Infinite Rejection Filters

Infinite rejection filters find applications in interference removal from adjacent channels. In this paper, starting with a simple L-section circuit, we present a comprehensive development of a bridged-T network that did not receive adequate attention and highlight its usefulness as a null circuit, its simplicity of configuration, and its advantage over other similar known networks. This circuit has a provision to tune the notch frequency by varying a single resistor in its shunt arm. Analytical expressions for the notch frequency and the range of tunability are provided using the equivalence between bridged-T and a symmetrical lattice circuit. In addition to the frequency response curves, we also present output pulse waveforms in the time domain. These figures help in making critical comparison of various configurations.