A D-Band Differential Phase Shifter Based on a Transmission Delay Line With Variable Inductors and Capacitors

A transmission delay line (TDL) differential phase shifter (PS) with 5-bit resolution, operating at D-band frequencies (120–146 GHz), is proposed. It provides bi-directional 180° phase shift characteristics with $50~\Omega $ input/output impedances. It consists of eight LC cells. Each unit cell has a series inductor and two shunt capacitors. The inductance is controlled with a switched coupled inductor (SCI), and the capacitances are controlled with variable capacitors. The 1st to 6th cells are identical, where a unit cell provides a 22.5° phase shift. The 7th and 8th cells are for phase shifts of 11.25°/22.5° and 5.625°/11.25°, respectively. These are achieved by using dual-switched coupled inductors (DSCI) and varactors in each cell. The proposed PS is designed in a 40-nm CMOS process, occupying 0.24 mm2 including I/O pads with a core size of 0.09 mm2. The maximum measured insertion loss was −17.2 dB at 142 GHz, and the loss variation across all 33 phases was within 1.5 dB.