A Wide Range Tunable Active Band Pass Filter Using Flexible Oxide TFTs Technology

This work presents a novel second order Band Pass Filter (BPF) designed using an all enhancement unipolar(ntype) amorphous indium gallium zinc oxide (a-IGZO) thinfilm transistor (TFT) technology, compatible with flexible substrates. This BPF utilizes a tunable active inductor based on a trans-conductance- $\mathbf{C}\left(\mathbf{G}_{m} \mathbf{- C}\right)$ topology. The circuit deploys an active inductor. BPF consists of an input transconductance stage ($\mathbf{g}_{m}$), a frequency-tunable LC tank, and an output buffer stage for Q-factor enhancement. The center frequency and Q-factor of the BPF can be independently tuned via control voltage, making it suitable for a wide range of bio-medical applications. Post-layout simulation results indicate that the BPF achieves a tuning range of center frequency from 100 Hz to 1 kHz by adjusting the bias voltage from 2.3 V to 2.8 V and shows a power consumption of $75 \mu \mathrm{~W}$ (at 100 Hz) and $80 \mu \mathrm{~W}$ (at 1 kHz), respectively with a supply voltage ($\mathbf{V}_{D D}$) not exceeding $\mathbf{4} \mathbf{V}$. Moreover, the BPF exhibits a maximum and minimum insertion loss of -3.8 dB and 5.1 dB with a $3-\mathrm{dB}$ bandwidth of around 300 Hz. This circuit occupies a total active area of $0.02 \mathrm{~mm}^{2}$. These parameters demonstrates that the proposed BPF can find potential applications in energy-efficient wearable and biomedical devices.