A Novel Synthesiser for Miniature SSB Radio Equipment

Abstract

There is an increasing requirement for small portable HF SSB radio equipment. A major problem encountered when designing such equipment is the lack of a simple inexpensive frequency synthesiser design which combines high resolution, low noise, low power requirements and small size. Two popular techniques normally used in modern SSB radio equipment include the Fractional N and Multi Loop systems. Both of these are difficult to miniaturise without loss of performance. The limitations of the above synthesiser systems are discussed in this paper. An alternative technique which meets the main requirements is also covered. This system employs a simple divide by N loop with a wide channel spacing. Interpolation between the channels is achieved by controlling the loop reference oscillator frequency. The interpolation can be modified by time sharing between two discrete frequencies produced by the oscillator, or an analogue proportional control can be used. Both methods are discussed. Details of an LSI chip designed for synthesiser systems using this technique is also given.