Method and system for clock recovery with adaptive loop gain control

1. A system, comprising:

a clock recovery unit having a gain adjustment unit, a first phase detector unit, a filter and a numerically controlled oscillator coupled in a closed loop, wherein an output of the first phase detector unit is coupled to the filter, an output of the filter is coupled to the numerically controlled oscillator, and wherein a signal provided by the output of the filter controls the numerically controlled oscillator based on a signal provided by the output of the first phase detector unit;

an estimation unit having a second phase detector unit and a gain estimation unit coupled in series, said gain estimation unit being configured to estimate a gain of said second phase detector unit;

wherein the estimated gain of said second phase detector unit includes a variable part; and

wherein said estimation unit and said clock recovery unit are configured to operate in parallel,

wherein the clock recovery unit is coupled to an output of the estimation unit, and the gain adjustment unit of the clock recovery unit is adapted to adaptively adjust loop gain of the closed control loop including the first phase detector unit based on the estimated gain of the second phase detector unit to achieve a constant loop gain.

2. The system according to claim 1 , wherein the estimated gain of said second phase detector unit is configured to feed said first phase detector unit.

3. The system according to claim 1 , wherein the system is adjustable such that the variable part of the estimated gain can be reduced to zero substantially canceled out.

4. The system according to claim 1 , wherein said clock recovery unit comprises a phase-locked-loop system.

5. The system according to claim 4 , wherein said phase-locked-loop system includes said filter, and the filter has perfect integrator path.

6. The system according to claim 1 , wherein said first phase detector unit and said second phase detector unit are Gardner phase detectors.

7. The system according to claim 1 , wherein the system is a communication system.

8. The system according to claim 7 , wherein the communication system is an optical communication system.

9. A method for phase recovery for a system, the system having a clock recovery unit and an estimation unit wherein the clock recovery unit is coupled to an output of the estimation unit, the clock recovery unit including a gain adjustment unit, a first phase detector unit a filter and a numerically controlled oscillator coupled in a closed loop, and the estimation unit including second phase detector unit and a gain estimation unit coupled in series, the method comprising:

receiving at the filter of the clock recovery unit a signal provided by an output of the first phase detector unit, controlling the numerically controlled oscillator of the clock recovery unit by a signal provided by an output of the filter and based on the signal provided by the output of the first phase detector unit;

estimating a gain of the second phase detector unit by the gain estimation unit, wherein the estimated gain of the second phase detector unit includes a variable part; and

adaptively adjusting loop gain of the closed control loop including the first phase detector unit by the gain adjustment unit and based on the estimated gain of the second phase detector unit to achieve a constant loop gain.

10. The method according to claim 9 , wherein the estimated gain of the second phase detector unit feeds the first phase detector unit.