J.A.C. Stewart

A vector corrected waveform and load line measurement system for large signal transistor characterisation

A vector corrected large signal measurement setup based on a microwave transition analyser has been developed to enable device output harmonic and waveform measurement with variable drive level, frequency, DC bias and fundamental load impedance. A novel capability of this system is the ability to plot the device dynamic load lines during measurement so that nonlinear effects can be investigated as a function of bias and load impedance in real time. Load line results are shown for a MESFET and an HBT device and the effect of load impedance on device behaviour is described.<<ETX>>

Characteristics of trenched coplanar waveguide for SiMMIC applications

A novel low loss trenched aluminium CPW transmission line structure, fabricated on a selection of high, medium and low resistivity silicon substrate materials, is reported. In comparison with conventional aluminium conductor CPW line structures, RF losses are reduced. For 10 K/spl Omega/ cm high resistivity material, this reduction may be as much as 0.5 dB/cm at 30 GHz, achieved by etching longitudinal trenches in the silicon substrate material. For medium resistivity substrates (700-1000 /spl Omega/ cm,) a 13 /spl mu/m deep trench reduces measured line loss from 3.9 dB/cm to 3.4 dB/cm at 30 GHz. For low resistivity silicon substrate material (10-20 /spl Omega/ cm), RF losses can be improved by 36 dB/cm at 30 GHz with 80 /spl mu/m deep trenches. The effect of the trench depth on the characteristic impedance of these CPW lines is reported.

Contact effects on HF loss of CPW high resistivity silicon lines

This paper shows that the HF losses of CPW lines realized on 5-10 K/spl Omega/cm HRS (High Resistivity Silicon) substrates are strongly affected by the derivative of the I-V curves, ie. HF losses are higher where the I-V characteristic changes most rapidly. As a result the excess HF loss due to choice of quiescent bias voltage can be as high as 0.3-0.4 dB/cm. The implication of the effect is that by proper dc biasing of a CPW line on HRS substrate minimum HF loss can be achieved. This is of importance when active devices are to be biased through line interconnects.

Nonlinear MESFET parameter estimation using harmonic amplitude and phase measurements

This paper presents the use of harmonic amplitude and phase measurements in a new approach to nonlinear modeling of the frequency dispersive MESFET. Optimisation based nonlinear parameter estimation and a novel method for direct extraction of nonlinear dynamic drain characteristics are described Improved performance prediction using this new method is illustrated.<<ETX>>

A novel approach for the large signal analysis and optimisation of microwave frequency doublers

An approach is described for the large-signal analysis and optimization of microwave frequency doublers. A large-signal lumped-element model is used for an NE 71000 chip MESFET with a two-level harmonic balance program to analyze and optimize a target ideal doubler. A practical circuit is built to synthesize the ideal doubler requirement. To verify the method experimentally, a single-ended doubler operating from 7-14-GHz has been used as a demonstrator. Agreement between experiment and theory is excellent. The method described is transferable to multipliers of higher order, and to higher frequencies.<<ETX>>

A 7.5-GHz super regenerative detector

In this paper, simulated and measured results are presented for a microwave-integrated-circuit super regenerative detector operating at 7.5 GHz and brief comparisons made to a monolithic-microwave integrated-circuit super regenerative detector operating at 34 GHz. The sensitivity of the 7.5-GHz detector was measured at -83-dBm (AM, 1 kHz, 100 % mod) RF signal for 12 dB (signal + noise + distortion)/(noise + distortion). Simulation results show that, to produce a sensitive super regenerative detector, a high rate of change in loop gain of the oscillator circuit with respect to the gate bias (quenching) voltage and a high maximum loop gain at the point of detection is required. It has also been shown, by simulation and measurement, that the detection frequency of the super regenerative detector is lower than the normal free-running oscillation frequency.

HBT active antenna as a self oscillating Doppler sensor

This paper investigates the use of Heterojunction Bipolar Transistors (HBTs) as the working device in an active antenna for a self detection system. The devices used here are GaInP-GaAs HBTs from the GMMT F40 process. The design and performance of an active antenna based on this device is presented. A new large signal model is used to develop the active antenna described in this paper. The element oscillates at 11.40 GHz and produces approximately 5 mW of radiated power. A minimum detectable signal (MDS) of -99 dBm in a 10 Hz bandwidth has been measured.

Silicon interconnects for millimetre wave circuits

Recently high resistivity silicon (HRS) has been reported as an alternative to Gallium Arsenide as a high frequency MMIC foundry material. By employing aluminium metallized high resistivity silicon as a multilayer low cost interconnect medium passive structure (eg antennas, filters etc) can be fabricated at microwave and millimetre wavelengths. This paper demonstrates that thin metallization of aluminium can yield acceptable performance as coplanar waveguide circuit interconnects and can be used for direct circuit realization. A circuit example of the use of 1 ¿m aluminium metallization for the patterning antenna resonator is described. Various measurement issues are elaborated including the problem of contact resistance due to oxidation of the aluminium metallization.

Analysis of HEMT harmonic generation using a vector nonlinear measurement system

A study of HEMT harmonic generation was carried out using a Vector Nonlinear Measurement System to measure drain and gate waveforms. The cause of second and third harmonic nulls with increasing input power, and their direct relation to the output IV characteristics is shown. The effect of DC drain current variation with increasing input drive level is also explained. The results indicate the potential for exploiting harmonic nulling behaviour in circuit applications. Analysis of second harmonic dependency on quiescent operating point shows a doubling mode with intrinsic suppression of unwanted third harmonic.

Comparison of GaAs MESFET DC models

A comparative study of ten GaAs MESFET DC models, including three variations, is described. The computations have been carried out using an interactive program for nonlinear parameter extraction and sensitivity analysis (INTERSECT). The study concluded that W.R. Curtices cubic model (1985), with seven parameters, provides the best fit to the two sets of MESFET DC characteristics used.<<ETX>>