PXI-5441 Datasheet, PDF (2/7 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
Figure 1. Onboard Signal Processing uses the PXI-5441’s FPGA to perform in-line
processing of the waveform data stored in the module’s memory.
In addition to being an arbitrary waveform generator with
waveform sequencing capability, the PXI-5441 uses the OSP
functions to perform:
Quadrature digital upconversion with impairments
In quadrature upconversion, I and Q complex waveform data is
stored in waveform memory and is passed to the OSP block. OSP
then shapes and interpolates the data using the FIR filters,
interpolates it up to a high sample rate using the CIC filters, and then
upconverts the data to a programmable carrier frequency up to
43 MHz. You can choose to suppress the lower or upper modulation
sideband by adjusting the NCO in-phase and quadrature output
phase settings.
For modeling channel effects and testing the robustness of a receiver,
the OSP can add several impairments to the signal on the fly (during
waveform generation). IQ Gain Imbalance and DC offset
impairments are added by adjusting the per-filter gain and offset
settings, while quadrature skew and frequency error can be
introduced by adjusting the I or Q carrier phase and frequency.
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10.0M
15.0M
20.0M
25.0M
Frequency (Hz)
30.0M
35.0M
40.0M
Figure 2. Frequency spectrum of a W-CDMA physical layer signal digital
upconverted and generated by the PXI-5441 with Onboard Signal Processing.
(External sample clock = 92.16 MHz)
Baseband interpolation
Useful for generating smooth baseband signals, such as I and Q
signals, you can use the PXI-5441’s OSP block to interpolate low
sample rate waveforms to a much higher sample rate, thereby
improving the output frequency spectrum by relocating zero-order
sample-and-hold reconstruction images to higher frequencies. With
the images at higher frequencies, the PXI-5441’s 7th order low-pass
analog filter can greatly suppress them without disturbing the
signals’ amplitude response or phase information. For example,
a waveform created at 10 kS/s sample rate could be interpolated to
10.24 MS/s by using 4x FIR interpolation and 256x CIC
interpolation. The upsampled signal is then passed to the DAC which
can also interpolate by 2, 4, or 8x resulting in an effective sampling
rate of 81.92 MS/s (8x DAC interpolation). Since the original
waveform was sampled at only 10 kS/s, rather than 81.92 MS/s, a
1:8,192 compression ratio is achieved, resulting in dramatically faster
waveform computation and download times. Alternatively, the
resulting compression can be used to efficiently store data in the
PXI-5441’s onboard memory allowing for much longer playback
times without streaming from arrays of high-speed disk drives. Long
playback times are essential for improving the statistical significance
of many communications measurements and displays such as bit
error rate, trellis plots, and constellation plots.
Amplitude modulation (AM)
By using only the in-phase (I) path of the OSP block, you can
generate an AM radio signal by directly downloading the message
signal into onboard memory. The message signal scales the
amplitude of the NCO’s programmable frequency output.
Single tone and function generation
Using the OSP block’s NCO, the PXI-5441 can generate sine, square,
triangle, ramp and other standard and user-defined waveforms just
as function generator does. The frequency of the output waveform
may be adjusted during generation with 355 nHz resolution for
generating phase continuous frequency sweeps and hops. The phase
is also adjustable relative to other synchronized instruments, the
PXI 10 MHz reference clock or an externally supplied reference clock.
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