PXI-5441 Datasheet, PDF (3/7 Pages) National Instruments Corporation – 100 MS/s, 16-bit Arbitrary Waveform Generator with Onboard Signal Processing

100 MS/s, 16-bit Arbitrary Waveform
Generator with Onboard Signal Processing
DAC Interpolation
The NI 5441 uses digital interpolation to improve the output signal
quality of smooth waveforms. Every digital-to-analog converter
(DAC) produces reconstruction images in the frequency domain as
a result of the conversion process. Appearing at |f_o ± nf_s|, where f_o is
the frequency of the desired signal and f_s is the sampling rate,
reconstruction images are undesirable for smooth signals, such as
sine waves.
Typically, arbitrary waveform generators suppress the
reconstruction images by using high-order low-pass filters with
a cutoff frequency near the generator’s Nyquist frequency (50 MHz
for a 100 MS/s sample rate). By using a high-order filter with such
a low cutoff frequency, the filter’s non-idealities, such as passband
ripple and non-linear phase significantly affect the generator’s
performance. The NI 5441 uses digital interpolation to increase
the effective sample rate, relocating the reconstruction images to
higher frequencies.
duration is unknown before generation, a hardware or software
trigger can advance the generator to the next waveform in the
sequence. The NI 5441 implements advanced triggering behavior
with four trigger modes: single, continuous, burst, and stepped. For
a detailed discuss of these modes, please consult the NI Signal
Generators Help Guide available at ni.com/manuals.
Sequence Sequence
Sequence
Waveform Waveform _{• • •} Waveform _{Instructions Instructions • • • Instructions} Free
1
2
n
1
2
m
Memory
Figure 4. NI’s SMC-based arbitrary waveform generators increase test throughput by
storing all the waveforms and sequences required for a set of test in onboard memory.
NI’s SMC-based generators have the unique capability to store
multiple sequences and their associated waveforms in the generator’s
onboard memory (Figure 4). In automated test situations involving
multiple tests each requiring a different waveform sequence, all of the
sequences and waveforms can be downloaded once at the beginning
of the test cycle and held in the generator’s memory for the entire
session. By downloading all required waveforms and sequences once,
instead of repeatedly reloading them for each test, the SMC-based
generators save test time and improve test throughput.
Figure 3. Using a combination of digital interpolation and analog filtering, the NI 5441
greatly reduces the DAC reconstruction images as shown for the 10 MHz sine signal
generated at 100 MS/s using 4x interpolation for a 400 MS/s effective sampling rate.
(Noise floor is limited by the measurement device.)
By doing so, the required analog filter cutoff frequency is increased
which lessens the filter’s distortion effects. The combination of
digital interpolation and analog filtering enable the NI 5441 to have
excellent passband flatness and improved image rejection ensuring a
low-distortion output signal.
Timing and Synchronization
Using T-Clock synchronization technology, multiple NI 5441’s can
be synchronized for applications requiring a greater number of
channels, such as I/Q signal generation or multiple IF generation for
MIMO systems. Since it is built into the SMC, T-Clock can
synchronize the NI 5441 with SMC-based high-speed digitizers and
digital waveform generator/analyzers for tight correlation of analog
and digital stimulus and response. Using onboard calibration
measurements and compensation, T-Clock can automatically
synchronize any combination of SMC-based modules with less
than 500 ps_rms module-to-module skew. Greatly improved from
traditional synchronization methods, the skew between modules
does not increase as the number of modules increases. To achieve
even better performance, a high-bandwidth oscilloscope can be used
to precisely measure the module-to-module skew. Using the
oscilloscope measurement for calibration information, T-Clock can
achieve < 20 ps_rms module-to-module skew (Figure 5).
For sharp waveforms, such as square waves, pulses, and video signals,
interpolation and analog filtering can be disabled resulting in fast
rise/fall times and low pulse aberration (overshoot, undershoot, etc).
Waveform Sequencing and Triggering
The NI 5441 can be programmed to sequence and loop a set of
waveforms. Several methods can be used to advance through the
sequence of waveforms. In some cases, the duration of each
waveform is known in advance, so the generator can be programmed
to loop each waveform a specified number of times. When the
Figure 5. Using the Synchronization and Memory Core’s T-Clock synchronization,
multiple NI 5441 can achieve less than 20 ps channel-to-channel skew.
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