RF3145 데이터 시트보기 (PDF) - RF Micro Devices
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RF3145 Datasheet PDF : 18 Pages
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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 VRAMP signal is multiplied and the collector voltages are regulated to the multiplied VRAMP voltage. The basic circuit is
shown in the following diagram.
TX ENABLE
VRAMP
VBATT
H(s)
RF IN
TX ENABLE
RF OUT
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.
PdBm
=
10 ⋅ log
-(--2----⋅---V----C----C----–-----V----S---A---T---)--2-
8 ⋅ RLOAD ⋅ 10–3
(Eq. 1)
There are several key factors to consider in the implementation of a transmitter solution for a mobile phone. Some of them are:
• Effective efficiency (ηEFF)
• 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
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 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-----------------------
PDC
⋅
100
(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 for-
mula becomes (Equation 3):
14 of 18
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Rev A4 DS050919
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