Single Active Parameter Tunable Simple Band-Pass Filter: Methods for Tunability Range Extension

R. Sotner, J. Petrzela, O. Domansky, L. Langhammer (Brno Univ. of Techn., Czech Republic), T. Dostal (College of Polytechnics Jihlava, Czech Republic)

This paper compares three possible methods of center frequency adjusting in simple single active parameter controllable second order band-pass filter. Limited range of driving voltages serving for tuning of electronically controllable applications is the problem of modern low-voltage systems due to reduced power supply voltage. Therefore, methods how to obtain similar bandwidths of adjustability in comparison to standard linear control applied in systems with DC driving voltage/current range below one decade should be studied. Lossless integrator (its transconductance subpart) implemented in the structure of the filter was solved as three different subcircuits allowing three different methods of its electronic adjusting, i.e. linear, quadratic and exponential dependence of transconductance gm on DC driving voltage VSET. It results to square root, linear and exponential dependence of center frequency of the filter on VSET. The last method allows to reach at least four-times wider range of tunability of center frequency in comparison to standard implementation of linearly controllable integrator in the same range of VSET. PSpice simulations confirm intended features of proposed methods.