Peter Heymann

Direct extraction of HBT equivalent-circuit elements

We present an analytical method for determining the heterojunction bipolar transistors (HBTs) equivalent-circuit elements. Its special feature is that it does not need measurements of test structures nor optimizations. The new algorithm for extracting the intrinsic elements exploits the information contained in the frequency dependence of the network parameters. This leads to a fast algorithm with a unique solution. The method is validated treating GaInP-GaAs HBTs.

Scalable GaInP/GaAs HBT large-signal model

A scalable large-signal model for heterojunction bipolar transistors (HBTs) is presented. It allows exact modeling of all transistor parameters from single finger elementary cells to multifinger power devices. The scaling rules are given in detail. The model is verified by comparison with measurements of GaInP/GaAs-HBTs.

Unified model for collector charge in heterojunction bipolar transistors

The base-collector capacitance and the collector transit-time in GaAs-based heterojunction bipolar transistors depend not only on base-collector voltage, but also on collector current. This has to be taken into account in a large-signal model. However, since collector transit-time and capacitance are both caused by the charge stored in the collector space-charge region, it is not possible to model them independently of each other. This paper investigates the interrelation between collector capacitance and transit-time due to transcapacitance effects, and presents an analytical unified description for both quantities, that is derived from measurement-extracted small-signal equivalent circuits. The model is verified by comparison of simulation and measurement data.

Experimental evaluation of microwave field-effect-transistor noise models

Extensive GaAs field-effect-transistor noise measurements are used to compare noise models with the aim of recommending the most useful one for monolithic-microwave integrated-circuit design. The evaluation is based on noise and S-parameter measurements of metal-semiconductor field-effect transistors and high electron-mobility transistors with different gatewidths in the frequency range of 0.05-26 GHz. The models under investigation differ in the number of independent coefficients necessary to calculate the four noise parameters of the device. The broad frequency range including radio-frequency frequencies down to 50 MHz requires two different noise measurement systems with special modifications for optimum performance. In conclusion, the two-parameter Pospieszalski model turns out to be the most suitable one.

De-embedding of MMIC transmission-line measurements

The determination of transmission-line characteristic impedance and propagation constants from two-port S-parameter measurements is disturbed by half-wavelength resonances. We demonstrate this effect for on-wafer measurements of coplanar lines. Two networks representing end effects embed the line and strongly enhance the resonant effect. The de-embedding consists in determining these networks and subtracting them from the measured chain matrix. It is shown that simple shunt admittances are sufficient for modeling of the end effects. Three methods of de-embedding are presented.<<ETX>>

Compact Large-Signal Shot-Noise Model for HBTs

A new description of the shot noise in HBTs is proposed that accounts for the correlation of the sources. It can easily be included in large-signal models, thus significantly improving the RF noise description. Common nonlinear bipolar transistor models thus far neglect the correlation, which deteriorates the model accuracy towards higher frequencies. It is shown that the collector delay in InGaP/GaAs HBTs dominates the shot noise correlation. Hence, the collector time-delay description of the large-signal model is capable of providing suitable noise correlation time constants. The model is verified against measurements of InGaP/GaAs HBTs with three different epitaxial layer designs.

Large Area AlGaN/GaN HEMTs Grown on Insulating Silicon Carbide Substrates

Large periphery Al 0.25 Ga 0.75 N/GaN-HEMTs on SiC-substrates are fabricated on a 2-inch process line using stepper lithography. DC characteristics reveal current densities above 1.2 A/mm and intrinsic transconductances of 360 mS/mm. Depending on device size the maximum frequency of oscillation f max varies from 27-79 GHz. With these devices a power density of 5.2 W/mm and a power level of 13.8 W is achieved at 2 GHz.

Modeling of low-frequency noise in GaInP/GaAs hetero-bipolar transistors

Accurate low-frequency noise modeling is a prerequisite for oscillator phase-noise simulation. In this paper, the LF noise sources of GaInP/GaAs HBTs are investigated. It turns out that the 1/f-noise model must contain two sources, the base-emitter diode and the emitter resistance. Quantitatively, excess noise power at 100 kHz scales with the square of collector current-density.

On Compact HBT RF Noise Modeling

Accurate RF noise modeling of heterojunction bipolar transistors requires a proper model for the correlation of the shot-noise sources based on the respective time constant. This is incompatible with the present large-signal models, which, therefore, rely on non-correlated shot-noise sources and are not capable of predicting the RF noise with sufficient accuracy. In this paper, we propose a new configuration of the shot-noise sources which approximates the correlation by taking advantage of the large-signal models equivalent circuit topology. The model is verified by measurements.

Multiharmonic generators for relative phase calibration of nonlinear network analyzers

Multiharmonic generators are of interest for determining coupler phase dispersion of nonlinear network analyzers inherently dealing with nonsinusoidal waveforms for RF current-voltage (I-V) measurements. Supported by simple waveform analysis, two on-wafer devices are experimentally evaluated: a single diode and a nonlinear transmission line (NLTL). The investigation uses an active harmonic load-pull system with 2 GHz fundamental frequency. It turns out that the NLTL is well suited as a reference generator. We present measurement examples of phase dispersion for different directional couplers up to 18 GHz and the application to RF I-V waveforms of a 1-W power HBT with harmonic load tuning.