Phase noise and accuracy in quadrature oscillators (original) (raw)
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A CMOS low-noise low-power quadrature LC oscillator
2009 IEEE International Symposium on Circuits and Systems, 2009
A new quadrature LC voltage-controlled oscillator circuit configuration for CMOS technology is presented. In the proposed circuit two identical cross-connected LC-VCOs are coupled together via the bulk of the cross-connected MOS transistors and the bulk of the MOS varactors. No additional components are needed for coupling the core oscillators. Therefore, no extra noise sources and power consumption are added to the circuit, which results in good phase noise and low power consumption. The circuit can operate with V dd as low as 0.5 V. A linear analysis of the quadrature operation of the circuit is also provided. The same coupling scheme can be used for multiphase signal generation. Index terms-Low-noise, low-power, low-voltage, quadrature LC voltage-controlled oscillators (LC-QVCO), multiphase. I.
IEEE Transactions on Circuits and Systems I: Regular Papers, 2014
This paper presents a study of quadrature phase error due to various systematic mismatches and loading effects on the oscillation frequency in a tapped-capacitor parallel coupled LC-tank oscillator. Vector based analysis is carried out to evaluate the general oscillating condition. Closed-form expressions for oscillation frequency and quadrature accuracy in the presence of loading are derived for the case of weak coupling. It is shown with rigorous analysis, for the first time, that the tapped-capacitor LC-tank oscillator exhibits oscillation frequency that is independent of loading conditions. The analysis clearly demonstrates that the effects of mismatch in tapped-capacitors on quadrature accuracy can be minimized by proper choice of coupling factor and shows that the error due to these tapped-capacitors is independent of the quality factor of the tank. Results from Spectre simulations are used to validate the analytical results.
Very low noise current- shaped optimally coupled CMOS LC quadrature VCO
IEICE Electronics Express, 2010
This paper presents a new low phase noise quadrature voltage-controlled oscillator (QVCO). Coupling phase shifts of 90 • in conjunction with center-tapped capacitor impedance transformers are exploited to optimally couple two VCOs. DC and AC path of the switching and coupling pairs are de-coupled to allow operation in saturation for large oscillation amplitudes. The switching and coupling transistor pairs operate in class-C mode which increases the DC to RF efficiency. Also, these transistors alternate from strong inversion to accumulation region, decreasing the intrinsic device flicker noise. Simulations confirm the superiority of the proposed circuit in comparison with the prior published QVCOs in terms of phase noise performance.
A Capacitively Coupled Multi-Stage LC Oscillator
IEIE Transactions on Smart Processing and Computing, 2015
Coupling with a ring of capacitors introduces in-phase coupling current in multi-stage LC oscillators, increasing coupling strength and phase spacing accuracy. Capacitive coupling is effective at high-frequency applications because it increases coupling strength with the operating frequency. However, capacitive loading from the ring lowers operating frequency and reduces the tuning range. Mathematical expressions of phase noise and phase spacing accuracy with capacitive coupling are examined here, and transistor-level simulations confirm the effectiveness of the capacitive coupling.
A new low-phase noise direct-coupled CMOS LC-QVCO
IEICE Electronics Express, 2009
A new LC quadrature voltage-controlled oscillator (LC-QVCO), made with direct coupling of two CMOS LC-VCOs, is presented. In the proposed circuit two identical cross-connected LC-VCOs are coupled together by directly connecting the bulk of the crossconnected transistors of one VCO to the bulk of the MOS varactors of the other VCO in such a way no extra devices are needed for coupling. Thus, no extra noise sources and power consumption are added to the core VCOs and results in high performance of QVCO. A Linear analysis of the circuit and the result of simulation in a 0.18 μm CMOS technology are presented. The same proposed coupling scheme can be used for multiphase signal generation as well. Simulation shows the proposed QVCO can operate with supply voltage as low as 0.5 V .
