Understanding Inductor-Originated Single-Event Frequency Transients in CMOS LC -Tank Oscillators: Causes, Effects, and System Impacts

Abstract

Single-event frequency transients (SEFTs) in integrated complementary metal oxide semiconductor (CMOS) LC-tank voltage-controlled oscillator (VCO) and digitally-controlled oscillator (DCO), widely used in frequency synthesizer circuits, have recently been observed and linked to single-event effects (SEEs) in on-chip planar spiral inductors. This work provides an explanation of the underlying causes of these transients, presenting, for the first time, a general model to characterize their behavior and examine their system-level impact. Previously reported experimental observations are validated through heavy-ion microbeam irradiation experiments on two- and four-turn spiral inductor test structures, supported by theoretical analysis and simulations. The study highlights that both the patterned ground shield (PGS) and the inductor geometry significantly influence the polarity and magnitude of SEFT peak deviations. In addition, the results confirm that these deviations are frequency-dependent, with their magnitude increasing at higher operating frequencies. At the system level, SEFTs are demonstrated to induce phase errors in phase-locked loops (PLLs), potentially causing data transmission errors in high-speed communication links. The experimental results are obtained from test circuits fabricated using a 65-nm CMOS process, operating at a nominal frequency of 2.56 GHz with a supply voltage of 1.2 V.