multiplexing five analog signals  - Page 1
Forum section: electronics / general

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 01:29:18 pm
content: so, I have to multiplex five analog signals in the range of -2V..2V from { Source0, Source1 } to Target0Target0 <= mux( Source0, Source1 ) on selectWhat do you suggest to physically implement the multiplexer? Micro-rele'?I have never done something similar, but I know it's similar to the technology used to implement KVM for computers.A KVM (that doesn't stand for Kernel virtual machine or similar staff) is a device that multiplex two or more computer's keyboard's and video's sources (from computers) to a physical input/output devices (the physical keyboard and mouse, and the CRT/LCD).Now, for the VGA, these signals, concerning the RGB, are analogic, while the synchronism is digital, as well as the PS/2 signals are completely digital.In my case, I have 5 analog signals... I can't use a KVM, but I can "copy" its idea

author: Marco
author_rank: Super Contributor
timestamp: June 15, 2018, 01:55:50 pm
content: What's wrong with some SPDT analogue switch ICs?

author: JPortici
author_rank: Super Contributor
timestamp: June 15, 2018, 02:19:24 pm
content: depending on the signal bandwidth it could be as simple as a CD4051

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 15, 2018, 02:23:26 pm
content: DC/AC-Frequency?Accuracy?Current?Source&Destination Impedance?Distance?

author: Marco
author_rank: Super Contributor
timestamp: June 15, 2018, 02:27:49 pm
content: Quote from: JPortici on June 15, 2018, 02:19:24 pmAFAICS he wants 5PDT, the 4051 (SP8T) is not very efficient to implement that.

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 02:40:31 pm
content: Source and Destination impedance is 50 OhmThere are 400-600 mm of distance between source and destination.The bandwidth is something like 100MhzThe signal range is -2V .. 2V, with a current of 20mA maxand good accuracy is mandatory.Not so easy (for me)

author: JPortici
author_rank: Super Contributor
timestamp: June 15, 2018, 02:42:19 pm
content: you are right, i misread.i though 2x SP5T, not 5x SPDT. So, depending on the other parameters besides voltage range 2x 4053 may suffice-- Given the bandwidth i would probably use 5x SPDT relaysOtherwise I know that there are analogue switch ICs with 50 ohm paths for high bandwidth applications..

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 02:44:14 pm
content: the time to switch from source0 to source1 is also a constraint: must be inferior to 10u sec

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 02:51:21 pm
content: Quote from: legacy on June 15, 2018, 01:29:18 pmWhen I wrote Micro-rele', I meant SPDT relays, sorry for my lapses of memory(edit:I have to multi-task too much job, switching fromfield programmable Gatorades(fpga-s), to MPUs, to analog-fish&chips, and back again to digital-stuff .... and why on the why? I also have to write all the boring documentation that needs to be written? ... can't it be done by pretty secretaries?!? ... for sure my customers haven't yet understood this is the best way to see the label out of my office, "out for vacation")

author: Ian.M
author_rank: Super Contributor
timestamp: June 15, 2018, 02:56:08 pm
content: More questions that need to be answered by the O.P. for us to make useful suggestions:Do the signals need to be DC coupled?.Does your device have both positive and negative supply rails?.You certainly aren't going to get 10us switching times from mechanical relays, and unbuffered analog switches are problematic when you need 100MHz bandwidth and matched 50R impedance.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: June 15, 2018, 03:07:06 pm
content: I've done that for VGA signals with 4053s and it worked wonderfully. Are you sure you need 100 MHz bandwidth?

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 03:09:40 pm
content: > Do the signals need to be DC coupled?there is no DC component, and the min frequency is 20HzSay, the bandwidth is 20hz ... 100Mhz> Does your device have both positive and negative supply rails?yesQuoteYup. It's a damn problem, apparently (and conceptually) it sounds not tricky, but the more you look at constraints the more you understand it's complex. Anyway, I don't know WHY I have to handle even this task, I am not the right guy, I was looking at KVMs as examples, definitively they are not the good thing to look at, I mean I know someone solved this problem in some way for the company called "Discreet Logic" that provides solutions for SGI in the 2000s. If you name SGI and Discreet Logic in the same sentence ... you are sure you are not talking about a piece of cake

author: legacy
author_rank: Super Contributor
timestamp: June 15, 2018, 03:15:54 pm
content: Quote from: GeorgeOfTheJungle on June 15, 2018, 03:07:06 pmNot sure, I have never seen a single wave crest for any frequencies above 50Mhz by attaching the probe of my spectrum analyzer in what the customer sent to me, and the spectrum of their testing equipment seems condensed around 30Mhz, but it's written in the customer's letter as a constraint "needed" - they wrote -100Mhz of bandwidth.I have to phone them to have a confirm

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 15, 2018, 03:19:25 pm
content: The DC or 20Hz makes it expensive, normal RF switches start at 300KHz - 10MHz and can be had for under $1. However, because you need DC you need something like 5 of those:https://nl.mouser.com/datasheet/2/609/HMC545A_545AE-760918.pdfThat's about $3 per piece...

