Phase locked loop for reducing electromagnetic interference

Abstract

A phase locked loop (PLL) for reducing electromagnetic interference (EMI) is provided. The PLL is not sensitive to a manufacturing process, consumes less power, occupies a small layout space, and can flexibly control a modulation frequency and a modulation rate flexibly. The PLL for reducing the EMI controls the signals having a phase difference, which is n-times (where n is an integer) the basic delay time of the output signals from a voltage controlled oscillator (VCO), and determines the modulation rate. Then, the PLL repeats the procedure during the cycle of a pre-defined modulation frequency. The PLL for reducing the EMI not only reduces the EMI, but also does not require a ROM. Therefore, the layout space can be reduced and broad frequency ranges can be obtained. In addition, since the phase difference of the output signals of the VCO is controlled by logic circuits, the PLL is insensitive to changes in the manufacturing process.