A 4-bit SiGe passive phase shifter for X-band phased arrays

This paper presents a 4-bit passive phase shifter for X-band (8-12 GHz) phased-arrays, implemented in 0.25-μm SiGe BiCMOS process. All bits are digitally controlled. The 22.5° and 45° bits are based on switched low-pass network while the 90° and 180° bits are based on switching between high-pass/low-pass filters. Filters are implemented using on-chip spiral inductors and high-Q MIM capacitors. Switching functionality is obtained by isolated NMOS transistors employing resistive body floating technique. All bits are optimized to minimize the RMS phase error. Ordering of bits is optimized so as to minimize the overall insertion loss. Simulated insertion loss is 12±2 dB and RMS phase error is less than 2° over X-band frequencies.