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: June 15, 2018, 03:20:42 pm
content: Good, if 30 MHz might do:http://www.ti.com/product/CD4053Bthese work fine I can say for sure.

author: Marco
author_rank: Super Contributor
timestamp: June 15, 2018, 03:24:03 pm
content: Tons of ICs which can do it, how about 2xFSA2367. The ability to handle negative signals without a negative supply is convenient.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: June 15, 2018, 03:26:14 pm
content: If signals are AC coupled you don't need a negative supply.

author: David Hess
author_rank: Super Contributor
timestamp: June 15, 2018, 03:36:00 pm
content: Quote from: legacy on June 15, 2018, 02:40:31 pmWhoa, 50 ohm environment and 100 MHz bandwidth? That rules out practically all analog switch type multiplexers. 5 inputs is a rather inconvenient number.Relays are the easiest to understand solution.Linear Technology made some current feedback amplifiers which can multiplex their outputs that would be perfect for this but they are now hidden and unfindable in Analog Device's selection guides.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 15, 2018, 04:34:55 pm
content: Something like this may be close to what you need:http://www.analog.com/en/products/switches-multiplexers/buffered-analog-multiplexers/adv3222.html#product-overview

author: joeqsmith
author_rank: Super Contributor
timestamp: June 19, 2018, 12:06:59 pm
content: I have no idea what country you are in but you could look at the vintage 59307A off eBay. Simple to program if you are already setup for GPIB. Even if you don't, you may be able to just use the relays from them.

author: Gibson486
author_rank: Frequent Contributor
timestamp: June 19, 2018, 07:15:33 pm
content: I used the SPI version of this before to make a multplexing AVR porgammer.http://www.analog.com/media/en/technical-documentation/data-sheets/ADG726_732.pdf

author: MT
author_rank: Super Contributor
timestamp: June 19, 2018, 11:15:29 pm
content: There used to be analog RF multiplexers around. Harris

author: splin
author_rank: Frequent Contributor
timestamp: June 20, 2018, 12:23:31 am
content: Quote from: Marco on June 15, 2018, 03:24:03 pmOmly 10dB of off isolation at 100MHz. Worse still 55pF on capacitance = 58MHz BW when driven from 50 ohm source.How about OPA3875 triple 2:1 video mux?Or TS3USB221? 1.1GHz BW, 6pF Con. Approx -55dB crosstalk and off isolation at 100MHz. Vcc max is 3.6V but can switch 5V signals. Ron rather high at 6 ohms, but with only 6pF you could afford to parallel several.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: June 21, 2018, 06:31:31 am
content: I thought that perhaps Video switch matrix ICs would do.Searching for that I ran into this:http://www.datasheetlib.com/datasheet/99336/sky13299-321lf-evb_skyworks-solutions.html

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 22, 2018, 12:58:42 pm
content: My first go would also be an analog switch aka 4051 / 4051 / 4053. There are lots of variants of these, and some variants go down to 5 ohm series resistance. Just saw a bunch of them in the EEVblog Teardown of the Rigol 1054Z ( EEVblog #650 or so from 2015), where these are used in the frontend.For signal integrity you probably want to add some buffer or line driver.

author: dmills
author_rank: Super Contributor
timestamp: June 22, 2018, 08:36:42 pm
content: A 'Bus Switch", likely from Fairchild springs to mind for some reason, FST series probably, maybe a couple of FST3125s or suchlike?Regards, Dan.

author: bullonwheels
author_rank: Contributor
timestamp: June 25, 2018, 03:37:35 am
content: I used the most used analog multiplexer CD4052. Best multiplexor for analog signals.

author: Geoff_S
author_rank: Regular Contributor
timestamp: June 25, 2018, 03:40:21 am
content: Would something like the Analog ADGS5414 work for you ?http://www.analog.com/media/en/technical-documentation/data-sheets/ADGS5414.pdf

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2018, 12:05:48 pm
content: The LT1398 and LT1399 were the parts I was thinking of and the datasheet shows an example of a 3 channel multiplexer made with an LT1399.

author: quickengprojects
author_rank: Newbie
timestamp: June 26, 2018, 10:58:23 am
content: As you are working with very low voltage, so it is preferred to pick the multiplexers with slightly high resistance that block too much current running from your circuit.