Fast and efficient algorithm to design noise-shaping FIR filters for high-order overload-free stable sigma-delta modulators

Abstract

This paper presents a fast and efficient algorithm to design FIR noise transfer functions (NTFs) for overload-free stable high-order /spl Sigma//spl Delta/ modulators. In the design, three parameters, filter order, oversampling ratio (OSR) and l/sub 1/-norm of the impulse response are specified, and the in-band peak of the amplitude response is minimized under the specification. The design problem is formulated as a linear minimax problem, in which the stability condition limits the l/sub 1/-norm of the impulse response of the NTF. The proposed algorithm can fast and efficiently solve the problem by iteratively utilizing the simplex method. In numerical examples, it is confirmed that the proposed algorithm can design near optimum /spl Sigma//spl Delta/ modulators and besides is far faster and more efficient than the conventional design methods. Besides, by the proposed algorithm simulation results reveal the existence and achievable performance of rigorously stable /spl Sigma//spl Delta/ modulators up to the order 199. Then it is revealed that a single-bit /spl Sigma//spl Delta/ modulator for OSR 64 can have an in-band peak amplitude -96.2[dB], while rigorously ensuring the stability, and this modulator achieves a high SNDR 107.6[dB] for a sinusoidal input signal. In addition, it is demonstrated that a rigorously stable nine-level /spl Sigma//spl Delta/ modulator has an in-band peak amplitude -105.3[dB] for OSR 16 only by optimizing the high order NTF.