A 4-bit broadband CMOS phase shifter using magnetically coupled all-pass networks

Using magnetically coupled all-pass networks (MCAPNs) for phase-shifter design, the tradeoff between the amount of phase shift and the bandwidth over which the phase shift remains constant can be exploited. In this work, a 4-bit fully-differential phase shifter is designed at 2.45 GHz based on MCAPNs in TSMC 0.18μm CMOS process with the goal of maximizing the phase-shift bandwidth. Measurement results show that the rms phase error is less than 3° from 1.28 GHz to 4.23 GHz, corresponding to a bandwidth of 107%. Over the entire bandwidth, the return losses are greater than 7.7 dB and the amplitude error is within ±1.5 dB. At 2.45 GHz, the average insertion loss is 10.3 dB.