[問題] dB運算的問題
小弟不才 有個小問題想請教高手們
dB=10*log(Power/1W)
dBm=10*log(Power/1mW)
1.假設在RF系統中以50歐姆為基準,一個Ain=226mV 換算成dBm方法是:
10*log( (Ain^2/50) /1mW) =0dBm
但記得在以前類比電路算Gain時,也是常常用Gain(dB)=10*log(Vout/Vin)^2
=20*log(Vout/Vin)
我想了一下覺得是這樣推的:
Gain(dB)=Pout(dB)-Pin(dB)=10*log(Vout^2/Rout)-10*log(Vin^2/Rin)
但這樣不太對,希望有人幫忙指點哪裡出錯了。
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