GB1365607A - Frequency synthesizer - Google Patents

Abstract

1365607 Frequency synthesizers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 20 April 1972 [23 April 1971] 18312/72 Heading H3A A frequency synthesizer comprises a first control loop 2 including a mixer 10, a detector 11 and a controlled oscillator 1, the latter being locked to a frequency equal to a harmonic of the output F 1 of a first reference generator 3 minus (or plus) a frequency shift determined by the detector 11, a second control loop 7 for stabilizing the outputs F 1 , F 2 of the first reference and a second reference generator 3, 6 respectively at an adjustable frequency difference determined by a variable divider 12 so that the output F 2 of 6 has a harmonic corresponding to the output F 0 of the controlled oscillator 1, and a third control loop 9 for disturbing the synchronization of oscillator 1 when the above correspondence is not achieved. The detector 11 may be a phase discriminator or a frequency discriminator (11, Fig. 2, not shown) operating at the desired shift frequency. The loop 7 also includes a pulse mixer 5 for obtaining the frequency difference of outputs F 1 , F 2 and a phase discriminator 15 for comparing the above frequency difference with the divided output of generator 3. When the required output F 0 does not correspond to a harmonic of F 2 , a pulse mixer 8 applies an alternating voltage via a capacitor 16 and a low pass filter 14 to unlock oscillator 1. In the embodiment of Fig. 2 (not shown), the detector 11 is formed by a tuned circuit follosed by a diode detector. It has also been indicated that a frequency discriminator of the type used in the embodiment of Fig. 2 (not shown) may be connected in series with the phase discriminator 11 and the output of one of the discriminators may be optionally used to control the oscillator 1. Further, the fixed divider 13 may be programmed to provide one of two fixed shift frequencies.