Process Invariant Biasing of Ring Amplifiers Using Deadzone Regulation Circuit

In this paper, process invariant biasing is proposed for robust operation of ring amplifiers. The ring amplifier is an efficient solution for high accuracy amplification in sub-micron CMOS process. A traditional ring amplifier structure requires an external control voltage, defined as the deadzone voltage, to set the optimum quiescent current at the output stage. Other structures of ring amplifiers use on-chip resistors or current starved inverters to set the deadzone voltage. Since the deadzone voltage is a function of the threshold voltage of transistors in the output stage inverter, ring amplifiers are susceptible to process variations. In this paper, a deadzone regulation circuit is proposed that utilizes a constant current source and a negative feedback loop to regulate the quiescent current of the output stage inverter across process corners. Transistor level simulations are used to validate the operation of the proposed deadzone regulation technique across FF, TT and SS corners in a 65nm CMOS process. The design example uses a current starved inverter based ring amplifier in a switched capacitor amplifier to achieve a closed loop gain of 4 with a settling accuracy of ≤ 0.05% and operated at a sampling rate of 125MHz.