Patent ID: 8374573

Claim:
An automatic vehicle identification (AVI) receiver for processing signals received thereby to recover information encoded in carrier frequency signals generated at a specific frequency by a transmitter and identifying an authorized vehicle, said receiver comprising: an input terminal adapted to be coupled to an inductive loop defining a detection zone for receiving signals from the loop; a filter unit coupled to said input terminal for permitting signals at said specific frequency present on said input terminal to pass therethrough and for substantially attenuating all other frequency components of signals present on said input terminal, said filter unit having an output; a variable gain amplifier having an input coupled to said output of said filter unit for amplifying signals input thereto and for limiting the amplitude of signals amplified thereby to a maximum value, said variable gain amplifier having a gain control signal input and an output, said variable gain amplifier having an operating range with a linear portion; an amplitude detection circuit having an input coupled to said output of said variable gain amplifier and a gain control signal output coupled to said gain control input of said variable gain amplifier for sensing the amplitude of signals received from said variable gain amplifier and for generating a gain control signal for controlling the gain of said variable gain amplifier so that the signals input to said variable gain amplifier are operated on within said linear portion and the amplitude of signals amplified by said variable gain amplifier are limited to said maximum value; and a carrier-to-pulse conditioning circuit having an input coupled to said output of said variable gain amplifier for converting carrier frequency signals present at the output of said variable gain amplifier to a binary pulse train signifying the temporal length of each active carrier period and the temporal length of each quiescent carrier period, said carrier-to-pulse conditioning circuit having an output.