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參數(shù)資料
| 型號： | LMV242LD |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 通信及網(wǎng)絡 |
| 英文描述： | Dual Output, Quad-Band GSM/GPRS Power Amplifier Controller |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, DSO10 |
| 封裝： | 3 X 3 MM, LLP-10 |
| 文件頁數(shù)： | 13/16頁 |
| 文件大?。?/td> | 560K |
| 代理商： | LMV242LD |
Application Section
(Continued)
Extra attenuation Z between the coupler and the RF input of
the LMV242 can be achieved by 2 resistors R
X
and R
Y
according to
Figure 3
, where
Z = 20 LOG (R
IN
/ [R
IN
+ R
Y
])
or
e.g. R
Y
= 300
results in an attenuation of 16.9 dB.
To prevent reflection back to the coupler the impedance
seen by the coupler should be 50
(R
O
). The impedance
consists of R
in parallel with R
Y
+ R
IN
. R
X
can be calculated
with the formula:
R
X
= [R
* (R
+ R
)] / R
Y
R
X
= 50 * [1 + (50 / R
Y
)]
e.g. with R
Y
= 300
, R
IN
= 50
→
R
X
= 58
.
BASEBAND CONTROL OF THE LMV242
The LMV242 has 3 baseband-controlled inputs:
V
RAMP
signal (Base band DAC ramp signal)
TX_EN is a digital signal (performs the function
“Shutdown/Transmit Enable”).
Band Select (BS)
V
RAMP
Signal
The actual V
input value sets the RF output power. By
applying a certain mask shape to the “Ramp in” pin, the
output voltage level of the LMV242 is adjusting the PA
control voltage to get a power level (P
/dBm) out of the
PA, which is proportional to the single ramp voltage steps.
The recommended V
voltage range for RF power con-
trol is 0.2V to 2.0V. The V
input will tolerate voltages
from 0V to V
without malfunction or damage. The V
input does not change the output level until the level reaches
about 206 mV, so offset voltages in the DAC or amplifier
supplying the R
signal will not cause excess RF signal
output and increased power consumption.
Transmit Enable
Power consumption requirements are supported by the
TX_EN function, which puts the entire chip into a power
saving mode to enable maximum standby and talk time while
ensuring the output does not glitch excessively during
Power-up and Power-down. The device will be active in the
case TX_EN = High, or otherwise go to a low power con-
sumption shutdown mode. During shutdown the output is
pulled low to minimize the output voltage.
Band Select
The LMV242 is especially suitable for PAcontrol loops with 2
PA’s. The 2 outputs to steer the V
of the PA’s can be
controlled with the band select pin. When the band select is
LOW output2 is selected, while output1 is selected when
band select is HIGH. The not-selected output is pulled low.
Analog Output
The output is driven by a rail-to-rail amplifier capable of both
sourcing and sinking. Several curves are given in the “Typi-
cal performance characteristics”-section regarding the out-
put. The output voltage vs. sourcing/sinking current curves
show the typical voltage drop from the rail over temperature.
The sourcing/sinking current vs. output voltage characteris-
tics show the typical charging/discharging current, which the
output is capable of delivering at a certain voltage. The
output is free from glitches when enabled by TX_EN. When
TX_EN is low, the selected output voltage is fixed or near
GND.
FREQUENCY COMPENSATION
To compensate and prevent the closed loop arrangement
from oscillations and overshoots at the output of the RF
detector/error amplifier of the LMV242, the system can be
adjusted by means of external RC components connected
between Comp1 and Comp2. Exact values heavily depend
on PA characteristics. A good starting point is R = 0
and
C = 68 pF. The vast combination of PA’s and couplers
available preclude a generalized formula for choosing these
components. Additional frequency compensation of the
closed loop system can be achieved by adding a resistor
(and if needed an inductor) between the LMV242’s output
and the V
input of the PA. Please contact National Semi-
conductor for additional support.
TIMING DIAGRAM
In order to meet the timemask specifications for GSM, a
good timing between the control signals and the RF signal is
essential. According to the specifications the PA’s RF output
power needs to ramp within 28 μsec with minimum over-
shoot. To achieve this, the output of the PA controller should
ramp at the same time as the RF signal from the Base Band.
The ramp signal sets the controllers output to the required
value, where the loop needs a certain time to set this output.
Therefore the ramp should be set high some time before the
output has to be high. How much time depends on the setup
and the PA used. If the controllers shutdown functionality is
used, the shutdown should be set high about 6 μsec before
the ramp is set high.
20079530
FIGURE 4. Simplified PA Control Loop with Extra
Attenuation
L
www.national.com
13
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LMV242LD/NOPB | 功能描述:射頻檢測器 RoHS:否 制造商:Skyworks Solutions, Inc. 配置: 頻率范圍:650 MHz to 3 GHz 最大二極管電容: 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:SC-88 封裝:Reel |
| LMV242LDX | 功能描述:射頻檢測器 RoHS:否 制造商:Skyworks Solutions, Inc. 配置: 頻率范圍:650 MHz to 3 GHz 最大二極管電容: 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:SC-88 封裝:Reel |
| LMV242LDX/NOPB | 功能描述:射頻檢測器 RoHS:否 制造商:Skyworks Solutions, Inc. 配置: 頻率范圍:650 MHz to 3 GHz 最大二極管電容: 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:SC-88 封裝:Reel |
| LMV242MDA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual Output, Quad-Band GSM/GPRS Power Amplifier Controller |
| LMV242MEA DIE | 制造商:Texas Instruments 功能描述: |
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