A comparator circuit includes: a comparator, coupled between a power voltage and a ground voltage, configured to perform a comparison according to a set of input signals to generate a comparison signal; a current source; and positive feedback circuits. The comparator circuit includes a set of input terminals and sets of transistors respectively coupled between a power voltage and a node or a ground voltage. The positive feedback circuits perform positive feedback operations on the node to generate instant currents on the node, to make the comparator switch the comparison signal in response to transition of the set of input signals in real time. Any of the positive feedback circuits includes: a first switch, configured to enable or disable said any positive feedback circuit in response to transition of the comparison signal; and a set of transistors, configured to generate a second current corresponding to the first current.