Chapter 5 Analog Output
NI 6124/6154 User Manual 5-2 ni.com
The main blocks featured in the S Series analog output circuitry are as
follows:
•AO FIFO—The AO FIFO enables analog output waveform
generation. It is a first-in-first-out (FIFO) memory buffer between the
computer and the DACs that allows you to download all the points of
a waveform to your board without host computer interaction.
•AO Sample Clock—The DAC reads a sample from the FIFO with
every cycle of the AO Sample Clock signal and generates the AO
voltage. For more information, refer to the AO Sample Clock Signal
section.
•Isolation Barrier and Digital Isolators—(NI6154 Only) The digital
isolators across the isolation barrier provide a ground break between
the isolated analog front end and the chassis ground. For more
information about isolation and digital isolators, refer to the NI 6154
Isolation and Digital Isolators section of Appendix A, Device-Specific
Information.
•DAC—Digital-to-analog converters (DACs) convert digital codes to
analog voltages.
Minimizing Glitches on the Output Signal
When you use a DAC to generate a waveform, you may observe glitches
on the output signal. These glitches are normal; when a DAC switches from
one voltage to another, it produces glitches due to released charges. The
largest glitches occur when the most significant bit (MSB) of the DAC code
switches. You can build a lowpass deglitching filter to remove some of
these glitches, depending on the frequency and nature of the output signal.
Visit ni.com/support for more information about minimizing glitches.
AO Data Generation Methods
When performing an analog output operation, there are several different
data generation methods available. You can either perform software-timed
or hardware-timed generations:
•Software-Timed Generations—With a software-timed generation,
software controls the rate at which data is generated. Software sends a
separate command to the hardware to initiate each DAC conversion. In
NI-DAQmx, software-timed generations are referred to as On Demand
timing. Software-timed generations are also referred to as immediate
or static operations. They are typically used for writing a single value
out, such as a constant DC voltage.