Design and Analysis of OTA Based 5th Order Chebyeshev Filter.

Abstract

Today, with the development in the field of telecommunication and video processing applications, the components, that are the main building blocks of communication equipments, have caught the eyes of many research scholars. These developments in wireless communication have motivated many design challenges. Design of filter, which is one of the basic circuits used in these systems, is the most critical and important issue as this block contributes to the overall power consumption of receivers. All the filters can be designed in different ways depending upon the applications for which they are being designed. Filters can be classified on the basis of response characteristics, components used, signals used, or mathematical approximations. One of the mathematical approaches is Chebyshev filter, which is the very much popular and widely used filter. Further, the filter implementation can be either active or passive. But typically for very low frequency applications (< 10 MHz), active filters are suitable, in which the prototype element values are too large to be implemented using discrete components. Video filters for industrial and broadcast applications require around 5 MHz cutoff frequencies. Thus, in order to solve the very purpose Chebyshev filter is designed. In active implementation of filter, an active device has to be chosen for a desirable response of the filter. A range of devices like Operational Amplifier, Difference Differential Amplifier (DDA), and Operational Transconductor Amplifier (OTA) etc. can be used to design an active filter. After extensive study, of all the choices Operational Transconductor Amplifier is chosen to design a Chebyshev filter. Amongst all the topologies of OTA, on the basis of literature survey, Folded Cascode OTA is chosen as it allows shorting of input and output terminals with negligible swing limitations. The design procedure for a single stage Folded Cascode OTA is developed using design equations. The circuit designed is then simulated on Tanner EDA tool. The simulated results are validating the theoretical values. The passive network of the 5th order Chebyshev filter is chosen and all the passive components, like resistors, inductors are implemented using the active device (OTA), to get the active network of 5th order Chebyshev filter. The result of the designed filter schematic is then compared with the layout drawn on Tanner EDA tool. The passband frequency response of 5.77 MHz and gain of 0 dB is achieved after simulation which, well justifies that the filter may be used for video applications like HDTV (High Definition Television) in broadband communication. Change in transconductance and hence the 3dB-frequency of filter due to change in bias voltage of the OTA, is analyzed. The results of the analysis are in accordance with the literature. Finally an equation is proposed that relates the two parameters, transconductance gm and 3dB-frequency.