[sdiy] Crosspoint Switch [was: Which programable chip?]

[Neil Johnson]

Hi,

Joe Grisso wrote: 
> Sorry to jump in like this, but using the 405x in current mode was
> discussed in the last thread. Check out this reference:
> 
> http://www.dself.dsl.pipex.com/ampins/mixer/mixerdes.htm#7
> 
> You wire the switch in between Ri on the op-amp and the inverting
> input, which turns the voltage presented on the other side of Ri into
> a current flowing through the inverting input. It's that virtual
> ground, man! ;-)

But ... only if you have the matching switch to ground when the 'through' switch is open.  Otherwise there won't be any protection and the input will see pretty much the input voltage ( assuming that Rsw(open) >> Ri ).

Neil
--
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