Patent ID: 8909068

Claim:
A skew estimator for estimating a skew in a coherent receiver, the skew estimator comprising: four phase detectors configured to detect a respective phase of an X-polarized in-phase signal (XI), an X-polarized quadrature-phase signal (XQ), a Y-polarized in-phase signal (YI) and a Y-polarized quadrature-phase signal (YQ) to obtain four phase signals; an adder configured to provide a sum signal by adding the obtained four phase signals; four blocks for the obtained four phase signals, wherein each block corresponds to one phase signal out of the obtained four phase signals, and each block comprises: a subtractor configured to provide a difference signal between the sum signal and a respective phase signal out of the obtained four phase signals, a low-pass filter configured to filter the output difference signal, a determiner configured to determine the sign of the filtered differential signal to obtain a sign signal, and an integrator configured to integrate the obtained sign signal to provide an estimated skew (φ XI ) of the respective phase signal.