Analysis and elimination of hysteresis and noisy precursors in power amplifiers

Power amplifiers (PAs) often exhibit instabilities leading to frequency division by two or oscillations at incommensurate frequencies. This undesired behavior can be detected through a large-signal stability analysis of the solution. However, other commonly observed phenomena are still difficult to predict and eliminate. In this paper, the anomalous behavior observed in a Class-E PA is analyzed in detail. It involves hysteresis in the power-transfer curve, oscillation, and noisy precursors. The precursors are pronounced bumps in the power spectrum due to noise amplification under a small stability margin. The correction of the amplifier performance has required the development of a new technique for the elimination of the hysteresis. Instead of a trial-and-error procedure, this technique, of general application to circuit design, makes use of bifurcation concepts to suppress the hysteresis phenomenon through a single simulation on harmonic-balance software. Another objective has been the investigation of the circuit characteristics that make the noisy precursors observable in practical circuits and a technique has been derived for their elimination from the amplifier output spectrum. All the different techniques have been experimentally validated

Robust Randomness Amplifiers: Upper and Lower Bounds

A recent sequence of works, initially motivated by the study of the nonlocal properties of entanglement, demonstrate that a source of information-theoretically certified randomness can be constructed based only on two simple assumptions: the prior existence of a short random seed and the ability to ensure that two black-box devices do not communicate (i.e. are non-signaling). We call protocols achieving such certified amplification of a short random seed randomness amplifiers. We introduce a simple framework in which we initiate the systematic study of the possibilities and limitations of randomness amplifiers. Our main results include a new, improved analysis of a robust randomness amplifier with exponential expansion, as well as the first upper bounds on the maximum expansion achievable by a broad class of randomness amplifiers. In particular, we show that non-adaptive randomness amplifiers that are robust to noise cannot achieve more than doubly exponential expansion. Finally, we show that a wide class of protocols based on the use of the CHSH game can only lead to (singly) exponential expansion if adversarial devices are allowed the full power of non-signaling strategies. Our upper bound results apply to all known non-adaptive randomness amplifier constructions to date.Comment: 28 pages. Comments welcom

An experimental SMI adaptive antenna array for weak interfering signals

A modified sample matrix inversion (SMI) algorithm designed to increase the suppression of weak interference is implemented on an existing experimental array system. The algorithm itself is fully described as are a number of issues concerning its implementation and evaluation, such as sample scaling, snapshot formation, weight normalization, power calculation, and system calibration. Several experiments show that the steady state performance (i.e., many snapshots are used to calculate the array weights) of the experimental system compares favorably with its theoretical performance. It is demonstrated that standard SMI does not yield adequate suppression of weak interference. Modified SMI is then used to experimentally increase this suppression by as much as 13dB

The cryomechanical design of MUSIC: a novel imaging instrument for millimeter-wave astrophysics at the Caltech Submillimeter Observatory

MUSIC (Multicolor Submillimeter kinetic Inductance Camera) is a new facility instrument for the Caltech Submillimeter Observatory (Mauna Kea, Hawaii) developed as a collaborative effect of Caltech, JPL, the University of Colorado at Boulder and UC Santa Barbara, and is due for initial commissioning in early 2011. MUSIC utilizes a new class of superconducting photon detectors known as microwave kinetic inductance detectors (MKIDs), an emergent technology that offers considerable advantages over current types of detectors for submillimeter and millimeter direct detection. MUSIC will operate a focal plane of 576 spatial pixels, where each pixel is a slot line antenna coupled to multiple detectors through on-chip, lumped-element filters, allowing simultaneously imaging in four bands at 0.86, 1.02, 1.33 and 2.00 mm. The MUSIC instrument is designed for closed-cycle operation, combining a pulse tube cooler with a two-stage Helium-3 adsorption refrigerator, providing a focal plane temperature of 0.25 K with intermediate temperature stages at approximately 50, 4 and 0.4 K for buffering heat loads and heat sinking of optical filters. Detector readout is achieved using semi-rigid coaxial cables from room temperature to the focal plane, with cryogenic HEMT amplifiers operating at 4 K. Several hundred detectors may be multiplexed in frequency space through one signal line and amplifier. This paper discusses the design of the instrument cryogenic hardware, including a number of features unique to the implementation of superconducting detectors. Predicted performance data for the instrument system will also be presented and discussed

A correlation noise spectrometer for flicker noise measurement in graphene samples

