This paper proposes an alternative circuit technique for the implementation of the CMOS-based voltage differencing buffered amplifier (VDBA) with linearly tunable transconductance gain. The realization scheme is based on employing the current-mode squaring function circuit and a pair of active loaded differential-input amplifiers. The current squarer acts as the long-tail biasing current for the differential-input amplifier, achieving its linear tunability. Accordingly, the transconductance gain of the proposed CMOS VDBA is variable linearly and electronically through the external dc bias current. In addition to improve the linear input voltage range, the source degeneration technique is performed. An application of the proposed VDBA as an active tunable first-order all-pass filter has also been described. Simulation results performed using PSPICE program with TSMC 0.25 μm real CMOS technology evaluate the circuit performance and workability.

Keywords: Voltage differencing buffered amplifier (VDBA), Current squarer, MOS analog circuits, Electronically tunable circuit, All-pass filter