Phase equalization system for a digital-to-analog converter utilizing separate digital and analog sections

摘要

A phase equalization system for a digital-to-analog converter (DAC) includes a digital portion (10) having an interpolation section (14) for receiving a digital input and increasing the sampling frequency thereof for input to a delta-sigma modulator (16). A summing junction (24) is disposed between the interpolation circuit (14) and the delta-sigma modudlator (16) to allow an offset voltage to be summed therewith. This provides for D.C. offset, this offset being controlled by a calibration control (40). The output of the digital section (10) is input in an analog section (12), which has a one-bit DAC 21) that is input to an analog filter (22) for converting and filtering the one-bit digital stream output by the delta-sigma modulator (16). The interpolation circuit (14) includes a three stage interpolation filter comprising a first stage (50), a second stage (52) and a third stage (54). The second stage (52) is comprised of a finite impulse response filter (FIR) that has a nonlinear phase response. The nonlinear phase response of the interpolation filter (52) compensates for the phase deviation of the analog filter (22) from a linear phase response. Therefore, the composite phase provided by the combination of the phase equalization in the digital section (10) and the phase nonlinearity in the analog section (12) will result in a linear overall phase relationship for the DAC.