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.

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.

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.

–25.0

–30.0

Frequency (Hz)

10.0M

15.0M

20.0M

25.0M

30.0M

35.0M

40.0M

–105.0

–95.0

–85.0

–75.0

–70.0

–60.0

–50.0

–40.0

–100.0

–90.0

–80.0

–65.0

–55.0

– 45.0

–35.0

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)