[sdiy] Question about CMOS switches

[David G. Dixon]

> > Is there any problem driving analog switches in the DG series with
> switching
> > signals that swing to (or near) the rails (provided, of course, that the
> > switches are powered from the rails)?
> 
> Yeah, there is...
> 
> On devices like the DG409, the switch still works, but it injects a
> significant amount of charge into the analog lines.   So if you care about
> charge injection you'll need to limit the control voltage swing.
> 
> That's not mentioned in the data sheets; I discovered it the hard way.


Thanks, Don.  I too learned about charge injection the hard way when I was
revising the CGS Analog Shift Register with DG409, and there were specific
things I did with the supply voltages to the switch to minimize it.  In the
present circuit, this doesn't matter too much, as all I'm using the switch
for is to switch ground into TL07x comparator inputs.