The design of low-noise IMPATT diodes has been aided by theories describing the noise generation under small-signal conditions. A major deficiency in this procedure has existed in that there is no apparent connection between the small-signal behavior and the great increases in the noise observed in large-signal operation. As a remedy a theory has been developed for the noise generation at arbitrary signal levels by using a Read diode model. The theory is based on a linearization technique for calculating the spectrum of homogeneous noise with linear damping resulting in a separation of the large-signal and noise problems. The open-circuit noise voltage increases strongly at high signal levels due to nonlinear parametric interactions and gives rise to a rapid increase in the noise measure as a function of the generated microwave power. Operating parameters are derived that optimize the power-noise ratio. A long intrinsic response time is found to be beneficial in achieving high power as well as low noise. Other factors affecting the design and choice of material for IMPATT diodes are discussed. An important feature of the presented theory is that a complete design optimization with respect to the power-noise characteristics can be carried out provided reliable information exists about the ionization rates and the drift velocities. A simpler alternative is to obtain the physical quantities governing the power-noise behavior from small-signal admittance and noise measurements. Good agreement has been obtained with experimental power-noise measurements by this method. As an application of this procedure a state of the art comparison is given for GaAs, Ge, and Si diodes at 6 GHz.

Noise in IMPATT diodes: Intrinsic properties

IMPATT diode characterization on the basis of output power and the corresponding FM noise figure over a range of operating conditions is presented. The characterization consists of families of power noise curves obtained for a phase-locked IMPATT oscillator where the supply current, load conductance, and the operating frequency are parameters. It is shown that the maximum output power and minimum FM noise are not achieved concurrently. In particular FM transmitter application, it is shown that the best performance for each type of diode was obtained when operated at less than maximum power (and at reduced efficiency) where the system benefits from the attending lower noise. Better system performance, this application, was obtained with the GaAs IMPATT diode. The power-noise characterization defines the optimum operating conditions for an IMPATT diode and provides a valid basis for the comparison of diodes for specific applications.

Power-noise characterization of phase-locked IMPATT Oscillators

This paper studies the scattering of a plane wave by an active corrugated structure in which each slot region is connected to a microwave solid‐state amplifier. Consequently, not only are we able to control the phase of the reflected wave but also its power gain. An exact solution to this problem has been obtained by the residue calculus method under the assumption that only the TEM wave propagates and is amplified in the slot region. Numerical results are presented for illustrating the scattering properties as a function of the slot dimension and the amplifier gain. An approximate but much simplified analytical expression for the reflection coefficient is derived and it should be found useful in other scattering problems (such as the design of a reflector antenna) by the ray‐tracing method. A related problem of surface wave propagation on the active corrugated structure and its potential application as a high‐power amplifier are also discussed.

Electromagnetic Wave Scattering from an Active Corrugated Structure

A new approach to IMPATT diode circuit design to achieve freedom from parametric instabilities is described. Necessary and sufficient conditions are described in the frequency domain for the load impedance presented to the diode terminals. A number of unconditionally stable circuits have been developed for flat-profile GaAs diodes using this approach. Three of these circuits have been built and tested experimentally in 11-GHz IMPATT oscillators and amplifiers. These experimental circuits have been free of parametric instability, even when driven into full RF saturation. In a systems application practical constraints such as cost, RF loss, and tunability will require compromises which will degrade the stability, and it may not always be possible to achieve complete stability for a given diode.

IMPATT Diode Circuit Design for Parametric Stability

A frequency-independent lumped equivalent circuit is proposed for characterizing the large-signal behavior of IMPATT diodes. It has five elements including a negative resistance, two of which are quadratic functions of the single-frequency RF voltage across the device. It is used for computer-aided analysis and the design of reflection-type negative-resistance amplifiers employing IMPATT diodes. The frequency response of the amplifier is calculated for different input power levels and the nature of the results is found to be in agreement with published experimental results.

Large-Signal Equivalent Circuit for IMPATT-Diode Characterization and Its Application to Amplifiers

A technique for measurement of the large-signal single-frequency microwave amplifier admittance of avalanche diodes is described, and results are presented for silicon and germanium avalanche diodes. Single-frequency amplifier operation can provide a unique characterization of diode-admittance variation with RF drive for diodes operated near the optimum transit angle (the case in which all harmonic voltages are negligibly small compared to the fundamental). Such characterization is useful for predicting diode performance for circuits in which the harmonic voltages are not large enough to have an appreciable effect on the diode admittance at the fundamental frequency. A process of matching quadratic forms to the above admittance data which may be used for calculation of diode terminal admittance and power output is discussed. The usefulness of the measurement technique is illustrated by the agreement of the calculated maximum power output with the measured power output in a single-transformer coaxial circuit. The corresponding circuit admittance may be used for circuit-design purposes and for evaluating variations in diode-assembly techniques. The ability to obtain the diode equivalent circuit as a function of incident power allows studies in the design of the associated semiconductor device. For example, one has the capability of obtaining an accurate single-frequency large-signal model near the optimum transit angle, a model which can be studied without building a circuit. With this model it is possible to carry out optimization procedures at considerable savings of time and money.

R.L. Frank

Papers

Large-Signal Silicon and Germanium Avalanche-Diode Characteristics