An Oversampled Multi-bit CMOS D/A Converter For Digital Audio With 115dB Dynamic Range

In digital audio applications there is a growing interest in highly oversampled 1b D/A converters. Nowadays some of these devices reach true 18b performance. The main advantages are obvious. At first order, no complex analog circuits are required, and the differential linearity is always guaranteed. Furthermore, the concept fits well with other digital circuitry for integration of complex functions. To obtain the required dynamic range for digital audio, the enormous quantization noise of one bit is shaped to out-band frequencies by a higher-order noise-shaper. However, this sometimes leads to intermodulation distortion of the operational amplifiers, which might result in unwanted fuzzy signals within the audio band. An oversampled 5b D/A converter reduces the above-mentioned problem as the amplitude of the quantization noise is reduced by about 30dB. For low signal levels, the converter acts as and has the advantages of a true 1b converter.