A digital circuit comprises a plurality of functional circuits and a finite state machine. Each functional circuit comprises a digital macro, a resistance control device and at least one device with capacitance. The digital macro is coupled to a ground. The resistance control device is electrically connected between the digital macro and an always-on power mesh. The at least one device with capacitance is electrically connected between the resistance control device and the ground. The finite state machine is electrically connected to the resistance control device, and is configured to adjust the resistance of the resistance control device.