Design of Second Order Lowpass and Bandpass Filter Using Single VDDDA and Its Modification as Sinusoidal Oscillator

This paper introduces an electronically controllable voltage mode analog biquad filter which is designed based on the series resistor-inductor-capacitor (RLC) topology. The proposed second order filter employs one active device, voltage differencing differential difference amplifier (VDDDA) and three passive elements (one resistor and two grounded capacitors). The natural frequency (ω
₀
) is controlled electronically as well as quality factor (Q) by changing the bias current. Two filter responses, lowpass (LP) and bandpass (BP) functions with unity voltage gain are simultaneously achieved. The proposed voltage-mode biquad filter consists of two input voltage nodes with high impedance. These input voltages are employed to select the inverting or non-inverting filter response. The sinusoidal oscillator is realized by slight modification of the proposed voltage-mode biquad filter. The sinusoidal voltage output node is low impedance. With this configuration, the proposed sinusoidal oscillator can be connected to other circuits without requirement of the additional buffer devices. The proposed filter and sinusoidal oscillator employ a few in number of the passive and active devices (also with grounded capacitors). The proposed circuits are interesting for monolithic integrated circuit (IC) realization. Pspice simulation program and TSMC 0.18m CMOS process parameters with ±0.9V are employed to verify the functionality of the presented biquad filter and sinusoidal generator.