NI PXI/PCI-5411/5431
Waveform Generation

The NI 5411/5431 generates waveforms in two modes: Arbitrary Waveform Generation and Function Generation. Use Arbitrary Waveform Generation mode for any arbitrary waveform generation, and use Function Generation mode for standard frequency generation such as sine, TTL, square, and triangular waveforms.

Arbitrary Waveform Generation mode, which has more features and is more flexible than Function Generation mode, allows you to define waveforms as multiple waveforms. You can link and loop these waveforms in any order you want. Function Generation mode is better for generating standard waveforms that are repetitive in nature, such as sine, TTL, square, and triangular waveforms. Function Generation mode limits you to one waveform, and the waveform size must be exactly equal to 16,384 samples.

The following figure shows a block diagram of the data path for waveform generation.

The data for waveform generation can come from either the waveform memory module or DDS lookup memory, depending on the mode of waveform generation. This data is interpolated by a half-band digital filter and then fed to a high-speed DAC. The data has a pipeline delay of 26 Sample clocks through this digital filter. Although the digital filter can be disabled through software, there is still a 26 Sample clock delay.

On the NI 5411/5431, the high-speed DAC is always updated at 80 MHz, but the maximum Sample clock for waveform memory is 40 MHz. The sample clock for the waveform memory can be further divided by a 16-bit counter. Therefore, the slowest sample rate is 40 MHz divided by 65,536, which is 610.35 Hz.

s Note  For Function Generation mode, the actual sample rate of the DAC is always set at 40 MHz.

• NI 5431

When using the NI-Video application programming interface, to achieve a maximum update rate of exactly 40 MHz, you must set the video waveform type to PAL with the software. If the setting is NTSC, the maximum sample rate is not exactly 40 MHz. When programming with NI-FGEN, the maximum sample rate is exactly 40 MHz.

• NI PXI-5411/5431

You can use an external clock source as the Sample clock. To avoid device problems, do not change the frequency of this clock during waveform generation. Change the frequency only before initiating the waveform generation. If any malfunction occurs, stop the waveform generation and reset the device to a known state before restarting.

NI 5411/5431 signal generators also support an internal high-resolution clocking mode. When you use this type of clock, you can set the Sample clock frequency to any value from 0–40 MHz with a resolution of approximately 40 mHz. This mode is useful for applications that require a precise clock source that is impossible with the default counter-based clocking scheme.