Low-distortion low-voltage operational transconductance amplifier

Introduction: Recent research shows a high demand for highly linear operational transconductance amplifiers (OTAs) with an aim to reduce total harmonic distortion (THD) [1–4]. However, most of these linearisation techniques may present important drawbacks such as reduced effective transconductance and significant power consumption. On the other hand, low power supply and power consumption solutions are needed for handheld products. However, the scaling down of threshold voltage does not follow the drop in the nominal supply voltage. As the available voltage headroom becomes limited, many existing circuit techniques in the analogue domain cannot be applied. Moreover, mismatch issues are also critical owing to the use of deep sub-micro processes [5]. Consequently, the second-order harmonic distortion cannot be eliminated properly. Without focus on linearisation, the linearity of the OTA will be rather poor. Very often, large gate–source voltages are required in order to improve OTA linearity, but the supply voltages limit this benefit especially for low-voltage applications. Therefore, a new OTA is proposed in this Letter, which is based on the flipped voltage follower (FVF) [6] and source degeneration techniques. Use of source degeneration optimises the linearity and the power supply is reduced by the FVF technique.