This paper presents a new multi-loop delta-sigma modulator which overcomes the necessity of high DC gain opamps that were needed in previous multi-loop modulators. Enabling the use of low gain opamps also allows low-voltage operation due to the reduced number of transistors between the power supply rails. In addition, all the digital filters are removed from the output of this modulator to minimize the overall system requirement. Instead, an in-loop digital addition facilitates the desired noise transfer functions of both loops. This combines stability advantage of the multi-loop structure with relaxed circuit requirement of the single-loop modulator. A fourth order modulator is implemented in a 0.18 mum CMOS technology to demonstrate this concept. Measurement results show that, with open-loop opamp gain of less than 35 dB, the implemented prototype IC achieves over 74 dB SNDR at an oversampling ratio of 16. The sampling frequency is 20 MHz and the total power dissipation is 3.2 mW at 1.2 V supply.

74 dB SNDR Multi-Loop Sturdy-MASH Delta-Sigma Modulator Using 35 dB Open-Loop Opamp Gain

Electromechanical multi stage noise shaping (MASH) sigma–delta modulator (ΣΔM) has the advantages of inherent stability, high dynamic range, and high overload input level compared with the single loop sigma–delta-modulator approach. In this paper, a fourth order electromechanical MASH is studied by Simulink modelling and hardware implementation using surface mount PCB technology. The accelerometer used in the study is fabricated using a Silicon on Insulator (SOI) wafer with a device layer thickness of 50 μm, using a dicing free and dry release process. The experimental results confirm the concept of the MASH structure and show its potential as a closed loop interface concept for a high performance capacitive MEMS accelerometer. The 4th order MASH electromechanical ΣΔM system improves the performance of the 2nd order electromechanical ΣΔM by 20 dB, and shows a noise floor of −110 dB. Furthermore, the system is capable of handling an acceleration input of up to ±1.5 g. However, the MASH-ΣΔM is sensitive to the sensor and system parameters variation; it exhibited performance degradation of 10 dB, due to a leakage of the quantization noise to the input signal.

Multi stage noise shaping sigma–delta modulator (MASH) for capacitive MEMS accelerometers

An extended version of sturdy MASH delta-sigma modulators is presented in this paper. Improved performance is achieved using in-band zero optimization. The challenges towards high order multi-loop modulators are discussed and a new multi-loop modulator is presented. This modulator benefits from a MASH architecture in the final loop to preserve stability, while the main loop benefits from relaxed circuit building blocks of the SMASH structure. Extensive simulation results are provided to prove the efficiency of this structure.

/pdf/multi-loop-efficient-sturdy-mash-delta-sigma-modulators-2odyeznerj.pdf

Multi-loop efficient sturdy MASH delta-sigma modulators

In this paper, a new control structure based on the dual quantization technique is presented for an electromechanical sigma–delta modulator (EM- $\Sigma \Delta \text{M}$ ) applied to a microelectromechanical system (MEMS) accelerometer. The modulator adopts a 2-0 multistage noise shaping structure (MASH2-0), taking the advantage of the intrinsic linearity of single-bit quantization and the reduced quantization error of multibit quantization in a single modulator. The sensor system is studied by the system-level modeling and the hardware implementation based on the field-programmable gate array technology. The study shows that, MASH2-0 shares the benefits of a MASH2-2 architecture of having an inherent stability, a high overload input level, and a high dynamic range compared with single-loop EM- $\Sigma \Delta \text{M}$ . However, the MASH2-0 architecture benefits from a considerably simpler implementation, while achieving a higher dynamic range and a higher signal-to-noise ratio compared with a MASH2-2 and a fourth-order single-loop $\Sigma \Delta \text{M}$ architecture. A capacitive MEMS accelerometer was designed and employed with this control system. Within a bandwidth of 1 kHz, the sensor achieved a noise floor level of −130 dB and a bias instability as low as $20~\mu \text{g}$ at an integration time of 40 s. Simulation estimated a full scale of ±20 g acceleration. The investigation confirms the concept of the MASH2-0 structure and shows its potential as a closed-loop interface for high-performance capacitive MEMS accelerometers. [2015-0071]

/pdf/design-and-implementation-of-a-mash2-0-electromechanical-4qlk8c5the.pdf

Design and Implementation of a MASH2-0 Electromechanical Sigma–Delta Modulator for Capacitive MEMS Sensors Using Dual Quantization Method

