RF3145PCBA-41X RFMD [RF Micro Devices], RF3145PCBA-41X Datasheet - Page 14

• Manufacturer Part Number: RF3145PCBA-41X
• Description: QUAD-BAND GSM/EDGE/GSM850/DCS/PCS POWER AMPLIFIER MODULE
• Manufacturer: RFMD [RF Micro Devices]

Theory of Operation
The indirect closed loop is essentially a closed loop method of power control that is invisible to the user. Most power con-
trol systems in GSM sense either forward power or collector/drain current. The RF3145 does not use a power detector. A
high-speed control loop is incorporated to regulate the collector voltages of the amplifier while the stages are held at a
constant bias. The V
The basic circuit is shown in the following diagram.
By regulating the power, the stages are held in saturation across all power levels. As the required output power is
decreased from full power down to 0dBm, the collector voltage is also decreased. This regulation of output power is
demonstrated in Equation 1 where the relationship between collector voltage and output power is shown. Although load
impedance affects output power, supply fluctuations are the dominate mode of power variations. With the RF3145 regu-
lating collector voltage, the dominant mode of power fluctuations is eliminated.
There are several key factors to consider in the implementation of a transmitter solution for a mobile phone. Some of
them are:
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
2-532
η
P
EFF
dBm
• Effective efficiency (η
• Current draw and system efficiency
• Power variation due to Supply Voltage
• Power variation due to frequency
• Power variation due to temperature
• Input impedance variation
• Noise power
• Loop stability
• Loop bandwidth variations across power levels
• Burst timing and transient spectrum trade-offs
• Harmonics
RF3145
=
=
n
-------------------------------- 100
10
∑
m
=
⋅
1
log
P
P
N
DC
EFF
–
(
-------------------------------------------
8 R
P
2 V
RAMP
IN
⋅
is defined by the following relationship (Equation 2):
⋅
⋅
LOAD
CC
signal is multiplied and the collector voltages are regulated to the multiplied V
–
EFF
V
⋅
SAT
10
)
3 –
)
2
TX ENABLE
TX ENABLE
VRAMP
RF IN
H(s)
VBATT
RF OUT
EFF
.. (η
EFF
Rev A4 050919
RAMP
considers the
voltage.
(Eq. 1)
(Eq. 2)