Two New and Improved Electronically Adjustable Voltage-Mode Multifunction Biquadratic Filters With Independent Control of Band-Pass, High-Pass, and Low-Pass/Regular Notch Filter Gains

In this study, two new and improved electronically adjustable voltage-mode (VM) biquadratic filters using three off-the-shelf LT1228 integrated circuits (ICs), two grounded capacitors (GCs), and six resistors are proposed for independent control of the band-pass (BP), high-pass (HP), and low-pass/regular notch (LPN/RN) filter gains. Each proposed electronically adjustable VM multifunction biquadratic filter has one input and six output voltages, enabling simultaneous realization of one low-pass (LP), two BP, two HP, and one LPN/RN filtering responses from the same configuration. Each filter parameter, namely the pole angular frequency (
$\omega _{o}$
) and quality factor (
$Q$
), can be electronically controlled and orthogonally adjusted by the corresponding LT1228 bias current
$I_{B}$
. In special cases, the parameters of
$\omega _{o}$
and
$Q$
can be electronically controlled and independently adjusted. Each electronically adjustable VM multifunction biquadratic filter has one high input impedance and three low output impedances for independent control of BP, HP, and LPN/RN filter gains. Due to its one high input impedance and three low output impedances, each proposed filter is suitable for cascaded VM circuits without external voltage buffers. Pspice simulations are used to verify the theoretical structure analysis of each proposed LT1228-based electronically adjustable VM multifunction biquadratic filter. Furthermore, experimental tests are performed using three off-the-shelf LT1228 ICs, and several passive components to verify and evaluate the performance of each proposed LT1228-based biquadratic filter.