Subject: Re: Current Source Multiplexer
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Date: Thu, 21 Nov 2002 14:45:27 GMT
NNTP-Posting-Date: Thu, 21 Nov 2002 15:45:27 MET
> I have a project about to start that requires the use of a current
> multiplexer. Specifically there are N current sources ranging between
> 1 nA and 10 mA, only one of which should appear at the output.
> Has anyone ever had to deal with a circuit like this? I am hoping for
> a circuit that will not degrade bandwidth or introduce error, even at
> 1 nA (impossible I know, but I can always hope:)
> Typical multiplexers I have seen are intended to operate on voltage
> sources and would have too high of a crosstalk (~25 dB) to be of much
> use for this design.
When you take a 16bit DA-converter with current output such as the AD420,
you have everything in one chip with 3ms settling time 0...20mA range with
300nA resolution. Better you won't make. you can take a second one and drive
a 1:1024 current mirror, but linearity and settling time will be worse.
What do you need a 10^7 range for? Testing a log amp or what?
You can always take (reed) relays to switch this kind of small currents or
diode rings, which are faster. But a lot depends on your test_object, which
will have a certain impedance at the input, preventing it to be fast.
electronic hardware designer