A clock circuit which may include a first clock input for receiving a first clock signal and a second clock input for receiving a second clock signal. A clock calibration unit is connected to the first clock input and the second clock input. The calibration unit may calibrate the second clock signal relative to the first clock signal. The clock calibration unit may have a calibration output for outputting a calibrated clock signal. The clock circuit may include a switch unit connected to the first clock input and the calibration output. The switch unit can select a selected clock signal selected from the first clock signal and the calibrated signal. The switch unit has a switch output for outputting the selected clock signal. A switch control unit is connected to the switch unit for controlling which signal is selected based on a selection criterion and a clock circuit output is connected to the switch unit for outputting the selected clock signal.