# What is an adc with pseudo-differential inputs?

J

#### [email protected]

Jan 1, 1970
0
Hi. I've done some reading (eg Horowitz & Hill and other books), but I
can't find an explanation to what pseudo-differential inputs is. Could
someone explain or direct me to an application note?

Thanks

Juan Herrera

C

#### Chris

Jan 1, 1970
0
Hi. I've done some reading (eg Horowitz & Hill and other books), but I
can't find an explanation to what pseudo-differential inputs is. Could
someone explain or direct me to an application note?

Thanks

Juan Herrera

Hi, Juan. Pseudo-differential inputs means the ADC actually has two
inputs. The ADC measures both inputs, then calculates and gives you
the difference between the two.

You have to be aware that pseudo-differential input range doesn't mean
the same thing as input range. You can have single supply +5V ADCs
which advertise an input range of +5V to -5V. This merely means the
difference between the two inputs -- you're still limited to a 0 to
+5V amplitude on either input.

Good luck
Chris

B

#### Bob Masta

Jan 1, 1970
0
Hi, Juan. Pseudo-differential inputs means the ADC actually has two
inputs. The ADC measures both inputs, then calculates and gives you
the difference between the two.

You have to be aware that pseudo-differential input range doesn't mean
the same thing as input range. You can have single supply +5V ADCs
which advertise an input range of +5V to -5V. This merely means the
difference between the two inputs -- you're still limited to a 0 to
+5V amplitude on either input.

Maxim has a discussion of differential and pseudo-differential inputs
at:
http://www.maxim-ic.com/appnotes.cfm/an_pk/1108

Note that the advantage of true differential inputs is that any
common mode noise is removed automatically by the implicit
subtraction of the + and - inputs. Pseudo-differential typically
doesn't do that (or at least, not as well) since the + and - channels
are independent and are typically not converted at the same time.
So only low frequencies and DC are removed by this method...
but that's still useful for devices that have DC common mode
present, like strain gages, etc.

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator

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