Abstract: A system for correlating a sampled received analog signal against a sampled reference waveform which is approximated by three quantized levels. The three levels are organized to minimize undesirable odd harmonics with the reference and to maximize the correlator output signal-to-noise ratio. The invention comprises first and second signal summers and first, second and third registers each having M corresponding stages and logic for generating and entering into the first, second and third registers, respectively, a quantized form of the received signal, at least one two-level reference signal, and at least one two-level enable signal corresponding to the at least one two-level reference signal.

Abstract: A system for determining the frequency of any received tone segment of N possible time synchronous tone segments each having a period T.sub.1 and each having one of N predetermined frequencies. The system comprises a first shift register having M stages, a second register also having M stages each being aligned with one of the M stages of the first shift register, sampling logic for samping each received tone segment into P samples where P is less than M and P-M=L, and logic for serially entering the P samples into the first shift register. Also provided is a time generator for generating 2N I and Q sampled reference tones each having P samples and representing one of the N predetermined frequencies, and for successively entering the 2N sampled reference tones into the second register at a rate M/WT.sub.