US 7,110,477 B2 · Gaussian frequency shift keying digital demodulator

Abstract

A digital demodulator employing a digital differential detection mechanism based on extracting phase differences directly from the I and Q signals after downconversion to zero-IF and image rejection are performed. The phase of the input I and Q signals is determined using the principle that the phase is equivalent to arctan ( Q I ) . A lookup table stores the values of the arctan function preferably in a reduced size format. The size of the lookup table can be reduced significantly by storing arctan values for the first quadrant only (i.e. 0 to 90°) and taking advantage of the fact that the phase values for the other three quadrants can be derived from those of the first with some correction applied depending on the signs of the I and Q input samples. Phase extraction logic is provided that is operative to map the phase into the entire 0 to 360° range of phase values (i.e. −π to +π radians) based on the signs of the I and Q signals. The phase difference between a current phase value and the previous phase value is then calculated. It is these phase differences that reflect the frequency deviations present in the transmitted signal which represent the original modulating signal. A ‘click’ removal filter circuit is provided to remove the discontinuities in the phase difference output that occur when the 2π radians value is crossed.

Claims29

Dependent claims

A differential detector for use in a digital frequency shift keying (FSK) receiver, comprising:

first means for receiving a scaled I signal and a scaled Q signal and determining the absolute value thereof to yield an absolute scaled I signal and an absolute scaled Q signal;
an arctan lookup table (LUT) for outputting a first phase value in accordance with each absolute scaled I signal and absolute scaled Q signal pair;
and
second means for generating a delta phase value in accordance with said first phase value and a previous first phase value delayed one symbol time.

1 more element

Dependencies are inferred from the claim text.

Gaussian frequency shift keying digital demodulator

Life of this patent

Gaussian frequency shift keying digital demodulator

Life of this patent

Abstract

Claims29