US Patent 7006030 Semiconductor integrated circuit device and audio appliance employing it

A semiconductor integrated circuit device has an analog signal conductor and a digital signal conductor formed on a single circuit board. In the lowest layer is laid a polysilicon conductor as the digital signal conductor, on top thereof is laid a first aluminum conductor as a shielding conductor, and further on top thereof is laid a second aluminum conductor as the analog signal conductor. With this structure, it is possible to give the highest priority to improving the transmission quality of analog signals and simultaneously reduce transfer of noise from the digital signal conductor to the analog signal conductor.