Input considerations for SAR ADCs

RE: Input considerations for SAR ADCs

user4090349 — Mon, 03 Jul 2017 11:20:17 GMT

Hello, what will happen if I connect a full differetial signal to pseudo-differential ADC or if I connect a pseudo differential signal to full differential ADC

RE: Input considerations for SAR ADCs

BX27 — Wed, 04 May 2016 04:19:56 GMT

very good!

RE: Input considerations for SAR ADCs

Amit Kumbasi — Mon, 25 Aug 2014 18:14:58 GMT

Great question e-bird! It depends.

1. Typically, for fully differential input SARs, the common mode voltage Vcm = (AINP+AINM)/2 is fixed. There will be a row in the data sheet that shows the range for Vcm. You cannot connect signal to one input and ground the other (unless it is stated explicitly in the PDS) as the comon mode voltage will keep varying with the input.

2. For true-differential input SARs, you can connect single ended signals directly as the common mode voltage can vary (has to be be with in the spec). ADS8861/ADS8881 are some of the SARs that have true-differential inputs. By doing so a portion of the dynamic range will be lost.

3. In some SARs such as ADS8321/ADS8323, the inputs can be driven by single-ended signals or differential signals. This will be stated explicitly in the datasheet. Please note that in such devices, the REF voltage will be half of analog supply voltage (AVdd) and hence the overall dynamic range will be half of what can be achieved with fully differential devices where REF can go upto AVdd.

Hope that helps!

RE: Input considerations for SAR ADCs

e-bird — Thu, 21 Aug 2014 15:32:30 GMT

Nice article! For a fully differential input SAR ADC which requires complementary input, if I connect a single ended signal directly, will the SAR ADC still give the correct code with limited dynamic range, or the ADC won’t work at all with wrong code?

RE: Input considerations for SAR ADCs

DAVID FELIPE GARCIA — Tue, 01 Jul 2014 23:49:02 GMT

dispositivos fundamentales para el desarrollo electrónico

RE: Input considerations for SAR ADCs

Amit Kumbasi — Thu, 26 Jun 2014 21:47:15 GMT

Sure thing!

RE: Input considerations for SAR ADCs

Ahmet Cetin — Mon, 23 Jun 2014 20:33:29 GMT

Very informative. Thanks Amit.