National Instruments 779655-01 PXI Waveform Generator

The 779655-01 is a 20 MHz function generator under the PXI‑5402 model series by National Instruments. It has one channel of output that uses a BNC connector type. This waveform generator can generate a wide variety of signals, including new signals like pseudorandom noise and DC signals, in addition to typical functions like sine, square, triangle, and ramp waveforms.

Using direct digital synthesis (DDS) technology, the 779655-01 can accurately create signals ranging from -5 V to +5 V with a DAC resolution of 14 bits. With an output voltage of up to ±5 V (ACpk + DC), it offers versatility for a range of applications. The amplitude range is 5.64 mVpk-pk to 10 Vpk-pk for a 50 Ω load and 11.28 mVpk-pk to 20 Vpk-pk for a high-impedance load, depending on the load impedance.

With an AC amplitude accuracy of +2.0% of amplitude +1 mV and -1.0% of amplitude -1 mV, as well as an offset accuracy of ±0.5% of offset ±2 mV, this waveform generator guarantees great signal production precision. In addition, it has waveform summing capabilities to combine the outputs of several signal generators and software customizable output impedance (50 Ω or 75 Ω).

The 779655-01 features a Phase-Locked Loop (PLL) Reference Clock with sources such as REF IN and PXI_CLK10 for accurate triggering and synchronization. It provides frequency accuracy with a lock time of 70 ms (normal) and 200 ms (maximum), depending on the PLL Reference Clock source. There are choices for edge detection, a minimum pulse width of 25 ns, and support for a variety of trigger sources and modes, including Single, Continuous, Stepped, and Burst modes.

Accuracy maintenance over time requires calibration, and the 779655-01 provides both external and self-calibration options. Software-initiated self-calibration takes about 105 seconds to finish and makes use of an integrated 24-bit ADC and precise voltage reference. Using calibration constants stored in nonvolatile memory, external calibration sets the voltage reference, ADC, and VCXO, among other components. In order to maintain specifications, calibration should be done no later than two years after the last external calibration.