Digital-to-analog converter with delta-sigma modulation

摘要

The digital-to-analog conversion apparatus operates to convert an digital input into a corresponding analog output. A digital filter is provided for oversampling the digital input having a varying value represented in the form of multiple bits. A delta-sigma modulator operates to effect delta-sigma modulation of the oversampled digital input to reduce a number of the multiple bits for requantizing the oversampled digital input with a certain S/N ratio. A low-pass filter is provided for converting the requantized digital input into an analog output. A level detecting circuit is provided for detecting when the value of the digital input falls below a predetermined level. A shifting circuit is disposed upstream of the delta-sigma modulator and is responsive to the detected results for increasing the value of the digital input so as to improve the S/N ratio in the delta-sigma modulator. An attenuator is disposed downstream of the delta-sigma modulator and is responsive to the detected results for effecting decreasing compensation for the increased value of the digital input while substantially maintaining the improved S/N ratio so as to produce an analog output corresponding to the digital input.