Coupling-Shielded Inductor for High Isolation Between PA and LC-Based DCO

Abstract

This letter presents a novel coupling-shielded inductor. The inductor has a magnetic coupling shield ring (CSR), designed with an Al pad metal. The CSR has an electromotive force-induced current, which flows in such a direction as to oppose the magnetic field from an aggressor. As a result, the proposed inductor can be protected from the attack of a power amplifier (PA) with a strong magnetic field. The inductor is applied in an LC-based digitally controlled oscillator (DCO) to verify the enhancement of isolation. It was fabricated by a 55-nm 1P6M CMOS process. Using the CSR, the isolation between the DCO and PA is increased by about 11 dB without degradation of the DCO performance. The DCO with CSR has a low phase noise of -114.5 dBc/Hz at 1 MHz with 0.74-mW power consumption.