3

National Instruments • Tel: (800) 433-3488 • info@ni.com • ni.com

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

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.

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.

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

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

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.

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

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

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.

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.)

Waveform

1

Waveform

2

Waveform

n

• • •• • •

Sequence

Instructions

1

Sequence

Instructions

2

Sequence

Instructions

m

Free

Memory

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.