A CML digital circuit includes a load coupled between a power supply node and at least one output node and a logic circuit component coupled to the output node. The logic circuit component has at least one data input node. The logic circuit component comprises a first circuit module and a second circuit module. A first tail current source is coupled to the first circuit module. A second tail current source is coupled to the second circuit module. A first switch is coupled between the power supply node and the first tail current source. A second switch is coupled between the power supply node and the second tail current source, wherein the first switch is triggered to deactivate the first circuit module when the second circuit module is operating and the second switch is triggered to deactivate the second circuit module when the first circuit module is operating.