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To JT : non T analog switches?

Actually, the standard 4053 and its copies do not have a T arrangement.

A few things on those datasheets. One, the NLAS4501 says SPDT, but it's clearly an SPST switch! (Use an NLAS1053 or NLAS4053 for SPDT.) Second, the NLAS323 datasheet says "Ultra Low < 5 pC Charge Injection," but hey, that's not even low, let alone Ultra-low! Sheesh! Those are cute parts, but go to Analog Devices for low and ultra-low charge injection, below 1pC.

--
 Thanks,
    - Win
Reply to
Winfield Hill
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I don't either, I'm not familiar with those part numbers.

I did the LVX4051, LVX4052, LVX4053. They have conventional switches, NOT T-arranged.

I referred to this once before...

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...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

A while ago I asked how analog switches could pump current in the following condition:

>Quizz: how do you pump fraction of a uA through the resistors with the > >switch wired as below? > > > > 4053 > > .------------. > > | | ___ > > | |--|___|- GND > > ___ | o---/| 50K > > GND -|___|--|---o--__ | > > 50K | o--- | ___ > > | \\|--|___|- GND > > '------------' 50K > > Good point, it probably IS charge injection. The measured effect of > that WOULD vary with R value, as John seems to be seeing.

That's pretty obvious in this configuration. But the real situation was

> > > 4053 > > .------------. > > | | > > | |--||- GND > > ___ | o---/| 1u > > GND -|___|--|---o--__ | > > 50K | o--- | > > | \\|--||- GND > > '------------' 1u >

How do you pump fraction of a uA through the resistor with the switch wired as above?

The answer is because the 4053 has 3 switches connected in a T arrangement to obtain high off isolation, the grounding switch conducting some of the injected charges to ground.

Now I need a SPST with low injected charges (pC order) switch with *no* T arrangement, and ultra low leakage (few pA order) and Ron under say 50R.

I'd like to not resort to the SD200 mosfets.

The Onsemi NLAS323 or NLAS4501 seems a perfect fit (typical 0.1pA to 1pA leakage, Ron = 10R, Qinj=0.4pC), except I don't know how they are designed.

Jim, I think you said you've designed some switches of the Onsemi series.

Do you have any info on thoses?

And there's one strange point in the datasheet, which is the Ron vs temperature.

--
Thanks,
Fred.
Reply to
Fred Bartoli

You could design better overload capability right into the preamp.

--
 Thanks,
    - Win
Reply to
Winfield Hill

Hello Win,

Or use quad diodes.

Regards, Joerg

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Reply to
Joerg

"Joerg" a écrit dans le message de news:uPUvf.42876$ snipped-for-privacy@newssvr29.news.prodigy.net...

it's

Second,

hey,

parts,

1pC.

Sorry Joerg, but I didn't give all the story. pA level leakage, low charge, but also few 10s of nV level thermal recovery, high isolation on high impedance and low noise. I'm afraid a diode bridge won't do.

This is for a sample&hold or more precisely a block and pass switch (don't know how to call that better) which will be ahead of my low noise preamplifier and will allow the DUT transient recovery analysis without suffering from the low noise preamplifier recovery. (few 10s nV accuracy after a 0.5V transient).

But I'm now more carefully looking at some AD parts I discarded before and a (very) few look promising.

--
Thanks,
Fred.
Reply to
Fred Bartoli

Hello Fred,

That may not be a job for diodes. Although you can achieve zero charge injection.

As Win said a saturation-proof amp would help. Also, look at T/R switches such as those used in ultrasound equipment. There we have to stomach pulses up to 200V and the receiver has to be able to hear the grass grow within a usec or so after that.

Regards, Joerg

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Reply to
Joerg

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