Design of Advanced Linear Circuits and Systems

我的研究目的是设计和开发能够使用模拟电路执行一些最简单的数学函数的新电路。其中几个功能包括放大、滤波、乘法、除法、感测和信号的一般处理。需要不断地重新检查这些功能，因为技术正在快速变化，在一种集成电路技术中可能工作良好的东西可能必须在另一种集成电路技术中进行修订。 这种功能的一个例子是对数或指数数模转换器(DAC)功能，我正在寻找在新的集成电路技术中实现该功能的新方法。这是为了应对与电源和晶体管尺寸缩小相关的挑战。我对新的对数和指数乘法D/A放大器的研究集中在对对数和指数函数使用一阶和可能的二阶近似，并扩展这些函数的动态范围以满足实际需要。期望通过使用这些近似函数可以在不造成过多损失的情况下获得硬件节省。对数DAC在自动增益控制电路和增益或音量控制中得到应用。 信号一般处理的另一个例子是在滤波器设计中。所有电子电路都使用通过低频或高频、某一频带或消除某一特定频带的滤波器。我提出的和尚未开发的许多研究的目的是允许更多的选择最近引入的与这些新滤波器的频率响应相关的参数，从而允许比传统方法更精确的滤波器设计。 为了实现这一目标，对新的滤波电路设计的研究集中于分数电容在滤波结构中的新兴和令人兴奋的使用。这种独特且相对未经探索的元素具有这样的特性，即它的阻抗不再是纯虚构的，而是它的阻抗具有实数分量。这种元件的特性在大多数材料中是不存在的，到目前为止，我们的团队已经使用这种元件在滤光器中产生了不寻常的特性，如不对称和尖锐的滤光片响应，这些特性是商业电容器或传统方法无法获得的。 作为我们正在进行的研究的一部分，我还发现它们可以用于模拟人体组织的电行为，农业和寻找癌症。虽然分数级电容器目前还不能商业化，但整个研究有可能给电气工程的许多其他学科带来革命性的变化，同时也是交叉学科。为什么，因为分数微积分在控制和系统辨识中的长期使用并没有真正应用于解决电气工程问题和寻找新的做事方法。因此，我的研究工作试图增加在模拟分数滤波和建模元件属性领域的一般知识。后一种应用可能有助于一般的生物阻抗测量，或表征组织或监测生理变化。这里的任何发现都可以进一步用作癌症检测和监测由于其他健康状况引起的生理变化的潜在诊断工具。有了这种应用，对使用间接测量技术的低成本、可穿戴/可植入的监测设备的需求在监测和可能降低健康成本方面都变得非常有用。

My research is aimed at designing and developing new circuits capable of performing some of the simplest mathematical functions using analog circuits. Several of these functions include amplification, filtering, multiplication, division, sensing, and the general processing of signals. There is a need to constantly reexamine such functions because technology is rapidly changing and what may work well in one integrated circuit technology may have to be revised in another. One example of such a function is a logarithmic or exponential digital to analog converter (DAC) function that I am seeking new ways to implement in new integrated circuit technologies. This is to meet the challenges associated with shrinking power supplies and transistor sizes. My research into new logarithmic and exponential multiplying D/A amplifiers is focused on using first and possibly second order approximations to logarithmic and exponential functions, and expanding the dynamic range of those functions to meet realistic requirements. The expectation is that hardware savings may be gained without excessive losses through the use of these approximation functions. Logarithmic DACs find application in automatic gain control circuits and gain or volume controls. Another example of general processing of signals is in filter design. All electronic circuits use filters that pass low or high frequencies, a band of frequencies, or eliminate a particular band of frequencies. Much of my proposed and yet untapped research is aimed at allowing more choice of several recently newly introduced parameters associated with the frequency response of these new filters, hence allowing more precise filter design, than conventional methods. To accomplish much of this, research into new filter circuit design is focused on an emerging and exciting use of fractional capacitors in filter structures. This unique and relatively unexplored element has the property that its impedance is no longer pure imaginary, but it has a real component to its impedance. This element whose properties are not found naturally in most materials has been used by our group to date to produce unusual characteristics in filters such as asymmetry and sharp filter responses that are not available through commercial capacitors or conventional means. As part of our ongoing research I have also discovered they can be used in modeling the electrical behavior of human tissue, agriculture and looking for cancers. While fractional capacitors are presently not available commercially, this entire research has the potential to revolutionize many other disciplines of electrical engineering, all the while being cross discipline. Why, because fractional calculus long time use in controls and system identification has not been really applied to addressing electrical engineering problems and seeking new ways of doing things. My research work therefore seeks to add to the general body of knowledge both in the area of analog fractional filtering and modeling element properties. The latter application, to possibly aid in bioimpedance measurements in general, or characterizing tissue or monitoring for physiological changes. Any discoveries made here can be further used as a potential diagnostic tool for cancer detection and monitoring physiological changes due to other health conditions. With this application, the need for low-cost, wearable/implantable monitoring devices using indirect measurement techniques becomes extremely useful in both monitoring and possibly keeping health costs down.