Abstract: On the basis of analyzing internal input circuit of ADC 1210 12 bits A/D converter, an improved connection of external circuit is derived in this paper.It operates only from a single power supply voltage of +5.12V to complete bipolar analog voltage A/D conversion for input D.C signal of 0±5.12V.Its resolution and accuracy are identical with those of the normal connection,but its power dissipation is less,Moreover,its input or output digital signal levels are the same as the level of 5V CMOS integrated circuits. In other words,it can match with TTL IC or 5V CMOS IC without any interface circuit.