Measurement bandwidth enhancement in phase lock loops

Claim 2

In a control loop of predetermined bandwidth and of the type wherein an input signal and feedback signal are compared to provide an error signal to a loop filter which in turn controls a feedback circuit which provided the feedback signal, a method of measuring said error signal over a bandwidth which extends to frequencies below the loop bandwidth, said method comprising the steps of: processing the output signal from said low pass loop filter through a circuit having a transfer characteristic which matches the transfer characteristic of said feedback circuit; summing the processed output signal with said error signal; and measuring the amplitude of the summed signals.

Claim 3

The method according to claim 1 wherein said loop is a phase lock loop and said error signal is a phase error signal representing phase variations in said input signal, said loop further comprising: a voltage controlled oscillator which provides said feedback signal at a frequency proportional to the amplitude of the output signal from said low pass loop filter; and wherein said processing involves integrating said output signal from said low pass filter.

Claim 4

The method according to claim 2 further comprising the step of alternatively metering said error signal and the summed signals.

Claim 5

A phase lock loop for providing a phase measurement signal indicative of phase jitter appearing on an input signal of predetermined nominal frequency, said loop being characterized in that said phase measurement signal has a frequency bandwidth with a low frequency cut off below the low frequency cut off of the loop bandwidth, said loop comprising: a voltage-controlled oscillator for providing a VCO signal which varies from said predetermined nominal frequency in proportion to the level of control voltage applied thereto; a phase comparator means for providing an error signal indicative of the phase difference between said input and VCO signals; low pass loop filter means responsive to said error signal for providing said control voltage to said voltage controlled oscillator; integrator means for integrating said control voltage; and summing means for summing the amplitudes of said error signal and said control voltage to provide said phase measurement signal.

Claim 6

A phase lock loop for providing a phase measurement signal indicative of phase jitter appearing on an input signal of predetermined nominal frequency, said loop being characterized in that said phase measurement signal has a frequency bandwidth with a low frequency cut off below the low frequency cut off of the loop bandwidth, said loop comprising: a voltage-controlled oscillator for providing a VCO signal which varies from said predetermined nominal frequency in proportion to the level of control voltage applied thereto; a phase comparator means for providing an error signal indicative of the phase difference between said input and VCO signals; low pass loop filter means responsive to said error signal for providing said control voltage to said voltage controlled oscillator; integrator means for integrating said control voltage; and summing means for summing the amplitudes of said error signal and said control voltage to provide said phase measurement signal.

Claim 7

The combination according to claim 4 further comprising: a metering circuit; and switch means for alternatively applying said error signal and said phase measurement signal to said metering circuit.

Claim 8

A control loop of the type which provides a measurement signal indicating variations in a predetermined parameter of an input signal, said loop being characterized in that its bandwidth has a low frequency cut-off which is higher than the low frequency cut-off of the measurement signal bandwidth, wherein said loop comprises: comparator means arranged to receive two signals and provide an error signal having an amplitude proportional to the difference in said predetermined parameter between said two signals; loop filter means responsive to said error signal for providing a control signal; feedback means having a predetermined transfer function responsive to said control signal for providing a feedback signal; means for applying said feedback signal to said comparator means as one of said two signals; means for applying said input signal to said comparator as the other of said two signals; circuit means having the same transfer function as said feedback means for passing signals passed by said filter means to provide a first voltage; and summing means for summing said first voltage with said error signal amplitude to provide said measurement signal.

Claim 9

A control loop of the type which provides a measurement signal indicating variations in a predetermined parameter of an input signal, said loop being characterized in that its bandwidth has a low frequency cut-off which is higher than the low frequency cut-off of the measurement signal bandwidth, wherein said loop comprises: comparator means arranged to receive two signals and provide an error signal having an amplitude proportional to the difference in said predetermined parameter between said two signals; loop filter means responsive to said error signal for providing a control signal; feedback means having a predetermined transfer function responsive to said control signal for providing a feedback signal; means for applying said feedback signal to said comparator means as one of said two signals; means for applying said input signal to said comparator as the other of said two signals; circuit means having the same transfer function as said feedback means for passing signals passed by said filter means to provide a first voltage; and summing means for summing said first voltage with said error signal amplitude to provide said measurement signal.

Claim 10

The loop according to claim 6 further comprising: a metering circuit; and switch means for alternatively applying said measurement signal and said error signal to said metering circuit.

Claim 11

The loop according to claim 6 wherein said predetermined parameter is phase, wherein said feedback means includes a voltage controlled oscillator connected to receive and be controlled by said signals passed by said low pass loop filter means, and wherein said comparator means is a phase detector.

Claim 12

The combination according to claim 5 wherein said integrator means has a transfer characteristic which matches the transfer characteristic of said voltage controlled oscillator.