Extended Noise Shaping in Sigma-Delta Modulator Using Cross-Coupled Paths

In this paper, combined with time-interleaving, noise coupling is used to achieve considerable improvement in the performance of sigma-delta modulator. Two types of noise-coupling, unextended and extended coupling, are presented for N-path architecture based on first-order sigma-delta modulator which can enhance the effective order of noise shaping without significant overhead. In the general condition, the optimum couplingmatrices are obtained analytically to achieve the desired noise shaping. It is also shown that the proposed N-path first-order sigma-delta modulator provides (2N - 1)th-order noise shaping. However, the unextended coupling provides th-order. To verify the proposed method, the macro-level simulations show that third-order and fifth-order noise shaping were achieved in two-path and threepath first-order sigma-delta modulators with extended noise coupling, respectively. Likewise, the ADS software's simulation result of the switched-capacitor circuit implementation confirms the effectiveness of the proposed method.