A Low-Voltage Linear OTA Employing a Triple-Tail Cell and an Active Voltage Divider

A triple-tail cell possesses a wide linear input voltage range in spite of its simple configuration. The tripletail cell requires a voltage divider. In practical implementation, the maintenance of the intrinsic linearity necessitates a resistive voltage divider that has low resistances. This makes the input resistance of the tripletail cell low. This paper presents a method to realize high input resistances of the triple-tail cell. An active voltage divider is employed. The output resistances of the active voltage divider are lowered by current feedback. Thus, although the operating current is reduced, the output resistance is sufficiently low. This enables the voltage divider to have high input resistance. A third-order gyrator-C filter composed of the triple-tail cell is analyzed through SPICE simulation. Further, the characteristic variations of the triple-tail cell and the voltage divider due to transistor mismatches are analyzed. It is shown that the characteristic variations of the voltage divider affect strongly the transconductance of the triple-tail cell. The results of Monte Carlo simulation show that the proposed circuit is feasible.