N. Scheinberg

Monolithic GaAs transimpedance amplifiers for fiber-optic receivers

The authors describe the design of transimpedance amplifiers using GaAs MESFET technology. A GaAs transimpedance preamplifier for fiber-optic receivers has been fabricated with two gain stages and an inducer-FET load structure that reduces noise. The two-stage amplifier design provides increased open-loop gain as compared with a single-stage design, and greater closed-loop stability than a three-stage amplifier. An automatic-gain-control (AGC) circuit that varied the value of the feedback resistor was incorporated into the design. >

A low cost high performance MMIC low noise downconverter for direct broadcast satellite reception

A low-cost single-chip receiver designed for use as a direct-broadcast satellite (DBS) receiver operating over 11.7 to 12.2 GHz is described. The chip comprises a low-noise amplifier, an image filter, an active mixer, an IF filter, an IF amplifier, and a local oscillator, replacing about 50 discrete components in a typical outdoor DBS receiver. The unit is housed in a low-cost hermetic package and requires only a dielectric resonator for proper operation. With power supplies of +6 V and -5 V, the typical noise figure is about 5 dB, with a conversion gain of about 36 dB. The device is manufactured using a 0.5- mu m, buried p-layer GaAs MESFET IC process without substrate vias.<<ETX>>

A computer simulation model for simulating distortion in FET resistors

The power law that governs harmonic distortion states that the second harmonic, when plotted as a function of input power, will have a slope of two on a log scale, and the third harmonic will have a slope of three. This power law is fundamental to the use of intercept points by radio-frequency circuit designers to predict distortion levels from a knowledge of the input signal level. It is shown in this paper that the standard formulation of field effect transistor (FET) models violates this power law for FETs biased at V/sub ds/=0. The problem is shown to arise from discontinuities in the high order derivatives which occur because V/sub gs/and V/sub gd/ are interchanged in the computer models when V/sub ds/ switches sign. A model is presented which does not switch these variables and the new model is shown to follow the correct power law.

A capacitance model for GaAs MESFETs

A capacitance model for a GaAs MESFET suitable for implementation in the circuit analysis program SPICE is presented. The model consists of nonlinear capacitances that are a function of two voltages. Such a model gives rise to ordinary nonlinear capacitances and transcapacitances. The placement of these elements in the Y matrix is shown. The empirical equations for the gate charge of a GaAs MESFET given provide an accurate SPICE model for the gate charge and capacitances of a MESFET. A comparison of measured capacitance values with the modeled values gives close enough agreement for circuit simulation purposes. >

High-speed GaAs operational amplifier

An operational amplifier has been designed and fabricated using GaAs MESFETs. This amplifier is a general-purpose monolithic GaAs op amp designed as as a stand-alone component. The amplifier has a differential input, an open-loop gain in excess of 60 dB, and is internally compensated. The high open-loop gain (60 dB at 100 kHz) was achieved by using gain stages with positive feedback. The op amp incorporates a current-mirror level-shifting stage which allows the op amp to operate over a wide power-supply range (/spl plusmn/5-9 V). Previous designs have diodes to achieve level shifting, a practice that precludes operation over a wide supply range. This op amp is a true analog to its silicon counterparts, but it has a higher gain-bandwidth product.

An accurate MESFET model for linear and microwave circuit design

A MESFET model has been presented in a form suitable for implementation in a circuit analysis program such as SPICE. This model accurately predicts I/sub DS/ and its partial derivatives over all terminal voltages from DC to several gigahertz. The nonlinear capacitances C/sub GS/ and C/sub GD/ are also included in the model. Secondary effects often ignored in other models have been included by adding additional terms and parameters to the equations. >

GaAs switched capacitor DC-to-DC converter

A switched capacitor DC-to-DC negative converter fabricated in GaAs MESFET technology is introduced in this paper. The converter has an oscillator that runs at 250 kHz, and requires two external capacitors, 0.1 and 1 /spl mu/F. The converter runs off a wide range of supply voltage, 2 to 10 V, and has a typical output impedance of 75 /spl Omega/. A typical open circuit voltage conversion efficiency of 99.6% is achieved. The circuit can be integrated with other GaAs circuits to provide an on-chip negative supply. Measured, simulated and analytical results are introduced in this paper.

A high-performance, miniaturized X-band active mixer for DBS receiver application with on-chip IF noise filter

A GaAs monolithic microwave integrated circuit (MMIC) dual-gate FET active mixer at X-band is described that is designed for direct broadcast satellite (DBS) applications. All of the components of the mixer, including biasing circuitry, RF, LO, and IF matching networks, as well as the IF noise filter, are implemented monolithically into a 25-mil*30-mil area. The design was process tolerant, and layout was compact for manufacturability and low cost. The mixer was integrated monolithically into a complete single-chip DBS low-noise block (LNB) converter. The active mixer has a conversion gain of 5.5 dB and a single-sideband noise figure of 8.5 dB. The circuit is manufactured using a 0.5- mu m gate length, buried p/sup -/ depletion mode MESFET process without substrate-through via holes. >

A monolithic GaAs low power L-band successive detection logarithmic amplifier

This paper describes a temperature compensated L-band GaAs MMIC successive detection logarithmic amplifier featuring low power consumption. The amplifier achieved log-linearity of /spl plusmn/2.5 dB and a dynamic range of 60 dB over a 100/spl deg/C temperature range. This device shows no sacrifice of performance over larger, labor intensive hybrid MIC approaches. >

Reduction of low-frequency noise in a DC-2.5 GHz GaAs amplifier

The low-frequency noise of a monolithic GaAs DC-2.5 GHz amplifier has been investigated in the frequency band of 100 Hz-1 MHz. As much as 8-10 dB reduction in noise power (for 100 Hz-10 kHz) has been achieved through the use of a buffer layer grown by MOCVD (metalorganic chemical vapor deposition). The amplifiers fabricated on horizontal bridgman (HB) wafer also offer an improvement of approximately 5 dB (in the frequency band of 100 Hz-4 kHz) as compared to undoped LED (liquid-encapsulated Czochralski) substrates. More importantly, the amplifiers made on MOCVD buffer substrates and HB wafers do not show low-frequency oscillations within the bias range, while those fabricated on undoped LEC and light Cr-doped LEC substrates exhibit coherent oscillations.<<ETX>>