RF3145 查看數據表（PDF） - RF Micro Devices
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RF3145 Datasheet PDF : 18 Pages
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RF3145
Theory of Operation
Overview
The RF3145 is a dual-mode, quad-band power amplifier module that is compatible with both GSM and EDGE applications. The
device operates in a broad frequency range that includes the GSM850, GSM900, DCS1800, and PCS1900 frequency bands.
Integrated band select, mode select, and power control features are also integrated to provide digital control of various fea-
tures.
Band select provides digital selection of the GSM850/900 or DCS1800/PCS1900 band. VMODE provides digital control of the
gain in the GSM900 band. Due to gain expansion at input powers below the 1dB compression point, low gain mode is provided
to maintain the noise power performance in EDGE applications. However, this feature is not required in the
DCS1800/PCS1900 bands. Therefore, VMODE controls only the gain in the GSM850/900 band. (This feature is not provided in
the DCS/PCS band.)
The integrated power control feature employs an indirect closed loop method that uses collector control to regulate output
power. Collector control design architecture has several advantages, including simplifying the phone design, as well as mini-
mizing gain and linearity variation in EGDE applications. Integrated power control eliminates the need for a complicated control
loop design. The indirect closed loop is fully self-contained and does not require loop optimization. It can be driven directly
from the DAC output in the baseband circuit.
The RF3145 mode of operation is a function of the input power level and the VMODE logic level. In GSM applications, the input
power is held constant in the range of +2dBm to +5dBm, and the output power is controlled using the VRAMP input. The
required input power for GSM/GPRS applications is typically 3dB to 4dB higher than the 1dB compression point. GSM/GPRS
applications use GMSK modulation, which is constant envelope and is not sensitive to amplitude non-linearities. Therefore the
power amplifier may be operated in deep class AB which offers high efficiency. However, in EDGE applications, the 3π/8
rotated 8-PSK constellation shown in Figure 1 contains both phase and amplitude information.
Figure 1. EDGE 3Pi/8 Rotated 8-PSK Constellation
Therefore, EDGE applications require a linear power amplifier to transfer EDGE modulation with minimal distortion. Changing
VRAMP in linear applications will cause distortion to the EDGE modulated signal, and is not recommended. If the VRAMP signal is
lowered in EDGE applications, the voltage on the collectors of the power amplifiers will also be lowered (lower than the 1dB
compression point). In EDGE applications, the VRAMP input should be held constant at VRAMP(MAX), and the input power is
ramped to meet the EDGE burst mask. Typical EDGE systems use a VGA to provide this RF ramp input to the power amplifier.
Theory of Operation
Rev A4 DS050919
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
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