VCO-Based Continuous-Time Delta-Sigma ADC for Bridge Sensor Applications
Date Issued
2015
Date
2015
Author(s)
Ho, Ming-Yen
Abstract
Bridge sensors have been widely applied to accurate measurement of physical quantities such as temperature, pressure, strain or altitude. In order to meet these requirements, conventional biomedical sensor readout systems use multiple stages, typically including a low noise amplifier, an anti-aliasing filter and a discrete-time (DT) delta-sigma modulator (∆ƩM). As a result, such a system involves several high-gain loops with total open-loop gain, far exceeding the required gain of a closed loop. Hence, it can lead to more power dissipation and increase the complexity in the design of analog biomedical sensor readout system. The architecture proposed in this study is a Gm-C-based continuous-time (CT) delta-sigma modulator (∆ƩM) with a VCO-based quantizer. The architecture replaces original sensor readout system and draws a lot of attention due to its inherent anti-alias filtering, inherent DEM for DAC, producing high input impedance, low power consumption and high resolution. However, the usage in precision applications such as a bridge sensor readout system is limited by the non-linearity input stage. Additionally, the nonlinear transfer function of VCO also severely limits the total system performance. Hence, the following method is taken to solve these issues. In our work, we employ an identical nonlinear element in the negative feedback path. It can cancel the even order harmonic tones and suppress the nonlinearity of input. We use parameter scaling technique to reduce VCO input swing. Compared with previous VCO-based ADC, it is the simplest way to improve VCO non-linearity. The proposed work is designed and implemented in TSMC 90-nm CMOS technology. The system bandwidth is designed at 1 kHz with 1MHz sampling frequency. It consumes 586 uW from a 1V supply.
Subjects
Low Power
VCO-based ADC
Bridge Sensor Application
Delta-Sigma Modulator
Type
thesis
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