Promax MO-180 Manual De Usuario página 100

Figure 3.- AM-AM curve of the amplifier we want to linearise (blue); Ideal amplifier with a
normalised gain of 0 dB (green); Level at the output of the NLPD block which linearises the
In the case of an ideal amplifier, the AM-AM curve would be a straight line with
slope 45° (green line). In practice, however, we have an AM-AM characteristic like the
one shown in blue. For instance, a relative input power of P
1.4 dB (9.011 dB, a little bit beyond the 1 dB compression point of the amplifier). In
order to linearise the amplifier at this particular input level, we have to increase the
amplitude of the input sample by 2.2 dB so that the output power now becomes 10.4
dB. Thus, the amplitude of the correction gain is (red curve):
Note: that there is an input power (approximately P
which the amplifier cannot be linearised as that would require an infinite correction
gain.
The phase θ
multiplying by —1 the phase in the AM-PM curve corresponding to an input power of P
+ G dB.
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The NLPD block allows to define between 2 and 16 points with relative input
powers P ranging from —12 dB to +12 dB with 0.1 dB of resolution. As mentioned
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above, these levels are referred to the RMS level of the COFDM signal.
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amplifier for input powers up to 12 dB (red).
=
G 20 log g
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10
of the complex correction gain can be obtained by simply
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.
= + =
2 . 2 dB @ P 10 . 4 dB
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= 12 dB in this example) beyond
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USER'S MANUAL MO-180
= 10.4 dB is attenuated
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04/2008
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