On a multiple-output waveform generator box, I want to have a test connector that can be programmed to snoop one of eight analog signals. The frequency range is up to about 1 MHz, and I'd like to keep the crosstalk down.
So I want an 8:1 mux that either grounds the unselected inputs, or has the equivalent of t-switches inside. I don't think I know the proper search terms for something like this.
Any suggestions for parts?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
for RF switches, absorptive is with 50R, reflective with 0R
if you can do you own selection logic, maybe adg902 ?
-Lasse
Yeah, something like the 902 would work, but an 8:1 mux would be nice, to save parts.
I was looking at ADG1208, which seems to have great crosstalk specs, until you see the test circuit, fig 36.
That's downright cheating. They get 6 dB for free with that extra 50 ohm resistor, and another 10 dB or so from the 100+ ohm switch "on" resistance working into the 50 ohm VNA.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
maybe a tree of adg936s ?
having multiple layers of switching should also help with isolation
-Lasse
Shorting the intermediate steps (out of phase with the connection) helps a lot, too. Capacitance, and all that.
Why not bring out all eight channels to a rotary switch? Isn't that cheaper, after you add in the display of which-signal-is-being-snooped? MOS switches are nice, but capacitance and series resistance make them unappealing sometimes.
On a sunny day (Fri, 17 Oct 2014 16:01:28 -0700) it happened John Larkin wrote in :
Sounds like you need to search for crossbar.
Maxim used to makes some nice video crossbar switches. I haven't looked, lately.
-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
Good old CD4051?
-- Silvar Beitel
Yeah, it's hard to beat a real switch, or a relay, for electrical performance.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
There are two main families of 8:1 mux's, the CD4051 types and the DG408 types. The 408s tend to be higher performance... wider bandwidth, higher voltage supplies, better protections, lower crosstalk.
It would be nice to mux +-10 volt signals, up to 1 MHz, with low crosstalk. Since this will be a scope monitor connector, the crosstalk can be whatever it is... I'd just prefer less.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
signals.
has
Don't you need to analyze figure 38?
?-)
I can isolate the signals with opamps, so I don't care about cross-coupling between mux inputs. But when I select one input channel to drive the output, I don't want to see others leaking into the output signal.
So s-d off coupling matters more than s-s coupling.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The DG538A claims internal T switch structure. Not sure about input range, I think +/-5V.
piglet
If you are using opamps to isolate the inputs, can you use opamps with a shutdown feature and only enable the one opamp that's needed?
Allan
That's how I made a screamingly fast sample-and-hold back in my youth, patents...
3,638,041 Sample and Hold Trigger Circuit3,643,110 Sample and Hold Circuit
PDF's available on my website. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I need four 8/1 test-output mux's, so that would be 32 opamps. It would work, but something simpler would be nice.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Perhaps roll your own T-switches using multiple 4053's? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Again, lots of parts.
If I can't find a great 8:1 mux, I'll just live with the best I can find. These are scope test outputs, so some crosstalk can be admitted and tolerated.
Hard rotary switches are still a possibility, if we can make room on the small panel.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Nice part. Yes, it does have t-switches. Thanks.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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