Improvement Technique of Tuning Range for Local-Feedback MOS Transconductor

T. Ohbuchi, F. Matsumoto (National Defense Academy, Japan)

The 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 is expressed by sinh function, is utilized for a low-power and low-transconductance linear OTA. However, the LFB OTA has a limit of tuning range of transconductance because of a local-feedback structure. To improve the tuning range, a local-feedback circuit which is composed of pMOS is used for replacing the conventional local-feedback circuit which is composed of nMOS. The validity of the proposed OTA is confirmed by simulations. The conventional LFB OTA has a limit of the operating current which is used for tuning of the transconductance. The proposed transconductor does not have a limit of operating current. The frequency characteristics, the CMRR, and the input refereed noise of the proposed OTA is not deteriorated as compared with 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.