Engineering Notes
POWER RF AMPLIFIERS TECHNICAL REFERENCE MATERIAL
Graceful Degradation
Solid state power amplifiers contain many isolated transistors in parallel at the output. There is a significant
advantage in "graceful degradation" compared to tube amplifiers. A failure of the tube results in the total loss
of output power while the failure of a parallel transistor still yields significant output power. Another
significant advantage is that transistors do not change output power as a function of time whereas tubes continue
to drift.
For N combined devices, the RF power output as a function of device failures is obtained by the following formula:
Po = Pt (( N - Nf ) / N)2
where: Po = Output Power
Pt = Total Po without transistor failures
N = Total number of devices
Nf = Total number of failed devices
| N |
REDUCTION IN OUTPUT POWER
WITH A SINGLE DEVICE FAILURE |
| dB |
% |
2
4
8
16
32
64 |
-6.02
-2.50
-1.16
-0.56
-0.28
-0.14 |
75
44
23
12
6
3 |
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