Frequency synthesizer using frequency control based on a narrow band within spectrum of harmonics

摘要

1,122,299. Automatic frequency control systems. C.I.T.- COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 8 Dec., 1966 [8 Dec., 1965], No. 55006/66. Heading H3A. A variable frequency oscillator 14 is locked to the frequency of a selected harmonic of a reference oscillator 11 which feeds an harmonic generator 12 and a high-pass filter 13, the two signals being fed to a mixer 15 feeding a phase discriminator 18 through a narrow band filter 17, the other input to the phase discriminator being one of the harmonics of the reference oscillator below the pass band of filter 13 and being supplied through a second narrow band filter 16 so that phase comparison is always at the same frequency whatever the output frequency, The output frequency is selected by inserting a corresponding number in a register 29 which sets a counter 23. Initially the frequency of the oscillator 14 is swept by a generator 19 until it reaches the frequency F B of a second reference oscillator 26 when a mixer 21 produces an output which changes over a bistable circuit 28 energizing a relay 22. Thereafter each time the frequency of oscillator 14 passes through an harmonic of oscillator 11, an output from mixer 15 steps down the counter 23 by 1. When the counter is stepped down to a count of 1 it produces an output on line 30 which energizes relay 20, thereby putting the oscillator 14 under control of the phase discriminator 18. The output from the phase discriminator on line 31 also energizes relay 24; if synchronism is lost and this relay is deenergized, the supply source 25 and differentiating circuit 27 generate a pulse which restores the bi-stable circuit 28 and re-sets the counter 23 to the count stored in register 29 so that the frequency-finding operation is started again.