A combined 10-bit analog-to-digital converter (ADC) consisting of a 3-bit unclocked ADC and a 7-bit serial ADC is described. The range of convertible voltages is 0-10.23 V; a count unit is 10 mV. The maximum conversion time (1.3 msec) is smaller by a factor of 8 than that of a 10-bit serial ADC.