A Small-Area 2nd-Order Adder-Less Continuous-Time ΔΣ Modulator With Pulse Shaping FIR DAC for Magnetic Sensing

Abstract

This work presents a small-area 2nd-order continuous-time ΔΣ Modulator (CTΔΣM) with a single low dropout regulator (LDO) serving as both the power supply for the CTΔΣM and reference voltage buffer. The CTΔΣM is used for digitising very low amplitude signals in applications such as magnetic tracking for image-guided and robotic surgery. A cascade of integrators in a feed-forward architecture implemented with an adder-less architecture has been proposed to minimise the silicon area. In addition, a novel continuous-time pulse-shaped digital-to-analog converter (CT-PS DAC) is proposed for excess loop delay (ELD) compensation to simplify the current drive requirements of the reference voltage buffer. This enables a single low-dropout (LDO) voltage regulator to generate both power supply and Vref for the DAC. The circuit has been designed in 65-nm CMOS technology, achieving a peak 82-dB SNDR and 91-dB DR within a signal bandwidth of 20 kHz and the CTΔΣM consumes 300 μW of power when clocked at 10.24 MHz. The CTΔΣM achieves a state-of-the-art area of 0.07 mm.