Patent ID: 7250883

Claim:
An A/D converter for converting an analog input current into a digital output signal having a plurality of bits, the A/D converter comprising: plural stages of series-connected computation cells, the number of which is equal to the number of bits in said plurality of bits of the digital output signal, the computation cells respectively being supplied with a plurality of input currents, having a plurality of reference currents to compute differences between the corresponding input currents and the reference currents, and outputting a plurality of currents in accordance with absolute values of said differences; and an encoder, connected to the computation cells, for determining values for the plurality of bits based on the computations of the computation cells, wherein each computation cell includes: a first comparison unit for subtracting the corresponding reference current from the corresponding input current to generate a first current; and a second comparison unit for subtracting the corresponding input current from the corresponding reference current to generate a second current; each computation cell outputting current that is equal to one of the first current and the second current.