A CMOS transconductance amplifier architecture with wide tuning range for very low frequency applications

A pseudodifferential CMOS operational transconductance amplifier (OTA) with wide tuning range and large input voltage swing has been designed for very small G(m)'s (of the order of a few nanoamperes per volt). The OTA is based on a modified four-quadrant multiplier architecture with current division. A common-mode feedback circuit (CMFB) structure has been proposed and designed using floating-gate transistors to handle large differential signals. Large on-chip capacitors are emulated through impedance scaling circuits. The circuits, fabricated in a 1.2-mum CMOS process, have been used to design a fourth-order bandpass filter and a relaxation oscillator. Experimental results are in good agreement with the theoretical results.