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Logarithmic Scale for amplifier gain

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mannu2612

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Why is it that converting a power gain ratio to dBs is calculated by multiplying the log of the ratio by 10.i.e,
Power(db)=10log(Pout/Pin)
whereas converting voltage(&current) ratios to dBs is calculated by multiplying the log of the ratio by 20.i.e,
20log(Vout/Vin)
 

They are all power ratios, not voltage/current ratios. So, 10x the power is 10dB. If you have 10x the voltage then you have 100x the power so it is 20dB. So, while you might use voltage or current in the calculation, what you are really trying to calculate is the power ratio resulting from that voltage. I hope that makes sense!

Keith.
 
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