A 0.9V 600MHz 4th-order analog filter with feed-forward compensated OPAMP in CMOS 28nm

In this paper a 600MHz 4th order low-pass analog filter in CMOS-28nm is presented. The transfer function is obtained with the cascade of two Active-RC Rauch biquadratic cells. Each cell is based on a novel OPAMP optimized for very high frequency operation achieving a Unity Gain Bandwidth (UGBW) > 7GHz. The developed three stage folded OPAMP exploits a feed-forward compensation technique to maximize bandwidth and an improved Common Mode Feedback Circuit (CMFB) necessary to reduce parasitic poles and to guarantee acceptable CMFB phase margin. The OPAMP is able to manage the very low V DD /V TH ratio of the 28nm process lowering its input common mode voltage in respect with input and output common mode voltage of the whole filter. The prototype consumes 11.4mW from a single 0.9V supply voltage, achieving 600MHz of bandwidth with an in-band integrated noise of 750μV RMS . The IIP3 calculated at 400 and 450MHz is 12.5dBm.