A 0.5-V MI-OTA-Based Shadow Universal Filter with Integrated Passband Gain Compensation and Low-Pass Control for Low-Frequency Applications

This paper presents a novel voltage-mode shadow universal filter based on multiple-input operational transconductance amplifiers (MI-OTAs). The multiple-input functionality of the OTA is implemented using the multiple-input bulk-driven MOS transistor (MIBD-MOST) technique, which enables low supply voltage operation and a wide input voltage swing. Additionally, the use of subthreshold operation contributes to the low-power consumption of the OTA. The proposed shadow filter is implemented using a voltage-mode universal filter, in which the low-pass section is employed to control the natural frequency through an external amplifier. The proposed filter provides both non-inverting and inverting transfer functions of low-pass filter (LPF), high-pass filter (HPF), band-pass filter (BPF), band-stop filter (BSF), and all-pass filter (APF). The circuit was designed and simulated using Cadence Virtuoso, utilizing TSMC’s 65-nm 1P9M CMOS technology. The total silicon area of the MI-OTA measured 148 µm × 89 µm. Operating at a supply voltage of 0.5 V and a cutoff frequency of 31.2 Hz, the filter achieved an overall power consumption of 350 nW. Experimental validation was conducted using a prototype implemented with commercially available LM13700N integrated circuits, confirming the filter’s functionality and effectiveness. The proposed design is well-suited for low-voltage, low-power applications, particularly in low-frequency biosignal processing and sensor interface systems.