Detailed computer analysis of LSA operation in CW transferred electron devices

Abstract

In the first part of the paper the importance of the microwave circuit parameters on the attainment of LSA oscillation in ideal uniform devices is investigated. It is shown to be desirable for the circuit to have high-dynamic impedance. In consequence stray capacity at the device, due to the device configuration or to the mounting arrangement, is to be avoided. The existence of a capacity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</tex> in parallel with the cold-device capacity C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> effectively raises the lower limit for LSA operation to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n/f &gt; 2 \times 10^{4}[(C+C_{0})/C_{0}]</tex> . In the second part of the paper devices with typical doping and mobility profiles are considered to operate in circuits with low-dynamic impedance as well as in circuits with high-dynamic impedance. The results presented show that the LSA operating efficiency can be very sensitive to certain inhomogeneities, notably doping ramps of order 12½ percent and high-resistivity regions at the cathode contact. The efficiency degradation is, however, very dependent on the circuit in which the device is operating. Finally it is shown that the efficiency of a CW device may be raised by several percent in some cases by compensating for the mobility profile with a suitable doping gradient.