Abstract: A clock input circuit for a portable information medium is provided which has a low power consumption and extends the communication range of the portable information medium. The clock input circuit receives an input signal via an antenna of the portable information medium and generates a clock signal based on the input signal. Also, the clock input circuit contains an attenuator, a control signal generator, a selector circuit, and a clock signal processor. The attenuator receives the input signal and outputs at least one attenuated signal. The control signal generator inputs the input signal and generates at least one control signal based on an amplitude of the input signal. The selector circuit inputs the at least one attenuated signal and creates an output signal based on the at least one attenuated signal and the at least one control signal. The clock signal processor inputs the output signal and generates the clock signal based on the output signal.