Low Input Impedance IZO TFT Transimpedance Amplifiers With Current Buffer for Sensing and Transfer Applications

A structure for a low input impedance current buffer transimpedance amplifier (CBTIA) is presented, which holds great potential for flexible bioelectronic applications requiring high linearity sensing and transmission. Based on this structure, a tunable CBTIA and a low input impedance CBTIA circuits are implemented. The former utilizes a current sink input mode, where the voltage at the drain of common gate transistor is fed back to the gate of input current sink transistor in order to achieve low input impedance. A self-biasing optimization (SBO) technique is proposed for self-regulation of voltage headroom at each node. Additionally, the active load constructed by pseudo current source converts the current to voltage. Due to the current sink input mode, this design ensures that adjusting the transimpedance gain does not affect the input impedance. Furthermore, in the second circuit design, feedback is provided to the gate of an SBO regulated transistor in order to achieve even lower input impedance. The proposed CBTIAs were successfully implemented using 10- $\mu$ m IZO TFT technology. Test results show that the tunable CBTIA achieves a transimpedance gain range of 15.2 K to 47.4 K $\Omega$ while maintaining an unchanged 2 K $\Omega$ input impedance, and the low input impedance CBTIA achieves an input impedance less than 1.3 K $\Omega$ with a 61.7 K $\Omega$ transimpedance.