Chapter 3 Analog Output© National Instruments Corporation 3-3 E Series User ManualPolarity Selection(NI 6020E, NI PXI-6030E, NI PCI-6031E, NI PXI-6040E, NI 6052E, PCI-MIO-16E-4,and PCI-MIO-16XE-10 Devices Only) With these devices, you can configureeach AO channel for either unipolar or bipolar output. All other E Seriesdevices are configured for bipolar output only. A unipolar configurationhas a range of 0 to V ref at the analog output. A bipolar configuration has arange of –V ref to +V ref at the analog output. Vref is the voltage referenceused by the DACs in the AO circuitry and can be either the +10 V onboardreference or for supported devices, an externally supplied reference within±11 V. You do not need to configure both channels for the same range.Selecting a bipolar range for a particular DAC means that any data writtento that DAC is interpreted as two’s complement format. In two’scomplement format, data values written to the AO channel can be eitherpositive or negative. If you select unipolar range, data is interpreted instraight binary format. In straight binary mode, data values written to theAO channel range must be positive.Reglitch Selection(NI 6052E and NI 6070E/6071E Devices Only) In normal operation, a DACoutput glitches whenever it is updated with a new value. The glitch energydiffers from code to code and appears as distortion in the frequencyspectrum. Each analog output contains a reglitch circuit that generatesuniform glitch energy at every code rather than large glitches at the majorcode transitions. This uniform glitch energy appears as a multiple of theupdate rate in the frequency spectrum. Notice that this reglitch circuit doesnot eliminate the glitches; it only makes them more uniform in size.Reglitching is normally disabled at startup and the software canindependently enable each channel.Minimizing Glitches on the Output SignalWhen you use a DAC to generate a waveform, you may observe glitcheson the output signal. These glitches are normal; when a DAC switches fromone voltage to another, it produces glitches due to released charges. Thelargest glitches occur when the most significant bit (MSB) of the DACcodeswitches. You can build a lowpass deglitching filter to remove some ofthese glitches, depending on the frequency and nature of the output signal.Visit ni.com/support for more information about minimizing glitches.
