Electronically Tunable Current-Mode Differential-Type Class-AB Logarithmic-Domain Filter for Biomedical Applications

This paper presents a novel second-order current-mode differential-type class-AB logarithmic-domain low-pass filter optimized for biomedical applications. The proposed design is based on the state-space synthesis approach and employs a simple differential-type class-AB configuration to achieve high performance with minimal component usage. The circuit is implemented using NPN-type transistors (AT&T CBIC-R, NR200N-2X) and grounded capacitors, ensuring low power consumption, compactness, and ease of integration. Operating at a supply voltage of 1.2 V, the filter exhibits a power consumption of 1.19[Formula: see text]mW, maintains a total harmonic distortion below 1%, and achieves a dynamic range of approximately 60[Formula: see text]dB. The filter offers electronic tunability of its gain, natural frequency and quality factor through external current adjustments. PSpice simulations demonstrate that by varying external currents between 12.5[Formula: see text] [Formula: see text]A and 100[Formula: see text] [Formula: see text]A, the cutoff frequency can be tuned from 777[Formula: see text]kHz to 6.216[Formula: see text]MHz. Additionally, tunability in the range of 100[Formula: see text]Hz to 10[Formula: see text]kHz is achieved by adjusting bias currents from 8[Formula: see text]nA to 0.8[Formula: see text] [Formula: see text]A, making the filter particularly suitable for biomedical signal processing. Specifically, the cutoff frequency can be configured to 100[Formula: see text]Hz for electrocardiogram and electroencephalogram signals or 500 Hz for electromyogram signals, effectively addressing noise filtering requirements in biomedical applications.