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The linear dynamic range is determined by three parameters: (1) noise floor; (2)
gain of the amplifier; and (3) linear output power of the amplifier. The range
between the noise floor and the 1 dB gain compression point is the linear
dynamic range.
The lowest input signal level that produces a detectable output is determined
by the thermal noise generated within the amplifier itself. Any signal below this
"noise floor" causes an amplifier output with a signal-to-noise ratio of less than
one, which requires special techniques to recover useful information. The noise
floor may be calculated from:
Pni (dBm) = -114 dBm +10 log B + NF
where
Pni = effective input noise power in dBm
B = noise bandwidth of amplifier or system in MHz
NF = amplifier or system noise figure in dB
Note: Noise bandwidth can be approximated by the 3 dB bandwidth of the
amplifier gain response. Note that the published bandwidth of most HP
amplifiers is not the 3 dB bandwidth, but is the flat gain response region. It is
suggested that bandwidth be limited by external filtering or system selectivity.
When performing sensitivity calculations, it is usually assumed that the actual
minimum detectable signal (MDS) is some level above the noise floor (typical
value is 3 dB).
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