A 60-GHz Four-Element Beam-Tapering Phased-Array Transmitter With a Phase-Compensated VGA in 65-nm CMOS

This paper reports a 60-GHz four-element beam-tapering phased-array transmitter with a lower sidelobe level (SLL). The array factor and the error vector magnitude (EVM) were calculated to explain the low sidelobe characteristic of a nonuniform amplitude array and to emphasize the importance of phase compensation, respectively. The phase-compensated radio frequency (RF) variable gain amplifiers (VGAs) were proposed to compensate the gain variance of phase shifters and, simultaneously, excite the nonuniform amplitude to each array element. The proposed VGA improves the relative phase error by 2 degrees and the OP1dB by 2.4 dB within a gain control range of 5 dB, compared to the current steering without any compensation. Implemented in a commercial 65-nm CMOS process, the integrated array chip displays an root-mean-square (rms) gain error of <0.53 dB and an rms phase error of <8.8 degrees in the frequency range of 57-66 GHz, while consuming a dc power of 403.2 mW and occupying a chip area of 2.88 mm(2). The fabricated array was integrated with a 1 x 4 Teflon array antenna to verify the beamforming and beam-tapering operations. With proper gain and phase control, the integrated array decreases the SLL by up to 5.2 dB, and the minimum SLL is -15.2 dB. To the best of the authors' knowledge, this is the first report on the implementation of CMOS beam-tapering arrays in the 60-GHz band.