High frequency log domain all pass filter based on KHN topology

Abstract

In this study, a current mode Log domain Class AB differential type all pass filter based on KHN structure has been synthesized by using the state space method and by adopting translinear circuits for the first time. The proposed circuit is synthesized for high frequency applications, i.e. around 100 MHz. Varying the values of the current sources of the circuit, the natural frequency of the filter can be tuned electronically. The circuit is simulated in PSpice by using both idealized and real transistors that are suitable for high frequency operations. Simulations showed that amplitude response of the system remains almost constant for 6 decades between 10 kHz and 10 GHz. Moreover, natural frequency of the filter can be set by electronically changing the source currents between 2 mA and 7 mA. In addition to these simulations, THD and noise analysis are carried out. The obtained results are given. © 2008 IEEE.