Oxide TFT Frontend Amplifiers for Flexible Sensing Systems
Yuming Xu, Zhaohui Wu, Bin Li, Sunbin Deng, Wei Zhong, Guijun Li, Dongxiang Luo, Fion Sze Yan Yeung, Hoi Sing Kwok, Rongsheng Chen
Abstract
This article presents a frontend amplifier based on the 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> channel length n-type only indium–tin-oxide (ITO)-stabilized ZnO thin-film transistors (TFTs) on glass substrate. The amplifier has an external-bias ac-coupled, open-loop capacitor bootstrap structure. The area and power consumption are 41 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 0.1 mW (8-V supply), respectively. Electrical measurement results show a gain of 20 dB, a bandwidth of 3 Hz–6 kHz, a common-mode rejection ratio (CMRR) up to 42 dB, an input impedance of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}\Omega $ </tex-math></inline-formula> , and an input-referred noise of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$106 ~\mu \text{V}_{rms}$ </tex-math></inline-formula> (integrated from 1 to 200 Hz). The noise efficiency factor (NEF) and power efficiency factor (PEF) of the amplifier are, respectively, 248 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.9\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , which is comparable among the state of the arts. The amplifier is successfully used to measure the heart-rate signal, which demonstrates its practicality.