Compact Fast-Hopping Frequency Synthesizer for Spread-Spectrum Systems

This paper describes a compact synthesizer developed* for an Air Force spread-spectrum system. The prototype from TRW (ref. 1) covers the 1280-1535 MHz range in integral MHz steps, with a hopping speed of approximately 25 nanoseconds. As all the output frequencies are obtained by multiple mixing of only two clock-referenced input tones, the long-term stability of the output is as good as that of the clock. The overall architecture is that of an iterative synthesizer, with four identical stages of divide-and-mix. A 1×4 switch at each stage chooses the additional tone to be mixed in. Use of four identical modules facilitates the use of custom RF LSI chips, leading to the achievement of small size and low cost.