A Low-Power Analog Adder and Driver Using a-IGZO TFTs

Abstract

This paper presents a novel low-power analog circuit, with n-type IGZO TFTs that can function as an adder operator or be designed to operate as a driver. Experiments were set to show summation of up to four signals. However, the design can easily be expanded to add higher number of signals, by appending a single TFT at the input per each additional signal. The circuit is simple, uses a single power supply irrespective to the number of input voltage signals, and shows good accuracy over a reasonable range of input values. By choosing proper TFT dimensions, the topology can replace the typical output drivers of TFT amplifiers, namely the common-drain with current source biasing, or the common-source with diode connected load. The circuit was fabricated with a temperature that does not exceeds 200 °C. Its performance is characterized from measurements at room temperature and normal ambient, with a power supply voltage of 12 V and a load of $\approx ~4$ pF. The proposed circuit has shown a linearity error less than 3.2% (up to an input signal peak-to-peak value of 2 V), a power consumption of $78~ {\mu }\text {W}$ and a bandwidth of $\approx 115$ kHz, under worst case condition (when it is adding four signals with the same frequency). It has shown superior performance in terms of linearity when compared to the typical drivers considered in this study. In addition, it has shown almost the same behavior when measurements were repeated after one year. Therefore, the proposed circuit is a robust viable alternative to conventional approaches, being more compact, and contributes to increase the functionality of large-area flexible electronics.