rf3145 RF Micro Devices, rf3145 Datasheet - Page 14

• Manufacturer Part Number: rf3145
• Description: Quad-band Gsm/edge/gsm850/dcs/pcs Power Amplifier Module Rf3145
• Manufacturer: RF Micro Devices

RF3145
The indirect closed loop is essentially a closed loop method of power control that is invisible to the user. Most power control
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
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 out-
put power, supply fluctuations are the dominate mode of power variations. With the RF3145 regulating 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 current
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
and antenna and is a more accurate measurement to determine how much current will be drawn in the application). η
defined by the following relationship (Equation 2):
Where P
mula becomes (Equation 3):
14 of 18
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
=
=
N
is the sum of all positive and negative RF power, P
n
-------------------------------- 100
10
RAMP
∑
m
=
⋅
1
log
P
P
signal is multiplied and the collector voltages are regulated to the multiplied V
N
DC
–
(
-------------------------------------------
8 R
P
2 V
IN
⋅
⋅
⋅
LOAD
CC
EFF
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at ([phone] or [e-mail].
–
V
⋅
)
SAT
10
3 –
)
2
TX ENABLE
TX ENABLE
VRAMP
RF IN
IN
H(s)
the input power and P
VBATT
RF OUT
EFF
DC
.. (η
is the delivered DC power. In dB the for-
EFF
considers the loss between the PA
RAMP
voltage. The basic circuit is
Rev A4 DS050919
(Eq. 1)
(Eq. 2)
EFF
is