分贝(工程应用)(国外英文资料).doc

分贝(工程应用)(国外英文资料) Decibels (engineering applications)!!! DB (Decibel, DB) is a pure counting unit, originally meant to indicate the ratio of the two variables, no units. In engineering applications, seemingly different definitions (just looking different) are often seen. For power, dB = 10*lg (A/B). For voltage or current, dB = 20*lg (A/B). Here, A, B represent the power values or current and voltage values that participate in the comparison. The meaning of dB is simply a brief representation of the number of large (followed by a long string of 0) or very small (in front of a long string of 0). If (here to power as an example): X = 100000 = 10^5 X (dB) = 10*lg (X) dB= 10*lg (10^5) dB= dB 50 X = 0.000000000000001 = 10^-15 X (dB) = 10*log (X) dB= 10*log (10^-15) dB= -150 dB in general, in engineering, between dB and dB not only addition and subtraction, multiplication and division. Which is the most used method: dBm minus dBm is actually two phase power, signal power and noise power is the division of signal-to-noise ratio (SNR). For example: 30dBm - 0dBm = 1000mW/1mW = 1000 = 30dB. DBm plus dBm is actually two power multiplication, without actual physical meaning. In the field of electronic engineering, the amplifier gain is dB (DB). The ratio between the amplifier output and the input is the amplification factor, the unit is times, such as 10 times amplifier, 100 times amplifier. When using decibel as a unit, the amplification is called gain, which is the two name of a concept. The relationship between conversion dB and magnification of electricity is: A (V) (dB) =20lg (Vo/Vi); voltage gain A (I) (dB) =20lg (Io/Ii); current gain of Ap (dB) =10lg (Po/Pi); power gain DB definition of voltage (current) with different gain and power gain formula but, we all know that the relationship between power and voltage and current is P=V^2/R=I^2*R. With this formula, the gain values of the two are the same: 10lg[Po/Pi]=10lg[(Vo^2/R) / (Vi^2/R)]=20lg (Vo/Vi). There are three main