A circuit includes a comparator, a first circuit, and a second circuit. The comparator includes a first input node, a second input node, and an output node. The first circuit is configured to generate a temperature-dependent reference current at the second input node of the comparator. The second circuit is coupled with the second input node of the comparator. The second circuit is configured to increase a voltage level at the second input node of the comparator in response to the temperature-dependent reference current when a signal at the output node of the comparator indicates a first comparison result, and decrease the voltage level at the second input node of the comparator when the signal at the output node of the comparator indicates a second comparison result.