The Intrinsic Noise Figure of the MESFET Distributed Amplifier

This paper calculates the intrinsic noise figure of the MESFET distributed amplifier assuming, for simplicity, only the Van der Ziel gate and drain noise sources, and produces an expression for the noise figure of a distributed amplifier containing n identical devices. For large gain and Iarge n, a simple expression exists for the product nZ/sub pi g/, where Z/sub pi g/ is the pi-characteristic impedance of the gate line, which minimizes the overall noise figure of the amplifier. This approximate expression is compared with the corresponding expression for a resonant ampfifier using the same MESFET with the same noise sources and with the optimum source impedance for minimum noise figure. Although the resonant amplifier has a slightly lower noise figure, the need to use a circulator to remove the mismatch associated with the optimum source impedance removes this slight advantage.     

The effects of parasitic capacitance on the noise figure of MESFETs

The parasitic capacitance due to the gate pad and the gate feed area of a MESFET plays an important role in the low-noise performance of the device. Its effects on the noise figure have been measured and analyzed for π-FET device geometries. It is shown that there is an optimum unit gate width for the minimum noise figure. This optimum unit gate width depends on the device structure and the processing parameters. When the effects of parasitic capacitances are included, H. Fukui's (1979) equation predicts noise figures that are in good agreement with the experimental data     

Noise in distributed MESFET preamplifiers

The theory of noise in a distributed MESFET preamplifier is developed. From this, it is shown that the equivalent input noise current density of a distributed preamplifier of an optical receiver can be improved by using large gate line matching impedance and appropriate scaling of the MESFET width. A front-end tuning circuit was designed using filter theory to further improve the noise performance of the preamplifier. A monolithic GaAs MESFET distributed preamplifier was fabricated with on chip front-end tuning components. Using a 35 μm InGaAs p-i-n photodiode, the preamplifier was shown to have an equivalent input noise current density of 8 pA/√Hz and an 8 GHz bandwidth. To date, this is the best known result for a 0.8 μm GaAs MESFET process     

栅极导电层Au迁移导致放大器失效原因分析

针对限幅低噪声放大器使用过程中出现输出不稳定现象,利用扫描电镜和能谱仪对场效应管栅极表面的金属缺失层和栅源之间的金属堆积物进行微观分析,寻找放大器工作不正常的原因。结果表明:场效应管栅极Au层的电迁移,使导线局部电阻增大,温度升高,导致Au的热迁移加重,引起导线出现孔洞和栅源中间堆积金属颗粒,使栅极导线出现开路和栅源极间产生不稳定接触,最终导致场效应管的工作参数漂移和放大器工作不正常。     

Noise in two-tier matrix amplifiers

A noise theory for the two-tier matrix amplifier is developed that permits the computation of the amplifier's noise figure as a function of the active device and circuit parameters. The computed results based on the noise parameters of a GaAs MESFET with gate dimensions 0.25 μm×200 μm are discussed. In addition, a comparative study is done on the performance data from a 2×4 matrix amplifier and its equivalent two-stage distributed amplifier. Finally, the noise characteristics of two 2×4 matrix amplifiers incorporating GaAs MESFETs processed on either ion-implanted or VPE (vapor-phase epitaxial) substrate material are compared with those measured on actual amplifiers     

MMIC compatible lightwave-microwave mixing technique

The work presented here concerns the mixing of a microwave signal with a modulated optical signal in a MESFET. A brief theoretical analysis of the mixing mechanism is given in terms of the input signal parameters and device characteristics. Experimental results for the IF response of the MESFET as a function of RF frequency, incident optical power, optical modulation depth and gate bias voltage are shown. The IF response and the noise figure of the MESFET below 700 MHz were smaller than those of a p-i-n detector/Schottky mixer combination     

Sensitivity analysis of integrated InGaAs MSM-PD's and HEMToptoelectronic receiver array

A sensitivity analysis is given of a long wavelength optoelectronic receiver array consisting of InAlAs/InGaAs interdigitated Metal Semiconductor Metal photodetectors (MSM-PD's) and a HEMT preamplifier. It is shown that the capacitance varies with the finger width and spacing for a MSM-PD with same active area. Analytical expressions are derived for calculating the sensitivity of the receiver array by means of the equivalent circuit models of the MSM-PD's array and the HEMT. Major noise sources in the receiver array, such as shot noise in the photodetectors, thermal noise in the resistors, gate and drain noises as well as their correlation term in the HEMT, are considered. The influences of geometric parameters of the MSM-PD's and HEMT on the sensitivity of the receiver array are investigated. The optimum gate width of the HEMT is determined for a given MSM-PD array to obtain a high receiver sensitivity. It is also demonstrated that the optical signal related shot noise from the MSM-PD's makes a substantial contribution to the total noise of the receiver array     

