A digital signal data retiming and clock extraction apparatus including a series of three data latches (111, 121, 131), connected in cascade, means for applying digital data signals to the first latch, means for clocking (701) the first and third latches in phase with the data signals input to the first latch, means for clocking the second latch in antiphase with the data signals input to the first latch, coincidence detection means (201) to which are applied the digital data signal (A) input to the first latch, the data signals output (B) of the second latch and the data signals output (C) of the third latch, the coincidence detection means being arranged to derive output data signals (X) in accordance with the algorithm X = B. (A-C), and a first phase lock loop feedback means (Q1, Q2, 301) whereby the output data signals (X) of the coincidence detection circuit control the timing of the clocking means to maintain the phase relationship with the digital data signals input to the first latch.