RF3133 Просмотр технического описания (PDF) - RF Micro Devices
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RF3133 Datasheet PDF : 16 Pages
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RF3133
Talk time and power management are key concerns in transmitter design since the power amplifier has the highest cur-
rent draw in a mobile terminal. Considering only the power amplifier’s efficiency does not provide a true picture for the
total system efficiency. It is important to consider effective efficiency which is represented by ηEFF. (ηEFF considers the
loss between the PA and antenna and is a more accurate measurement to determine how much current will be drawn in
the application). ηEFF is defined by the following relationship (Equation 2):
m
∑ PN – PIN
ηEFF
=
n----=-----1----------------------- ⋅ 100
PDC
(Eq. 2)
Where PN is the sum of all positive and negative RF power, PIN the input power and PDC is the delivered DC power. In dB
the formula becomes (Equation 3):
P----P---A----+-----P----L---O---S---S
-P---I--N-
ηEFF
=
1----0------------1---0-------------–-----1---0----1--0--
VBAT ⋅ IBAT ⋅ 10
(Eq. 3)
Where PPA is the output power from the PA, PLOSS the insertion loss, PIN the input power to the PA and PDC the deliv-
ered DC power.
The RF3133 improves the effective efficiency by minimizing the PLOSS term in the equation. A directional coupler may
introduce 0.4dB to 0.5dB loss to the transit path. To demonstrate the improvement in effective efficiency consider the fol-
lowing example:
Conventional PA Solution:
PPA = +33 dBm
PIN = +2 dBm
PLOSS = -0.4 dB
VBAT = 3.5 V
IBAT = 1.1 A
ηEFF = 47.2%
RF3133 Solution:
PPA = +33 dBm
PIN = +2 dBm
PLOSS = 0 dB
VBAT = 3.5 V
IBAT = 1.1 A
ηEFF = 51.72%
The RF3133 solution improves effective efficiency 5%.
Output power does not vary due to supply voltage under normal operating conditions if VRAMP is sufficiently lower than
VBATT. By regulating the collector voltage to the PA the voltage sensitivity is essentially eliminated. This covers most
cases where the PA will be operated. However, as the battery discharges and approaches its lower power range the
maximum output power from the PA will also drop slightly. In this case it is important to also decrease VRAMP to prevent
the power control from inducing switching transients. These transients occur as a result of the control loop slowing down
and not regulating power in accordance with VRAMP.
Rev A6 050909
2-469
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