A Lumped-Circuit Study of Basic Oscillator Behavior

In the course of routine locking-bandwidth measurements on IMPATT diodes in the 50-60 GHz range, some observations were made that could not be accounted for by the simple theory 1-4 of injection locked oscillators. In particular, locking ranges of about 100 MHz for -- 40 dB injected power were measured, indicating an extremely low effective circuit Q-factor ( ^ 5 ) . In addition this range was asymmetrical about the free-running frequency, and was not exactly proportional to the injected voltage. On occasions there was at one end of the locking range a hysteresis between locking and unlocking conditions. Other phenomena commonly observed during tuning experiments on solid-state oscillators include the following: (i) A discontinuous change in frequency (here referred to as a "jump") as a parameter is varied (bias current, perhaps, or a tuning stub). If the tuning is reversed the jump occurs at a displaced frequency ("hysteresis"). (ii) In the neighborhood of a jump, the hitherto single line spectrum may acquire sidebands at displacements of order 0.1 to 1 percent. (Hi) Under some circuit conditions a broadband noisy output may be obtained. 255