Computer aided design of high order active OTA-C filters using Quad configuration

Electronics, named the technology of the today's modern age, is growing rapidly and almost everyday presents many new and useful products for the human being. Most of these products consist of circuits that select the electrical signals according to their frequencies and put these signals into another form. These kinds of circuits are known as filters, and have many applications in electronics from daily use to the high technology. At the beginning of this century, most of voice-frequency filters were realized using discrete RLC passive circuits. For these networks, inductors were a problem since they were large components, difficult to produce and tune. In the 1950s, it was understood that the more advantageous filters could be obtained if the inductors were replaced by active networks. Therefore, designers started to commonly use the active-RC networks, which were composed of op amp's, compared to the former technique [1]. Together with the rapid growth of the integrated circuit technology, many active and passive components became realizable in very small silicon chips. Especially, VLSI technology presents many advantages to the designers. Today, with the use of switched-capacitor filters ( SC filters ), the disadvantages of analog filters have been eliminated. Meanwhile, time-constants (RC) can be accurately obtained with the ratio of two MOS capacitors multiplied by a clock frequency. Moreover, resistors can be simulated with the capacitors. So, an important amount of silicon area can be saved. SC filters do not require an additional tuning and they can be tuned electronically [1], [2]. However, these types of filters can not operate properly at higher frequencies than voice frequencies because of the op amp's limited bandwidth. Digital filters have also some limitations such as computation time, analog- digital conversion time and especially Nyquist rate. Continuous-time analog filters do not have such frequency limitations as in SC and digital filters and theoretically can use all available frequency band. Thus, they can be used at high frequencies more realibly than the other two filter types. Because op amps are highly developed and cheap components, they have been used in the discrete active filter design for many years. However, in order to integrate analog and other signal processing circuits in the same silicon chip, more compatible gain devices,OTAs, were required. OTAs can be easily integrated in the IX