摘要
现代集成电路技术的飞速发展有力推动了便携式医疗电子设备的发展和普及。然而由于此类设备应用环境较为特殊,使得此类设备的电源设计面临诸多挑战,包括解决电池供电电源的超长时间稳定工作,以及适应新能源电池的低电压供电工作等技术瓶颈问题。
有鉴于此,本文针对便携式医疗电子设备的电源管理,就低压低功耗高效率电源系统的设计技术展开研究,论文的主要内容和创新包括：
1、新能源技术领域研究的发展和它的特点,为便携式医疗电子设备技术瓶颈的突破带来了转机。然而新能源电池(如太阳能光伏电池和温差热电池)应用中的一个难题是其过低的输出电压。对此,论文提出超低电源电压下的直流转换技术研究,采用亚阈值方案给出一个可在接近器件阈值电压的低压电源下正常工作的升压电路设计,并提供升压转换。该方案实现的特点是无需借助特殊工艺,在满足超低电源电压工作的同时,降低了制造成本。
在设计中借助环形振荡器以及多级片上电荷泵的帮助,升压转换器控制电路获得升压转换的初始能量；经过优化的超低功耗电压检测模块不但有效控制了整体电路的面积成本,其功耗也在可以接受的范围之内。在控制方面,升压转换器引入了开环恒定导通时间控制器,最大限度降低其控制电路的复杂度,降低了整体功耗。所设计的电路最终经过流片测试,验证了设计目标。
2、在对能耗要求苛刻的便携式医疗电子设备应用中,降低电源管理系统本身功耗具有重要意义。对此论文采用基于突发模式临界导通COT控制方式,在保证电源管理系统性能的同时有效降低了控制电路的复杂度,从而有利于减小功耗。功率级的建模分析帮助实现了芯片面积和功耗、效率之间的最佳平衡。针对该系统设计的亚阈值状态基准电路和电压迟滞窗口比较电路,有效控制了电路的整体功耗,保证了系统转换效率。相关的流片测试结果验证了所提出方案的可行性。
3、与电感型转换电路相比,电荷泵的优势在于其更小的体积和更低的成本,特别适合应用于便携式医疗电子设备等场合。无电感设计也使得电荷泵在EMI方面更具优势。为此,本论文提出一种用于电荷泵的变频调制控制方式,利用负反馈结构控制电荷泵的开关频率,实现对电荷泵输出的调制。为了保证系统参数设计的合理性,论文对电荷泵功率级进行了详细的数学模型分析。最终该方案以一个交叉耦合结构两倍升压电荷泵进行了流片验证。测试结果显示相较传统控制方案,新的变频控制模式在纹波和效率方面都有较大优势。
With the development of modern integrated circuit technology, the cost of electronic devices has been cutting down and the system integration level has been constantly improved. This has become a strong impetus to the development and popularization of portable medical electronic equipment. However, the power management system design also faces many critical challenges as people require more power performance for environment-&-application-specific systems. Designing a long-lifetime stable working battery powered system and accommodating the system to new energy technology batteries which provides very low voltage would be important for these days' engineers.
In view of this, this paper focuses on several critical issues in developing low-power high efficient power management systems in portable medical electronic devices. The main contents and innovations include:
1. The development of new energy technologies and portable medical devices has broken the bottleneck of portable medical electronic equipment technology. However the output voltage of solar cells and thermal batteries is too low. In this regard, this thesis proposed an ultra-low voltage DC-DC conversion technology to realize a boost converter which is powered by a sub-threshold voltage source and is able to boost the input voltage into a usable output voltage level. The boost converter obtains the start-up energy with the help of an on-chip ring-oscillator and a multi-stage charge pump. A voltage detector is designed with optimized power consumption and area. An open-loop COT controller is used to simplify the control circuit. The system is verified by simulation and experimentation.
2. Overall power consumption of the power management system is particularly important in the portable medical electronic equipment applications where total power consumption is very low. This thesis proposed a COT controller based on a critical conduction mode to reduce the complexity and power consumption of the controller while maintaining its performance. A power stage model is used to seek a best tradeoff between chip area, power consumption and efficiency. The specially designed sub-threshold voltage reference circuit and hysteretic voltage comparator help to control total power cost. The system is verified by simulation and experimentation.
3. Charge pumps are known for their small size and low cost and low EMI because of its non-inductor nature. This thesis proposed a variable frequency control technology with feedback for charge pumps to achieve high efficiency and low output voltage ripple. An detailed model for the charge pump power stage is given to guide the system design. The simulation and testing results showed that the new control technique have a great advantage compared to conventional charge pump control schemes.
引文
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