This research discusses the theoretical investigation, simulation and hardware implementation of the ElectroMechanical Multi-stAge noise SHaping (EM-MASH) sigma delta modulator (ΣΔM). The potential advantages of an EM-??M MASH compared to single-loop high-order ΣΔMs applied to inertial MEMS sensors are its inherent stability and high overload input level due to the use of lower order ΣΔMs in its individual stages. Furthermore, MASH has the advantages of high dynamic range and high noise shaping performance because of its overall high-order ΣΔM architecture. So far, the EM-MASH has not been sufficiently explored. This study is expected to serve as solid basis for the application of EM-MASH. In this research, various EM-MASH architectures (MASH21, MASH22, MASH211, MASH221 and MASH222) were theoretically studied, and the results were validated with simulations. A fourth order EM-MASH22-ΣΔM was theoretically examined and successfully implemented with a capacitive MEMS accelerometer, which includes a second order EM-ΣΔM loop cascaded with a purely electronic second order ΣΔM. The quantization noise from the first loop is digitised by the second loop and then cancelled by digital filters, whereas the quantization noise from the second loop is shaped by the second loop filter and a digital filter, which together provide fourth order noise shaping. The performance of EM-MASH22 was compared with that of a single-loop fourth order EM-ΣΔM (SD4). Both architectures were investigated by system level modelling and hardware implementation using surface-mount PCB technology. The results show that (a) both architectures achieve the same noise floor level of 19 µg/√Hz; (b) MASH22 is unconditionally stable, whereas SD4 is only conditionally stable; and (c) MASH22 achieves a higher overload input level and a higher dynamic range than does SD4. Furthermore, the research presents a novel EM-MASH-ΣΔM that employs a dual quantization technique and adopts a 2-0 structure (EM-MASH20). With a simpler and configurable composition, MASH20 is aimed at exhibiting a performance higher than that achieved with the MASH22 structure. The MASH20 does not require a second-stage ΣΔM, which reduces the complexity of the digital filters compared to those required for the MASH22; thus, the digital filter matching is more easily achievable. The study shows that the MASH20, like the MASH22, has an inherent stability, high overload input level, and high dynamic range compared to single-loop ΣΔM. However, the MASH20, with its simpler implementation, achieved a higher dynamic range and signal-to-noise ratio than the MASH22 and the SD4. A capacitive MEMS accelerometer was designed and employed with MASH20. Within a bandwidth of 1 kHz, the sensor achieves a noise floor level of 15 µg/√Hz, a full-scale acceleration of ±20 g and a bias instability of 20 µg for a period of three hours. The EM-MASH-ΣΔM is sensitive to the variation of the sensing element parameters and other analogue parameters, both of which are subject to manufacturing tolerance and imperfections. This causes a leakage of the quantization noise in the final output and degrades the modulator performance. The research explored a calibration method to solve this problem by utilizing the digital domain capabilities. The method is based on the optimization algorithm which was investigated using MATLAB. The research confirms the concept of the EM-MASH structure and proves that it is applicable as a closed-loop interface for high-performance capacitive MEMS inertial sensors.

Multi stage noise shaping (MASH) sigma delta modulator for capacitive MEMS inertial sensors

An enhanced version of Sturdy MASH (SMASH) (2) delta-sigma modulator is proposed. This structure takes advantage of the well-known stability of the MASH structure while greatly reducing its sensitivity to imperfect circuit blocks. Furthermore, no digital noise cancellation filters are needed. Hence there is no matching requirement for the analog and digital paths. With the proposed enhancement in noise shaping, the first and second stage quantization noise experience different (thus mixed) orders of noise shaping, and the accuracy of this modulator is comparable of that of the MASH structure. Simulations results and mathematical analysis demonstrate the effectiveness of this structure. Delta-Sigma modulators (DSMs) are mostly used in high- accuracy, low-to-medium bandwidth applications, benefiting from oversampled operation. Oversampling allows achieving high accuracy without necessarily using accurate circuit elements. This, however, comes at the cost of a higher sampling frequency. For wide-band applications, the sampling frequency may need to be over 200 MHz to satisfy the required SNR. This may require large bias power for the amplifiers in the modulator, and the speed of the amplifiers may exceed the transit frequency of the given technology. To decrease this high sampling frequency, while maintaining the

/pdf/mixed-order-sturdy-mash-modulator-5dd5y6joi5.pdf

N. Maghari

Papers

Mixed-Order Sturdy MASH ˚ - Modulator