ABSTRACT 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.
Kulej et al. (2026) studied this question.