Code-Modulated Embedded Test for MM-wave Phased Array
Code modulation can be applied to the phase shifters within a phased array to allow for a parallel, in-situ measurement of each element’s response either on chip or packaged with antennas. In this talk, we present the concept of built-in test of phased arrays using code-modulated interferometry. Our code-modulated embedded test (CoMET) technique has a small circuit overhead in the form of a weakly-coupled high-frequency test channel, optional digital modulators for each element, and then a simple direct detector. This power detector downconverts the code-multiplexed signal to baseband and creates a code-modulated “interference” response. Through selection of appropriate codes, Cartesian signal correlations of the array can be demodulated, from which individual element amplitude and phase can be extracted. Also, inter- and intra-element correlations can be used to extract both quadrature error per element and phase offset introduced by the built-in distribution network. We illustrate the performance of CoMET using both behavioral models and 60-GHz circuit prototypes, which each indicate amplitude and phase extraction errors less than 1 dB and 4 degrees, respectively.