Method and apparatus for eliminating count scatter introduced by phase-locked loop frequency multipliers

Claim 2

A frequency measuring system for precision determination of the frequency of an incoming AC signal comprising a phase-locked loop multiplier system to which said incoming signal is delivered including a voltage controlled oscillator having an output frequency at a multiple of the frequency of the incoming signal, means for measuring said output frequency of said voltage controlled oscillator as a measure of the frequency of said incoming signal, means for transmitting said output signal from said voltage controlled oscillator to said frequency measuring means for a predetermined time interval and means for synchronizing the initiation of said transmission with a predetermined point in the cycle of said incoming frequency signal.

Claim 3

A frequency measuring system as claimed in claim 1 wherein said synchronizing means comprises means for synchronizing the initiation of transmission with one of the zero crossings of said incoming signal.

Claim 4

A frequency measuring system as claimed in claim 1 wherein said means for transmitting said output signal to said measuring means comprises a gate circuit coupled between the voltage controlled oscillator and the measuring means, said synchronizing means controlling the time at which turn on of said gate occurs.

Claim 5

A magnetometer system comprising means for producing precessions of atom portions at their Larmor frequency of precession in a magnetic field to be measured and converting said precessions to an incoming alternating signal, a phase-locked loop multiplier system coupled to said means for receiving said incoming signal and including a voltage controlled oscillator operating at a multiple of the frequency of the incoming signal, means for measuring the output frequency of said voltage controlled oscillator as a measure of the strength of said magnetic field, means for transmitting the output signal from said voltage controlled oscillator to said frequency measuring means for a predetermined time interval, and means for synchronizing the initiation of said transmission with a predetermined point in the cycle of the incoming precession frequency signal.

Claim 6

A magnetometer system comprising means for producing precessions of atom portions at their Larmor frequency of precession in a magnetic field to be measured and converting said precessions to an incoming alternating signal, a phase-locked loop multiplier system coupled to said means for receiving said incoming signal and including a voltage controlled oscillator operating at a multiple of the frequency of the incoming signal, means for measuring the output frequency of said voltage controlled oscillator as a measure of the strength of said magnetic field, means for transmitting the output signal from said voltage controlled oscillator to said frequency measuring means for a predetermined time interval, and means for synchronizing the initiation of said transmission with a predetermined point in the cycle of the incoming precession frequency signal.

Claim 7

A magnetometer system as claimed in claim 4 wherein said magnetometer is a nuclear free precession magnetometer.

Claim 8

A magnetometer system as claimed in claim 4 wherein said magnetometer is an atomic resonance magnetometer.

Claim 9

A magnetometer system as claimed in claim 4 wherein said means for transmitting said output signal to said frequency measuring means comprises a gate circuit coupled between said voltage controlled oscillator and the measuring means, said synchronizing means controlling the time at which the turn on of said gate occurs.

Claim 10

A magnetometer system as claimed in claim 4 wherein said synchronizing means comprises means for synchronizing the gate opening with one of the zero crossings of said incoming signal.

Claim 11

A frequency counting system for deteRmining the frequency of an incoming alternating signal of variable frequency f comprising, a phase detector, a voltage controlled oscillator for producing an alternating signal output at approximately Nf, where N is a predetermined number greater than 1, a frequency divider circuit for dividing the alternating signal Nf from the oscillator by N to produce an output at approximately f, said signal output from the divider and said incoming alternating signal being transmitted as two inputs to said phase detector to produce an error signal output from the detector related to the frequency difference between the two input signals, a feedback circuit for coupling said error signal to said voltage controlled oscillator to thereby tune said oscillator to the frequency Nf, a frequency counter, a gate circuit for transmitting the output signal of said voltage controlled oscillator to said frequency counter for a predetermined time interval, said counter measuring the frequency thereof, and means for controlling the turn on time of said gate in synchronism with the incoming alternating signal so that each successive frequency counting interval commences at a predetermined point in the cycle of the incoming alternating signal.

Claim 12

A frequency counting system for deteRmining the frequency of an incoming alternating signal of variable frequency f comprising, a phase detector, a voltage controlled oscillator for producing an alternating signal output at approximately Nf, where N is a predetermined number greater than 1, a frequency divider circuit for dividing the alternating signal Nf from the oscillator by N to produce an output at approximately f, said signal output from the divider and said incoming alternating signal being transmitted as two inputs to said phase detector to produce an error signal output from the detector related to the frequency difference between the two input signals, a feedback circuit for coupling said error signal to said voltage controlled oscillator to thereby tune said oscillator to the frequency Nf, a frequency counter, a gate circuit for transmitting the output signal of said voltage controlled oscillator to said frequency counter for a predetermined time interval, said counter measuring the frequency thereof, and means for controlling the turn on time of said gate in synchronism with the incoming alternating signal so that each successive frequency counting interval commences at a predetermined point in the cycle of the incoming alternating signal.

Claim 13

A frequency counting system as claimed in claim 9 wherein said last means operates in response to one of the zero crossings of the incoming signal cycle.

Claim 16

The method as claimed in claim 11 wherein the step of synchronizing the start of the count with the incoming signal comprises synchronizing with one of the zero crossings of the incoming signal.