A method for improving the signal-to-noise ratio (SNR) of sigma-delta modulators with one-bit quantization is presented. The two-level feedback signal of a standard sigma-delta modulator is replaced by a multilevel signal, which is a superposition of two parts. One part s(n) represents a rough estimate of the instantaneous amplitude of the input signal (prediction signal), and the other y/sub b/(n) is the sign of the quantizer output, multiplied with constant b. Compared to a nonadaptive modulator, the amplitude of y/sub b/(n) is reduced. Therefore, less noise power is introduced in the quantizer, and the SNR is considerably enhanced. Signal s(n) is derived numerically from the quantizer output y/sub 0/(n) according to a particular adaptation algorithm. Except for the DC-level of s(n), sequence y/sub 0/(n) contains the full digital information of the modulator input signal. From y/sub 0/(n), a digital multilevel sequence w/sub 0/(n) can be calculated, which represents the digital modulator output. The price paid for the improved SNR is a moderate slew rate limitation of the input signal. The approach is basically suited for a wide class of sigma-delta modulators. Here, simulation results and an example for a practical implementation of an adaptive sigma-delta modulator of first order are presented.
[1]
Nuggehally Sampath Jayant,et al.
Adaptive delta modulation with a one-bit memory
,
1970,
Bell Syst. Tech. J..
[2]
Gabor C. Temes,et al.
Oversampling Delta Sigma Data Converters
,
1991
.
[3]
C. M. Zierhofer.
Numerical adaptive delta modulation-a technique for digital signal representation in ASIC applications
,
1991,
[1991 Proceedings] 6th Mediterranean Electrotechnical Conference.
[4]
Gabor C. Temes,et al.
Oversampling delta-sigma data converters : theory, design, and simulation
,
1992
.
[5]
G. Temes.
Delta-sigma data converters
,
1994
.
[6]
Martin Vetterli,et al.
Deterministic analysis of oversampled A/D conversion and decoding improvement based on consistent estimates
,
1994,
IEEE Trans. Signal Process..
[7]
R. Schreier,et al.
Delta-sigma data converters : theory, design, and simulation
,
1997
.