Why Does PXIe-5122 Bandwidth Equal Its Sampling Rate?

Issue Details

The NI product page for the PXIe-5122 shows that the maximum sampling frequency is 100 MHz, which makes me wonder why the analog bandwidth is also listed as 100 MHz. For the PXIe-5922, the bandwidth is defined as 0.4 times the sampling frequency, which seems more reasonable. But in the case of the PXIe-5122, the bandwidth and maximum sampling frequency are the same.

Solution

The difference in bandwidth behavior between the PXIe-5122 and other modules like the PXIe-5922 is due to historical differences in the underlying technology used in NI oscilloscope modules.

Older modules like the PXIe-5122 use undersampling techniques, allowing them to capture signals in the second Nyquist zone. This is particularly useful in spectral measurement applications, where signals are repetitive and predictable.

At the time of the PXIe-5122’s development, it was not feasible to find analog-to-digital converters (ADCs) that offered 14-bit resolution with 100 MHz bandwidth while still meeting Nyquist sampling criteria.

As a result, the PXIe-5122 was designed with a bandwidth equal to its maximum sampling rate to maximize performance within those constraints.

Additional Information

Newer modules like the PXIe-5172 and PXIe-5163/5164 offer 14-bit resolution with 100 MHz bandwidth while adhering to Nyquist sampling. The FlexRIO product family (e.g., 5763/5764) also provides modern alternatives.