US Patent 7451174 Multi-level soft detector-quantizer

An analog electronic circuit is proposed that e.g. computes the symbol likelihoods for PAM or QAM signal constellations. The circuit has at least one set of M transistors connected to a common current source. A multiplier/adder generates the voltages to be applied to the transistors from a value y and a set of M expected values in such a way that the currents through the transistors correspond to the likelihood that the value y corresponds to the expected values. The circuit can be used for signal demodulation and various other applications.