Fully Controllable First Order Current Mode Universal Filter Composed of BJTs and a Grounded Capacitor

In the last two decades, current-mode (CM) circuits have received more attention. These types of circuits offer many advantages such as wider bandwidth, bigger dynamic range, better linearity and more IC suitability when compared with voltage mode (VM) topologies [1, 2]. In addition to this, electronic tunability is also one of the other important issues in electronic design since it allows us to control characteristics of circuit easily, i.e. resonance frequency of filter [3]. In a tunable circuit, electronically control can be achieved via biasing currents in BJT technology. In the literature, many CM and VM filters have been presented [4-10]. However, some of the reported circuits suffer from shortcoming of electronic tunability [5]. Quite a large number of filters composed of basic building block(s) such as current conveyors were also previously reported whereas each of the blocks use tens of transistors [3-8]. This paper presents an electronically tunable CM first order universal filter employing only a grounded capacitor and fewer BJTs [11] when compared with previously published ones. The proposed filter can produce all the standard filter functions i.e. low-pass, high-pass and allpass filters. Cut-off frequency can be tunable and filter types can also be controllable by simply changing the values of some current sources. The introduced circuit is free from critical passive component matching conditions and cancellation constraints, and provides high output impedance yielding easy cascadability. Moreover, second order band-pass filter obtained by cascading low-pass filter and high-pass filter is also presented as an application. The validity of proposed filter is verified through PSpice simulations.