A gm/ID method based 0.5V-subthreshold operational amplifier with current subtractor adaptive biasing circuit for ultra-low power application

This work presents a subthreshold operational amplifier with current subtractor adaptive biasing circuit designed using a formulated design methodology based on g
m
/I
D
method. A subthreshold operational amplifier is an operational amplifier that offers ultra-low power consumption. This is to replace conventional operational amplifiers in most IC by which the application are for RFID, WSN, IoT, and other recent technologies that operates in a power scarce environment. Although many studies have been made about subthreshold operational amplifier, there are many issues regarding on its specification and its robustness. Using current subtractor adaptive biasing technique, issues involving the low slew rate and process variation are solved. Using g
m
/I
D
method to size the transistors, the study arrived to a subthreshold operational amplifier with an open loop gain of 60.5dB, a phase margin of 64.4˚ and a unity gain bandwidth of 233kHz which is well within the range of application for low speed — low switching applications such as sensor networks, RFIDs and biomedical devices, where speed performances are not critical. This work has a slew rate of 4.66V/us, CMRR of 70dB and PSRR of 74dB. It consumes power of only 0.5uW and a die area of 708 um × 648 um with a core area of 95.94 um × 68 um.