Transistor crystal oscillators and the design of a 1-Mc/s oscillator circuit capable of good frequency stability

The paper describes in detail a two-transistor series-resonance oscillator circuit, in which two point-contact diodes in parallel provide amplitude limitation. No transformer is required. The particular ATcut crystal used has aQ-value of just over 250 000, and the oscillator frequency increases by approximately 1.5 parts in 108per volt increase in the 10 V d.c. supply. By adding a variable-capacitance diode, this variation may be reduced severalfold. The crystal dissipation is less than 1 ¿W, giving a low rate of frequency drift due to crystal ageing. The paper also discusses the relative properties of various well-known oscillator circuits, and gives tables of useful design formulae. One conclusion is that a simple one-transistor Pierce oscillator is capable, when correctly designed, of a much better performance than that usually associated with valve versions of the circuit. Satisfactory operation at a crystal dissipation of about a microwatt is quite feasible without employing additional circuits for amplitude control. An unusual crystal equivalent circuit is derived for use particularly in parallel-resonance oscillators, and this leads directly to a simple alternative explanation of the Marconi FMQ system for frequency modulating a crystal oscillator.