Two-Port Transmission Line Parameters Approach Modeling and Design Centering of Integrated Continuous-Time Filters

Design centering is one of the important process followed for the accurate design of integrated continuous time filters where the filter frequency response is tuned to match the ideal in presence of non-idealities such as finite gain of the OTAs/Opamps and parasitics. One of the efficient method adopted is the space-mapping where the filter response is tuned in the ‘model space’ and the results are interpreted in the actual ‘filter space’ resulting in a time efficient process. This method demands the filter to be modeled and state-space approach has been the choice for modeling. This paper proposes a two- port transmission-line parameter based approach for modeling a class of filters. The paper compares the proposed process with that of the conventional state-space method. The demonstration is carried out on a 2nd order Butterworth low pass Gm-C filter having Cochlea architecture. The filter is designed to operate on a 0.5 V supply in 0.18 μm standard CMOS process. The paper brings out the limitations of state-space based approach for accurate modeling in the regime of low voltage design and demonstrates how the proposed two-port parameter based approach can be used for better accuracy.