a plurality of current-controlled delay groups, coupled to a transmission wire, wherein a first current-controlled delay group comprises one first current-controlled delayer, at least one second current-controlled delay group comprises a plurality of second current-controlled delayers and each of the first current-controlled delayer and the plurality of second current-controlled delayers provides a delay according to a control voltage;

a plurality of switches, wherein each of the plurality of switches is coupled between the each of the plurality of current-controlled delay groups and the transmission wire, wherein each of the plurality of switches is turned on or off according to a bit of an enable signal applied thereto

wherein the plurality of current-controlled delay groups respectively correspond to the plurality of switches, and number of the plurality of switches is equal to number of the plurality of current-controlled delay groups.