Self-calibration techniques for a second-order multibit sigma-delta modulator

Design techniques for self-calibration of the digital-to-analog converter DAC in a multibit sigma-delta modulator are described. When used in conjunction with dynamic element matching, self-calibration provides linearity performance suitable for digital audio applications. The dynamic element matching circuitry provides the mechanism of determining device mismatch for self-calibration. Practical circuit details and an effective calibration method are discussed. Test results from a l-μm CMOS test chip are presented. In this test system, a second-order loop with a 3-b quantizer achieves an 89-dB dynamic range and -91-dB harmonic distortion after calibration. In addition, a new method of detecting the presence of tones is described, using the entropy of the spectrum of the decimation filter output