9,236 research outputs found
Accurate on-wafer power and harmonic measurements of mm-wave amplifiers and devices
A novel integrated test system that accurately measures on-wafer S-parameters, power levels, load-pull contours and harmonics over 1 to 50 GHz is presented. The system measures power and S-parameters with single contact measurements and integrated hardware. There are two keys to this system: first, the network analyzer samplers are used as frequency-selective power meters with large dynamic ranges; second, all measurements are vector-corrected to the device under test reference planes. The capabilities and accuracy were demonstrated by measuring the power at the fundamental frequency and four harmonic frequencies of a 50-GHz traveling wave amplifier and the load-pull contours of a MODFET at 30 GH
Non-steady relaxation and critical exponents at the depinning transition
We study the non-steady relaxation of a driven one-dimensional elastic
interface at the depinning transition by extensive numerical simulations
concurrently implemented on graphics processing units (GPUs). We compute the
time-dependent velocity and roughness as the interface relaxes from a flat
initial configuration at the thermodynamic random-manifold critical force.
Above a first, non-universal microscopic time-regime, we find a non-trivial
long crossover towards the non-steady macroscopic critical regime. This
"mesoscopic" time-regime is robust under changes of the microscopic disorder
including its random-bond or random-field character, and can be fairly
described as power-law corrections to the asymptotic scaling forms yielding the
true critical exponents. In order to avoid fitting effective exponents with a
systematic bias we implement a practical criterion of consistency and perform
large-scale (L~2^{25}) simulations for the non-steady dynamics of the continuum
displacement quenched Edwards Wilkinson equation, getting accurate and
consistent depinning exponents for this class: \beta = 0.245 \pm 0.006, z =
1.433 \pm 0.007, \zeta=1.250 \pm 0.005 and \nu=1.333 \pm 0.007. Our study may
explain numerical discrepancies (as large as 30% for the velocity exponent
\beta) found in the literature. It might also be relevant for the analysis of
experimental protocols with driven interfaces keeping a long-term memory of the
initial condition.Comment: Published version (including erratum). Codes and Supplemental
Material available at https://bitbucket.org/ezeferrero/qe
Uniqueness of the thermodynamic limit for driven disordered elastic interfaces
We study the finite size fluctuations at the depinning transition for a
one-dimensional elastic interface of size displacing in a disordered medium
of transverse size with periodic boundary conditions, where
is the depinning roughness exponent and is a finite aspect ratio
parameter. We focus on the crossover from the infinitely narrow () to
the infinitely wide () medium. We find that at the thermodynamic
limit both the value of the critical force and the precise behavior of the
velocity-force characteristics are {\it unique} and -independent. We also
show that the finite size fluctuations of the critical force (bias and
variance) as well as the global width of the interface cross over from a
power-law to a logarithm as a function of . Our results are relevant for
understanding anisotropic size-effects in force-driven and velocity-driven
interfaces.Comment: 10 pages, 12 figure
Multiport VNA Measurements
This article presents some of the most recent multiport VNA measurement methodologies used to characterize these highspeed digital networks for signal integrity. There will be a discussion of the trends and measurement challenges of high-speed digital systems, followed by a presentation of the multiport VNA measurement system details, calibration, and measurement techniques, as well as some examples of interconnect device measurements. The intent here is to present some general concepts and trends for multiport VNA measurements as applied to computer system board-level interconnect structures, and not to promote any particular brand or produc
On methods to determine bounds on the Q-factor for a given directivity
This paper revisit and extend the interesting case of bounds on the Q-factor
for a given directivity for a small antenna of arbitrary shape. A higher
directivity in a small antenna is closely connected with a narrow impedance
bandwidth. The relation between bandwidth and a desired directivity is still
not fully understood, not even for small antennas. Initial investigations in
this direction has related the radius of a circumscribing sphere to the
directivity, and bounds on the Q-factor has also been derived for a partial
directivity in a given direction. In this paper we derive lower bounds on the
Q-factor for a total desired directivity for an arbitrarily shaped antenna in a
given direction as a convex problem using semi-definite relaxation techniques
(SDR). We also show that the relaxed solution is also a solution of the
original problem of determining the lower Q-factor bound for a total desired
directivity.
SDR can also be used to relax a class of other interesting non-convex
constraints in antenna optimization such as tuning, losses, front-to-back
ratio. We compare two different new methods to determine the lowest Q-factor
for arbitrary shaped antennas for a given total directivity. We also compare
our results with full EM-simulations of a parasitic element antenna with high
directivity.Comment: Correct some minor typos in the previous versio
Zero-Temperature Properties of the Quantum Dimer Model on the Triangular Lattice
Using exact diagonalizations and Green's function Monte Carlo simulations, we
have studied the zero-temperature properties of the quantum dimer model on the
triangular lattice on clusters with up to 588 sites. A detailed comparison of
the properties in different topological sectors as a function of the cluster
size and for different cluster shapes has allowed us to identify different
phases, to show explicitly the presence of topological degeneracy in a phase
close to the Rokhsar-Kivelson point, and to understand finite-size effects
inside this phase. The nature of the various phases has been further
investigated by calculating dimer-dimer correlation functions. The present
results confirm and complement the phase diagram proposed by Moessner and
Sondhi on the basis of finite-temperature simulations [Phys. Rev. Lett. {\bf
86}, 1881 (2001)].Comment: 10 pages, 16 figure
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