A 54.4-mW 4th-order quadrature bandpass CT ΣΔ modulator with 33-MHz BW and 10-bit ENOB for a GNSS receiver

Abstract

A 4th-order quadrature bandpass continuous-time sigma-delta modulator for a GNSS receiver is presented. With significantly wide bandwidth, the modulator is able to digitalize the down-conversed GNSS signals in two adjacent signal bands simultaneously. This makes it possible to realize simultaneous dual-frequency reception from two satellite systems with one receiver channel instead of two independent channels. A direct RZ feedback is introduced into the input of the last integrator to realize ELD compensation. Power-efficient amplifiers are employed in the active RC integrators, and self-calibrated comparators are used to implement the low-power 3-bit quantizers. Implemented in 180nm CMOS, the modulator achieves 62.1dB peak SNDR, 64dB DR and 59.3dB image rejection ratio (IRR), and consumes 54.4mW from a 1.8V power supply.