Improvement technique of tuning range for local-feedback MOS transconductor

A local-feedback transconductor (LFB OTA) is a linear OTA operating in a saturation region. In addition, the LFB OTA operating in a subthreshold region, whose transfer characteristics are expressed by a sinh function, is utilized for low-power and low-transconductance linear OTAs. However, the LFB OTA has a limit of a tuning range of a transconductance because of a local-feedback structure. To improve the tuning range, a local-feedback circuit which is composed of pMOS transistor is used for replacing the conventional one which is composed of nMOS transistor. The proposed OTA operating in the subthreshold region works as long as a reference current source circuit works. The operating current is used to tune the transconductance of the proposed OTA. The frequency characteristics, the CMRR, and the input refereed noise of the proposed OTA are almost the same as that of the conventional LFB OTA. From the Monte Carlo simulation, the sensitivity to the size mismatch of the proposed OTA is smaller than the one of the conventional LFB OTA. The validity of the proposed technique is confirmed by simulations.