A method for improving the signal-to-noise ratio (SNR) ofnsigma-delta modulators with one-bit quantization is presented. Thentwo-level feedback signal of a standard sigma-delta modulator isnreplaced by a multilevel signal, which is a superposition of two parts.nOne part s(n) represents a rough estimate of the instantaneous amplitudenof the input signal (prediction signal), and the other yb(n)nis the sign of the quantizer output, multiplied with constant b.nCompared to a nonadaptive modulator, the amplitude of yb(n)nis reduced. Therefore, less noise power is introduced in the quantizer,nand the SNR is considerably enhanced. Signal s(n) is derived numericallynfrom the quantizer output y0(n) according to a particularnadaptation algorithm. Except for the DC-level of s(n), sequence y0n(n) contains the full digital information of the modulator inputnsignal. From y0(n), a digital multilevel sequence w0n(n) can be calculated, which represents the digital modulatornoutput. The price paid for the improved SNR is a moderate slew ratenlimitation of the input signal. The approach is basically suited for anwide class of sigma-delta modulators. Here, simulation results and annexample for a practical implementation of an adaptive sigma-deltanmodulator of first order are presented
展开▼
