Feed-forward ΔΣ modulators topologies design for broadband communications applications

This paper presents a design methodology for low-distortions (feed-forward) Delta-Sigma (ΔΣ) modulators topologies used in next generations wireless applications. Thus, optimized folded cascode OTA and telescopic OTA gain-boosting are selected to implement the switched capacitor (SC) integrator. First, a second order ΔΣ modulator is implemented for 2MHz bandwidth. Second, a 2-2 cascaded ΔΣ modulator is designed for 2MHz and 10MHz bandwidths in order to improve the modulator performances. These modulators are implemented using system-level simulations as well as device-level simulations implemented with SC circuits in AMS 0.35μm CMOS process. Device-level simulations results indicate that the 2
^nd
and the 2-2 cascaded ΔΣ modulators achieve respectively SNRs of 43dB and 38dB over bandwidths of 2MHz and 10MHz with over-sampling ratios 16 and 8.