CORRELATION DETECTING CIRCUIT

PURPOSE:To ensure the stable working of a correlation detecting circuit despite the uncertainty of carrier wave pull-in phase, by obtaining the correlation quantity to each orthogonal component of an interference wave mixing into a desired wave. CONSTITUTION:A discriminator 3P performs a code reproduction for one side of orthogonal components of a desired wave mixed with an interference wave sent from an input terminal IP, and an interference component upsilon=acostheta is extracted by a subtractor 5P. While the orthogonal component is obtained through input terminals 2P and 2Q at the interference wave side, and code reproductions are carried out by discriminators 4P and 4Q to obtain orthogonal components UP= cos(theta+alpha) and UQ=cos(theta+alpha+90 deg.). Based on these orthogonal components, the correlation with an error differential upsilon is detected by multipliers 6P and 6Q. The outputs of these multipliers are processed by LPF7P and 7Q to obtain outputs (a/2).cosalpha and (a/2).sinalpha respectively. Therefore the voltage V synthesized by an adder 8 via a rectifying circuit 13 is set as V=(a/2).(¦cosalpha¦+¦sinalpha¦). Thus the correlation can be detected although the carrier waves different in pull-in phase alpha is set at + or -90 deg..