Huan-Shang Tsai

Ga 2 O 3 (Gd 2 O 3 )/InGaAs enhancement-mode n-channel MOSFETs

We have demonstrated the first Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) insulated gate n-channel enhancement-mode In/sub 0.53/Ga/sub 0.47/As MOSFETs on InP semi-insulating substrate. Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) was electron beam deposited from a high purity single crystal Ga/sub 5/Gd/sub 3/O/sub 12/ source. The source and drain regions of the device were selectively implanted with Si to produce low resistance ohmic contacts. A 0.75-/spl mu/m gate length device exhibits an extrinsic transconductance of 190 mS/mm, which is an order of magnitude improvement over previously reported enhancement-mode InGaAs MISFETs. The current gain cutoff frequency, f/sub t/, and the maximum frequency of oscillation, f/sub max/, of 7 and 10 GHz were obtained, respectively, for a 0.75/spl times/100 /spl mu/m/sup 2/ gate dimension device at a gate voltage of 3 V and drain voltage of 2 V.

Demonstration of submicron depletion-mode GaAs MOSFETs with negligible drain current drift and hysteresis

We successfully fabricated submicron depletion-mode GaAs MOSFETs with negligible hysteresis and drift in drain current using Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) as the gate oxide. The 0.8-/spl mu/m gate-length device shows a maximum drain current density of 450 mA/mm and a peak extrinsic transconductance of 130 mS/mm. A short-circuit current gain cutoff frequency (f/sub T/) of 17 GHz and a maximum oscillation frequency (f/sub max/) of 60 GHz were obtained from the 0.8 /spl mu/m/spl times/60 /spl mu/m device. The absence of drain current drift and hysteresis along with excellent characteristics in the submicron devices is a significant advance toward the manufacture of commercially useful GaAs MOSFETs.

The optimal RLS parameter tracking algorithm for a power amplifier feed-forward linearizer

Digital signal processing (DSP) techniques have been proposed in recent years to adaptively track the control parameters of a power amplifier (PA) feed-forward linearizer. In most of the propositions, gradient-based searching algorithms are applied to the parameter tracking. In this paper, we propose an optimal RLS (recursive least square) parameter tracking algorithm, which significantly accelerates the convergence speed and eliminates the gradient noise. There exists two problems for the RLS algorithm. First, the least square solution is not the optimal solution because of the nonlinearity of the PA. Second, the vector modulator (VM) which introduces the control parameters into the linearizer circuit may not be accurate enough to provide a precise power gain and phase shift calculated by the DSP. We solve both problems, respectively, by rearranging the circuit components and by constraining the VM characteristics. We also present simulation results to verify the performance improvement of the proposed algorithm.

Investigation of current crowding effect on spiral inductors

High-Q inductors are the important elements for RF circuit design, especially in the cellular and PCS bands, where they are difficult to be realized. We discuss and explain the current crowding effect, which degrades the Q of the spiral inductor, as the number of turns increases. Both the method of moment (MOM) and the finite-difference time-domain (FDTD) technique are applied to this analysis.

High-speed multiplexers: a 50 Gb/s 4:1 MUX in InP HBT technology

We have implemented a monolithic electronic 50 Gb/s 4:1 MUX core in an InP-based HBT technology. This rate is the fastest achieved in a monolithic 4:1 MUX to our knowledge, and is currently limited by the speed limitations of our pattern generation equipment. Our 2:1 MUX is too fast for characterization at present, but we present evidence that the speed of the 2:1 MUX is at least 60 Gb/s.

Joint MLSE receiver with dynamic channel description

In this paper, we address the problem of receiving a digitally modulated signal in the presence of another identically modulated cochannel interfering (CCI) signal. We propose a joint MLSE algorithm that uses a dynamic channel description (J-MLSE/DCD). This algorithm deals with CCI more effectively while keeping the overall complexity low. In the proposed algorithm, we adaptively truncate the channels of both the desired signal and the CCI according to their individual power, thereby greatly reducing the complexity. We also describe the channel by using only a small number of channel parameters to reduce the channel mismatch before the Viterbi algorithm is applied. Analytic bit-error rate (BER) lower bounds for the J-MLSE algorithms in the time-varying specular multipath Rayleigh-fading channels are derived. Simulation results of the GMSK modulated signals used in the GSM system with path delay spread up to three symbols are presented. We find that the proposed algorithm performs significantly better than the spatial-whitened MLSE and is comparable to the high-complexity joint MLSE.

