8,173 research outputs found
Parametric resonance in tunable superconducting cavities
We develop a theory of parametric resonance in tunable superconducting
cavities. The nonlinearity introduced by the SQUID attached to the cavity, and
damping due to connection of the cavity to a transmission line are taken into
consideration. We study in detail the nonlinear classical dynamics of the
cavity field below and above the parametric threshold for the degenerate
parametric resonance, featuring regimes of multistability and parametric
radiation. We investigate the phase-sensitive amplification of external signals
on resonance, as well as amplification of detuned signals, and relate the
amplifier performance to that of linear parametric amplifiers. We also discuss
applications of the device for dispersive qubit readout. Beyond the classical
response of the cavity, we investigate small quantum fluctuations around the
amplified classical signals. We evaluate the noise power spectrum both for the
internal field in the cavity and the output field. Other quantum statistical
properties of the noise are addressed such as squeezing spectra, second order
coherence, and two-mode entanglement.Comment: 25 pages, 17 figure
The Schr\"odinger-Langevin equation with and without thermal fluctuations
The Schr\"odinger-Langevin (SL) equation is considered as an effective open
quantum system formalism suitable for phenomenological applications involving a
quantum subsystem interacting with a thermal bath. We focus on two open issues
relative to its solutions: the stationarity of the excited states of the
non-interacting subsystem when one considers the dissipation only and the
thermal relaxation toward asymptotic distributions with the additional
stochastic term. We first show that a proper application of the Madelung/polar
transformation of the wave function leads to a non zero damping of the excited
states of the quantum subsystem. We then study analytically and numerically the
SL equation ability to bring a quantum subsystem to the thermal equilibrium of
statistical mechanics. To do so, concepts about statistical mixed states and
quantum noises are discussed and a detailed analysis is carried with two kinds
of noise and potential. We show that within our assumptions the use of the SL
equation as an effective open quantum system formalism is possible and discuss
some of its limitations.Comment: 38 pages, 31 figure
Analysis and design of wideband voltage controlled oscillators using self-oscillating active inductors.
Voltage controlled oscillators (VCOs) are essential components of RF circuits used in
transmitters and receivers as sources of carrier waves with variable frequencies. This, together
with a rapid development of microelectronic circuits, led to an extensive research
on integrated implementations of the oscillator circuits. One of the known approaches
to oscillator design employs resonators with active inductors electronic circuits simulating
the behavior of passive inductors using only transistors and capacitors. Such
resonators occupy only a fraction of the silicon area necessary for a passive inductor,
and thus allow to use chip area more eectively. The downsides of the active inductor
approach include: power consumption and noise introduced by transistors.
This thesis presents a new approach to active inductor oscillator design using selfoscillating
active inductor circuits. The instability necessary to start oscillations is
provided by the use of a passive RC network rather than a power consuming external
circuit employed in the standard oscillator approach. As a result, total power consumption
of the oscillator is improved. Although, some of the active inductors with
RC circuits has been reported in the literature, there has been no attempt to utilise
this technique in wideband voltage controlled oscillator design. For this reason, the
dissertation presents a thorough investigation of self-oscillating active inductor circuits,
providing a new set of design rules and related trade-os. This includes: a complete
small signal model of the oscillator, sensitivity analysis, large signal behavior of the circuit
and phase noise model. The presented theory is conrmed by extensive simulations
of wideband CMOS VCO circuit for various temperatures and process variations. The obtained results prove that active inductor oscillator performance is obtained without
the use of standard active compensation circuits. Finally, the concept of self-oscillating
active inductor has been employed to simple and fast OOK (On-Off Keying) transmitter
showing energy eciency comparable to the state of the art implementations reported
in the literature
A time-variant analysis of the 1/f^(2) phase noise in CMOS parallel LC-Tank quadrature oscillators
This paper presents a study of 1/f/sup 2/ phase noise in quadrature oscillators built by connecting two differential LC-tank oscillators in a parallel fashion. The analysis clearly demonstrates the necessity of adopting a time-variant theory of phase noise, where a more simplistic, time-invariant approach fails to explain numerical simulation results even at the qualitative level. Two topologies of 5-GHz parallel quadrature oscillators are considered, and compact but nevertheless highly general, closed-form formulas are derived for the phase noise caused by the losses in the LC-tanks and by the noisy currents in the MOS transistors. A large number of spectreRF simulations, covering a wide range of working conditions for the oscillators, is used to validate the theoretical analysis
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