Patent ID: 7605735

Claim:
A digital-to-analog converter for converting a digital signal into an analog voltage corresponding to a polarity signal, comprising: an operational amplifier having a first input node, a second input node and an output node for outputting the analog voltage, wherein the second input node receives a reference voltage; an R-2R ladder network having a R-2R output node, a reference node and an input node, the R-2R output node connected to the first input node of the operational amplifier, the reference node receiving a reference voltage, and the input node receiving an input voltage, wherein the R-2R ladder network further comprises: a plurality of first resistors connected with a plurality of second resistors, said first resistors having a first resistance, and said second resistors having a second resistance, said second resistance having a double value of said first resistance; and a plurality of switches selectively connecting the corresponding second resistors to the first input node of the operational amplifier, or to the reference voltage selectively, controlled by the digital signal; and a polarity switch electrically connected to said input node of said R-2R network, selectively switching between a first input voltage and a second input voltage corresponding to the polarity signal, and outputting to said input node of said R-2R network.