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參數(shù)資料
| 型號： | LMV248 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Dual Band GSM Power Controller |
| 中文描述： | 雙頻GSM功率控制器 |
| 文件頁數(shù)： | 7/11頁 |
| 文件大?。?/td> | 289K |
| 代理商： | LMV248 |
Application Section
(Continued)
The LMV248 as a RF Power Amplifier (PA) Controller
The LMV248, a member of National Semiconductor’s family
of RF power amplifier (PA) power controllers, is used to
regulate the RF transmit power in TDMA (GSM, EGSM,
PCN, PCSAND DCS) mobile phones. Capable of controlling
up to two RF output amplifiers and of triple band operation
(GSM, DCS, and PCS) the device supports both bipolar and
FET RF power amplifiers including Silicon BJT, CMOS, SiGe
HBT, and GaAs HBT.
Figure 1 shows the basics of a typical LMV248 dual band
application. The key components are:
Two power amplifiers, usually for the GSM or DCS/PCS
bands.
RF directional couplers where two single or one dual
channel RF coupler could be used.
Up to three Schottky RF detector diodes, one for each
directional coupler output and one for temperature com-
pensation.
A RF diplexer.
A dual or tri-band antenna.
The block diagram in Figure 2 shows the LMV248’s internal
architecture. The LMV248 contains input filters and condi-
tioning amplifiers, an input summing network, detector bias-
ing current source, error amplifier, output band select func-
tion, and output drivers.
Power Supplies
The LMV248 supports a single supply with the battery volt-
age at V
DD
.
Digital Input Signals:
The LMV248 has two digital control signals:
Transmit enable signal, Tx_En.
Band select signal, BS.
The band select pin, BS, selects which band (i.e which
output and input channel) is active. A high enables Out_A, a
low enables Out_B. The transmit enable pin, Tx_En, is used
to enable the BS selected output during transmit (Tx) slots
and disable the outputs during receive (Rx) slots. Disabling
the output during the receive (Rx) slot shuts down the
LMV248’s output stages and the RF power amplifiers, con-
serving battery power. A high input on the transmit enable
signal, Tx_En, brings the amplifier out of shutdown within
about 4μs. The output is glitch-free when enabled by this pin.
When an output is either not selected by BS or Tx_En is low,
its level is near GND. Internally, the band select pin, BS,
selects the correct input line and output amplifier, and places
the external compensation network across the active ampli-
fier using analog switches.
Error Amplifier/Loop Compensation
The error amplifier (A1) controls the overall loop regulation
and response. Frequency compensation and stabilization of
the RF output power regulating loop is accomplished by a
capacitor (or resistor/capacitor network) across Comp1 and
Comp2 of the LMV248. This external network sets the
closed loop frequency response. In most cases this network
will simply be a capacitor. Conventional loop stability tech-
niques can be used in selecting this network, such as Bode
plots.
Analog Inputs
At VfA and VfB are voltages proportional to the RF power
output of channel A and channel B respectively. Each of
these signals is derived from the RF output power via a RF
directional coupler a capacitor and a Schottky RF detector
diode. A single two-channel RF coupler could be used in-
stead of the two single-channel RF couplers shown in Figure
1
If only one input and output is needed, just connect BS high
or low and use the selected channel. At the TC input, a
reference diode identical to the detector diodes, and ther-
mally coupled to them, is used for temperature compensa-
tion of the VfA and VfB signals.
VfA, VfB and TC are referenced to V
. A 10μA current sink
internal to the LMV248 connects to the VfA, VfB and TC pins
to bias the diodes. The quiescent voltage on all three pins is
one diode drop below V
. The actual Ramp input value sets
the RF output power. The recommended Ramp voltage
range for RF power control is 0.2V to 1.8V. The Ramp input
will tolerate voltages from 0V to V
without malfunction or
damage. This signal usually comes from the baseband con-
troller’s DAC (digital to analog converter), its shape being
defined by the relevant GSM, PCN, or DCS standard.
The Ramp input does not change the output level from the
idle level set by V
until the level reaches about 200mV,
so offset voltages in the DAC or amplifier supplying the
Ramp signal will not cause excess RF signal output and
increased power consumption. An internal RC filter with a
corner frequency of approximately 1.6MHz smooths the
Ramp signal, to eliminate step discontinuities at the base-
band DAC’s output. Ramp is ground referenced, so supply
variations are rejected.
V
HOME
is used to set the output selected by BS to the
threshold voltage of the RF power amplifier. The variable
V
HOME
voltage level supports different PAShut off thresholds
as well as boost output voltage to minimize phase delay at
low power levels. The V
voltage can be derived from a
reference, resistive voltage divider, or DAC output. The rec-
ommended V
HOME
voltage range for threshold control is 0V
to 2V. The V
input will tolerate voltages from 0V to V
without malfunction or damage. The minimum output voltage
at Out_A or Out_B set by V
is approximately 3.0 x
V
. V
is ground referenced. V
does not affect
the minimum voltage of the output not selected by BS.
For maximum performance a fine adjust is needed for
V
, since each individual RF power amplifier’s threshold
voltage is slightly different from the nominal datasheet value.
Analog Outputs
Outputs Out_A and Out_B are driven by rail-to-rail amplifiers
capable of both sourcing and sinking. Either output can
source 6mA and sink 2mA with less than 200mV voltage
drop over recommended operating conditions. The output is
free from glitches when enabled by Tx_En. When an output
is not selected by BS, its level is near GND.
Understanding the LMV248
Input Structure
The LMV248 simplified block diagram of Figure 2 shows the
IC’s internal structure. Input VfA goes through a resistor
(approximately 48.5k
) and analog switch to the inverting
input of the error amplifier A1. Input VfB goes through a
different resistor (also approximately 48.5k
) and analog
switch to the inverting input of the error amplifier A1. These
two analog switches are controlled by BS. VfA is selected
when BS is high and VfB is selected when BS is low. The
temperature compensation signal, TC, goes through a series
resistance of about 48.5k
, to the non-inverting input of the
error amplifier A1. This way the relatively large static DC
offset of the input signal is mostly removed from the differ-
ential signal to be amplified by A1, and the temperature
L
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7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| LMV248LQ | 功能描述:IC CTROL DUAL BAND PWR 16-LLP RoHS:否 類別:RF/IF 和 RFID >> RF 電源控制器 IC 系列:- 標準包裝:3,000 系列:- RF 型:GSM 頻率:450MHz ~ 2GHz 特點:四頻帶 封裝/外殼:8-VFBGA 供應(yīng)商設(shè)備封裝:8-MicroSMD（1.51x1.51） 包裝:帶卷 (TR) 其它名稱:LMV243BLX |
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| LMV2F-3M4 | 制造商:BACO Controls Inc 功能描述: |
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