A High Gain OTA With Positive Feedback for Ultra-Low Power Applications

This paper presents an ultra-low power operational transconductance amplifier (OTA) operating in the weak inversion region. To increase dc gain, two partial positive feedbacks are used in the input differential pair and its active loads of a current mirror OTA. For further gain improvement, the output resistance is enhanced by increasing the channel length of the output transistors. To understand the operation of this new OTA, dc transfer function as well as small-signal voltage transfer function are derived. In addition, the stable operation for positive feedback is verified through Monte Carlo analysis, root locus plot, and pole scatter plot for a feedback amplifier. The design and simulation of the OTA is performed using $0.18~\mu \text{m}$ CMOS technology. Compared to a normal OTA without positive feedback, this OTA features a dc gain enhancement of 36.08 dB, a slew rate improvement of 435.71%, and a unity-gain bandwidth enhancement of 6.68 times. Finally, the designed OTA dissipates an ultra-low power of 41.42 nW.