Re: Analog switch configuration?

"MRW" <mr.whatever@xxxxxxxxx> wrote in message
news:1161959390.069599.192720@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Good day, group!

My friend has this rough drawing of two analog switch configuration:
http://img175.imageshack.us/img175/9612/analogswitchesbf9.jpg

I say that the two SPST configuration would be better suited since it
would provide better isolation than the SPDT configuration. She says
otherwise. Am I wrong?


Since the circuit connects the two switches together, isolation is going to
be a function of the switches' OFF resistance, rather than crosstalk between
the two switches, so there's nothing to choose between the two
configurations.

I also told her that another switch would be required at the output of
DeviceA so its output will be isolated from the other signal path. She
thinks it's okay. Is there truth to her claim?

Thanks!


No, you're right, you need to disconnect the output of device A when
connecting 'Signal in' to Signal out', otherwise you will end up with two
outputs trying to drive one another. (I'm assuming that 'Signal in' is low
impedance and comes from some type of amplifier and that Device A is itself
some form of amplifier.

A simpler arrangement would be to connect 'Signal in' permanently to the
input of Device A and use the switch, (either arrangement shown in the
link), to select between the signals on Device A's input and output.

--
T

If it's not broken, don't fix it.



.

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