I am making the SDXC interface to operate at 25MHz, the clock voltage is around 1.8V. As i am increasing the frequency to operate at 50MHz i am observing decrease in clock voltage to 1.6V and further changing operating freq to 100MHz the voltage is further decreasing to 1.26V. I am not able to understand the relation. Can you please help me in understanding it the reason for decrease of voltage with increase in frequency of operation ?