GB1165325A - Improvements in or relating to Spectrum Frequency Generators - Google Patents

Abstract

1,165,325. Frequency synthesizing circuits; automatic frequency control systems. PLESSEY CO. Ltd. 1 Feb., 1967 [1 March, 1966], No. 8888/66. Headings H3A and H3F. A digital frequency synthesizer, Fig. 3, comprises a number of stages 25 ... 28 appertaining to the respective digits, the stage 28 corresponding to the least significant digit including a slave oscillator 18, the frequency of which is variable in dependence upon the setting of a control means 22, and the other stages 25, 26, 27 including a slave oscillator 18, the frequency of which is variable independence on the setting of a control means 22 and also on the signal applied to it from the stage corresponding to the digit of next lowest significance. In each of the stages 25, 26, 27 the signal from the slave oscillator 18 and that from the preceding stage are mixed in mixers 19, and the mixer output is fed to the control means 22 via a bandpass filter 21. The synthesizer may be employed as an oscillator 15 in a receiver, Fig. 2. Incoming signals are fed to first and second mixers 1, 5 each associated with a respective local oscillator 3, 6. The output from the digital oscillator 15 and local oscillator 6 are fed to mixer 16 and the resulting output is then fed together with the output from local oscillator 3 to a further mixer 8. The output from mixer 8 is compared with the signal from a reference source 13 to provide coarse 11, and fine 12 control for oscillator 3.