A Highly Linear Rail-to-Rail Operational Transconductance Amplifier

This paper presents an architecture for a rail-to-rail operational transconductance amplifier (OTA) that substantially improves the linearity of the output current dependence on the differential input voltage. The proposed method uses a simple input voltage scaling technique paired with a five-transistor negative feedback loops for the output stage to apply the scaled differential voltage across a resistor that guarantees linearity. By utilizing a resistor instead of previously used feedforward or transistor square model-based techniques relying on nonlinearity cancellation, the nonlinearity is removed systematically as the resistor is inherently linear. This approach has applications in signal processing environments, such as receiver and transmitter integrated circuits, suppressing heavily system inherent noise generated by deviations from an expected linear behavior. The proposed architecture has been implemented in 14nm FinFET technology. Spice simulations performed for the developed circuit show less than −65 dB of total harmonic distortion (THD) of the output current at 1 MHz for rail-to-rail input signal in the −40 to 125 degrees Celsius temperature range considering the supply voltage variation in $\pm 10 \%$ range.