Ali Fard

A study of phase noise in colpitts and LC-tank CMOS oscillators

This paper presents a study of phase noise in CMOS Colpitts and LC-tank oscillators. Closed-form symbolic formulas for the 1/f/sup 2/ phase-noise region are derived for both the Colpitts oscillator (either single-ended or differential) and the LC-tank oscillator, yielding highly accurate results under very general assumptions. A comparison between the differential Colpitts and the LC-tank oscillator is also carried out, which shows that the latter is capable of a 2-dB lower phase-noise figure-of-merit (FoM) when simplified oscillator designs and ideal MOS models are adopted. Several prototypes of both Colpitts and LC-tank oscillators have been implemented in a 0.35-/spl mu/m CMOS process. The best performance of the LC-tank oscillators shows a phase noise of -142dBc/Hz at 3-MHz offset frequency from a 2.9-GHz carrier with a 16-mW power consumption, resulting in an excellent FoM of /spl sim/189 dBc/Hz. For the same oscillation frequency, the FoM displayed by the differential Colpitts oscillators is /spl sim/5 dB lower.

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This paper presents a rigorous phase noise analysis in the 1/f2 region for the differential CMOS LC-tank oscillator with both nMOS and pMOS switch pairs. A compact, closed-form phase noise equation is obtained, accounting for the noise contributions from both tank losses and transistors currents, which allows a robust comparison between LC oscillators built with either one or two switch pairs. The fabricated oscillator prototype is tunable between 2.15 and 2.35 GHz, and shows a phase noise of -144 dBc/Hz at 3 MHz offset from the 2.3 GHz carrier for a 4 mA bias current. The phase noise figure-of-merit is practically constant across the tuning range, with a minimum of 191.5 dBc/Hz. A reference single-switch-pair oscillator has been implemented and tested as well, and the difference between the phase noise levels displayed by the two oscillators is very nearly the one expected from theory

1/{\rm f}^{2}

This work presents an analysis of phase noise in the 1/f2 region displayed by both single-ended and differential bipolar Colpitts oscillators. Very accurate and rigorous symbolic phase noise expressions are derived, enabling a deeper insight into the major mechanisms of phase noise generation, and providing new tools for design optimization. Phase noise expressions for the cross-coupled differential-pair LC-tank oscillator are derived as well. The theoretical analysis is validated on a 3 GHz differential bipolar Colpitts VCO implemented in a 0.35 mum SiGe process. Measurements show a phase noise of -123 dBc/Hz or less at 1MHz offset frequency from the 2.8-3.1 GHz carrier, for a phase noise figure-of-merit of at least 183 dBc/Hz across the tuning range. A very good agreement between theory, numerical simulations, and measurements is observed

Phase Noise Performance of CMOS Differential-Pair LC -Tank Oscillators

The phase-noise theory and design of a differential CMOS LC-tank VCO with double switch pair is presented. A formula for the minimum achievable phase noise in the 1/f2 region is derived. The 2.15 to 2.35GHz 0.3mum CMOS VCO has a phase noise of -143.9dBc/Hz at 3MHz offset and draws 4mA from a 2.5V supply

An Analysis of

A 3.5-5.3 GHz, low phase noise CMOS VCO with switched tuning for multi-standard radios is presented in this paper. Design of low phase noise and small amplitude variations across the operating frequency is shown to be important aspects in wide-band VCO. An analytic expression for the output amplitude of the VCO is derived as a function of the switched capacitor resonator Q. The linear-time variant model was used for prediction of the phase noise and for deciding a proper tank current to achieve the minimum phase noise and amplitude variations across the frequency range. The results are verified in a fully integrated 0.18 /spl mu/m VCO with measured phase noise levels of less than -115 dBc/Hz at 1 MHz offset from the carrier while dissipating 6 mW of power.

1/f^{2}

The work presents a single monolithic wide band VCO for multi-standard radios. Analysis on a differential switched capacitor circuit is performed. Its impact on phase noise and power dissipation is especially addressed. The analysis is demonstrated and verified in a fully integrated CMOS VCO that consumes 2.7 mA from a 1.8 V supply and operates with a wide frequency band from 3.5-5.3 GHz. The measured phase noise is less than -110 dBc/Hz at 1 MHz offset within the entire tuning range.

Phase Noise in Bipolar Colpitts Oscillators (With a Digression on Bipolar Differential-Pair LC Oscillators)

A low phase noise CMOS LC quadrature VCO (QVCO) with a wide frequency range of 3.6-5.6 GHz, designed in a standard 0.18 /spl mu/m process for multi-standard front-ends, is presented. A significant advantage of the topology is the larger oscillation amplitude when compared to other conventional QVCO structures. The QVCO is compared to a double cross-coupled LC-tank differential oscillator, both in theory and experiments, for evaluation of its phase noise, providing a good insight into its performance. The measured data displays up to 2 dBc/Hz lower phase noise in the 1/f/sup 2/ region for the QVCO, when consuming twice the current of the differential VCO, based on an identical LC-tank. Experimental results on the QVCO show a phase noise level of -127.5 dBc/Hz at 3 MHz offset from a 5.6 GHz carrier while dissipating 8 mA of current, resulting in a figure of merit of 181.3 dBc/Hz.

A 2.3GHz LC-tank CMOS VCO with optimal phase noise performance

An improved high-performance dynamic-logic tristate phase-frequency detector architecture is derived through extensive time domain analysis. In particular, the impact of the reset times on the maximum operating frequency and phase characteristics of the phase-frequency detector is discussed. The analysis is verified for the presented improved architecture and excellent agreement between theory and simulation is observed. The phase-frequency detector architecture is proven to function for supply voltages below 1 V and has an increased frequency capability of more than 20% with a power consumption of 10 /spl mu/W at 500 MHz input frequency.

Phase noise and amplitude issues of a wide-band VCO utilizing a switched tuning resonator

In this paper a comparison between two widely used VCO topologies, in standard 0.35 /spl mu/m CMOS technology is presented. The VCOs, based on an NMOS and a complementary structure, are designed to operate in a wide band frequency range suited for future multi-standard WLAN radios. The comparisons are carried out from the perspectives of tuning range, power dissipation and phase noise. The results, which are based on simulations, show that both circuits are applicable for the targeted operation band of 4.5-6.5 GHz, while the complementary VCO shows less power consumption and lower phase noise levels.

A low power wide band CMOS VCO for multi-standard radios

This paper presents a low-phase-noise differential bipolar Colpitts VCO, implemented in a 0.35/spl mu/m BiCMOS process. A time-variant phase noise analysis yields closed- form symbolic expressions for the dominant noise sources in the 1/f/sup 2/ phase-noise region. Measurements show a phase noise of -123 dBc/Hz at 1MHz offset from a 2.8-3.1 GHz carrier, for a figure-of-merit of 183 dBc/Hz. A very good agreement between the derived theoretical formulas, spectreRF simulations, and measurements is observed.