3,954 research outputs found
Solar-pumped laser Final report
Solar pumped modulated laser to generate coherent radiation at optical wavelengths for long range, real time television data transmissio
High-frequency performance of Schottky source/drain silicon pMOS devices
A radio-frequency performance of 85-nm gate-length p-type Schottky barrier (SB) with PtSi source/drain materials is investigated. The impact of silicidation annealing temperature on the high-frequency behavior of SB MOSFETs is analyzed using an extrinsic small-signal equivalent circuit. It is demonstrated that the current drive and the gate transconductance strongly depend on the silicidation anneal temperature, whereas the unity-gain cutoff frequency of the measured devices remains nearly unchanged
GaN-based HEMTs for Cryogenic Low-Noise Applications
Radio-astronomy deals with signals and radiations of extremely weak intensity. Also, it requires robust and rugged technologies able to sustain and prevent the Radio Frequency Interferences (RFI). Complying with the required high sensitivity, Low Noise Amplifiers (LNAs) operating at cryogenic temperatures are key elements in radio astronomy instrumentation. Thus far, advanced semiconductor technologies but with limited power-handling capabilities have been traditionally employed as LNAs. Over the past decades, Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) were demonstrated at room temperature to offer a combination of both excellent low-noise operation and a superior high-power handling performance compared to other materials. In addition, a number of studies indicated a promising potential for the GaN technology to operate at cryogenic temperatures. However, the cryogenic noise performance of the GaN-HEMTs remained unexplored so far.This thesis investigates the potential of GaNâbased HEMTs for low-noise operation at these cryogenic temperatures. Established characterization and modeling approaches were employed for this purpose. As a main result, this work reveals a first estimation of the noise performance of GaN-HEMTs at cryogenic temperatures of ~10 K which compares to other more advanced technologies in this field. This was achieved through the extraction of a model, based on experimental noise measurements, describing the microwave noise behavior at cryogenic temperatures at the device level. The model predicts the noise contribution of GaN-HEMTs at cryogenic temperatures with respect to the frequency of operation, the dissipated power, and the total periphery of the device. Hence, it constitutes the basis for the design of future GaN-based LNAs which fulfill the different requirements set by the demanding cryogenic applications.The extracted cryogenic noise model was used to identify and analyze the role of the different physical parameters of the device, over which a technological control might be possible in the future in order to improve the assessed noise performance of the cryogenic GaN-HEMTs. From that perspective, GaN-HEMTs featuring superconducting Niobium (Nb)-gates were demonstrated for the first time. The successful integration of superconducting Nb-gates into AlGaN/GaN HEMTs was demonstrated on different samples, showing a suppression of the gate resistance independently of the width and length of the gate below a critical temperature \u1d447\u1d450 < 9.2 K. The superconductivity of the gate leads to the cancellation of the associated noise contribution. Comparing the noise performance of the resulting devices to that of the conventional Gold (Au)-gated GaN-HEMTs, it was concluded that further management of the deviceâs self-heating is required to enable the full potential of the Nb-gate by maintaining its superconductivity while operating at optimum-noise bias conditions
Compact Digital Predistortion for Multi-band and Wide-band RF Transmitters
This thesis is focusing on developing a compact digital predistortion (DPD) system
which costs less DPD added power consumptions. It explores a new theory
and techniques to relieve the requirement of the number of training samples and
the sampling-rate of feedback ADCs in DPD systems. A new theory about the
information carried by training samples is introduced. It connects the generalized
error of the DPD estimation algorithm with the statistical properties of
modulated signals. Secondly, based on the proposed theory, this work introduces
a compressed sample selection method to reduce the number of training samples
by only selecting the minimal samples which satisfy the foreknown probability
information. The number of training samples and complex multiplication operations
required for coefficients estimation can be reduced by more than ten
times without additional calculation resource. Thirdly, based on the proposed
theory, this thesis proves that theoretically a DPD system using memory polynomial
based behavioural modes and least-square (LS) based algorithms can be
performed with any sampling-rate of feedback samples. The principle, implementation
and practical concerns of the undersampling DPD which uses lower
sampling-rate ADC are then introduced. Finally, the observation bandwidth of
DPD systems can be extended by the proposed multi-rate track-and-hold circuits
with the associated algorithm. By addressing several parameters of ADC
and corresponding DPD algorithm, multi-GHz observation bandwidth using only
a 61.44MHz ADC is achieved, and demonstrated the satisfactory linearization
performance of multi-band and continued wideband RF transmitter applications
via extensive experimental tests
- âŚ