RF3133PCBA RFM [RF Monolithics, Inc], RF3133PCBA Datasheet - Page 10

• Manufacturer Part Number: RF3133PCBA
• Description: QUAD-BAND GSM850/GSM/DCS/PCS POWER AMP MODULE
• Manufacturer: RFM [RF Monolithics, Inc]

Overview
The RF3133 is a quad-band GSM/DCS/PCS power amplifier module that incorporates an indirect closed loop method of
power control. This simplifies the phone design by eliminating the need for the complicated control loop design. The indi-
rect closed loop is fully self contained and required does not require loop optimization. It can be driven directly from the
DAC output in the baseband circuit.
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 RF3133 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 RF3133 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:
• Effective efficiency (
• 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
2-468
P
dBm
RF3133
=
10
log
-------------------------------------------
8 R
2 V
RAMP
LOAD
eff
CC
)
signal is multiplied and the collector voltages are regulated to the multiplied V
–
V
SAT
10
3 –
2
Theory of Operation
TX ENABLE
TX ENABLE
VRAMP
RF IN
H(s)
VBATT
RF OUT
Rev A4 030527
RAMP
voltage.
(Eq. 1)