Patent ID: 7876253

Claim:
An A/D conversion circuit comprising: a plurality of circuit units, connected in a tree structure, for outputting an N-bit A/D conversion result, each of the circuit units including: an input terminal for receiving an analog input current; a current transfer circuit for transferring current in accordance with the analog input current to a plurality of current paths; a plurality of constant current sources, connected to the plurality of current paths, for supplying the plurality of current paths with currents evenly divided in accordance with the number of conversion bits, N, in the amplitude range of the analog input current; a plurality of current output terminals, connected between the plurality of constant current sources and the current transfer circuit, for outputting current obtained by subtracting the current transferred to the current paths from the current supplied from each of the constant current sources; and an encoder circuit for encoding an output signal that is in accordance with the current obtained from the subtraction and generating a digital signal in accordance with the analog input current, wherein the plurality of circuit units include a preceding stage circuit unit and a plurality of subsequent stage circuit units having an input terminal connected to a plurality of current output terminals of the preceding stage circuit unit.