Patent ID: 7283082

Claim:
A DAC (digital to analog converter) for converting a digital input word including an M-bit MSB subword, an N-bit mid-subword, and a P-bit LSB subword to an analog output signal, the DAC comprising: (a) a string DAC including 2 M string resistors each sequentially connected to the next by a plurality of tap voltage conductors, respectively, a first group of switches for selectively coupling an upper tap voltage of a selected string resistor to one of a first string DAC output conductor and a second string DAC output conductor and for selectively coupling a lower tap voltage of the selected string resistor to the other of the first and second string DAC output conductors in accordance with decoding of the M-bit MSB subword by a MSB subword decoder; (b) an interpolation sub-DAC for monotonically interpolating a voltage between the first and second string DAC output conductors in response to decoding of the N-bit mid-subword by a first decoder, the interpolation sub-DAC including i. interpolation operational amplifier circuitry including 2 N differential transistor pairs, and ii. multiplexing circuitry receiving the upper and lower tap voltages from the first and second string DAC output conductors for distributing the upper and lower tap voltages to various inputs of the differential transistor pairs in response to outputs of the first decoder in accordance with values of the N-bit mid-subword; and (c) a P-bit delta sigma modulator for producing a delta sigma modulated signal including sequences of pulses the density of which correspond to values of the P-bit LSB subword and applying the delta sigma modulated signal to an input of the multiplexing circuitry to control alternate supplying of the upper and lower tap voltages to an input of a differential transistor pair of the interpolation operational amplifier circuitry selected by a second decoder in accordance with the N-bit mid-subword to monotonically average a contribution of the selected differential transistor pair to generation of the analog output signal in accordance with the values of the P-bit LSB subword.