Electronic tuning of stable transferred electron oscillators

The problem of electronic tuning of microwave osciilator structures characterized by high energy storage and hence low noise is considered. The evolution of a wide-band varactor tuned J-band oscillator is described, and analytical criteria are presented which determine the position of the varactor diode and the theoretical maximum tuning range available including Varactor loss. Experimental results confirm the validity of the circuit model used for the proposed oscillator structures.     

Device physics of TRAPATT oscillators

This paper utilizes a simplified physical model to describe TRAPATT (TRApped Plasma Avalanche Triggered Transit) operation. By yielding on computational accuracy, a complete high-efficiency device design is generated and the dependence of operation on physical parameters is elucidated. The extreme complexity of the precise differential equations describing TRAPATT operation has made the calculation of a single diode-circuit configuration a tour de force. However, by observing the important features of such a solution, a simplified approach giving realistic answers has been evolved. A theoretical device design has been evolved. This design provides device width and impurity density as a function of TRAPATT frequency, and indicates a decreasing degree of "reach through" with increasing frequency. In addition, the explicit dependence of width and impurity density on the diode's reverse saturation current has been obtained. The launching of the avalanche zone through the diode, and, in particular, the limitations implicit in the recovery to a swept-out state, are of broad significance in other types of diodes, particularly p-i-n switches and "snap" diodes.     

Characterization of avalanche diode TRAPATT oscillators

The characteristics of a coaxial avalanche diode oscillator circuit are calculated and compared with experimental results. The circuit admittance, as seen at the diode terminals, is calculated in the frequency domain for "optimally tuned" experimental conditions. The impulse response function of the circuit, as obtained from the transformed admittance, is used to obtain time-evolution solutions of the avalanche diode circuit system. The impulse response is more general than the previously employed differential equation characterization of a lumped element equivalent circuit. The simulation presented of the high-efficiency mode of oscillation allowed no adjustable parameters and is in excellent agreement with experiment. The simulation verifies the original TRAPATT [1] explanation for the high-efficiency mode of oscillation.     

Analytical analysis of experimental TRAPATT amplifiers and oscillators

A method of analysis of TRAPATT amplifiers and oscillators has been developed, based upon a simple diode model and circuit impedance measurements. Calculations for fundamental and second-harmonic extraction devices are shown to be in good agreement with experimental measurements.     

Behavior and dynamics of optically controlled TRAPATT oscillators

The experimental behavior of optically controlled TRAPATT oscillators is described and results of a detailed numerical analysis of the dynamics of this optical control are presented. Wide ranges in illumination level and circuit tuning conditions are considered in order to investigate the extent of the optical control and to bring out various features of this control. It is shown that illumination of the TRAPATT diode results in increased electrical activity and serves to produce substantial shifts in oscillation frequency and power. A salient feature of this optical control is that the variations in frequency and power are dependent on the frequency to which the oscillator circuit is tuned, making it possible to adjust the characteristics of the frequency and power control. The observed behavior is shown to be the result of an optical enhancement of the carrier avalanche process which acts to control the dynamics of plasma formation and, in turn, the final density of the trapped plasma. Results of the calculations are found to be in good agreement with experiment and to indicate that further improvement in the degree of control can be obtained with optimized device structures.     

Numerical investigation of turn-on conditions in TRAPATT oscillators

A computer simulation of TRAPATT diode-circuit interactions has been used to study high-frequency oscillatory phenomena that are seen experimentally to occur simultaneously with TRAPATT initiation. The simulation combines a solution of the diode internal dynamics using the method of characteristics with a time-domain coaxial-circuit analysis. By determining its dependence on circuit and diode bias conditions, the high-frequency oscillation is shown to be a relaxation, not an IMPATT oscillation. The relaxation oscillation can be tuned by adjusting to TRAPATT bias current to minimize TRAPATT start-up time. A two-step (high-low) bias pulse, or ingenious utilization of ringing in the bias circuit, can also be used to minimize start-up time.     

Theory for power output and efficiency of silicon TRAPATT oscillators

A TRAPATT analysis is employed to obtain theoretical results for the efficiency and power output of silicon p+-n-n+ avalanche diodes at different frequencies. This is done for a range of doping densities and depletion-layer widths, and enables detailed design curves to be deduced.     

Computer tuning of hybrid audio oscillators

A hybrid tantalum thin-film and beam-lead silicon device will be incorporated in the Bell System's Touch-Tone telephones of the future. This RC multifrequency audio oscillator will replace the LC device presently used in the Touch-Tone keyboards. The tuning process for the RC device requires that the tantalum thin-film resistors be custom adjusted to calculated values; and a tuning system driven by a small process-control computer has been designed to fulfill this function.     

Use of low dielectric constant substrates for microstrip time-delay triggered TRAPATT oscillators

Our experimentation with microstrip trapatt oscillators of the type described by Davies et al.1 has indicated that the feasibility of such a design is dependent on the ratio of strip width to dielectric height (W/h) for the substrate used for a given microstrip-line impedance. For example, realisation on a polyguide substrate (?r = 2.32) of 1.58 mm height failed to give coherent oscillation due to unexpected transient voltage variations shown up by time-domain-reflectometry tests. However, simple modifications to the microstrip design to remove the transient voltage variations led to considerable improvement in the performance of the oscillator, and coherent behaviour was then obtained.     

Magnetic tuning of coaxial IMPATT oscillators

Frequency tuning of an IMPATT coaxial microwave oscillator, using variation of susceptibility of a 5 Oe linewidth y.i.g. sphere, is described. A deviation sensitivity of 2MHz/Oe is determined experimentally. Qualitative explanation is offered for the discrepancy between this value and the theoretically predicted sensitivity.     

Wide-range tuning of solid-state microwave oscillators

Equations are derived that give the electronic tuning range of solid-state microwave oscillators in terms of the Q factor of the tuning device and the available power output. For currently available varactors the tuning range is severely limited by the Q factor but some exchange of power output for the tuning range is possible. It is shown that series tuning is superior to shunt tuning.     

Effects of diode-package cutoff frequency on TRAPATT operation

The cutoff frequency of two ideal types of package is considered, and is shown to limit the maximum rate of rise of voltage for triggering the TRAPATT mode in a commonly employed circuit. The letter also places the negative-inductance concept employed in the analysis on a mathematical foundation.     

Effect of leakage current on the power output of s band TRAPATT oscillators

The effect of externally enhanced leakage current on S band TRAPATT diodes is reported. Without enhanced leakage, the TRAPATT has an effective leakage current density of the order of 0·4 A/cm2. Calculations indicate that the leakage current due to carrier storage provides the electron density for initiating the avalanche process.     

Varactor diode for tuning high-power solid-state microwave oscillators

A novel varactor diode has been developed for tuning high-power microwave solid-state oscillators. The resulting output power against frequency remains much flatter than conventional high-power varactor-tuned oscillators.     

Effect of varactor Q-factor on tuning sensitivity of microwave oscillators, including reverse tuning

It is shown how the effect of resistive losses in a varactor diode can drastically affect the tuning characteristics of millimetre-wave oscillators and can even cause the oscillator to tune in the reverse direction.     

X band c.w. TRAPATT oscillators using ring diodes on diamond heat spreaders

TRAPATT diodes for X band c.w. operation have been made using both double-epitaxy and diffusion techniques. These p+nn+ devices are fabricated in ring configurations and mounted on type-IIA diamond heat spreaders. A c.w. TRAPATT performance of 3.3 W and 18.5% efficiency has been achieved at 8 GHz using these diodes.