PURPOSE: To widen the dynamic range for sensing voltage by comparing the first input current with the second input current, and at the same time, generating a signal only when the first input current exceeds the second input current by a specified amount.

CONSTITUTION: An L1 processing circuit 106, a C1 processing circuit 110 and a CO processing circuit 114 match the voltage of an L1 line 138, a C1 line 146 and a CO line 150 to respective reference voltage, so that an electric potential drop is caused at both ends of registers RL1, RC1 and RC0. Thus, currents IL1, IC1 and IC0 are generated, and added at addition nodes 202, 206 and 210. The scum current of an L2/L1 addition node generates IL1DIF differential current equal to (IL2-IL1) at the L1 processing circuit 106, and the differential current flows toward the addition node 202. In a similar manner, the C1 processing circuit 110 generates ICIDF differential current equal to (IL2-IC1), and the CO processing circuit 114 generates ICODF differential current equal to (IL2-IC0). The processing circuits 106, 110 and 114 mirror-process the obtained differential current for rectification. The rectified differential currents are supplied to comparators 118, 120, 122, 124 and 126, respectively, and then coupled with reference currents Iref1-Iref5.