Abstract: To provide a high-speed, high-resolution current mode D/A converter, the present invention provides: (1) a current mode D/A converter comprising a resistor-type D/A converter circuit 2 having a digital decoder circuit 3, a plurality of resistors 5, and a plurality of switches turned on and off by the digital decoder circuit 3 and a highly linear transconductor 4 for receiving voltage output from the resistor-type D/A converter circuit 2 and providing current output; and (2) a transconductor comprising a first transistor differential pair and a second transistor differential pair connected to each other with their polarities reverse and having different transconductance values and current sources connected to the first and second transistor differential pairs respectively, wherein different signal voltages being proportional to input signal voltages input to the transconductor are applied to the first and second transistor differential pairs.

Abstract: An improved subranging or comparator circuit is provided for an analog-to-digital converter. As a subranging circuit, the circuit produces a residual signal representing the difference between an analog input signal and an analog of a digital representation. This is achieved by subdividing the digital representation into two or more parts and subtracting from the analog input signal analogs of each of the individual digital portions.In another aspect of the present invention, the subranging circuit comprises two sets of differential input pairs in which the transconductance of one differential input pair is scaled relative to the transconductance of the other differential input pair. As a consequence, the same resistor string may be used for two different digital-to-analog converters of the subranging circuit.