The clock signal is the dominant source of electromagnetic interference (EMI) for many digital electronic devices. EMI generated by these electronic devices must be suppressed to avoid interference with other electronic devices and to satisfy FCC regulations. The present invention seeks to reduce EMI emissions by phase-modulating the clock signal using tunable delay lines. Phase modulation causes a spreading of the energy spectrum of the clock signal thereby reducing EMI emissions. In addition, the present invention is capable of generating a wide energy spectrum in a short time interval. Furthermore, the present invention can be similarly applied to other signals which exhibit a periodic or timing nature due to a correlation with the clock signal.