Frequency counting apparatus and method

A method for determining the phase of a periodic reference signal at a predetermined time, the method comprising:

• 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 a.sub.n representing the phase of the reference signal at the predetermined time.

A device for determining the time of occurrence of a sampling time t.sub.n in a time period that extends from a first measurement time t.sub.a to a second measurement time t.sub.b, the device comprising:

• 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 t.sub.n and t.sub.b, and for producing a corresponding first count signal X.sub.n ;
• 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 Y.sub.n ;
• a correction circuit for producing phase signals a.sub.n and b.sub.n representing the phase of the clock signal at measurement times t.sub.a and t.sub.b respectively;
• and
• processing means for receiving the count and phase signals, for adjusting count signals X.sub.n and Y.sub.n based upon the phase signals to produce corrected count signals X.sub.nc and Y.sub.nc, and for determining the sampling time t.sub.n relative to t.sub.a by determining the quotient X.sub.nc /Y.sub.nc.

A method for determining the time of occurrence of a sampling time t.sub.n in a time period that extends from a first measurement time t.sub.a to a second measurement time t.sub.b, the method comprising:

• 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 t.sub.n and t.sub.b, and for producing a corresponding first count signal X.sub.n ;
• 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 Y.sub.n ;
• producing phase signals a.sub.n and b.sub.n representing the phase of the clock signal at measurement times t.sub.a and t.sub.b respectively;
• and
• adjusting count signals X.sub.n and Y.sub.n based upon the phase signals to produce corrected count signals X.sub.nc and Y.sub.nc, and determining the sampling time t.sub.n relative to t.sub.a by determining the quotient X.sub.nc /Y.sub.nc.

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:

• 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 t.sub.n in a time period that extends from a first measurement time t.sub.a corresponding to the occurrence of the characteristic of the input signal preceding t.sub.n to a second measurement time t.sub.b corresponding to the occurrence of the characteristic of the input signal following t.sub.n, 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 t.sub.n and t.sub.b, and for producing a corresponding first count signal X.sub.n ;
• (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 Y.sub.n ;
• and
• (iii) a correction circuit for producing phase signals a.sub.n and b.sub.n representing the phase of the clock signal at measurement times t.sub.a and t.sub.b, 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 X.sub.n and Y.sub.n for each sampling time based upon the phase signals for that sampling time, to thereby produce corrected count signals X.sub.nc and Y.sub.nc for each sampling time, and means for measuring the number of cycles C.sub.n of the input signal that occur in the sampling interval by determining N plus the quotient X.sub.nc /Y.sub.nc for the first sampling time minus the quotient X.sub.nc /Y.sub.nc for the second sampling time.

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:

• 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 t.sub.n in a time period that extends from a first measurement time t.sub.a corresponding to the occurrence of the characteristic of the input signal preceding t.sub.n to a second measurement time t.sub.b corresponding to the characteristic of the input signal occurring following t.sub.n, the step of determining the time of occurrence of each sampling time t.sub.n comprising:
• (i) determining a first count value by counting the number of cycles of the clock signal that occur between times t.sub.n and t.sub.b and producing a corresponding first count signal X.sub.n ;
• (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 Y.sub.n ;
• and
• (iii) producing phase signals a.sub.n and b.sub.n representing the phase of the clock signal at measurement times t.sub.a and t.sub.b, respectively;
• and,
• adjusting count signals X.sub.n and Y.sub.n for each sampling time based upon the phase signals for that sampling time, to thereby produce corrected count signals X.sub.nc and Y.sub.nc for each sampling time, and measuring the number of cycles C.sub.n of the input signal that occur in the sampling interval by determining N plus the quotient X.sub.nc /Y.sub.nc for the first sampling time minus the quotient X.sub.nc /Y.sub.nc for the second sampling time.