An operational amplifier for high performance pipelined ADCs in 65nm CMOS

A CMOS fully differential high gain-bandwidth (GBW) product operational amplifier (OpAmp) is presented in this paper. In order to achieve a high gain, the Nested gain-boosting technique [1] is employed. The design is implemented in a 1.1V standard 65nm CMOS process. The DC-gain of the OpAmp is larger than 77.9dB with the unity-gain frequency of 4.61GHz while achieving 76.2 degrees of phase margin (PM). Applying the maximum input swing, the output signal settles to 0.01% accuracy in less than 3.8ns. The output total harmonic distortion (THD) of the OpAmp is 0.586% for maximum signal swing at the frequencies near Nyquist frequency with the input-referred noise of 5.4nV/
_√Hz
. The high GBW product of this design makes it suitable for 12-bit 200MS/s pipelined ADC applications.