RF3140PCBA-41X RFMD [RF Micro Devices], RF3140PCBA-41X Datasheet - Page 10

• Manufacturer Part Number: RF3140PCBA-41X
• Description: QUAD-BAND GSM850/GSM900/DCS/PCS POWER AMP MODULE
• Manufacturer: RFMD [RF Micro Devices]

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 η
loss between the PA and antenna and is a more accurate measurement to determine how much current will be drawn in
the application). η
Where Pn is the sum of all positive and negative RF power, P
the formula becomes (Equation 3):
Where P
ered DC power.
The RF3140 improves the effective efficiency by minimizing the P
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 at F=1785MHz:
RF3140 Solution:
The RF3140 solution improves effective efficiency by 5%.
Output power does not vary due to supply voltage under normal operating conditions if V
V
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 V
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 V
2-500
η
η
P
P
BATT
EFF
EFF
V
V
LOSS
LOSS
P
P
P
P
I
I
BAT
BAT
BAT
BAT
PA
IN
PA
IN
RF3140
. By regulating the collector voltage to the PA the voltage sensitivity is essentially eliminated. This covers most
=
=
= +33.5 dBm
= +3 dBm
= -0.4 dB
= 3.5 V
= 1.16 A
= +33.5 dBm
= +3 dBm
= 0 dB
= 3.5 V
= 1.16 A
PA
n
-------------------------------- 100
10
------------------------------------------------ -
∑
m
=
is the output power from the PA, P
V
P
----------------------------- -
1
BAT
PA
P
P
N
DC
+
10
P
EFF
–
⋅
LOSS
I
P
BAT
IN
is defined by the following relationship (Equation 2):
–
⋅
⋅
10
10
P
------- -
10
IN
η
EFF
h
EFF
= 50.3%
= 55.16%
RAMP
LOSS
.
the insertion loss, P
IN
the input power and P
LOSS
term in the equation. A directional coupler may
IN
the input power to the PA and P
DC
is the delivered DC power. In dB
RAMP
EFF
is sufficiently lower than
. (η
EFF
RAMP
Rev A9 060217
considers the
DC
to prevent
the deliv-
(Eq. 2)
(Eq. 3)