System and method for measuring modulation distortion error vector magnitude (EVM) of a device under test (DUT)

A system for measuring modulation distortion (MD) error vector magnitude (EVM) of a device under test (DUT), the system comprising:

• a power splitter configured to split a radio frequency (RF) signal output by the DUT into a first RF signal and a second RF signal;
• a first channel configured to acquire and digitize the first RF signal without demodulating the first RF signal;
• a second channel configured to acquire and digitize the second RF signal without demodulating the second RF signal;
• a processing unit and a memory storing instructions that, when executed by the processing unit, cause the processing unit to:
• perform time alignment, phase alignment and complex equalization of the first RF signal from the first channel and the second RF signal from the second channel;
• measure first MD error vectors of the equalized first RF signal and second MD error vectors of the equalized second RF signal;
• perform cross-correlation of the first and second MD error vectors across the first and second channels to provide cross-correlated MD error vectors of the RF signal output by the DUT;
• average the cross-correlated MD error vectors over symbols and packets of the RF signal;
• and
• divide the averaged cross-correlated MD error vectors by signal power of an ideal signal to obtain cross-correlated MDEVMs over a time period or bandwidth of a waveform of the RF signal,
• wherein performing the cross-correlation of the first and second MD error vectors and averaging of the cross-correlated MD error vectors suppress contribution of uncorrelated noise introduced by the first and second channels to the first and second MD error vectors, respectively.

A non-transitory computer readable medium storing instructions for measuring modulation distortion (MD) error vector magnitude (EVM) of a device under test (DUT) that outputs a radio frequency (RF) signal, which is split by a power splitter into a first RF signal and a second RF signal, wherein the first RF signal is acquired and digitized in a first channel without being demodulated and the second RF signal is acquired and digitized in a second channel without being demodulated, wherein when executed by a processing unit, the instructions cause the processing unit to:

• perform time alignment, phase alignment and complex equalization of the first RF signal from the first channel and the second RF signal from the second channel;
• measure first MD error vectors of the equalized first RF signal and second MD error vectors of the equalized second RF signal;
• perform cross-correlation of the first and second MD error vectors across the first and second channels to provide cross-correlated MD error vectors of the RF signal output by the DUT;
• average the cross-correlated MD error vectors over symbols and packets of the RF signal;
• and
• divide the averaged cross-correlated MD error vectors by signal power of an ideal signal to obtain cross-correlated MDEVMs over a time period or bandwidth of a waveform of the RF signal,
• wherein performing the cross-correlation of the first and second MD error vectors and averaging of the cross-correlated MD error vectors suppress contribution of uncorrelated noise introduced by the first and second channels to the first and second MD error vectors, respectively.