A circuit includes a stacked circuit layer, a plurality of test contact points, and a comparator. The stacked circuit layer includes a plurality of reference capacitors each having a reference capacitance. Each of the test contact points is electrically connecting to an under-test capacitor of an under-test module. The comparator compares the reference capacitance of one of the reference capacitors with an under-test capacitance of the under-test capacitor corresponding to one of the test contact points to measure a range of the under-test capacitance.