Pseudo Differential Inputs and Interval Sampling

[ASharma]

I have two separate but related questions:

1.  Several posts in this Discussion Forum state that the negative terminal of a Pseudo Differential signal is connected to ground through a capacitor in order to filter out AC and leave DC.  However this recent tutorial on

[ASharma]

Sorry for the botched question from earlier...

Several posts in this Discussion Forum state that the negative terminal of a Pseudo Differential signal is connected to ground through a capacitor in order to filter out the AC and leave the DC.  However this recent tutorial on ni.com states that the negative terminal is connected to ground through a low value resistance (not a capacitor) in order to act as a bias resistor:  http://zone.ni.com/devzone/cda/tut/p/id/6962.  Which is right?

Thanks in advance...

[RT4CY]

Thanks for posting on the NI forums!  You can use a capacitor in parallel with a bias resistor in order to further reduce noise.  However, you can technically have a pseudo differential input configuration without this capacitor.  As long as there is a resistor between AI 0- and ground, you are providing a path to ground for the bias current.

Take a look at the Field Wiring developer zone article.  As you can see in Table 1, two resistors provide return paths to ground for bias currents in differential mode.  The main difference (physically) is that pseudo differential mode provides a return path to ground only for the negative lead.

[ASharma]

Thanks!