Frequency counting apparatus and method
First Claim
1. A device for determining the phase of a periodic reference signal at a predetermined time, the device comprising:
- charge storage means;
current source means;
first switch means connected between the current source means and a reference potential;
second switch means connected between the current source means and the charge storage means; and
control means connected to receive the reference signal and a signal representing the predetermined time, the control means including means for sensing a periodic characteristic of the reference signal, means for causing the current source means to be disconnected from the reference potential at the predetermined time, means for causing the current source means to be disconnected from the charge storage means upon the occurrence of said characteristic after the predetermined time, and means for measuring the voltage on the charge storage means after the occurrence of said characteristic and for producing therefrom a phase signal an representing the phase of the reference signal at the predetermined time.
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Accused Products
Abstract
A device and method for measuring the frequency of an input signal by measuring the number of cycles of the input signal that occur in a sample interval between successive sampling times tn. An integer counter determines an estimated integer number of input signal cycles, and fraction counters determine fractional counts by counting cycles of a clock signal during time intervals between a first measurement time before the sampling time and a second measurement time after the sampling time. A correction circuit refines the fractional counts by determining the phase relationships between the clock and input signals at each measurement time. The correction circuit includes a constant current source, a capacitor, a first switch connected between the constant current source and a reference potential, a second switch connected between the constant current source and the capacitor, and a control circuit for the switches. The control circuit disconnects the current source from the reference potential at each measurement time, and disconnects the current source from the capacitor upon the next occurance of a periodic characteristic of the clock signal that occurs after the measurement time. The voltage on the capacitor then provides the required phase relationship.
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Citations
30 Claims
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1. A device for determining the phase of a periodic reference signal at a predetermined time, the device comprising:
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charge storage means; current source means; first switch means connected between the current source means and a reference potential; second switch means connected between the current source means and the charge storage means; and control means connected to receive the reference signal and a signal representing the predetermined time, the control means including means for sensing a periodic characteristic of the reference signal, means for causing the current source means to be disconnected from the reference potential at the predetermined time, means for causing the current source means to be disconnected from the charge storage means upon the occurrence of said characteristic after the predetermined time, and means for measuring the voltage on the charge storage means after the occurrence of said characteristic and for producing therefrom a phase signal an representing the phase of the reference signal at the predetermined time. - View Dependent Claims (2, 3, 4)
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5. A method for determining the phase of a periodic reference signal at a predetermined time, the method comprising:
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commencing the charging of a charge storage means at a known rate at the predetermined time; stopping the charging of the charge storage means upon the occurrence of a periodic characteristic of the reference signal that occurs after the predetermined time; and measuring the voltage on the charge storage means after the occurrence of said characteristic and for producing therefrom a phase signal an representing the phase of the reference signal at the predetermined time. - View Dependent Claims (6)
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7. A device for determining the time of occurrence of a sampling time tn in a time period that extends from a first measurement time ta to a second measurement time tb, the device comprising:
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means for providing a periodic clock signal having a period shorter than the time period between the measurement times; first counter means for determining a first count value by counting the number of cycles of the clock signal that occur between times tn and tb, and for producing a corresponding first count signal Xn ; second counter means for determining a second count value by counting the number of cycles of the clock signal that occur between the measurement times, and for producing a corresponding second count signal Yn ; a correction circuit for producing phase signals an and bn representing the phase of the clock signal at measurement times ta and tb respectively; and processing means for receiving the count and phase signals, for adjusting count signals Xn and Yn based upon the phase signals to produce corrected count signals Xnc and Ync, and for determining the sampling time tn relative to ta by determining the quotient Xnc /Ync. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method for determining the time of occurrence of a sampling time tn in a time period that extends from a first measurement time ta to a second measurement time tb, the method comprising:
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providing a periodic clock signal havin a period shorter than the time period between the measurement times; determining a first count value by counting the number of cycles of the clock signal that occur between times tn and tb, and for producing a corresponding first count signal Xn ; determining a second count value by counting the number of cycles of the clock signal that occur between the measurement times, and for producing a corresponding second count value Yn ; producing phase signals an and bn representing the phase of the clock signal at measurement times ta and tb respectively; and adjusting count signals Xn and Yn based upon the phase signals to produce corrected count signals Xnc and Ync, and determining the sampling time tn relative to ta by determining the quotient Xnc /Ync. - View Dependent Claims (15, 16, 17, 18)
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19. A device for measuring the frequency of an input signal by measuring the number of cycles of the input signal that occur in a sample interval between first and second sampling times, the device comprising:
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means for providing a periodic clock signal having a frequency higher than that of the input signal; integer counter means including means for sensing a periodic characteristic of the input signal, and for producing therefrom an integer signal representing an estimated integer number N of cycles of the input signal that occur in the sampling interval; fraction measurement means for determining the time of occurrence of each sampling time tn in a time period that extends from a first measurement time ta corresponding to the occurrence of the characteristic of the input signal preceding tn to a second measurement time tb corresponding to the occurrence of the characteristic of the input signal following tn, the fraction measurement means comprising; (i) first counter means for determining a first count value by counting the number of cycles of the clock signal that occur between times tn and tb, and for producing a corresponding first count signal Xn ; (ii) second counter means for determining a second count value by counting the number of cycles of the clock signal that occur between the measurement times and for producing a corresponding second count signal Yn ; and (iii) a correction circuit for producing phase signals an and bn representing the phase of the clock signal at measurement times ta and tb, respectively; and processing means for receiving the integer signal and the count and phase signals for each sampling time, the processing means including means for adjusting count signals Xn and Yn for each sampling time based upon the phase signals for that sampling time, to thereby produce corrected count signals Xnc and Ync for each sampling time, and means for measuring the number of cycles Cn of the input signal that occur in the sampling interval by determining N plus the quotient Xnc /Ync for the first sampling time minus the quotient Xnc /Ync for the second sampling time. - View Dependent Claims (20, 21, 22, 23, 24, 25)
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26. A method for measuring the frequency of an input signal by measuring the number of cycles of the input signal that occur in a sample interval between first and second sampling times, the method comprising:
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providing a periodic clock signal having a frequency higher than that of the input signal; sensing a predetermined periodic characteristic of the input signal and producing therefrom an integer signal representing an estimated number N of cycles of the input signal that occur in the sampling interval; determining the time of occurrence of each sampling time tn in a time period that extends from a first measurement time ta corresponding to the occurrence of the characteristic of the input signal preceding tn to a second measurement time tb corresponding to the characteristic of the input signal occurring following tn, the step of determining the time of occurrence of each sampling time tn comprising; (i) determining a first count value by counting the number of cycles of the clock signal that occur between times tn and tb and producing a corresponding first count signal Xn ; (ii) determining a second count value by counting the number of cycles of the clock signal that occur between the measurement times and producing a corresponding second count signal Yn ; and (iii) producing phase signals an and bn representing the phase of the clock signal at measurement times ta and tb, respectively; and
,adjusting count signals Xn and Yn for each sampling time based upon the phase signals for that sampling time, to thereby produce corrected count signals Xnc and Ync for each sampling time, and measuring the number of cycles Cn of the input signal that occur in the sampling interval by determining N plus the quotient Xnc /Ync for the first sampling time minus the quotient Xnc /Ync for the second sampling time. - View Dependent Claims (27, 28, 29, 30)
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Specification