A capacitive digital isolator with adaptive frequency control is proposed to reduce the power consumption while maintaining high data rates and low propagation delays. An on-off keying modulation is employed in a differential output transmitter with a local oscillator (OSC). By adjusting the frequency of the OSC according to the pulse width of the input signal, the currents dissipation of OSC is greatly reduced from 919 μA to 48.4 μA at 1 Mbps data rate and 456.2 μA at 100 Mbps data rate, respectively. The receiver mainly consists of a pre-amplifier and an envelope detector for low propagation delays.