Using PSpice's DigStim for Analog Signals

[Bob Penoyer]

I'm having trouble using/understanding the use of DigStim.

DigStim1 under Capture appears to offer analog functions (EXP, PULSE,
PWL, SFFM, and SIN) as well as digital functions (Clock, Signal, Bus)
options in the New Stimulus window. But when I create an analog
stimulus and run PSpice, I get meaningless output.

For example, if I create a PULSE stimulus and simply connect a probe
to the output, I get a digital probe output (with a black probe at the
output) in which the logical output appears to be indeterminate. If I
connect the DigStim1 output to a resistor to ground, the probe is then
green (i.e., analog) but the result is a constant voltage of about
1.35V for a set of 3.5V pulses.

PULSE, EXP, etc. plot out in the DigStim1 editor as expected after
completing the Attributes assignments. But I don't see these
characteristics when I run PSpice.

What, if anything, am I doing wrong?

 

[Jim Thompson]

I'm having trouble using/understanding the use of DigStim.

DigStim1 under Capture appears to offer analog functions (EXP, PULSE,
PWL, SFFM, and SIN) as well as digital functions (Clock, Signal, Bus)
options in the New Stimulus window. But when I create an analog
stimulus and run PSpice, I get meaningless output.

For example, if I create a PULSE stimulus and simply connect a probe
to the output, I get a digital probe output (with a black probe at the
output) in which the logical output appears to be indeterminate. If I
connect the DigStim1 output to a resistor to ground, the probe is then
green (i.e., analog) but the result is a constant voltage of about
1.35V for a set of 3.5V pulses.

PULSE, EXP, etc. plot out in the DigStim1 editor as expected after
completing the Attributes assignments. But I don't see these
characteristics when I run PSpice.

What, if anything, am I doing wrong?

Using Capture.

Seriously, read up on A/D interface selection.

...Jim Thompson

 

[Charlie Edmondson]

I'm having trouble using/understanding the use of DigStim.

DigStim1 under Capture appears to offer analog functions (EXP, PULSE,
PWL, SFFM, and SIN) as well as digital functions (Clock, Signal, Bus)
options in the New Stimulus window. But when I create an analog
stimulus and run PSpice, I get meaningless output.

For example, if I create a PULSE stimulus and simply connect a probe
to the output, I get a digital probe output (with a black probe at the
output) in which the logical output appears to be indeterminate. If I
connect the DigStim1 output to a resistor to ground, the probe is then
green (i.e., analog) but the result is a constant voltage of about
1.35V for a set of 3.5V pulses.

PULSE, EXP, etc. plot out in the DigStim1 editor as expected after
completing the Attributes assignments. But I don't see these
characteristics when I run PSpice.

What, if anything, am I doing wrong?

Bob,
the DigStim1 is a stimulus editor part, something that Jim doesn't fool
with. He used traditional stim1(or 4, or 8, etc.) parts when he needs a
digital stimulus. He also uses a Vpulse when he needs a pulse waveform,
and other basic parts. For an old master, they are much easier to set
up, and are a lot less confusing.

In your case, you opened the stimulus editor, and added a new stimulus
to the file. You also gave it a name. If you look at the digstim1
part, you will notice an IMPLEMENTATION property. This would be the
name of the stimulus you just created. However, it need to be digital,
not analog, since this is a digital part. If you want an analog pulse
waveform, use a VSTIM part.

Charlie

 

[Bob Penoyer]

On Thu, 03 Aug 2006 09:10:08 -0700, Charlie Edmondson

In your case, you opened the stimulus editor, and added a new stimulus
to the file. You also gave it a name. If you look at the digstim1
part, you will notice an IMPLEMENTATION property. This would be the
name of the stimulus you just created. However, it need to be digital,
not analog, since this is a digital part. If you want an analog pulse
waveform, use a VSTIM part.

Thanks for your response. Apparently, Cadence provides both the
digital and analog stimulus selections in one window, the New Stimulus
window. It would have made a lot more sense to provide digital choices
for the digital stimulus and analog for analog.

Thanks again for your help.