单边接地MESFET及其寄生效应的分析模型

本文介绍了栅宽为150μm和240μm两种单边接地MESFET制造工艺及其在单片电路中的应用。这种器件结构可减小器件占用的GaAs芯片面积,提高电路布线的灵活性,并已应用于12GHz低噪声放大器GaAs单片电路,取得了良好效果。本文也给出了这种器件寄生效应的分析模型,并计算讨论了栅靶、空气桥以及接地块等寄生元件对器件的散射参数和噪声参数的影响。     

DC to 10-GHz mixer and amplifier GaAs IC's for coherent opticalheterodyne receiver

The authors describe a number of design techniques that are effective for enhancing sensitivity and bandwidth. A Gilbert-cell circuit with a single-to-balance conversion input buffer and a peaking circuit are adopted for the mixer. In addition, a wideband amplifier is proposed that adopts a novel multiple-feedback cascode FET amplifier configuration with an LC input matching network. Finally, a novel interconnection technique is proposed that improves impedance matching between ICs and the package over a wide frequency range up to 10 GHz. These ICs were fabricated using a 0.2-μm gate self-aligned GaAs MESFET process. These techniques could enable a highly sensitive multigigabit-per-second coherent optical heterodyne receiver to be implemented     

Active GaAs sensor element for dynamic pressure measurements

A piezoelectric pressure sensor is presented which consists of a GaAs MESFET in which the transverse piezoelectric effect is used to charge the gate pad. The MESFET itself acts as an integrated charge amplifier. The sensor gives output signals which are comparable to those of a much bulkier commercial measurement system. The sensitivity achieved is 200 mV/bar in the range 0-20 bar     

Crosstalk degradation caused by optical amplification in amultichannel FSK heterodyne system

The crosstalk degradation caused by an optical amplifier in a four-channel FSK (frequency-shift-keyed) heterodyne communication system is measured. A bit error rate (BER) floor of 3×10^-4 is observed when the channels are spaced by 200 MHz, FSK modulation at 45 Mb/s, and when the optical input signal is large enough such that the gain is compressed by 2 dB relative to its small-signal value. The receiver is substantially improved by reducing the optical power amplifier input. However, the sensitivity increases only to a maximum value beyond which it degrades as the optical power of the demodulated channel becomes small relative to the noise of the optical amplifier. The combined effect of the crosstalk and the amplifier noise yields an optimum sensitivity of 250 photons/b for BER=10^-9. This result is 5 dB poorer than the sensitivity obtained in the absence of an optical amplifier     

Designing FET's for broad noise circles

It is shown that the keys to broader noise circles are a lower minimum noise figure and a small optimum generator reflector coefficient. An optimum FET width for the smallest generator reflection coefficient and the broadest noise circles has been demonstrated with 0.25 μm MODFETs. A FET of optimum width also has the lowest noise figure with a 50 Ω generator. An expression is derived showing that the optimum gate width is inversely proportional to frequency, and that the optimum width should be a weak function of gate length for FETs optimally scaled for gate length     

Performance of GaAs MESFET's at Low Temperatures (Short Papers)

The noise- and s-parameters of a GaAs MESFET with 1-mu m gate Iength are characterized versus temperature. At room temperature, the noise figure measured at 12 GHz is 3.5 dB. At 90 K, the noise figure decreases to 0.8 dB (T/sub e/ = 60 K). The associated gain is 8 dB. The design of a cooled amplifier for the 11.7-12.2-GHz communication band is discussed. At 60 K, the three-stage amplifier exhibits 1.6-dB noise figure (T/sub e/ = 130 K) and 31-dB gain.     

