u201d or u201c eye diagram u201d as used herein the u201c eye pattern u201d or u201c eye diagram u201d refers to the image as seen on an oscilloscope in response to the digital data when the horizontal sweep rate is equal to the baud bit or clock rate such an oscilloscope display is widely known as an u201c eye pattern u201d due to its resemblance to the human eye further description of the u201c eye pattern u201d may be had by reference to u s pat no 3 721 959 which is incorporated by reference herein in addition the output 306 of exclusive or 305 is dependant upon the data input bit pattern for example if the data input is 1010 the output will be a square wave of frequency that is twice the clock rate however if the data input is 11001100 the output 306 of exclusive or 305 will be a square wave equal in frequency to the clock input if the data input is 1111000011110000 the output 306 of exclusive or 305 will be one half the input clock rate the error signal 306 of the hogge phase detectors in general exhibits a data dependant gain characteristic the error signal 306 is a combination of error signal combined with phase information the data output of flip flop 303 is coupled into conductor 315 the data coupled to conductor 315 is.