A Digitally Controlled Bidirectional 24–32-GHz Variable Gain Phase Shifter in 45-nm SOI CMOS

This brief presents a novel topology for a bidirectional variable gain phase shifter (VGPS) circuit. The proposed VGPS circuit includes an in-phase-power-splitting stage that evenly divides the input signal. These two resulting signals are then directed into two separate phase-only tunable components achieved through phase shifters (PSs). Careful selection of specific phase settings for the two PSs yields the desired overall gain and phase shift when their outputs are combined. The operational principle and theoretical analysis of the proposed VGPS circuit are provided. To evaluate the effectiveness of the proposed topology, a VGPS circuit demonstrator was implemented using 45 nm Silicon-on-Insulator CMOS technology. The demonstrator incorporates two reflection-type phase shifters and non-isolated splitters/combiners at the input/output, fitting within a compact area of
$0.179~mm^{2}$
. Measurement results reveal excellent gain and phase tuning ranges of 20 dB (ranging from -7.5 dB to -27.5 dB) and 360°, respectively. Moreover, the demonstrator maintains precise control over phase and gain ranges with a tuning step of 5.6°/1 dB while ensuring total root mean square phase and gain errors remain below 1.6° and 0.25 dB, respectively, across a bandwidth spanning 24-32 GHz.