The Design Of Fully Integrated Continuous- Time Active Filters

With the rapid development of the mobile communication and computer technology, the design of a high frequency fully integrated continuous-time filter has been paid great attention in microelectronics, circuits and systems. It is important for the realization of system on chip.In the dissertation, the international and national researches and development trends of the fully integrated continuous-time filter is systematically reviewed. The design methods of the OTA-C active filter are deeply studied. A design method with finite transmission zeros and high Q active filter is proposed. The SPICE simulated results show that the given method is suitable for continuous time full-integrated filter design. The simulated results are in accordance with the theory.The main achievements consist of following several aspects:1. On the basic of the MOS transistor models, current source is discussed and constructed. It has the features of low element sensitiveities, low voltage supply and low power consumption.2. With the essential exploration of the basic principles of operational transconductance amplifier (OTA) design, the improved design methods are introduced and the real OTA circuit design with auxiliary cross-coupled and common-mode feedback technology is given. Its amplitude characteristic is analyzed. The simulation results show that its linearity and bandpass performance are improved.3. The dissertation is mainly concerned with the design of fully integrated contionuous-time filters. The design methods of inductor simulation, leap-frog structure and casaded connection are discussed in detail. The design examples are presented respectively. The designed OTA is embeded in the filter circuit for computer simulation. The results show that the OTA-C filters have same performance with RLC filter and the theory is tested.4. In order to solve the difficult of OTA-C filter with finite transmission zeros and high Q, a practical procedure to derive an OTA-C active filter from the prototype of resistive doubly terminated LC passivefilter is proposed in the dissertation . The design procedure is based on Jacobi method and similar diagonal matrix. Jacobi method may avoid the difficulties of finding the roots of high order polynomial. The designed active filter is composed of OTA and ground capacitors. The derived filter structure can save the chip area and avoid the effects of parasitic capacitors in the circuit. Therefore, it has the characteristics of high stability and low sensitivities. Design examples of lowpass and highpass as well as bandpass filters are given respectively and the simulated results show that the given method is suitable for continuous time full-integrated OTA filter design.5. In the dissertation , the design strategy of the programmable operational transconductance amplifier (POTA) is proposed based on digital potentiometers and OTA circuit, the procedure of how to convert a passive LC filter to programmable active filter is described. Examples of second order and higher order filters are presented respectively. Simulation results show POTA allows the programmability of the cut-off frequency and Q of the active filter. It will improve the flexibility of active filter and reduce the cost of development.