We present a high-resolution digital correlation spectrum analyzer for the measurement of low frequency resistance fluctuations in graphene samples. The system exploits the cross-correlation method to reject the amplifiers' noise. The graphene sample is excited with a low-noise DC current. The output voltage is fed to two two-stage low-noise amplifiers connected in parallel; the DC signal component is filtered by a high-pass filter with a cutoff frequency of 34 mHz. The amplified signals are digitized by a two-channel synchronous ADC board; the cross-periodogram, which rejects uncorrelated amplifiers' noise components, is computed in real time. As a practical example, we measured the noise cross-spectrum of graphene samples in the frequency range from 0.153 Hz to 10 kHz, both in two- and four-wire configurations, and for different bias currents. We report here the measurement setup, the data analysis and the error sources

Weather satellite picture receiving stations, APT digital scan converter

The automatic picture transmission digital scan converter is used at ground stations to convert signals received from scanning radiometers to data compatible with ground equipment designed to receive signals from vidicons aboard operational meteorological satellites. Information necessary to understand the circuit theory, functional operation, general construction and calibration of the converter is provided. Brief and detailed descriptions of each of the individual circuits are included, accompanied by a schematic diagram contained at the end of each circuit description. Listings of integral parts and testing equipment required as well as an overall wiring diagram are included. This unit will enable the user to readily accept and process weather photographs from the operational meteorological satellites

Traveling-Wave Couplers for Longitudinal Beam-Type Amplifiers

The equations governing traveling-wave interaction between an electron beam and a slow-wave circuit are formulated in terms of amplitudes of circuit mode and slow and fast space charge modes. The resulting equations are solved to find expressions for the matrix which relates the mode amplitudes at the output of the traveling-wave coupler to the mode amplitudes at the input. The properties of this matrix are discussed and numerical values given for Kompfner Dip. Matrices for velocity jumps and drift regions are also given, and the characteristics of couplers which are preceded by or followed by a drift region and velocity jump are discussed. It is shown that necessary and sufficient conditions for the removal of beam noise from the fast space-charge wave by any lossless coupler are that, for a circuit input, there be no circuit output (M11 = 0) and no slow space-charge wave output (M21 = 0). These results are then applied to the design of fast space-charge wave couplers for longitudinal beam type parametric amplifiers

Experimental realization of an ideal Floquet disordered system

The atomic Quantum Kicked Rotor is an outstanding "quantum simulator" for the exploration of transport in disordered quantum systems. Here we study experimentally the phase-shifted quantum kicked rotor, which we show to display properties close to an ideal disordered quantum system, opening new windows into the study of Anderson physics.Comment: 10 pages, 7 figures, submitted to New Journal of Physics focus issue on Quantum Transport with Ultracold Atom

Resonators coupled to voltage-biased Josephson junctions: From linear response to strongly driven nonlinear oscillations

Motivated by recent experiments, where a voltage biased Josephson junction is placed in series with a resonator, the classical dynamics of the circuit is studied in various domains of parameter space. This problem can be mapped onto the dissipative motion of a single degree of freedom in a nonlinear time-dependent potential, where in contrast to conventional settings the nonlinearity appears in the driving while the static potential is purely harmonic. For long times the system approaches steady states which are analyzed in the underdamped regime over the full range of driving parameters including the fundamental resonance as well as higher and sub-harmonics. Observables such as the dc-Josephson current and the radiated microwave power give direct information about the underlying dynamics covering phenomena as bifurcations, irregular motion, up- and down conversion. Due to their tunability, present and future set-ups provide versatile platforms to explore the changeover from linear response to strongly nonlinear behavior in driven dissipative systems under well defined conditions.Comment: 12 pages, 11 figure

Stability analysis of digital microwave power amplifiers

This work presents a stability analysis of microwave power amplifiers (PAs) driven by binary pulse trains, as in the case of class-S PAs. First, using a simplified digital PA test bench in class-D configuration, different qualitative behaviors are obtained when varying the pulsewidth, including subharmonic and incommensurable oscillations. The mechanisms affecting the stability properties are studied with a harmonic balance-based formulation, by means of pole-zero identification and bifurcation detection. A sufficiently high number of harmonic components must be considered, together with the Krylov decomposition for an efficient computation of the inverse of the Jacobian matrix. It is demonstrated that, when varying the pulsewidth, the distinct pairs of complex-conjugate poles may shift to the right-hand side of the complex plane and, therefore, lead to different kinds of unstable behavior. This phenomenon is related to the dependence of the critical poles on the average value of the input signal. Boundaries of the various types of unstable behavior are traced in the plane defined by the pulse repetition rate and pulsewidth, using bifurcation detection techniques. All the predicted phenomena have been confirmed experimentally. In a second step, the algorithms derived from the simple class-D circuit are transferred to study the stability of a more complex tri-band class-S amplifier. It has been analyzed versus the input bitrate, obtaining a fully stable behavior that has been validated experimentally.This work has been supported by the Spanish Government under contract TEC2014-60283-C3-1-R, the European Regional Development Fund (ERDF/FEDER) and the Parliament of Cantabria (12.JP02.64069)