Low-phase-noise LC quadrature VCO using coupled tank resonators in a ring structure
IEEE Journal of Solid-State Circuits, 2001
The concept of coupled resonators is employed in a ring VCO structure to reduce the phase noise. This architecture allows the design of low-phase-noise voltage controlled oscillators (VCOs) using integrated low-inductors. Quadrature differential outputs are also realized in this design. Two monolithic LC tanks are coupled together to implement a transimpedance resonator with an effective close to twice that of a single tank. In addition, the coupled tank's transimpedance resonator provides 90 phase shift. Four such stages are cascaded in a ring structure to provide I-Q differential outputs, and to further reduce the phase noise. A prototype of the VCO is built in a 0.35-m CMOS technology. The measured phase noise is 122 dBc/Hz at 600-kHz offset from 1.93 GHz. The VCO draws 9.2 mA from a 3-V supply, and occupies a chip area of 1.1 1.1 mm 2 .
IEEE Transactions on Circuits and Systems II: Express Briefs, 2012
A modified coupled method for multiphase oscillator is proposed and demonstrated in a standard 0.18-μm CMOS technology. A self-injection-coupled (SIC) technique is used to couple two current-reused differential voltage-controlled oscillators (VCOs). Compared with the conventional parallel-coupled quadrature VCO (QVCO), the proposed QVCO using the SIC technique presents low phase noise without increasing dc power consumption. The proposed SIC-QVCO at 16.28 GHz demonstrated a low phase noise of −125 dBc/Hz at 1-MHz offset frequency and a tuning range of 290 MHz. The dc supply voltage and current consumption are 1.8 V and 6 mA, respectively. The chip size of the proposed SIC-QVCO is 0.75 × 0.6 mm 2 .
Phase error analysis in CMOS injection-coupled LC quadrature oscillator (IC-QO)
International Journal of Circuit Theory and Applications, 2013
This paper presents a novel approach to study the phase error in source injection coupled quadrature oscillators (QOs). Like other LC QOs, the mismatches between LC tanks are the main source of phase error in this oscillator. The QO is analyzed where the phase error and oscillation frequency are derived in terms of circuit parameters. The proposed analysis shows that the output phase error is a function of injection current and the current of source equivalent capacitor. As a result, it is shown that increasing of tail current and LC tank quality factor decreases the phase error. Derived equations show that the phase error can be cancelled and even controlled by adjusting bias currents. To evaluate the proposed analysis and consequent designed QO, a 5.5 GHz CMOS QO is designed and simulated using the practical 0.18 mm TSMC CMOS technology. The experiments show good agreement between analytical equations and simulation results.
Analysis and design of a 1.8GHz CMOS LC quadrature VCO
IEEE Journal of Solid-state Circuits, 2002
This paper presents a quadrature voltage-controlled oscillator (QVCO) based on the coupling of two LC-tank VCOs. A simplified theoretical analysis for the oscillation frequency and phase noise displayed by the QVCO in the 1 3 region is developed, and good agreement is found between theory and simulation results. A prototype for the QVCO was implemented in a 0.35m CMOS process with three standard metal layers. The QVCO could be tuned between 1.64 and 1.97 GHz, and showed a phase noise of 140 dBc/Hz or less across the tuning range at a 3-MHz offset frequency from the carrier, for a current consumption of 25 mA from a 2-V power supply. The equivalent phase error between I and Q signals was at most 0.25 .
A Study of Phase Noise in CMOS Oscillators
This paper presents a study of phase noise in two inductorless CMOS oscillators. First-order analysis of a linear oscillatory system leads to a noise shaping function and a new definition of Q. A linear model of CMOS ring oscillators is used to calculate their phase noise, and three phase noise phenomena, namely, additive noise, high-frequency multiplicative noise, and low-frequency multiplicative noise, are identified and formulated. Based on the same concepts, a CMOS relaxation oscillator is also analyzed. Issues and techniques related to simulation of noise in the time domain are described, and two prototypes fabricated in a 0.5-m CMOS technology are used to investigate the accuracy of the theoretical predictions. Compared with the measured results, the calculated phase noise values of a 2-GHz ring oscillator and a 900-MHz relaxation oscillator at 5 MHz offset have an error of approximately 4 dB.