Design of an ultra low power third order continuous time current mode ΣΔ modulator for WLAN applications

Abstract

This paper presents a third order continuous time current mode ΣΔ modulator for WLAN 802.11b standard applications. The proposed circuit utilized feedback architecture with scaled and optimized DAC coefficients. At circuit level, we propose a modified cascade current mirror integrator with reduced input impedance which results in more bandwidth and linearity and hence improves the dynamic range. Also, a very fast and precise novel dynamic latch based current comparator is introduced with low power consumption. This ultra fast comparator facilitates increasing the sampling rate toward GHz frequencies. The modulator exhibits dynamic range of more than 60dB for 20MHz signal bandwidth and OSR of 10 while consuming only 914μW from 1.8V power supply. The FoM of the modulator is calculated from two different methods, and excellent performance is achieved for proposed modulator.