3,299 research outputs found
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
Modeling and performance of a 100-element pHEMT grid amplifier
A 100-element hybrid grid amplifier has been fabricated, The active devices in the grid are custom-made pseudomorphic high electron mobility transistor (pHEMT) differential-pair chips. We present a model for gain analysis and compare measurements with theory. The grid includes stabilizing resistors in the gate. Measurements show the grid has a peak gain of 10 db when tuned for 10 GHz and a gain of 12 dB when tuned for 9 GHz. The maximum 3-dB bandwidth is 15% at 9 GHz. The minimum noise figure is 3 dB. The maximum saturated output power is 3.7 W, with a peak power-added efficiency of 12%. These results area significant improvement over previous grid amplifiers based on heterojunction bipolar transistors (HBT's)
Applications of the optical fiber to the generation and to the measurement of low-phase-noise microwave signals
The optical fiber used as a microwave delay line exhibits high stability and
low noise and makes accessible a long delay (>100 microseconds) in a wide
bandwidth (about 40 GHz, limited by the optronic components). Hence, it finds
applications as the frequency reference in microwave oscillators and as the
reference discriminator for the measurement of phase noise. The fiber is
suitable to measure the oscillator stability with a sensitivity of parts in
1E-12. Enhanced sensitivity is obtained with two independent delay lines, after
correlating and averaging. Short-term stability of parts in 1E-12 is achieved
inserting the delay line in an oscillator. The frequency can be set in steps
multiple of the inverse delay, which is in the 10-100 kHz region.
This article adds to the available references a considerable amount of
engineering and practical knowledge, the understanding of 1/f noise,
calibration, the analysis of the cross-spectrum technique to reduce the
instrument background, the phase-noise model of the oscillator, and the
experimental test of the oscillator model.Comment: 23 pages, 13 figures, 41 reference
Brillouin amplification in phase coherent transfer of optical frequencies over 480 km fiber
We describe the use of fiber Brillouin amplification (FBA) for the coherent
transmission of optical frequencies over a 480 km long optical fiber link. FBA
uses the transmission fiber itself for efficient, bi-directional coherent
amplification of weak signals with pump powers around 30 mW. In a test setup we
measured the gain and the achievable signal-to-noise ratio (SNR) of FBA and
compared it to that of the widely used uni-directional Erbium doped fiber
amplifiers (EDFA) and to our recently built bi-directional EDFA. We measured
also the phase noise introduced by the FBA and used a new and simple technique
to stabilize the frequency of the FBA pump laser. We then transferred a
stabilized laser frequency over a wide area network with a total fiber length
of 480 km using only one intermediate FBA station. After compensating the noise
induced by the fiber, the frequency is delivered to the user end with an
uncertainty below 2x10-18 and an instability sigma(tau) = 2x10-14/(tau/second)
Harnessing optical micro-combs for microwave photonics
In the past decade, optical frequency combs generated by high-Q
micro-resonators, or micro-combs, which feature compact device footprints, high
energy efficiency, and high-repetition-rates in broad optical bandwidths, have
led to a revolution in a wide range of fields including metrology, mode-locked
lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum
optics. Among these, an application that has attracted great interest is the
use of micro-combs for RF photonics, where they offer enhanced functionalities
as well as reduced size and power consumption over other approaches. This
article reviews the recent advances in this emerging field. We provide an
overview of the main achievements that have been obtained to date, and
highlight the strong potential of micro-combs for RF photonics applications. We
also discuss some of the open challenges and limitations that need to be met
for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference
Ultra-stable long distance optical frequency distribution using the Internet fiber network
We report an optical link of 540 km for ultrastable frequency distribution
over the Internet fiber network. The stable frequency optical signal is
processed enabling uninterrupted propagation on both directions. The robustness
and the performance of the link are enhanced by a cost effective fully
automated optoelectronic station. This device is able to coherently regenerate
the return optical signal with a heterodyne optical phase locking of a low
noise laser diode. Moreover the incoming signal polarization variation are
tracked and processed in order to maintain beat note amplitudes within the
operation range. Stable fibered optical interferometer enables optical
detection of the link round trip phase signal. The phase-noise compensated link
shows a fractional frequency instability in 10 Hz bandwidth of 5x10-15 at one
second measurement time and 2x10-19 at 30 000 s. This work is a significant
step towards a sustainable wide area ultrastable optical frequency distribution
and comparison network
A Comprehensive Mixed-Mode Time-Domain Load- and Source-Pull Measurement System
We present a novel test set devised for nonlinear balanced device characterization using load-pull techniques. The system is capable of measuring the voltage and current waveforms at the calibration reference planes while independently tuning the device under test (DUT) source and load differential- and common-mode terminations. The test set is designed to address present and future large-signal multiport measurement needs, easing the characterization task while developing new multiport active device
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