Patent ID: 7477173

Claim:
A combined AD/DA converting apparatus carrying out AD conversion of an analog input signal to output a converted digital signal or carrying out DA conversion of a digital input signal to output a converted analog signal based on a conversion selection signal for selecting AD conversion or DA conversion, the converting apparatus comprising: an input signal selection circuit configured to select one analog signal out of a plurality of analog input signals to be output based on an input selection signal; an input sample hold circuit configured to sample and hold the analog input signal output from the input signal selection circuit; a DA converter configured to convert a digital signal into an analog signal to be output; a comparator circuit configured to output a comparison signal that indicates a size relation between the analog input signal output from the input sample hold circuit and the analog signal output from the DA converter; a sequential comparison register configured to define sequentially each place of a digital signal stored in the register based on the comparison signal output from the comparison circuit; a selection circuit configured to receive the digital signal stored in the sequential comparison register, the digital input signal, and the conversion selection signal, the selection circuit being configured to output the digital signal stored in the sequential comparison register to the DA converter when the conversion selection signal indicates AD conversion, and to output the digital input signal to the DA converter when the conversion selection signal indicates DA conversion; and a controlling unit configured to output the input selection signal when the conversion selection signal indicates DA conversion.