Noise-shaping D/A conversion

Abstract

In this chapter noise-shaping techniques to improve the dynamic range of a system will be described. Noise-shaping can be very useful when speed can be exchanged with accuracy. The quantization errors in a noise-shaping system are removed from the signal band of interest. Mostly the suppressed quantization errors appear enlarged as out-of-band noise in the system. With a simple filter these errors are removed. An increased dynamic range of the coder is obtained. In digital systems word length can intelligently be reduced using a noise-shaping operation without losing dynamic range significantly. An ultimate in bit reduction is obtained when the noise-shaping operation reduces the number of bits to 1. Examples of such an operation is sigma-delta analog-to-digital conversion or noise-shaping digital-to-analog conversion based on single-bit word-lengths. The advantage of a 1-bit converter is the extreme linearity of such a device. A very good differential linearity is obtained with these converters. The most important design criteria for these converters will be given. At the moment the dynamic range of a system must be enlarged, but the maximum clock rate of the system cannot be increased because of technology limitations, then a multi-bit digital-to-analog converter can be used in the feedback loop. At that moment, however, the linearity of the digital-to-analog converter determines the linearity and the distortion in the system. To overcome this problem Dynamic Element Matching or Continuous Current Calibration techniques can be used to obtain the extreme linearity of the D/A converter without needing extra trimming steps.