An LC Quadrature VCO Using Capacitive Source Degeneration Coupling to Eliminate Bi-Modal Oscillation

Abstract

A phase shift technique using capacitive source degeneration (CSD) is presented for LC quadrature voltage-controlled oscillators (QVCO), where capacitively degenerated differential pairs are used to couple the LC tanks to implement a phase-shifted transconductance and negative input resistance to compensate resonator losses, and to minimize the flicker noise contributions. The CSD technique not only introduces excess phase shift to eliminate undesired bi-modal oscillation, but inherently provides a large coupling ratio to improve quadrature phase accuracy. Compared to existing phase-shift LC-QVCOs, the proposed CSD-QVCO presents excellent phase accuracy and power efficiency. A prototype of the QVCO was fabricated in TSMC 0.18-m CMOS technology. The measured phase noise is 120 dBc/Hz at 3-MHz offset from 5-GHz carrier, with a power consumption of 6.4 mW from a 1.2-V supply.Index Terms-Bi-modal oscillation, phase noise, phase shift, quadrature VCO, voltage-controlled oscillator (VCO).

Reduction of 1/f 3 phase noise in LC oscillator with improved self-switched biasing

“…The former reduces power consumption by optimizing LC tank and oscillation amplitude, at the cost of significant degradation of close-in phase noise; the latter achieves excellent phase noise performance by deep switching, while each oscillator consumes more than five times power than proposed. Source degeneration capacitor is used in [19] to eliminate Bi-Modal oscillation and improve phase accuracy of quadrature oscillator, but the improvement of phase noise is limited since only up-conversion of flicker noise from cross-coupled pair is suppressed by the capacitor. Compared to other works which only reduce noise source or suppress conversion gain, the proposed SSB-DC oscillator shows superior close-in phase noise performance and FoM as both ways are adopted simultaneously, without additional consumption of die area and power.…”

A 0.6-V Quadrature VCO With Enhanced Swing and Optimized Capacitive Coupling for Phase Noise Reduction

“…However, the oscillation frequency of a QVCO will depart from the resonance frequency of individual VCO cores because of the coupling mechanisms. The behavior of the two VCO cores including coupling effects can be modeled by a simplified linear model [7], [15] [17], as shown in Fig. 12(a), where provides a negative resistance compensating the energy loss due to the equivalent resistance R of a LC tank, and represents the transconductance of the coupling mechanism between the two VCO cores.…”

“…Since one VCO core may lead or lag the other VCO core by 90 phase, is introduced to the coupling transconductance. For a conventional QVCO with parallel coupling transistors [24], the frequency deviation can be found with steady state analysis as (15) where the positive or negative sign depends on whether the iVCO leads or lags the qVCO by 90 ;…”

“…From (15), it is obvious that the larger the is, the larger the frequency deviation from becomes, which worsens the quality factor of the LC tank. It is desirable to decrease the coupling strength to improve the phase noise performance.…”

Methods and techniques for improving the figure of merit for wide tuning range quadrature voltage controlled oscillators

“…In conclusion, we have shown that for transformer-based oscillators the traditional quality Although, the architecture is claimed to naturally stabilize in the high frequency quadrature mode [36,22], in some cases the oscillator can jump between these two modes during operation, or start up in a mode other than the one intended [50]. Several solutions have been proposed; most involve introducing a phase delay into the coupling path [50][51][52]. While successful in solving the bi-modal oscillation problem, this phase delay reduces the effectiveness of current tuning in QVCOs.…”