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Design >> Analog Design >> Analog multiplexer design
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Message started by manodipan on Sep 22^nd, 2008, 3:01am

Title: Analog multiplexer design
Post by manodipan on Sep 22^nd, 2008, 3:01am

Hi all,
Can you guys help me get some references on analog multiplexer design ....Thank you for your help...

Title: Re: Analog multiplexer design
Post by loose-electron on Sep 29^th, 2008, 2:35pm

I think it would be valuable if you could be specific about what you need here. The basics of the question get covered in a lot of books on the topic.

Title: Re: Analog multiplexer design
Post by manodipan on Sep 30^th, 2008, 3:19am

Hi ,
Actually Analog multiplexer consists of switches and decoders to turn the correct switch on.Now I want to have many channels for which i have to determine what is the optimum set (8:1 or 16:1 or some other option) for good system performance.

Title: Re: Analog multiplexer design
Post by Berti on Sep 30^th, 2008, 4:05am

So what is your question?

Title: Re: Analog multiplexer design
Post by manodipan on Oct 1^st, 2008, 2:12am

Hi Berti,
Actually i have to design a 1000 channel frontend and ADC for sensing very week signals.Now one way is to put a mux in front to select the channel and do processing later;and the other is after processing in frontend putting a mux before ADC.However i have not seen any literarature where mux is put in front.Now i think for week signals,those switches in mux may creaste problem like KT/C noise,charge injection etc.Which one do you think is better in terms of processing few uV signals??

Title: Re: Analog multiplexer design
Post by thechopper on Oct 1^st, 2008, 3:29pm

Hi manodipan,

Placing the switches at the front end might create the problems you mentioned if the sensed signal is coming from a very low impedance source. However, if the source impedance is comparable or higher than the one from your switch, then it might not be that problematic.
In other words if offset and noise are critical placing them at the input might not be a good idea.
The advantage of placing them there is that the signal swing is negligible and nonlinearity can be neglected (which might also hurt you).

At the output you can forget about the offset and noise contribution from the mux switches (assuming your front end gain is enough to consider so), but you might end up having some linearity problems due to large signal swings.

So I would make the choice based on the parameter that the switches compromise that is less important for your application.

Regards
Tosei