Circuit for driving frequency standard such as tuning fork

Claim 2

In combination: a signal source having a resonant frequency: amplifier means connected to receive the signals from said source for amplifying said signals; oscillator means; first control means responsive to the frequency relationship between the signals produced by said amplifier means and the signals produced by said oscillator means for producing an output signal having a predetermined phase and frequency relationship to the signals produced by said signal source, when said signal source is operating at its resonant frequency; and second control means for connecting said first control means to drive said signal source when said output signal of said first control means has said predetermined phase and frequency relationship to the signal produced by said signal source and for connecting said amplifier means to drive said signal source at other times.

Claim 3

In the combination as set forth in claim 1, said first control means including frequency divider means responsive to said oscillator means and comparator means for comparing the frequency and phase of the signals produced by said frequency divider means with the frequency and phase of the signals produced by said amplifier means, and means responsive to the output signal produced by said comparator means for controlling the frequency of said oscillator means.

Claim 4

In the combination as set forth in claim 2, said frequency divider means comprising a counter.

Claim 5

In the combination as set forth in claim 1, said second control means including switch means for selectively connecting said signal source to receive signals from one of said amplifier means and first control means.

Claim 6

In the combination as set forth in claim 1, said oscillator means comprising a voltage controlled oscillator and said first control means comprising a comparator for controlling the frequency of said voltage controlled oscillator.

Claim 7

In the combination as set forth in claim 4, said second control means including a pair of flip flops, each connected to receive a signal from said first control means and another signal from said comparator means, one of said flip flops supplying signals to the other of said flip flops and said other flip flop connected to control said switch means.

Claim 8

The combination of: a frequency standard which, when driven into oscillation, tends to oscillate at its resonant frequency; amplifier means connected to receive the signal produced by said frequency standard and initially connected to drive said freQuency standard into oscillation; a phase locked loop driven by said amplifier means; and means responsive to a signal produced by said phase locked loop at a frequency having a predetermined relationship to the resonant frequency of said frequency standard and having a phase bearing a predetermined relationship to the phase of the oscillations produced by said frequency standard for connecting said phase locked loop to drive said frequency standard and disconnecting said amplifier means from driving said frequency standard.

Claim 9

The combination of: a frequency standard which, when driven into oscillation, tends to oscillate at its resonant frequency; amplifier means connected to receive the signal produced by said frequency standard and initially connected to drive said freQuency standard into oscillation; a phase locked loop driven by said amplifier means; and means responsive to a signal produced by said phase locked loop at a frequency having a predetermined relationship to the resonant frequency of said frequency standard and having a phase bearing a predetermined relationship to the phase of the oscillations produced by said frequency standard for connecting said phase locked loop to drive said frequency standard and disconnecting said amplifier means from driving said frequency standard.

Claim 10

The combination as set forth in claim 7 wherein said frequency standard comprises a tuning fork and means for translating the mechanical oscillations of said tuning fork into electrical oscillations.

Claim 11

The combination as set forth in claim 7 wherein said phase locked loop includes a voltage controlled oscillator, a frequency divider driven by said voltage controlled oscillator, and means for comparing the frequency of the signal produced by said frequency divider with that produced by said amplifier means.

Claim 12

The combination as set forth in claim 7 wherein said means responsive to a signal produced by said phase locked loop comprises means responsive to a signal at the resonant frequency of said frequency standard and in a predetermined phase relationship to the signal produced by said frequency standard.

Claim 13

The combination as set forth in claim 7 wherein said amplifier means comprises a high gain amplifier having a regenerative feedback loop, and further including means for effectively disabling said feedback loop when said phase locked loop is driving said frequency standard.

Claim 14

The combination as set forth in claim 11 wherein said amplifier means comprises four field effect transistors, the conduction paths of two connected essentially in series between an output terminal and one operating voltage terminal and conduction paths of the other two transistors connected essentially in series between said output terminal and the second operating voltage terminal, and wherein said feedback path extends between said output terminal on the one hand and the control electrodes of two of said transistors on the other hand, said two transistors comprising one between said output terminal and one of said operating voltage terminals and the other between said output terminal and the other operating voltage terminal, and wherein said means for effectively disabling said feedback path comprises means for effectively shortcircuiting the conduction paths of said last-mentioned two transistors.

Claim 15

The combination as set forth in claim 12 wherein the two transistors on one side of said output terminal comprise transistors of one conductivity type and the other two transistors comprise transistors of another conductivity type.