An optically isolated circuit device includes a first opto-isolator
circuit that is driven by a first clock signal, and the output of the
first opto-isolator circuit is used to drive a phase-locked loop (PLL)
that is configured to synthesize a second clock signal having a frequency
that is a multiple of the first clock signal frequency. The second clock
signal is used as an input to a suitable clocked circuit of a type that
benefits from optical isolation, such as an analog-to-digital converter
(ADC).