Design of High-Voltage-Tolerant Stimulators in Low-Voltage CMOS Process with Charge-Balanced and Energy-Efficient Properties for Biomedical Applications
| Autor: | Luo, Zhicong, 羅志聰 |
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| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Epilepsy is a group of neurological disorders resulting from excessive and abnormal discharges in the brain. Most epilepsy patients can be cured by the antiepileptic drugs (AEDs). However, approximately 30% of patients suffer from medically refractory epilepsy. Deep brain stimulation (DBS) therapy is a fairly new treatment for epilepsy and is being researched. A closed-loop DBS system that continuously monitors the brain’s activity is an ongoing engineering technology. However, a circuit designer faces a number of challenges while designing a stimulator, such as the realization of high-level integration, the efficient power delivery to the stimulators, the delivery of the safe electrical stimulation, and the reduction of medical costs. In this thesis, I have presented four new techniques to enhance some key specifications of stimulator such as enhancing the integration, reducing the size, improving the charge balance, and improving the power efficiency. First, a new technique for smoothing the charging current of charge pump is introduced and described. This technique is capable of reducing the smoothing capacitance in the power line, reducing the transient noise in the power supply line, and improving the electromagnetic emission (EME) behavior of the implantable devices. The theoretical analyses indicate that the charging current of 3-stage cross-couple charge pump can be smoothed greatly when the clock signals are separated averagely to each other. The charge pump with this new clocking scheme has been designed and successfully verified in a 0.18-μm 1.8-V/3.3-V CMOS process. Experimental results show that the charging current ripples of the charge pump are reduced by a factor of three. In addition, the power efficiency is improved. Second, a high-voltage-tolerant technique is introduced and described. The use of the stacked transistors with deep n-well layers made it possible to increase the operation voltage of the proposed stimulator to 12 V. Third, a precise charge-balanced technique is introduced and described. The stimulator with this new high-voltage-tolerant technique and precise charge-balanced technique has been designed and successfully verified in a 0.18-μm 1.8-V/3.3-V CMOS process. The reliability measurement results have verified that the proposed stimulator is robust. The stimulator can be fully integrated with the microcontroller or the biomedical signal processor into an SoC chip fabricated by using the LV CMOS technology for enhancing integration and reducing the size. The current memory cell with dual calibration loops and leakage current compensation ensures that the charge mismatch of stimulator is less than 0.25% and the residual average dc current is less than 6.6 nA with shorting operation. Four, a digitally dynamic power supply technique for multi-channel stimulator is introduced and described. The existing stimulators with dynamic power supplies use too much analog circuits, such as attenuator, ADC, amplifier, comparator, which lead to large layout area and power dissipation. In contrast, the proposed digitally dynamic power supply technique examines the operating region (triode vs. saturation) of the current generator by a simple PMOS inverter. The output of the charge pump is driven by a digital input, eliminating the need of decision-making analogue circuits. High power efficiency is achieved by optimising the efficiency of each circuit module and using the adaptive power supply. A 16-channel 12V-tolerant stimulator with this digitally dynamic power supply technique has been designed and successfully verified in a 0.18-μm 1.8-V/3.3-V CMOS process. The experimental results have shown that the proposed new digitally dynamic power supply technique for multi-channel stimulator can greatly improve the power efficiency. Final, the in vivo experiments verified that epileptic seizures could be suppressed by the electrical stimulation with certain stimulation parameters provided by the proposed stimulator. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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