Shadow universal filter with independent Q tuning at 0.45 V using MI-OTAs

This paper presents a novel shadow universal filter implemented in voltage mode, based on multiple-input operational transconductance amplifiers (MI-OTAs). The proposed shadow universal filter incorporates both non-inverting and inverting transfer functions for low-pass, high-pass, band-pass, band-stop, and all-pass responses within a single topology. The proposed filter is a shadow universal filter that employs low-pass and high-pass filters feedback to the input. It enables independent control of the quality factor for all filtering responses through an external amplifier, without altering the natural frequency. Moreover, during quality factor tuning, any variation in passband gain can be compensated by appropriately adjusting the input signal configuration. These advantages of the proposed shadow universal filter are enabled by the multiple-input capability of the operational transconductance amplifier (OTA), which is implemented using the multiple-input bulk-driven MOS transistor (MIBD-MOST) technique. The MI-OTA operates at an ultra-low supply voltage of 0.45 V and consumes only 270 nW of power. For the low-pass shadow filter configuration, a dynamic range of 48 dB was achieved at 1% total harmonic distortion. Experimental validation was conducted using a prototype implemented with commercially available LM13700N integrated circuits, confirming the filter's functionality and effectiveness.