied to the power line).  This is
> where the VCO can _receive_ spikes in the power lines, causing
> potentially unwanted VCO syncing.

I take the view that the only things that should connect to the supply
rails are op-amp supply pins and voltage reference bias resistors.
Anything that needs a voltage, such as the bias resistor for the
expo-converter, is fed from a +5V voltage reference---they're so cheap
these days its a crime not to sling one in (or two if you need a -ve
reference as well) and avoid any crap on the supply rails getting into
your signal path.

Cheers,
Neil

--
Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
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