A 60-GHz Polar Vector Modulator With Lookup Table-Based Calibration

Abstract

A 60-GHz polar vector modulator with a lookup table (LUT)-based calibration for a variable gain active phase shifter is presented. It consists of an input buffer, an I/Q generator, a vector summing amplifier, and 6-bit phase/gain digital-to-analog converters (DACs). It is very difficult to obtain accurate gain and phase characteristics of a polar vector modulator due to circuit imperfections, such as I/Q imbalance, current mismatches of DACs, and impedance variations over polar vector states. Thus, calibrations are essential to have accurate gain and phase states. This letter introduces an LUT-based calibration method to map possible 2(13) states (5-bit gain and 8-bit phase) onto targeted polar states, which minimizes gain and phase errors drastically. The proposed phase shifter with a generated LUT shows an rms gain and phase errors of 0.13 dB and 0.8 degrees, respectively, at the center frequency of 60 GHz. In addition, it has an rms gain and phase errors of <0.47 dB and <33 degrees in a 9-GHz bandwidth of 55-64 GHz with 4-bit gain and 5-bit phase resolutions. It was fabricated using a 28-nm bulk CMOS process. The core area and power consumption are 0.41 mm(2) and 15.4 mW, respectively.