Pulse or digital communications – Synchronizers
Reexamination Certificate
1998-01-14
2001-07-31
Pham, Chi (Department: 2631)
Pulse or digital communications
Synchronizers
C375S371000
Reexamination Certificate
active
06269135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to digital phase discrimination.
2. State of the Art
Phase discrimination is important in digital radio communications, in particular in any angle modulation digital radio receiver. Phase discrimination and frequency discrimination are closely related. Frequency discrimination is typically performed using analog circuitry, e.g. an IQ frequency discriminator. Analog frequency discriminators have substantial drawbacks. In the case of an IQ frequency discriminator, the discriminator requires a number of analog components, two A/D conversions and a numerical arctangent operation, rendering the circuit quite complex.
Known methods exist for producing a value representing the instantaneous phase of a signal using only digital logic elements. Various such methods are described in U.S. Pat. No. 5,084,669, incorporated herein by reference. In particular, the foregoing patent describes a digital circuit for determining the instantaneous phase of a signal, from which the instantaneous frequency may be obtained if desired. Although the implementation of the circuit is all digital, it is quite involved. An improved method and apparatus for determining in a simple, all-digital manner the instantaneous phase of a signal would therefore likely be well-received by those skilled in the art.
SUMMARY OF THE INVENTION
The present invention, generally speaking, provides a simple, all-digital method and apparatus for determining the phase of a first clock signal relative to a second clock signal. The first clock signal may be a digital approximation of a periodic analog signal such as an RF signal. A sampling technique is employed that produces a stream of digital bits containing relative phase information. From the stream of digital bits is formed a digital word indicative of the relative phase. 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.
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Corrielus Jean B.
Pham Chi
Tropian Inc.
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