Low-complexity joint MLSE receiver in the presence of CCI

We address the problem of receiving a digitally modulated signal in the presence of another identically modulated cochannel interference (CCI) signal. We propose a joint maximum-likelihood sequential estimation (MLSE) algorithm that uses a dynamic channel description (J-MLSE/DCD). This algorithm deals with CCI more effectively while keeping the overall complexity low. In the proposed algorithm, we adaptively truncate the channels of both the desired signal and the CCI according to their individual power, thereby greatly reducing the complexity. Simulation results for the GMSK modulated signals used in the Global System for Mobile Communications (GSM) system are presented. The proposed algorithm performs much better than the spatial-whitened MLSE and is comparable to the high-complexity joint MLSE.

The optimal RLS parameter tracking algorithm for a power amplifier feedforward linearizer

Digital signal processing (DSP) techniques have been proposed in recent years to adaptively track the control parameters of a power amplifier (PA) feedforward linearizer. In most of the propositions, gradient-based searching algorithms are applied to the parameter tracking. In this paper, we propose an optimal recursive least square (RLS) parameter tracking algorithm, which significantly accelerates the convergence speed and eliminates the gradient noise. There exist two problems for the RLS algorithm. First, the least square solution is not the optimal solution because of the nonlinearity of the PA. Second, the vector modulator (VM) which introduces the control parameters into the linearizer circuit may not be accurate enough to provide a precise power gain and phase shift calculated by the DSP. We solve both problems, respectively; by rearranging the circuit components and by constraining the VM characteristics. We also present simulation results to verify the performance improvement of the proposed algorithm.

A 1:4 demultiplexer for 40 Gb/s fiber-optic applications

The demultiplexer (DEMUX) is a critical component of a fiber communication system. In order to satisfy increasing demands for data, fiber systems will employ several wavelengths carrying 40 Gb/s data in the near future. The requirements for such systems dictate that the DEMUX handle at least 4 channels of 10 Gb/s SONET/SDH data. The challenge is to build a 1:4 DEMUX that is both manufacturable and cost-effective to be integrated onto a receiver board. The authors describe a monolithic four-channel DEMUX for 40 Gb/s applications which uses an AlInAs/InGaAs HBT technology from a commercial foundry. Measurements demonstrate 40 Gb/s operation for 0.3 Vpp single-ended data input and 0.6 Vpp differential clock input.

In/sub 0.5/(Al/sub x/Ga/sub 1-x/)/sub 0.5/ HEMTs for high-efficiency low-voltage power amplifiers: design, fabrication, and device results

In/sub 0.5/(Al/sub x/Ga/sub 1-x/)/sub 0.5/ high electron-mobility transistors (HEMTs) are expected to have higher two-dimensional electron gas density and larger current drive capability than both Al/sub 0.23/Ga/sub 0.77/As and In/sub 0.5/Ga/sub 0.5/P HEMTs due to the improved conduction-band offsets. In this paper, we performed a systematic investigation of the electrical properties of In/sub 0.5/(Al/sub x/Ga/sub 1-x/)/sub 0.5/P (0/spl les/x/spl les/1) material system lattice matched to GaAs. By considering the conduction-band offset, direct-to-indirect-band electron transfer, donor-related deep levels, and Schottky barrier height, a relatively narrow range of the Al content 0.2/spl les/x/spl les/0.3 was found to be the optimum for the design of In/sub 0.5/(Al/sub x/Ga/sub 1-x/)/sub 0.5/ HEMTs. Under 1.2-V operation, power transistors with the optimum aluminum composition show high drain current density, high transconductance, and excellent power-added efficiency (65.2% at 850 MHz). These results demonstrate that InAlGaP HEMTs are promising candidates for high-efficiency low-voltage power applications.