DIGITAL PHASE DETECTOR

• US 3,825,737 A
• Filed: 12/11/1972
• Issued: 07/23/1974
• Est. Priority Date: 12/21/1971
• Status: Expired due to Term

• Current Assignee: Alain Croisier
• Original Assignee: Alain Croisier
• Inventors: Croisier, Alain
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US05/313,893
• Time in Patent Office: 589 Days
• Field of Search: 235/186,197,152 328/72,63,166,167,133,155 329/104,129 325/320 178/68
• US Class Current: 708/4
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents

Abstract

A detector in which the phase theta of an applied sinusoid S R Sin theta is digitally obtained by determining the unit circle equivalent of the quadrant of the phase angle from the sign match or mismatch between the sinusoid S and its quadrature S R Cos theta and by determining the unit circle equivalent of an acute reference angle Alpha derived according to the relation Alpha tan 1 eln S ln S . The signal and its quadrature are periodically sampled and digitally sign and magnitude encoded. The digital magnitudes S and S are applied to table look-up devices to obtain ln S and ln S respectively. A digital subtractor forms ln S - ln S , which difference is then applied to a table look-up device to obtain Alpha . A logic element responsive to the encoded signs and the derived reference angle Alpha generates the coded equivalent to theta .

Claims

1. A digital phase detector comprising:

means responsive to an applied sinusoid S R Sin theta for forming a quadrature signal S R Cos theta ;

means for periodically sampling and for digitally sign and magnitude encoding the samples;

means responsive to the encoded magnitudes S and S for forming the difference signal L 1n S - 1n S ;

means for forming a signal Alpha representative of an acute reference angle on a unit circle according to the relation Alpha tan 1 eL ; and

means for adjusting the phase angle theta as a function of the match or mismatch of the signs of S and S defining the quadrant on a unit circle and the value of Alpha .

2. A digital phase detector according to claim 1, wherein the means for adjusting the phase angle theta modifies said angle according to the following table:

3. In a digital phase detector in which an applied sinusoid S R Sin theta and its derived quadrature signal S R Cos theta are sampled and digitally sign and magnitude encoded, the combination comprising:

first table look-up means responsive to the encoded signals at the addresses S and S for producing the signals 1n S and 1n S ;

binary adding means for forming a difference signal 1n S - ln S ;

second table look-up means responsive to the address represented by the difference signal for producing a signal Alpha equivalent of an acute reference angle on a unit circle, the angle Alpha being related to the difference signal as Alpha tan 1 e1n S - 1n S ; and

a logic arrangement for ascertaining the unit circle quadrant of the phase angle theta as a function of the similarity or difference in the sign of S and S such that for matching positive signs theta Alpha , for matching negative signs theta pi + Alpha , for a positive sign of S and a negative sign of S, theta pi - Alpha , and for a negative sign of S and a positive sign of S, - Alpha .

4. In a digital phase detector in which an applied sinusoid S R Sin theta '"'"''"'"''"'"''"'"' and its derived quadrature signal S R Cos theta '"'"''"'"''"'"''"'"' are sampled and digitally sign and magnitude encoded, the combination comprising:

first table look-up means responsive to the addresses represented by S and S for providing the signals 1n S and 1n S ;

binary adding means for forming the absolute difference signal L ln S - 1n S and a sign signal;

second table look-up means responsive to the addresses represented by L for providing a signal equivalent to an acute angle theta '"'"''"'"' on a unit circle in the range 0 <

theta '"'"''"'"' <

pi /4 according to the relation theta '"'"''"'"' tan 1 e L - pi /4; and

a logic arrangement for adjusting the phase angle theta '"'"''"'"''"'"''"'"' by ascertaining the equivalent unit circle quadrant as a function of the similarity or difference among the signs of S, S, and L, and algebraically combining the acute angle theta '"'"''"'"' with a specified constant.