Signal-to-Noise Ratio Measurements of Sound Source and Speaker System-in-Package (SiP)

We have developed a system-in-a-package (SiP) consisting of a sound source LSI and a speaker amplifier LSI for mobile applications, and have measured its signal-to-noise ratio (SNR). The sound source LSI chip is stacked on the speaker amplifier LSI chip with inserting a silicon spacer between these chips. Two types of interposers were applied to the SiP: one-metal polyimide tape and a two-metal glass epoxy board. When the output voltage of the speaker LSI was 5 V_p-p, the SNR of the digital-analog converter in the sound source LSI did not change. When it was 15 V_p-p, the SNR was about 1.5 dB worse than with 5 V_p-p. The SNR when the one-metal tape was used was about 1 dB worse than when the two-metal epoxy board was used. The noise source for this degradation was apparently the class-D amplifier in the speaker LSI. These results should be useful in the design for mixed-signal SiPs.