A second order sigma delta modulator using semi-uniform quantizer with 81dB dynamic range at 32x OSR

In this paper a new type of nonuniform quantizer, semi-uniform quantizer, is introduced. A k-bit semi-uniform quantizer uses the thresholds defined by a (k+1)-bit uniform quantizer and arranges them in such a way that small-amplitude inputs will be quantized by small quantization steps and vice versa. Under the condition that there is no DC offset at the modulator input, the use of semi-uniform quantizer achieves about 1-bit higher dynamic range compared with using a conventional quantizer, while the hardware complexity of the quantizers is the same. The measurement results of a prototype chip in 0.35µm CMOS process confirm the simulation results. At 32x oversampling ratio the 2nd order modulator achieves 81dB dynamic range, 56.3dB peak SNDR with a 3-bit semi-uniform quantizer. With a 3-bit uniform quantizer the dynamic range is 73dB and the peak SNDR is 52.6dB.