I'm trying to understand the role of bypass caps and bulk caps, applied specifically to FPGA and other digital ckts. Bypass caps provide a low impedance path to the noise on the supply lines and also supply switching currents for the logic devices. But what's the role of bulk caps? Henry ott's book says, the bypass caps need to charge quickly to make up for the lost charge. The bulk caps charge them up quickly. But why can't the supply charge these caps? Bypass caps are same as decoupling caps, right?