#1829

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IMSAI Guy

2 ай бұрын

Episode 1829 chip of the day
DG508 newer replacement
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Пікірлер: 25

@jimomertz 2 ай бұрын

The Keithley was reading about the same @6:33 !! It was 0.212kohm You crack me up the way you hand wave over it “oh it has a different burden voltage and the electrons are higher up there on the bench” 😅

@user-se5jc3gw1y 2 ай бұрын

Intercontact capacitance in the breadboard is something I've ran into before.

@mikebond6328 2 ай бұрын

What other kinds of capacitance should we worry about?

@silverXnoise 2 ай бұрын

Hydrogenated capacitance is very bad for your cholesterol.

@IMSAIGuy 2 ай бұрын

brain capacitance

@andymouse 2 ай бұрын

@@silverXnoise Like saturated fat capacitance.

@user-se5jc3gw1y 2 ай бұрын

@@mikebond6328 I just measured capacitance of about 2 pf between adjacent board contacts. It really depends on the component type, pin layout and the upper frequency you expect to see in your circuits. If your doing something at say 50MHz and/or need to maintain fast edges, one might consider avoiding these proto boards. I've been bit by them before.

@Penfold42 2 ай бұрын

Would be fun to sweep it on the nanoVNA

@edmaster3147 2 ай бұрын

Always great how casual the device gets critically inspected using the test-setup. Thank you, it's a great way of learning and I really enjoy it.

@herbertsusmann986 2 ай бұрын

Were you terminating that feed coax in 50 Ohms? If not, the higher frequency dips and bumps probably are not 100% real. I would have terminated the coax with 50 Ohms right at the input to the multiplexer. Also some resistance at the output of the mux is probably a good idea also, maybe 10K??

@g0ozs 2 ай бұрын

Maxim also used to do a combined analogue multiplexer and buffer amplifier for video applications as the MAX453, 454 and 455 which are better for high frequency work. They would be worth a video if you can get them - they work up to 25MHz or so and have good isolation between channels - sadly they are not still in production. The switching speed of these - 120ns or better - was also very good and in my work allowed timesharing of a single ADC for low MHz waveforms.

@mtwieg24 2 ай бұрын

Very recently I was working with another Maxim 8:1 analog mux and discovered an apparent silicon bug. Basically, whenever the mux switches, the chip sinks a large (sometimes nearly 10mA) current for a brief time (around 0.5us) from the path being turned off. This happens before the switch breaks, so it's effectively from the COM pin to GND. Datasheet makes no mention of this, and describes itself as break-before-make (technically true if you don't consider this glitch current to be a "make"). Might want to check if these chips suffer a similar issue.

@sefarkas0 2 ай бұрын

Put a resistor from out to gnd, to improve off leakage.

@transfunktionator 2 ай бұрын

The 14 MOhm on the Keithley look fishy. The 2015 supplies about 7V (Uref) via a ~10Meg resistor and measures the voltage drop in the high resistance ranges. With 20 pA leakage current, you should be in the GOhms, which the 2015 can't measure.

@markrages 2 ай бұрын

That's an $8 part. Not particularly cheap. Compare specs with ISL8405 or ADG series if you don't need 30V supplies.

@AnalogDude_ 2 ай бұрын

You lucky one, grab bag. Is that a big shop?

@IMSAIGuy 2 ай бұрын

kzfaq.info/get/bejne/jbmaotKVmNybhH0.htmlsi=63FsZql8EKg8Vhi6

@chronicfatigue5416 2 ай бұрын

You didn't show it as a mux/demux. Use two, put four signals into one and see if you get them out of the other.

@Bdix1256 2 ай бұрын

What store are you going to? I used to go to Fry’s and some surplus stores but they all closed. I’m in San Jose.

@IMSAIGuy 2 ай бұрын

kzfaq.info/get/bejne/jbmaotKVmNybhH0.htmlsi=63FsZql8EKg8Vhi6

@Bdix1256 2 ай бұрын

Thanks

@justinmijnbuis 2 ай бұрын

Would the characteristics be the same for both directions?

@IMSAIGuy 2 ай бұрын

yes

@jerrys2292 2 ай бұрын

In most of not all situations yes. The the analog switch circuit used is symmetrical. 2 p-channel mosfets with gates connected and 2 n-channel mosfets with gates connected, connect all sources, in/out terminals are 1 n-channel drain and 1 p-channel drain connected, driving n-channel gates to a higher voltage than the p-channel gates turns it on, you want to use opposing square waves, voltages above/below voltages applied to in/out turns on only n-channel/p-channel mosfets, power supply limit is your smallest vgs max for your mosfets, Sources are essentially floating and so should be given a DC discharge path, preferably to ground, through a large ish resistor, hundred's of k, or anti-parallel diodes to both power rails