US Patent 7733151 Operating clock generation system and method for audio applications

A clock signal generator (1) includes a phase locked loop (PLL) circuit (25) which requires a reference clock signal of at least a predetermined first frequency (fDIGCLK). A first clock signal (REFCLK) of a second frequency (fREF) that is substantially lower than the first frequency (fDIGCLK) is multiplied so as to produce a second clock signal (DIGCLK) which has a frequency at least as high as the first frequency (fDIGCLK) and which is phase-locked with respect to the first clock signal (REFCLK). The second clock signal (DIGCLK) is applied to a reference signal input of the PLL circuit (25), which produces an output clock signal (PLLCLK or CLKOUT).