Robert J. Bayruns

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. >

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. >

A GaAs 1.5 Gb/s clock recovery and data retiming circuit

High-speed data communications between computers will require clock and data recovery in the 800-Mb/s-to-1.6-Gb/s frequency range. Because the transmitter clock is almost always stable (i.e., locked to a crystal), a complicated phase-locked loop (PLL) or tracking filter is not required on the receiver end. A monolithic clock recovery and data retiming chip operating at 1.5 Gb/s is described. The circuit is implemented in a 0.5- mu m GaAs D-MESFET process and uses a high dielectric constant coaxial resonator for the clock filter. The chip and filter are both packaged in a metal 14-pin dual inline housing.<<ETX>>

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>>

An 8ns monolithic GaAs sample and hold amplifier

A sample and hold with 8ns acquisition time and 170MHz bandwidth will be described. The device uses ± 5V supplies and dissipates 600mW. The circuit contains a 500MHz operational amplifier, FET switching network and an ECL translator on a 1mm2die.

A wide dynamic range GaAs broadcast satellite tuner IC

Broadcast satellite tuners (BS tuners) used in set top boxes are fed a 950-2150 MHz input from the satellite dish IF. In apartment complexes the IF signal can be split, amplified, and supplied to many units. This IF input spectrum can consist of as many as 50 channels, each ranging in levels from -75 dBm to -15 dBm. Consequently the linearity requirements of the BS tuner are stringent. Typically pin diode attenuators are used at the input of the BS tuner to absorb this dynamic range. A transistor, the bootstrapped gate FET (BGFET), is small and behaves as a low-distortion variable resistor. Using this linear transistor, a BS tuner IC has an IIP3>+10 dBm and an AGC range of 20 dB. The noise figure over the full RF band of 950-2150 MHz is less than 7 dB. The circuit contains an LNA, AG, mixer, and oscillator and draws 50 mA from a +5 V supply. The chip is 0.37 mm/sup 2/ in a low-power GaAs MESFET technology and is packaged in an SOIC-16 package. The circuit is 4 times smaller than a previous GaAs BS tuner.

GaAs integrated circuits for consumer applications

GaAs integrated circuit technology, once considered only as the technology of the future, is finding its way into consumer applications in a big way. Millions of ICs per year are being shipped into the DBS (Direct Broadcast Satellite) and CATV (Cable Television) markets. GaAs ICs are not displacing Si ICs, but rather discrete circuits which have tended to dominate consumer receiver applications. It is our belief that Si ICs have not penetrated the discrete receiver applications because of the lack of on chip filters. In GaAs technology passive elements are higher Q and are the key for our successful entry into the consumer receiver market place.<<ETX>>

Design of low-noise wide-dynamic-range GaAs optical preamps

GaAs MESFET technology is ideal for use in lightwave receiver applications. FET devices have a fundamental advantage over BJT transistors in low noise applications because of their inherent high input impedance. Another advantage comes from the fact that FETs are majority carrier devices and can be easily used as feedback elements in automatic gain control applications.