The present invention pertains generally to detectors for demodulating digitalized information contained in communications carrier signals and particularly differentially encoded carrier signals.
Differentially encoded carrier signal systems for transmitting and receiving communications signals, wherein the information is contained in the differential of a characteristic of the carrier signal (phase, frequency, or amplitude) between consecutive bit intervals thereof are widely used. In these systems, the information is demodulated by comparing the carrier signal characteristic in each bit interval with the immediately preceding bit interval, the latter serving as a reference. For example, one commercial system known as Kineplex which is covered by U.S. Pat. No. 3,368,036, entitled "Demultiplexing & Detecting System For Predicted Wave Phase-Pulsed Data Transmission System" issued to R. C. Carter et al permits two bits of binary data to be transmitted and received per bit interval through differential phase shift keying where the carrier signal in a given bit interval can assume any one of four different phases with respect to the immediately preceding bit interval in odd multiples of 45.degree.. Although this system is highly effective at low data rates, the constraints imposed by the storage and sampling scheme for comparing the information contained in consecutive bit intervals militates against extending its utilization to the higher data rates finding current popularity. Moreover, the dual functions performed in each bit interval results in timing circuitry which is more sophisticated and expensive than otherwise required.
With the foregoing in mind, it is a primary object of the present invention to provide a new and improved means for synchronously detecting and demodulating the information contained in differentially encoded carrier signals.
It is a further object of the present invention to provide such a new and improved means which is particularly advantageous for use with carrier signals of the differential phase shift keying type.
It is still a further object of the present invention to provide such a new and improved means which affords extending the use of differential phase shift keyed carrier signals at higher data rates with simplified timing circuitry.
The foregoing objects, as well as others, and the means by which they are achieved through the present invention may best be appreciated by referring to the Detailed Description of the Preferred Embodiment which follows hereinafter together with the appended drawings.