Are digital inputs of data acquisition devices differential or single ended?

Question

I read that in almost all daq board datasheets the analog inputs are specified as single ended or differential inputs.

But the same daq have digital I/O ports. How can one understand whether the digital input is differential ended or single-ended. Or are the default one of them?

For example from a manual:

16 single-ended (SE) or eight differential (DIFF) analog input channels

Eight individually configurable digital I/O channels

As you see the differential or single input nature of the analog inputs are specified. But for digital inputs no information.

How is CM noise for a digital signal rejected ?

Which one of the opamp represents digital input?:

Edit:

The black is the pulse waveform below, and the red is the noise superimposed on it. So if the system were diff ended and inputs were diff ended the red CM noise would be rejected. But for digital inputs red will never be rejected since it is swinging between the thresholds?:

Answer 1

There will be no single/differential end digital i/o 's

1. single end: Measure the voltage between the input signal and analog ground.

2. differential end: measure the voltage between two distinct input signals.

digital inputs will be either HIGH/LOW with respect to Ground

CM noise rejection: actually lets say there is a bridge sensor. The sensor measurement of ADC is independent of the low level ground which makes it more free of noise. The reason for this is that the noise source is present on both signal leads and when in differential mode only the difference between the two leads is measured.

Regarding your both the images

first image is differential ended analog input

second one is single ended analog input

if a digital signal heve noise lets say, but

it will receive that data as

since usually in most of

TTL cirucits

0 to 0.8V - LOW

2 V to VCC - LOW

if in cmos

0 to 1/3VCC - LOW

2/3 to VCC - HIGH

there is a lot of width b/w LOW and HIGH