High Speed 1-bit Sigma Delta Modulators

Abstract

High speed 1-bit quantizer sigma delta (ΣΔ-) modulator topologies and some of their applications are discussed. It is shown that a 14-bit dynamic range can be achieved with the oversampling ratio of 16 by using cascaded high-order 1-bit ΣΔ-modulators whose noise transfer function can be modified by placing some of the zeros in the baseband. Compared to cascaded low-order ΣΔ-modulator structures, these modulators are less sensitive to circuit imperfections. The moderate requirements allow us to use simplified high speed circuit structures. The operational transconductance amplifier (OTA) structure realization based on the use of a minimum number of active transistors in the signal path is discussed. Also an example of ΣΔ-modulation in digital data transmission at the intermediate frequency is shown. This arrangement has some advantages over conventional systems including the fast recovery from the power-down mode, which is a crucial problem in the portable digital telecommunication applications.