I have a requirement to use an analog multiplexer - however, all of the high-end existing solutions seem to have on resistance values of around 0.8ohms.
I need the multiplexer to have an on resistance of only a few milliohms - so, assuming my logic is correct - given one has enough MCU pins available, there's nothing to stop you putting together an array of MOSFETs to build an analog multiplexer is there?
Afterall, isn't that all a multiplexer is - albiet with some added control circuitry to allow you to interface via SPI or similar? I guess the only concerns are things like ensuring you having a high enough voltage to drive the gate above the source if using NMOS?
EDIT - Just realised, this may belong in the multiplexing forum...
No, you misunderstand transmission gates used in analog switches - these are not power MOSFETs with vertical
current flow, they have channels isolated from the substrate. This is essential to allow more than one device per
The kind of MOSFET you put together in pairs to make a transmission gate have horizontal
current flow, no built-in source-drain diode and much higher Rds(on) values than power MOSFETs (which are
always vertical current flow, have integral source-drain diode. 0.8ohms is close to the limit of the technology.
Power MOSFETs cannot share a die (unless they also have a common drain terminal) since the current flows from
source at the top to drain on the underside. The built-in diodes are intrinsic to the design, and the vertical current
flow is why you can get sub-milliohm on resistances at all.
However I'm not saying you can't use power MOSFETs to solve your problem, but it won't be as simple as a
Note that your 0.8ohm device may have a surprisingly good spec for the difference in resistance between
channels, which may be all you need to care about.