High gain operational amplifier and a comparator with a-IGZO TFTs

This study presents a novel high gain operational amplifier (op-amp) and a comparator using n-type all enhancement amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The proposed op-amp employs regulated cascode topology in conjunction with capacitive bootstrap load, which enhances the gain to 159.87% (V/V) as compared to op-amp with bootstrapping load. In addition, common mode feedback is introduced in the circuit which improves the common-mode rejection ratio (CMRR) of the amplifier without hampering the output voltage swing. The proposed op-amp offers a voltage gain of 46.2 dB, phase margin of 67°, CMRR of 51.8 dB, unity gain frequency of 215 kHz and power consumption of 0.22 mW. Furthermore, a novel comparator circuit at a clock frequency of 50 kHz is reported. The power consumption of the circuit is 0.248 mW and it can discriminate a minimum voltage of 50 mV. The performance of the proposed circuits is demonstrated using an analytical model of a-IGZO in Cadence environment with a channel length of 20 µm at a supply voltage of 10 V. Further with the help of the circuits reported in this work, many sensing systems of practical importance can be developed, such as smart packaging and bio-medical wearable devices using flexible electronics.