The application of transistors to the generation of stable-frequency supplies for carrier telephone equipment

Frequency-division-multiplex telephone terminal equipment requires a series of stable carrier-frequency supplies, together with other frequencies for pilot and signalling purposes. The paper surveys the application of transistors to the generation of these supplies, with reference to circuits designed to meet typical requirements. Carrier supplies are usually derived from a single master oscillator and the design of such an oscillator with a long-term frequency stability of better than one part in 106 is discussed. Circuits for the derivation of groups of carrier frequencies from the master source are also described. These include harmonic generators and a divider of the regenerative-modulator type. Power levels required at the various carrier frequencies vary from a few milliwatts to several watts for different frequencies and applications. Some of the problems of obtaining stable amplification with transistors at high levels and high frequencies are illustrated by examples of amplifier design for frequencies up to 612kc/s. A particular problem is the supply of pilot signals having an extremely stable amplitude. The design of an effective constant-output amplifier for this purpose is described.