High-speed optical communications system

A method for processing data received over an optical fiber, the method comprising:

• receiving, by an optical front end, an optical signal;
• converting, by the optical front end, the optical signal into an analog signal;
• performing, by an analog front end, analog-to-digital conversion on the analog signal based on a sampling clock to generate a digital signal;
• applying a frequency domain equalization on the digital signal to produce a first equalized signal;
• generating, by a sampler of a timing recovery module, samples of the first equalized signal;
• generating, by a phase detector of the timing recovery module, a timing recovery phase error signal based on the samples, the timing recovery phase error signal representing a difference frequency between a local sampling clock and a transmit clock and to measure a period of the timing recovery phase error signal;
• initializing, in a frequency register of a loop filter, a control value with an initial value having a first sign, the initial value representing an estimate of a frequency error based on the measured period;
• determining, whether the frequency error increases or decreases;
• responsive to the frequency error increasing, re-initialize the control value of the frequency register with a second estimate of the frequency error having an opposite sign of the first sign;
• generating, by an oscillator of the timing recovery module, the sampling clock based on the control value in the frequency register;
• equalizing the first equalized signal by applying a second filter to produce a second equalized signal;
• demodulating the second equalized signal to generate a baseband signal;
• and
• detecting frames of the baseband signal for synchronization with a framer interface.

A timing recovery circuit for generating a sampling clock, the timing recovery circuit comprising:

• a sampler configured to generate samples of an input signal produced at a transmitter based on a transmit clock;
• a phase detector to configured generate a timing recovery phase error signal based on the samples, the timing recovery phase error signal representing a difference frequency between a local sampling clock and the transmit clock and to measure a period of the timing recovery phase error signal;
• a loop filter to filter configured to generate a control value for a frequency register, the loop filter configured to initialize the frequency register with an initial value representing an initial estimate of a frequency error based on the measured period, determine whether the frequency error increases or decreases, and responsive to the frequency error increasing, re-initialize the frequency register with a second estimate of the frequency error having an opposite sign of the initial value;
• and
• an oscillator to configured generate an oscillating signal having a frequency based the control value in the frequency register;
• and
• a phase interpolator configured to interpolate the oscillating signal to generate the sampling clock.