Note-PC Low Noise Headphone Interface Circuit And Woofer Power Amplifier Designs

Audio sound quality of current Note-PC is inferior to that of smart mobile phone because the noise floor of the CODEC,of which adopted in the former,is much higher than that of the later.Comparing the datasheet of the two CODEC,you will find the noise floor on major Note-PC CODEC can reach to 20?V,but the same item in smart mobile phone is about 1?V.To reduce the noise from earphone jack,a Low Noise Amplifier(LNA)was used.The noise gain concept was prompted because the different noise source has different noise gain.Noise model was created to simulate the noise on the path of earphone jack.The noise gain formula was given after finished analyzing of LNA feedback topology for each noise source in the path.To fix the voltage divider low noise design parameter,the parameter was regressed to the total noise calculation process.Finally,the calculated total noise at the earphone jack was 7.06?V,it can meet the design specifications requirement(<11.9?V).The test result of earphone jack output noise is 7.126?V.The gap is 0.066?V,the tolerance is 0.93%,less than 1%,of which approve the correction of the earphone output path noise model.And the output resistance decrease from 22? to 2.2?,measured result is 2.12?,meet design specification requirement.(2.2?±1?).The low frequency speaker,also called Woofer sound at very low frequency by set the bandwidth of power amplifier at the low frequency.The bandwidth test result:21.1086Hz-330.963Hz,within 10%10%tolerance,also meet the design spec.Note-PC Low Noise Headphone Interface Circuit and Woofer Power Amplifier Designs can reduce the earphone output path noise,and improved the Note-PC earphone path sound effectuation with the least cost,the design was applied in current design of our company.