Patent GB-1419566-A (GB)
Title: Circuit arrangement for driving frequency standard
IPC: H03B5/30
Filed: 1973-02-21
Abstract: 1419566 Electronic timepieces RCA CORPORATION 21 Feb 1973 [1 March 1972] 8454/73 Heading G3T [Also in Division H3] A timing circuit, e.g. for a car clock incorporating a synchronous motor, comprises a tuning fork reference frequency signal source 10 Fig. 1, an amplifier means 13 connected to amplify the reference signals and initially connected by switch means 17 to drive said fork into oscillation; oscillator means, e.g. voltage controlled oscillator (VCO) 16; first control means including a comparator 14 and frequency divider 19 which comparator compares the phase and frequency of the output from frequency divider 19 (which divides the output of the oscillator means), with that of the amplified reference signal and controls the oscillator means output frequency and phase accordingly; a second control means including a logic circuit 18 which controls the changeover switch means 17 so as to disconnect the amplifier 13 from the fork drive crystal 12 and connect the output of the oscillator means 16 to drive the fork 10 via the frequency divider 19 when the oscillator 16 is locked-in on the fork frequency, the fork oscillating at its resonant frequency. A frequency divider counter 20 divides the output frequency of divider 19 to a value e.g. 30Hz suitable for driving a synchronous motor 21 via a voltage regulator 22. The motor is coupled in known manner to time display means. In Fig. 1 a so-called charge pump 15 comprises a capacitor Cl, Fig. 2, which charges as a function of the difference signal binary outputs of the comparator 14. A voltage signal from Cl  controls the oscillator 16 to produce an output at four times the fork frequency, this output being divided by four by the divider counter 19. The oscillator 16 comprises first, second and third COSMOS inverter networks P 12N 12, P14N14 and P15N15 respectively, also a transmission gate P13N13 and regulating units P11 and N11 which have variable impedance and co-operate in the charge and discharge of a timing capacitor C2. Thus the cycle time is determined by the impedances of devices P11, P13, N 11, N13 the devices P13N13 being fixed in impedance. The impedances of P 11N11 are determined by the control voltage from Cl. When for instance the DC voltage of the control voltage is raised, the impedance value of P11 is increased and the impedance of N11 is decreased, the cycle time becomes longer and the oscillator frequency is reduced. When the threshold of P 11 is reached it becomes non-conductive and its impedance is not varied. However the impedance of N11 will continue to change with increasing control voltage. If the control voltage falls below the threshold of N11, it will stop conducting. In this condition the impedance of P11 will continue to change with the reduction in control voltage down to zero volts. The phase lock loop includes the comparator 14, Cl and its charging semi-conductors P10N10, the VCO 16 and the counter divider 19. The comparator 14 attempts to establish the relationship between the leading edge (0 degrees phase point) of the counter 19 output and that of the reference signal, and the resulting difference signal in binary form is fed to logic 18. When the circuit 18 recognizes that the phase lock loop has locked-in on the fork frequency signal, the circuit 18 conditions the semi-conductor switch 17 so that the drive of the fork is taken over by a 90 degrees (or 270 degrees) phase point signal from the counter 19 via switch 17, the amplifier 13 being disconnected from the drive crystal 12.