This paper introduces two new high-input impedance electronically tunable voltage-mode (VM) multifunction second-order architectures with band-pass (BP), low-pass (LP), and high-pass (HP) filters. Both proposed architectures have one input and five outputs, implemented employing three commercial LT1228 integrated circuits (ICs), two grounded capacitors, and five resistors. Both proposed architectures also feature one high-impedance input port and three low-impedance output ports for easy connection to other VM configurations without the need for VM buffers. The two proposed VM LT1228-based second-order multifunction filters simultaneously provide BP, LP, and HP filter transfer functions at Vo1, Vo2, and Vo3 output terminals. The pole angular frequencies and the quality factors of the two proposed VM LT1228-based second-order multifunction filters can be electronically and orthogonally adjusted by the bias currents from their corresponding commercial LT1228 ICs, and can be independently adjusted in special cases. In addition, both proposed VM LT1228-based second-order multifunction filters have two independent gain-controlled BP and LP filter transfer functions at Vo4 and Vo5 output terminals, respectively. Based on the three commercial LT1228 ICs and several passive components, simulations and experimental measurements are provided to verify the theoretical predictions and demonstrate the performance of the two proposed high-input impedance electronically tunable VM LT1228-based second-order multifunction filters. The measured input 1-dB power gain compression point (P1dB), third-order IMD (IMD3), third-order intercept (TOI) point, and spurious-free dynamic range (SFDR) of the first proposed filter were −7.1 dBm, −48.84 dBc, 4.133 dBm, and 45.02 dBc, respectively. The measured input P1dB, IMD3, TOI, and SFDR of the second proposed filter were −7 dBm, −49.65 dBc, 4.316 dBm, and 45.88 dBc, respectively. Both proposed filters use a topology synthesis method based on the VM second-order non-inverting/inverting HP filter transfer functions to generate the BP, LP and HP filter transfer functions simultaneously, making them suitable for applications in three-way crossover networks.

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 (ω 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 ω 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-theshelf LT1228 ICs, and several passive components to verify and evaluate the performance of each proposed LT1228-based biquadratic filter.INDEX TERMS LT1228, analog circuit design, integrated circuits, voltage-mode, filters.