Passive Post-Resonance Tuned Reflectors to Achieve Both 10-bit Phase-Shifting Resolution and Low Insertion Loss Across 20–30 GHz

Precise on-chip phase control of microwave transmission is critical to today’s signal processing and wireless communication electronics. Thus far, achieving even modest phase-shifting resolution has involved a complex mix of semiconductor switches and passive electromagnetic structures. These delay circuits operate near resonances that heavily attenuate and distort signals, limiting modulation bandwidth. In this article, we introduce a mechanism whereby miniature waveguide reflectors based on coupled resonances can be reprogrammed to evade loss. Central to their operation is that loss from these resonances is confined to low frequencies, while at high frequencies, the waveguides’ reflectivity is maximized and broadband phase variations, induced by those resonances, still persist. Since performance in the low-loss post-resonance spectrum is largely agnostic to the number of switches, ultra-fine digital tuning is possible. This breaks the historical tradeoff between loss and precision. When inserted in a reflective-type structure, a phase resolution of under 0.3° is achieved, surpassing state-of-the-art CMOS circuits by over three orders (bits) of magnitude while incurring only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5~\pm ~2.5$ </tex-math></inline-formula> dB of loss over the 20-30 GHz 5G MIMO band. The phase- shifter is highly linear, with an input third-order intercept point (IIP3) of over 25 dBm. Moreover, it consumes no DC power and occupies a sub-wavelength footprint of 0.064 mm2 in a 28 nm Fully Depleted Silicon-on-Insulator (FDSOI) CMOS platform. This makes it an optimal candidate for seamless integration in on-chip multi-gigabit data links, radio astronomy transceivers and control hardware for millimeter-wave qubits.