New applications of a sinusoidally driven InGaAsP electroabsorptionmodulator to in-line optical gates with ASE noise reduction effect

The authors propose new applications of a sinusoidally driven InGaAsP electroabsorption modulator to an inline optical gate for a 2R (reshape and retiming) repeater in optical amplifier systems, an n :1 optical demultiplexer in time division multiplexing systems, and an optical switch. The small polarization dependence of the modulator is essential for inline use. By utilizing the monotonic increase of the extinction ratio with increasing applied voltage, the electroabsorption modulator driven by a large-signal sinusoidal voltage can produce a time domain square-shaped gate function with variable gate width. Furthermore, amplified spontaneous emission noise of optical amplifier systems can be reduced in both time and wavelength domains at the off-state of the modulator, due to noninterferometric wide wavelength operation of the modulator. Experimental results for a 2R repeater, an n:1 (n=4, 8) optical demultiplexer, and optical gates for switching are also demonstrated at over 10-Gb/s repetition rate     

20-GHz Band Monolithic GaAs FET Low-Noise Amplifier

A 20-GHs band monolithic GaAs FET low-noise amplifier has been developed. Design and fabrication were performed by obtaining the transmission properties of the microstrip lines on a semi-insulating GaAs substrate. The developed monolithic amplifier consists of a submicron gate GaAs MESFET and the input and output distributed matching circuits on a semi-insulating GaAs substrate measuring 2.75 mm x 1.45 mm. A noise figure of 6.2dB and an associated gain of 7.5 dB were obtained at 21 GHz without any additional tuning adjustments.     

Optimal current for minimum thermal noise operation ofsubmicrometer MOS transistors

The wide band noise voltage (equivalent thermal noise voltage at the gate) of a submicron MOSFET, working in saturation, exhibits a minimum value at a certain drain current. This is supported by measurements and theoretical analysis based on a suitable thermal noise model. This macroscopic noise model attributes the thermal noise of the drain current to the superposition of two noise sources originating from two separate regions of the transistor's channel (a gradual channel approximation region and a saturation region). The existence of a minimum of the noise spectral density at an optimum drain current (I_opt), is well proved by measurements and is contradictory to the predictions of the current simulation program with integrated circuit emphasis (SPICE) models. An empirical way for evaluating analytically I_opt is given. The fact of the existence of a noise minimum for a submicron MOSFET, brings a phenomenological equivalence to the bipolar transistor and GaAs MESFET when they are employed at the first stage of an amplifier     

A new self-alignment technology for sub-quarter-micron-gate FETsoperating in the Ka-band

A self-alignment technology is proposed that allows fabrication of gates of less than 100 nm using conventional optical lithography. An offset gate structure is realized using this method. The technology is applied to high-power GaAs MESFETs consisting of many individual FETs. The uniformity of the FET characteristics is checked to show reproducibility. The input-output power characteristics of a MESFET with a 3.6-mm gate width were measured at 28 GHz. A linear gain of 4.0 dB and a saturation power of 0.8 W were obtained, demonstrating the overall effectiveness of this technology. It is shown that a 50-nm gate can be fabricated with this technology. A MESFET with a 90-nm gate length that was fabricated and evaluated at high frequency to demonstrate the technology is discussed     

GaAs field effect transistors fabricated by imprint lithography

A GaAs metal–semiconductor field-effect transistor (MESFET) has been realized based on mix-and-match fabrication using optical lithography for the ohmic contacts and imprint lithography for the gate. The gate length and width are 1.2 and 80 μm, respectively, the channel length is 4 μm. For the gate definition a Si-mold is embossed into a thin polymer film located on top of an n-doped GaAs layer. The gate is fabricated by metal evaporation and lift-off.     

Distribution of 1/ƒ noise in an epitaxial GaAs MESFET

A method was devised to determine the distribution of 1/ƒ noise generation in the conducting channel of a field-effect transistor. This newly devised method was applied to an epitaxial GaAs MESFET and the vertical distribution of 1/ƒ noise generation was determined. A noise current source, which represents noise generated in the conducting channel, was assigned to the conventional e_n-i_n representation, in which all the noises are represented by the equivalent noise voltage and current sources at the gate. The magnitude of each noise source was separately determined by measuring the dependence of noise output on the resistance in the gate circuit of the common source amplifier including the FET to be measured. Measurements were performed on a dual gate FET in the frequency range from 0.01 Hz to 25 kHz. It was shown that the more noise is generated in the portion next to the substrate than in the portion at the middle of the active layer.     

带前置光放大器的光接收机灵敏度分析

本文分析了半导体光放大器的噪声特性，并首次推导出带前置光放大器的接收机灵敏度公式。结果表明，除光放大器内增益外，光放大器入射端耦合效率是影响这种接收机灵敏度的主要因素，而且其最佳判电平高于原接收机。