Low-Power n-FET-Only Operational Transconductance Amplifier in Flexible IGZO TFT Technology

This paper presents an n-FET-only operational transconductance amplifier (OTA) fabricated in a flexible 0.6 µm IGZO TFT process. The architecture combines a resistive-load differential pair with a three-stage common-source amplification chain and avoids using weak-conduction TFT loads to set the high-side currents. Open-loop measurements across 10 dies show a median DC gain of 56.6 dB and an input-offset distribution of approximately −313 ± 419 mV. The unloaded open-loop output excursion reaches 3.18 V. In a unity-gain follower configuration, the median closed-loop −3 dB bandwidth is 3.7 kHz, and stable operation is observed without an explicit compensation capacitor. The cross-chip average supply current varies from approximately 10 µA to 16 µA over the input sweep, corresponding to approximately 33–53 µW at 3.3 V. These results demonstrate a low-power IGZO amplifier for low-frequency sensor interfaces, while input offset, load-driving capability and supply coupling remain important limitations of the present implementation.