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

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 213 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°, respectively, at the center frequency of 60 GHz. In addition, it has an rms gain and phase errors of <0.47 dB and <3.3° 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 mm2 and 15.4 mW, respectively.