The three-state-polarity-coincidence correlator (PCC'), a two-input detection device with dead zone clippers, has been investigated in detail. A criterion is devised to compare two detectors. Comparisons are made between the PCC' and several other types of detectors. The superiority of the PCC' in the detection of a weak signal embedded in an additive noise over the PCC and other detectors is demonstrated. It is shown, particularly for certain Gaussian inputs, that there exists a maximum relative efficiency with respect to the dead zone width of clippers or the clipping level "b". It is concluded that the PCC' can always be used to replace the PCC in a weak signal detection.