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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: MOSFET Analog Switch Question
Date: Mon, 21 Apr 2025 11:33:47 -0700
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On Mon, 21 Apr 2025 11:38:01 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 2025-04-20 00:46, john larkin wrote:
>> On Sat, 19 Apr 2025 12:48:23 -0800, Christopher Howard
>> <christopher@librehacker.com> wrote:
>> 
>>> Hi, I have some DG212BDJ Quad SPST CMOS Analog Switches. I am wondering
>>> if there is some significance, for each switch, to how the source and
>>> drain pins are used/fed. The data sheet says Analog Signal Range
>>> (V_Analog) is +/- 15 V, so it doesn't matter which way the current is
>>> moving across source and drain pins, right?
>>>
>>>
>>> Christopher Howard
>> 
>> It should be symmetric, happy conducting in either direction.
>> 
>> Don't let the signals go beyond the rails.
>
>Yup.  Otherwise, typically all the channels will get connected together 
>by way of the substrate.  It's a puzzle to debug, the first time it 
>happens to you--it's always the channel you're not focusing on that's 
>railed. ;)

Exactly. And the series fets will start to conduct before the ESD
diodes clamp the swing.

Roger the first-time perplexity.


>
>If you're worried about linearity, do note the switch resistance vs. 
>signal voltage curves, which are usually sort of moustache-shaped.

Don't load the switches if you want linearity.

>
>To avoid signal distortion, don't draw significant current through an 
>analog switch.

I just said that!

Charge injection is fun too. Drives some opamps bonkers.


>
>Cheers
>
>Phil Hobbs