Digital frequency sampling and discrimination

• US 6,219,394 B1
• Filed: 10/08/1997
• Issued: 04/17/2001
• Est. Priority Date: 10/08/1997
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Tropian, Inc. (Panasonic Holdings Corporation)
• Inventors: Sander, Wendell
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Corrielus, Jean B
• Application Number:
  US08/947,027
• Time in Patent Office: 1,287 Days
• Field of Search: 375/354, 375/377, 375/355, 327/45, 327/113, 327/115, 327/117, 327/144, 327/145, 327/48
• US Class Current: 375/355
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
• CPC Class Codes: H03D 13/006 and by sampling this signal by narrow pulses obtained from the second oscillation
• CPC Class Codes: H04L 7/0334 Processing of samples having at least three levels, e.g. soft decisions

Abstract

The present invention, generally speaking, provides a very simple, all-digital method and apparatus for determining the ratio of frequencies of two signals. One of the signal may be a known reference frequency, allowing the instantaneous frequency of an unknown input signal to be readily determined. A frequency sampling technique is employed that produces a stream of digital bits which contains information regarding the ratio of frequencies. From the stream of digital bits is formed a digital word indicative of the ratio of frequencies. The digital word may be formed using a digital filter. Advantageously, an extensive body of digital filtering techniques applicable to Sigma-Delta (sometimes referred to as Delta-Sigma) A/D converters may be applied directly to the digital stream. By using an appropriately-chosen weighting function, high accuracy may be obtained.

Claims

1. A method of determining a ratio of frequencies of a first clock signal and a second clock signal comprising:

sampling the first clock signal in accordance with the second clock signal to produce a stream of digital bits or symbols wherein a frequency ratio of the first and second clock signals is variable throughout a range including non-integer values; and

performing postprocessing of the stream of digital bits or symbols to form, from a substantial number of said digital bits or symbols, a digital word indicative of the ratio of frequencies;

wherein each digital bit or symbol of a sequence of consecutive digital bits or symbols represents a number of transitions n of a predetermined polarity of the first clock signal that occurred during a corresponding period in a sequence of consecutive periods of the second clock signal where n is a non-negative integer.

2. The method of claim 1, wherein forming the digital word comprises filtering the digital bits or symbols.

3. An apparatus for determining a ratio of frequencies of a first clock signal and second clock signal comprising:

means for sampling the first clock signal in accordance with the second clock signal to produce a stream of digital bits or symbols wherein a frequency ratio of the first and second clock signals is variable throughout a range including non-integer values; and

means for performing postprocessing of the stream of digital bits or symbols to form, from a substantial number of said digital bits or symbols, a digital word indicative of the ratio of frequencies;

wherein each digital bit or symbol of a sequence of consecutive digital bits or symbols represents a number of transitions n of a predetermined polarity of the first clock signal that occurred during a corresponding period in a sequence of consecutive periods of the second clock signal, where n is a non-negative integer.

4. The apparatus of claim 3, wherein said means for forming comprises a digital filter.

5. The apparatus of claim 4, wherein the digital filter employs a weighting function in which different weights are applied to different digital bits or symbols.

6. A circuit for producing a data stream indicative of a ratio of frequencies of two clock signals comprising a first input terminal to which a first clock signal is applied, a second input terminal to which a second clock signal is applied, and producing as an output signal a stream of digital bits or symbols wherein a frequency ratio of the clock signals is variable throughout a range including non-integer values, each digital bit or symbol of a sequence of consecutive digital bits or symbols representing a number of transitions n of a predetermined polarity of the first clock signal that occurred during a corresponding period in a sequence of consecutive periods of the second clock signal, where n is a non-negative integer, such that further processing of the stream of digital bits or symbols yields a digital word, formed from a substantial number of said digital bits or symbols, representing the ratio of frequencies.