An Ultralow-Power 0.5-V MI-OTA-Based Universal Filter for Efficient Low-Frequency Signal Processing

This work introduces novel universal filters implemented using multiple-input operational transconductance amplifiers (MI-OTAs). The MI-OTA is specifically designed for a minimal 0.5-V supply, achieving nano-watt level power dissipation, which positions the design as highly viable for demanding ultralow-power systems. The architecture employs a subthreshold, multiple-input, bulk-driven MOS configuration. This design not only extends the operational input voltage range but concurrently ensures minimal voltage and power consumption. The primary filter topology utilizes five MI-OTAs and two grounded capacitors to concurrently deliver all five standard filtering responses—low-pass, high-pass, band-pass, band-stop, and all-pass filter—from a single, fixed circuit structure. By integrating a sixth MI-OTA, the architecture becomes reconfigurable for operation in both voltage-mode (VM) and transimpedance-mode (TIM). This versatility yields both non-inverting and inverting transfer functions for all five fundamental responses, resulting in a total of 20 distinct output functions. This multifunctionality and power efficiency make the proposed designs exceptionally well-suited for low-frequency applications, such as bio-signal processing and sophisticated sensor interfacing circuits. Furthermore, a key feature is that the filter's natural frequency is electronically tunable across all responses. The MI-OTA was designed and simulated in Cadence Virtuoso, utilizing the TSMC 65-nm (1P9M) CMOS process. The device occupies a modest silicon footprint of 125 μm × 92 μm. Simulation results confirm a power dissipation of 150 nW at a 177-Hz cutoff frequency under the 0.5-V supply. Post-layout simulations verified the expected circuit performance. Finally, experimental validation was conducted using a discrete-component MI-OTA-based circuit built with the LM13700, thereby confirming the filter's correct operation.