Patent ID: 8391511
Filing Date: 2013-03-05
Classification: H03F

Abstract:
1. A semiconductor device including a digital audio circuit which converts an input digital signal into an analog audio signal and a DC-DC converter having a switching power source circuit, comprising: a first oscillating circuit which generates a first clock signal of a first frequency which is used when the digital audio circuit converts the input digital signal into the analog audio signal; a second oscillating circuit which generates a second clock signal of a second frequency which is used when switching control is applied to a switching element in the switching power source circuit; an audible frequency determining circuit which determines whether an absolute value of a difference between the first frequency and the second frequency is a predetermined maximum audible frequency or less; and a frequency changing circuit which causes the second oscillating circuit to change the second frequency of the second clock signal based on a result determined by the audible frequency determining circuit; wherein the frequency changing circuit causes the second oscillating circuit to change the second frequency of the second clock signal so that the absolute value of the difference between the first frequency and the second frequency is greater than the maximum audible frequency based on the result determined by the audible frequency determining circuit.