Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[Moved]: Using spare channels on front end of IC

Status
Not open for further replies.

qingcong

Newbie level 4
Joined
Aug 11, 2010
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,335
So not 100% sure I understand the problem I am going to ask, but I will give it a stab and see if it makes sense to anyone else.

The problem:
We have 4 electrical inputs that will go into an 8 channel analog front of an IC. Only 2 these electrical inputs are active at a time, but we wish to use all channels on the IC to improve performance (by improving performance I assume that means signal integrity, signal:noise, or something along those lines). The solution will involve multiplexing the 4 inputs that go into the 8 channel IC somehow.

My interpretation:
I'm guessing the solution is to multiplex it such that if electrical input 1 and input 2 are active, then input 1 will go into 4 channels on the IC and input 2 will go into the remaining 4 channels of the IC, BUT I'm not sure about this. Does anyone have a different interpretation of the problem and/or have a different solution?
 

What do you think you are going to improve by using
more channels?

Since only one at a time is selected, you will not be
improving on-resistance. The inputs do not act in
parallel for "on" conduction.

They do however act in parallel for shunt and series
leakage, capacitive loading. This is hardly ever beneficial.

Maybe paralleling could bring more ESD clamps into
play, if you are up against harsh input overstress
threats. But this seems like it ought to be handled by
something more explicitly suited to the role.

Now maybe redundancy could be useful to mitigate
intrinsic front end offset and drift (take the median
value, discard outliers) if each input has its own front
end amp in the "IC". but if the front end scheme
is all switches and a common front end amp / buffer,
no help there - switches don't contribute to offset
unless something is way bent. Not knowing anything
useful about this "IC" there's no way to judge that.

I would just tie the unused inputs to a ground or a
guard signal (if very low current) and put the guards
interdigitated with the signals so that signal-signal
coupling is reduced.

I don't have an interpretation of the problem because
the problem has not really been stated in a way that
tells me what the desired outcome, and the known
input challenges, are.
 

What do you think you are going to improve by using
more channels?



That's a good question and something I wasn't clear on either, however it is assumed in our problem statement that using the remaining channels will improve system performance. The people who wrote this problem statement have done it this way, so apparently they know the reasons, but I cannot ask them. I figured others on here might used this method of using spare channels and could shed some light on why it is done. So I guess there are two levels of solution to this problem - 1) the benefits to redundant channels and 2) how to implement it. I think I know 2), but not too clear on 1).
 

Okay scratch all of that. It is not the transducers that are only active 2 at a time. It is the 8 input channels on the IC. Only 2 channels on the IC are active at a time. So then we need to find a way to use the remaining 6 channels to improve performance. Does this make more sense?
 

I don't think that the question can be answered without knowing more about the transducer signal parameters and the kind of signal processing involved in the IC.

In some cases, parallel connection of signal channels can actually improve performance, e.g. if voltage noise is a limiting factor. In other cases, it might be meaningless or even worsen things.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top