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This paper describes a spread spectrum clock generation (SSCG) PLL that uses a dual-tone modulation profile. The proposed modulation profile consists of the weighted sum of triangular waves. A mathematical analysis is applied to find out the optimum weight. Experimental results show that the Δ-Σ fractional-N PLL with the clock modulator exhibits better performance than a traditional SSCG by more than 2dB at the 630MHz operation.