A theoretical and experimental investigation of dual-gate MESFET mixers is presented. Based on a detailed analysis of the different nonlinear modes of DGFET's, a computer-aided modeling procedure has been developed, which allowed to recognize and optimize critical circuit and bias conditions for high conversion gain and IF bandwidth. Theoretical results are in good agreement with experiments on a 12-GHz TV reception mixer with 8-dB conversion gain and 800-MHz bandwidth.

Dual-Gate MESFET Mixers

This paper describes the design, fabrication and performances of gallium arsenide monolithic circuits of each of the principal microwave functions of a 12 GHz DBS receiver. The technology includes the use of Czochralski grown semi-insulating substrates, ion implanted active layers and localised growth of lines and interdigital capacitances. The low noise amplifier presents a 3,6 dB noise figure with 7,3 dB gain in the r.f. band. A dual gate mixer is presented with 6,5 dB noise figure and 2 dB conversion gain. The stable local oscillator has 32 mW output power and a stability of +- 0,3 ppm/K.

http://ieeexplore.ieee.org/iel5/8178/24512/01112169.pdf

Monolithic Circuits for 12 GHz Direct Broadcasting Satellite Reception

A hybrid integrated 12 GHz receiver, fabricated on a 1 ×2N alumina substrate, contains a two single-gate FET preamplifier, one dual-gate FET self-oscillating mixer, IF matching and bias filters of all FETs. 11–14 dB conversion gain for a bandwidth of 400 MHz and an associated noise figure of 4.5–5 dB have been obtained.

12 GHz receiver with self-oscillating dual-gate MESFET mixer

Metal-semiconductor contacts showing rectifying properties are finding more and more applications in modern semiconductor devices technology(1) Apart from the fact that they are comparatively easy to fabricate and incorporate into integrated circuits, the main reason for their wide usage is that they do not exhibit minority carrier effects (e.g., long reverse recovery time, diffusion capacitance, etc.) similar to those observed in p-n junction devices. Various metal-semiconductor systems, investigated during the last two decades, are tabulated in Table 1. It can be seen from this table that the investigations are mainly centered round Schottky contacts based on Si and GaAs. Amongst the two, Si-based Schottky contacts are at present being used in a wide variety of devices and integrated circuits. Recent advances in GaAs material and processing techniques have, however, shown that not only can all of the semiconductor device structures realized in Si be fabricated in GaAs, but optical and very high speed integrated circuits can also be realized in the not-too-distant future. It is because of this as well as metallurgical and reliability considerations that the activity pertaining to GaAs-based Schottky contacts has increased appreciably during the last few years.

Fabrication and Characterization of Metal-Semiconductor Schottky Barrier Junctions

The metalorganic VPE process has been applied to the growth of GaAs-GaAlAs heterostructures suitable for FET devices. Two kinds of materials are examined; namely, insulating GaAlAs hetero-buffer and heterojunction p-GaAlAs-n-GaAs, The technology of device processing uses selective etching and self-alignment techniques. The heterobuffered FET's demonstrate effective electron confinement and the heterojunction HJFET's exhibit a built-in voltage of 1.4 eV. However, more has to be known on the transition at the heterointerface to improve the device performances.

The use of GaAs&#8212;(Ga, Al)As heterostructures for FET devices

A 12 GHz receiver front-end has been designed and realised which uses field-effect transistors for each of the three major functions of r.f. preamplifier, mixer and local oscillator. In each of these functions, the FET presents its particular advantages of low noise figure as an amplifier, a conversion gain as a mixer and a relatively high efficiency as an oscillator. An overall noise figure of 4 dB should be possible in production quantities. The structure and overall system performance will be described.

All FET Front-End for 12 GHz Satellite Broadcasting Reception

A planar Schottky diode of original structure has been developed using a suspended contact between the active diode area and the ohmic contact to increase the device cut-off frequency and make a low cost reliable device. Self-alignment techniques were used to define the active diode area. Cut-off frequencies in excess of 2 000 GHz have been measured and series resistances around 1.3 ohms. The diodes have been used in waveguide and microstrip mixer structures and conversion loss measurements will be presented.

High Performance GaAs Schottky Barrier Diodes using a Cantilevered Metal Contact

The performance of MESFET mixers used as down-converters from frequencies around 8 GHz to an intermediate frequency of 1 GHz is presented. Several possible mixer configurations have been considered and preliminary results are described involving the use of the MESFET in single as well as double device circuits. Experimental results concern the devices single sideband. noise figures and associated values of small signal conversion gain. Large signal saturation is discussed and results of third order intermodulation product are described. A single sideband noise figure of 7.8 dB associate with a gain of 8 dB at 7 GHz has been measured from a mixer using a single transistor.

Performance of Some GaAs Mesfet Mixers

An account of a computer model is presented which is designed to simulate the large signal behaviour of GaAs transferred electron amplifier diodes. Devices have been fabricated with a variety of doping profiles following the indications of the results of the simulation. Experimental results are reported concerning the small signal impedance, noise figure, large signal impedance, maximum added power and efficiency of a number of devices of different doping profiles. Indication is given of the large signal stability, the bandwidth of the negative resistance and the third order intermodulation product measured in these devices. The results, both of the computer simulation and measurements, suggest that more efficient amplifier diodes can be produced by using a shallow notch structure and that this configuration is not optimum for lowest noise factor.

Peter Harrop

Papers

All FET Front-End for 12 GHz Satellite Broadcasting Reception

High Performance GaAs Schottky Barrier Diodes using a Cantilevered Metal Contact

Performance of Some GaAs Mesfet Mixers

Large Signal Behaviour of Cathode Notch Stabilized T.E. Amplifier Devices