Apparatus and methods for digital-to-analog conversion using modified LSB switching

Abstract

A method and apparatus for converting a plurality of digital signals to an analog signal and m-bit digital-to-analog converter having an LSB current switch. A most significant m bits of an [m] n bit digital signal are applied to m bits, respectively, of the m bit digital-to-analog converter, and successive values of the n bit digital signal are substituted at a first frequency. An interpolation signal is produced at the first frequency. A least significant n-m bits of the n bit digital signal are applied to the interpolation circuit to cause it to interpolate between successive values of the n bit digital signal. An LSB current switch distinct from the m bit digital-to-analog converter produces an output signal in response to the interpolation signal. An analog output signal produced by the m bit digital-to-analog converter is combined with the output signal produced by the LSB current switch to produce an analog output signal with n bit resolution. The least significant n-m bits are applied to the inputs of an n-m bit up/down counter. Causing it to count up or down from the digital value of the least significant n-m bits at a second frequency that is 2.sup.n-m times the first frequency to thereby produce the interpolation signal on a carry output of the up/down counter. The settling times of the analog output signal occurring at the first frequency are thereby limited to the settling times of the output signal of the LSB current switch.

Dependencies are inferred from the claim text.