signal 504 from the reference circuit controller 516 for adjusting a number of steps of the reference circuit cdl 510 outputs of the reference circuit fdl 508 and the reference circuit cdl 404 are connected to inputs of a phase detector 414 that is preferably substantially identical to the main phase detector 102 the phase detector 414 provides a phase difference 415 preferably as up count and down count signals to the reference circuit controller 516 the reference circuit controller 516 provides a fully decoded set of control signals 418 to the reference circuit fdl 508 the reference circuit controller 516 may include a one state per flip flop type state machine wherein outputs of the flip flops directly provide the control signals to the first fdl 508 alternatively the reference circuit controller 516 may include an up down counter and a thermometer decoder for providing the control signals 418 to the reference circuit fdl 508 firstly a number of steps of the reference circuit cdl 510 is set to u201c 0 u201d that is the input 504 is set to a high impedance state a reference circuit controller 516 adjusts the control signals 518 provided to the reference circuit fdl 508 so that a delay of the reference circuit fdl 508 is substantially equal to a delay of the reference circuit cdl 510 by.