[sdiy] How to use an analog time-domain multiplexer?

Mike Bryant mbryant at futurehorizons.com
Fri Jun 4 13:10:40 CEST 2021


Totally agree with you.

Back before digital telecoms, analogue time multiplexing was tried but in the end frequency multiplexing (FDM) where each signal was shifted up to a higher frequency band turned out to be far better.


From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of The SynthiMuse via Synth-diy
Sent: 04 June 2021 11:35
To: Michael Zacherl
Cc: synth-diy
Subject: Re: [sdiy] How to use an analog time-domain multiplexer?

If I could put my 1/2 groats worth of input to this, my advice would be : please don't.
Digital comms would be the only reasonable answer to this, I believe.

A processor fast enough to read your analog channels and mux them in to a digital stream that could be sent around internally and the data picked off by small processors that can handle the comms and do local conversion back to analog with its internal dac. The ST arm chips ( if available) have 12bit DACs, most cheap PICs have 10bit.
Another advantage of the digital approach is that you could scramble the data stream so that any noise created would be gaussian.
It would be non-trivial to do the above, but if you want lots of data over a single wire, digital is the only way, I feel.
Trying to get it all working in the analog domain would be non-trivial-squared.
Just my opinion.
Gerry Murray

On Fri, 4 Jun 2021, 11:19 Michael Zacherl, <sdiy-mz01 at blauwurf.info<mailto:sdiy-mz01 at blauwurf.info>> wrote:

> On 04.06.2021, at 10:49, Tom Wiltshire <tom at electricdruid.net<mailto:tom at electricdruid.net>> wrote:
>
>
>> On 4 Jun 2021, at 09:42, Michael Zacherl <sdiy-mz01 at blauwurf.info<mailto:sdiy-mz01 at blauwurf.info>> wrote:
>>
>>
>>> On 04.06.2021, at 10:14, Tom Wiltshire <tom at electricdruid.net<mailto:tom at electricdruid.net>> wrote:
>>>
>>> For the bandlimiting filter, I don’t think it matters so much.
>>
>> Hi Tom, I don’t see why not?
>> What CC describes is the same process before an A/D-conversion and after a D/A-conversion, just without the binary part.
>> And IMHO of course Nyquist-Shannon applies here.
>
> Yes, of course it does. All I meant was that I don’t think the bandlimiting filter is so fussy about whether it should be Sallen-Key or MFB or whatever. For the reconstruction filter, I can see reasons why it should be MFB.

ok, I hear you! I just don’t see a Sallen-Key filter being used for “brick-wall” duties.

> But definitely both filters are needed, and this is exactly a sampling process without the ADC/DAC step.


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