Abstract: A spike filter circuit (11) has an input (12) for receiving an input signal comprising data bits and an output (13) for providing a filtered output signal. A data bit is characterized by a voltage magnitude and a minimum time period. The spike filter circuit (11) filters out any signal applied to the input (12) that has a period less than the minimum time period of a data bit. The spike filter circuit comprises a pulse width sense circuit (14), a Schmitt trigger (16), and a delay circuit (17). The pulse width sense circuit (14) is responsive to the input signal and filters out signals having a period less than the minimum time period of a data bit. The Schmitt trigger (16) is responsive the pulse width sense circuit (14), has predetermined threshold voltages to increase noise immunity, and buffers the output of the pulse width sense circuit (14).