A Commutated-LC RF Broadband Delay Circuit

This article presents a commutated-inductor–capacitor (commutated- $LC$ ) or switched- $LC$ circuit that acts as a radio frequency (RF) delay line. Thanks to its linear-periodically time-varying (LPTV) operation and fully passive implementation, it concurrently achieves long maximum delays, fine delay tuning steps, and wide instantaneous bandwidths while being low loss and highly linear. Unlike existing LPTV switched-capacitor broadband delays, the introduction of inductors in the proposed commutated- $LC$ delay circuit provides a new degree of freedom, allowing it to operate at a much higher RF with a wider instantaneous bandwidth. A proof-of-concept prototype in a 65-nm CMOS process demonstrates a measured 1.3-GHz 3-dB bandwidth around a 4.3-GHz RF, i.e., a 30% fractional bandwidth, when clocked at 250 MHz. The measured maximum delay is 1.4 ns with a 23-dB loss and noise figure; this loss or noise is orders of magnitude lower compared with fully passive linear-time-invariant RF delay lines operating at a similar frequency with the same delay. The measured IIP3 is +16 dBm.