0.5-V Nano-Power Versatile First-Order Filter Using a Single DDTA

This paper introduces a nano-power, voltage-mode versatile first-order universal filter that employs a single differential difference transconductance amplifier (DDTA). Ultra-low-voltage and low-power operation is achieved by biasing the DDTA transistors in the subthreshold region, while employing a multiple-input bulk-driven (MI-BD) technique to handle multiple signals on a single differential pair, thereby eliminating the need for redundant differential stages. Acting as a multiple-input multiple-output (MIMO) topology, the proposed circuit simultaneously delivers six fundamental filtering functions—covering non-inverting and inverting variants of low-pass, high-pass, and all-pass responses—while offering independent electronic control over the pole frequency. To demonstrate practical utility, two non-inverting all-pass filter blocks are combined with a voltage-gain amplifier to construct a functional quadrature oscillator. SPICE simulations in a 0.18-µm CMOS process demonstrate that the filter operates reliably from a 0.5-V supply, consuming only 97 nW of power while achieving a dynamic range of 59.41 dB at a pole frequency of 250 Hz. Finally, experimental results from a commercially available LM13700-based prototype demonstrate the functional topology and tuning capabilities, while full validation of the ultra-low-power operation is reserved for integrated CMOS realization.