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A 500-mV, 124.11-nW first-order universal shadow filter based on multiple-input DDTAs
Author(s)
Date Issued
July 1, 2026
Type
Article
Abstract
This paper proposes a novel first-order multifunction filter capable of simultaneously realizing non-inverting and inverting low-pass, high-pass, and all-pass filter responses using multiple-input differential difference transconductance amplifiers (MI-DDTAs). The design leverages the shadow filter technique, enabling electronic tuning of the pole frequency across all filter responses through an external voltage-controlled amplifier. This approach offers enhanced flexibility and reconfigurability, making it highly attractive for adaptive analog signal processing. The MI-DDTA core is implemented using a multiple-input bulk-driven MOS transistor architecture, optimized for ultra-low-voltage and ultra-low-power operation. Designed in Cadence Virtuoso using the 65 nm TSMC CMOS (1P9M) process, the proposed MI-DDTA occupies a compact silicon area of 171 μm × 119 μm. Operating from a 500 mV supply, the shadow filter achieves a dynamic range of 55.9 dB for a 200 mVpp input signal, with total harmonic distortion limited to 1%. Owing to its exceptionally low bias currents, the shadow filter exhibits a total power consumption of only 124.11 nW, making it well suited for energy-constrained biomedical and IoT sensor applications, where low-frequency signal processing, compact implementation, and high energy efficiency are essential. To validate the proposed concept, a discrete prototype was also developed using MI-DDTA configurations built with LM13700 operational transconductance amplifiers. The experimental results confirm the expected filter behavior and demonstrate the feasibility of the proposed design in practical scenarios.
Citation
Integration, 109, 2026