Analog Switch

[Starfire]

In some circuits an analog sw is very useful - the MAX 4644 or MAX 4599 can suffice

[Doug Coulter]

Yes, they are. I went to digikey to get a datasheet on that first number, and it's a pretty cool little thing for sure.
One of the issues they don't mention at the top of the sheet (and in this age of specsmanship, that's the first place you look for what's missing) is how much charge injection there is
from the switching signal....So as with most things, the application dictates whether one or another is best, as when making a sample/hold, this really matters, but for some other things, not so much. I don't recall the number, but I'd love to find the one Nat Semi made that was a full chopper -- it even had the oscillator in it. That would be insanely useful as a way go get DC through an AC only (eg all computer sound cards) A/D and recover the DC in software later on. Not that you couldn't use conventional switches and an inverting amplifier to get there just as well (but larger footprint). I've found some good stuff in the MAX line, but more often than not, if I don't need some special feature that it excels at, there's something else cheaper that is just as good, like plain old CMOS switches. MAX tends to be pricey.

Another trick I've used, and when it really worked well I almost didn't believe it, was to use a PIC output pin as a switch to ground. You can set these as either input (cmos, high impedance) or output, in software. So if you want to make an analog mux that just lets one signal through, you can just short the others to ground with this as required (you'd get a click if they had DC on them). That uP can be so low in ground bounce noise that you can do this with low level audio and not hear the switch transient at all, or noise from the uP code running (assuming you're not using other outputs to deliver real big currents also). Good for integrator resets too for things that have ground in the common mode range. I'm not saying you'd whip out a pic for just that job, but many of my projects already have one with some spare pins available and it's a nice trick in that case. And not only that, you can make it look like a variable R by switching from open to closed with some defined duty cycle, much faster than the signal in question, and lowpass out the HF noise from that later on.