Electronically tunable low-component-count current-mode biquadratic filter using dual-output current followers

In this paper, a realization of a current-controlled three-input single-output current-mode universal biquadratic filter using dual-output current followers (DO-CFs) as active components is described. Based on the use of the current-controlled conveyor working as the DO-CF, the proposed circuit employs only two DO-CFs and two grounded capacitors that provide the advantage of an electronic tuning capability and is of special interest from the IC fabrication point of view. By suitably selecting three input signals, the filter can realize all of the standard biquadratic filtering functions, i.e., lowpass, bandpass, highpass, bandstop and allpass, all at a high impedance output which enables easy cascading in the current-mode operation. The natural angular frequency (ωo) and the bandwidth (BW) of the proposed circuit can be tuned independently and electronically over a wide range by adjusting the external bias currents. In addition, no critical component matching conditions are required for all the filter response realizations, and both active and passive sensitivities are low. PSPICE simulation results are used to confirm the characteristics of the proposed circuit.