Time Derivation Method for Clocking a Correlation Detector Receiver for the Decoding of Diffuse Infrared Data
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
A technique is described whereby an infrared receiving circuit provides accurate clocking to a correlation detector, so as to significantly increase the distance sensitivity during infrared transmission of data. The circuit is unique in that the number of required transmitting diodes and receiving photodiodes is reduced as compared to the prior art. The concept, described herein, utilizes pulse position modulation (PPM) encoding, whereby one pulse is used within a field of allowable time slots, so that each time slot encodes a different data value. To encode n bits, 2n time slots are required. Fig. 1 shows an example of a PPM nibble "11 01" in a four-slot PPM. The PPM method of encoding has as its main advantage a low duty cycle, so as to reduce the operational temperature of the transmitting diodes.