TABLE OF CONTENTS The noise floor of wireless SOC devices continues to be reduced. A lower noise floor means smaller and smaller amplitude signals can be transmitted and received between wireless devices. These very low-level signals beg for the introduction of the term dBm. The dBm is used ubiquitously when discussing nearly every RF measurement of any RF or wireless SOC device. The formula for dBm is similar to that for decibels except that P ref is predefined to be one milliwatt (1 mW).
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The nice thing about this expression is that P mW is expressed in milliwatts and is the only variable, so dBm is used to measure absolute power. A "+" sign is assumed and used to indicate dB above one milliwatt. A "-" sign indicates dB below 1 milliwatt. As an example, the Digital Enhanced Cordless Telecommunications (DECT) standard can operate down to around -100 dBm. This translates to an absolute power of 100 dB below 1 mW (i.e., the absolute power equals 1 10 -13W)!
