CMOS OTA Principle And Its Application In Filters

The fully integrated continuous-time filters is inverstigated in the paper and is a frontal and hot field of microelectronic, circuits and system in the world. The continuous-time filter have been applied widely in many fields such as communications, electronic surveying, instrumentation, auto-control, etc.. It plays a important role in processing digital, analog and mixed signal in integrated circuit. The research on the OTA-C active filter has become a developing direction with bright prospects in the field of modern filter because of its high frequency nature, its ability of electronic control, and its easy compatibility with CMOS VLSI technology.Not only the realization circuit and typical application of the high-linear OTA-C filter, but also inverstigate the design principle,methods and realization circuit of high-order filter had been studied intensively in this dissertation. This thesis introduced the development of integrated circuit active filter, current research situation in demostic and abroad and its significance. The CMOS transistor physical structure, operating principle and circuit model are presented and used to design the basic elements such as CMOS active resistance, common-source and common-gate current mirror, the source coupled differences pairs, which are applied to design the whole intigrated circuits. The construct design and application of CMOS operational transconductance amplifiers have been studied widely and deeply in the thesis. After comparing and analyzing several modified operational transconductance amplifier circuit and their structure, we inverstigate the construct and propose a kind of high-linear transconductance operational amplifier whose structure, oprational principle and the implemented circuit are presented and verified by the spice simulation. The canonical OTAs application are analyzed and a new three-input single-output second order multifunction active filter was proposed in the paper. The filter circuit are composed of only three OTAs and two capacitances and the structure is simple and low sensitivity, which is proved to be correct and feasible by the result of SPICE simulation. The design methods of high-order continuous-time OTA-C filters such as the polycyclic loading back method and passive LC ladder type modeling method had been analyzed. The transfer function direct synthetic high-order filter design method and its principle were presented in this paper. The method is simple in theory and implemented easily by using low-order low-pass filter as the basic module to realize any type high-order filter. A four-order Butterworth filter has been designed and simulated as a example to indicate that this method is correct and feasible.