Thinking In dBm

When you think of power, you think of watts. It’s a different story with RF PAs, though. Not only is the gain of the amplifier given in dB, but the power output also is normally quoted in dBm. Get used to it. Just as a reminder, the gain is computed with the familiar formula:

dB = 10 log (P_o/P_i)

Power output is computed with a 1-mW reference:

dBm = 10 log (P_o/0.001)
P_o = 0.001 log^–1(dBm/10)

So you don’t have to get out the calculator, you can find a few reference points for your convenience in the table included with the online version of this article at www.electronicdesign.com.

See associated table