Suggestions wanted: 4x4 signal mux chip - Page 1
Forum section: electronics / projects

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 06:21:41 pm
content: I'm looking for suggestions for a chip.I have 4 digital signal lines, that I want to route to 4 IO lines off my board. I won't know in advance which are inputs and which outputs; some may even be purely bidirectional, so likely some kind of analog switch may be best here. I only need up to maybe 5V at 20MHz, nothing too high voltage or bandwidth. I'd like the ability to program in any permutation of which signal connects to which IO pin.A full 4x4 crossbar switch would work here, but it might be overkill for what I need. I don't fully need the arbitrary switching ability of a crossbar; I would suffice with four independent 1-of-4 mux switches, to select for each IO line, which signal drives it. Though I would really prefer to buy one single chip than fourCan anyone suggest something? My ideal chip would be four 1-of-4 mux switches, with common shared input lines, controlled by a serial line; say, writing 4 lots of 2bit values, one to drive each mux switch. That would be lovely. Will I find such a beastie? Does anyone know of something that might fit here?

author: Marco
author_rank: Super Contributor
timestamp: November 05, 2015, 07:00:08 pm
content: 4x4066?

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 07:05:39 pm
content: I don't fancy using a huge great FPGA just to perform some analog signal routingI'm aware of the 4066s, and I know I could stick four of them together to make a crossbar switch. Natively they'd need 16 bits of control information - I suppose I could attach two 74'595s and SPI out the 2 8bit bytes needed to set that up. But now that's 6 chips.Surely I can find just one chip to do this? My ideal block diagram looks like this:

author: bitslice
author_rank: Frequent Contributor
timestamp: November 05, 2015, 07:29:09 pm
content: Just put "crosspoint" into eBay searchhttp://www.ebay.co.uk/itm/321909760424DG844DN, 8x4 Wideband Video crosspoint array£2.50or a CD22101E, £3.50These things pop up all the time.

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 07:33:39 pm
content: Aha. Here's something that looks like it might do: an STMicroelectronics M22100.http://www.st.com/web/en/resource/technical/document/datasheet/CD00000471.pdf4x4 analog crosspoint switch. It has a slightly odd control interface though; you can write one bit of control information at a time by selecting a single switch address using the A/B/C/D lines, setting the required switch state on DI then strobing it in. Repeat a further 15 times for each other switch, to fully change the switch configuration. Hrm...I'd still prefer an SPI'ed one if I can find it...

author: bitslice
author_rank: Frequent Contributor
timestamp: November 05, 2015, 07:51:55 pm
content: Quote from: leonerd on November 05, 2015, 07:33:39 pmThat's a 10Mhz part, the DG844DN is a 300Mhz part.blob a 16pin PIC onto the side if you need SPI

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 08:02:02 pm
content: Ah yes, you're right - 10MHz. I see a Samsung pinwise equivalent that claims 40MHz though - the KT8592.The DG884DN looks like it could be a thing - a little overspec but at what seems to be £1 a chip I guess I can live with thatAnd yes, I can probably work around the odd control mechanism of it using some sort of MCU in front of it. This might be a winner...... if I can find a good source of it.

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 08:04:37 pm
content: Oh wait; on a closer reading of the DG884DN data sheet, it seems verymuch that it's built for being a unidirectional 8 inputs => 4 outputs selection. I'm wanting to switch bidirectional logic lines.

author: bitslice
author_rank: Frequent Contributor
timestamp: November 05, 2015, 08:06:46 pm
content: ^It says it can do negative signals, I thought that might imply bi-dir?Quote from: leonerd on November 05, 2015, 08:02:02 pmAh, so you are making say >100 of these things?I assumed this was a bench project or somethingHave a look at IDT then, they do some nice crosspoints

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 08:38:59 pm
content: It seems I'm unlikely to find exactly what I'm after in a single chip here. Hmm.OK so new plan - I could build this up using 4 4066-style chips, make the crossbar arrangement myself. I've then got 16 control lines that need fiddling somehow. I could stick two 74'595 chips on, I could use a single MCU of some kind...Or I could be a little fancier and wire up the board so that the actual permutations I want are all set by individual control lines - there's only a few specific arrangements I'll need, so I think I can probably wire-OR those together with a few diodes and whatnot. So maybe I only need 4 4066s in the end.

author: bitslice
author_rank: Frequent Contributor
timestamp: November 05, 2015, 08:56:31 pm
content: If you look at the app note for thishttp://www.alldatasheet.com/datasheet-pdf/pdf/169094/VISHAY/AN504.htmlit gives a resistive lumped model, to me that suggests the switching technology used is bidirectionaljust because it says IN->OUT, doesn't mean that is to be taken literally, not many people use crosspoints for anything other than routing.

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 09:01:56 pm
content: Huh. The AD75019 is a 16x16 version of exactly what I just described. At nearly £20 a pop it sounds a little expensive though.A more reasonable quarter-of-the-{size,price} is the ADG2188 - an 8x8 analog crosspoint. This one is I²C controlled but I can live with that. Still somewhat bigger than I had in mind, but that gives me space to expand perhaps

author: leonerd
author_rank: Regular Contributor
timestamp: November 05, 2015, 09:09:00 pm
content: Quote from: bitslice on November 05, 2015, 08:56:31 pmActually furthermore, the text does go on to call the chip a "bidirectional" crosspoint switch matrix. So maybe it is then...It would be nice if I could find anyone actually selling it though. Nothing on Farnell, that single auction on eBay. Mouser claims I can get them for £10 each but a minimum order quantity of 300.The ADG2188 is starting to look like my best shot here.

author: bitslice
author_rank: Frequent Contributor
timestamp: November 05, 2015, 09:42:58 pm
content: Like I said these pop up all the time, I missed out on a box of IDT16x16 because I was still thinking about it.Another auctionhttp://www.ebay.co.uk/itm/261614618710no idea of his stock levels but more than 10 at leastsame for the CD22101E, multiple people are selling them,and if you look you'll see there are lots of different types of crosspoint on offer.how many do you need?