Do multiplexers for photodiode arrays exist?

[e100]

A Google search turned very little.
Are analogue switches too leaky.
Are mechanical/reed switches the only viable option?


Mike

[Kleinstein]

CCD detectors are a kind of mulitplexer for photodiode arrays.

It depends on the current levels how much leakage you get, you just can not have very low on resistance and low leakage at the same time. So in principle CMOS switches could work with photo-diode arrays.

There are some switched intergrators to measure very small photo-currents - so there are really low leakage semicondctor switches (could be JFET or MOS). However the chips I know are rather expensive.

[Marco]

Just use a FET with sufficient (or some extra) capacitance. The current will go into the capacitor instead of leaking through it.

[T3sl4co1l]

Any device that performs "current steering" will do.  Assuming you don't need current integration right at the diode (which is what the CCD does: the integration is always in progress, with a sample-and-reset event every so often when you scan it).

A differential pair (using BJTs or FETs) can be generalized into a 1-of-N selector.  Drive the selected base/gate with logic high (assuming NPN/Nch and a sinking current tied to the common emitters/sources), and the others low.  (A standard e.g. 74HC238 will perform the 1-of-N selection.)  The current will be drawn through the respective collector/drain terminal.

An example application would be a tuned circuit on each output terminal, so that only radio signals that match up in frequency and in phase with the selector get detected.  Using a 1-of-4 counter/decoder, the outputs will be selected sequentially, in quadrature; if opposite pairs (0 and 2, 1 and 3) are linked to balanced tuned circuits, you have a synchronous quadrature detector!

Tim

[Silverio]

The key with photodiodes is to convert the current generated to voltage properly. Usually some amplification is done at the same time. In the past I've had some success using CMOS analog multiplexers for switching the signal coming from an opamp that converts the photodiode current to voltage.