A Feedforward 10× CMOS Current-Ripple Suppressor for Switching Power Supplies

With the advent of wireless microsensors and other microscale applications, switching supplies fully integrated on chip or into the package are desirable and often necessary. The problem with small inductors is that they exhibit low inductance and larger equivalent series resistance (ESR); in other words, they induce larger ripples in the output and higher conduction power losses. This brief presents and verifies a current-ripple suppression technique in which a discrete 2 × 2 × 1 mm 4.7-μH inductor is effectively multiplied by subtracting a replica of the inductor’s ac ripple current, allowing only a residual ripple to reach the output. Experimental results from a complementary metal–oxide–semiconductor integrated circuit prototype demonstrate a currentand output-ripple reduction of 10.8× and 25.8×, respectively. The ESR power savings in the smaller inductor favorably offset the quiescent power lost in the multiplier (128 mW), outperforming its higher nonmultiplied 47-μH counterpart at high loads (above 250 mA).