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參數(shù)資料
| 型號： | MAG-725M4 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Agilent MGA-725M4 Low Noise Amplifier with Bypass Switch In Miniature Leadless Package |
| 中文描述： | 安捷倫的MGA - 725M4低噪聲放大器，具有旁路開關(guān)在微型無鉛封裝 |
| 文件頁數(shù)： | 16/21頁 |
| 文件大?。?/td> | 404K |
| 代理商： | MAG-725M4 |
The simplest method of placing
the MGA-725M4 into the bypass
mode is to open-circuit the ground
terminals at Pins 1 and 3. With the
ground connection open, the
internal control circuit of the
MGA-725M4 auto-switches from
the amplifier mode into a bypass
state and the device current drops
to near zero. Nominal current in
the bypass state is 2
μ
A with a
maximum of 15
μ
A.
2
4
3
1
R
bias
Bypass Switch
Enable
Output & V
d
Input
Figure 9. MGA-725M4 Amplifier/Bypass State
Switching.
An electronic switch can be used
to control states as shown in
Figure 9. The control switch could
be implemented with either a
discrete transistor or simple IC.
The speed at which the
MGA-725M4 switches between
states is extremely fast and will
normally be limited by the time
constants of external circuit
components, such as the bias
circuit and the bypass and block-
ing capacitors.
The input and output of the
MGA-725M4 while in the bypassed
state are internally matched to
50
. The input return loss can be
further improved at 1900 MHz by
adding a 2.9 to 3.9 nH series
inductor added to the input. This
is the same approximate value of
inductor that is used to improve
input match when the MGA-725M4
is in the amplifier state.
Thermal Considerations
Good thermal design is always an
important consideration in the
reliable use of any device, since
the Mean Time To Failure (MTTF)
of semiconductors is inversely
proportional to the operating
temperature.
The MGA-725M4 is a compara-
tively low power dissipation
device. When biased at 3 volts and
20 mA for LNA application, the
power dissipation is 3.0 volts x
20 mA or 60 mW. The temperature
increment from the RFIC channel
to its case is then 0.060 watt x
200
°
C/Watt, or only 12
°
C. Sub-
tracting the channel to case
temperature rise from the sug-
gested maximum junction tem-
perature of 150
°
C, the resulting
maximum allowable case tempera-
ture is 138
°
C.
The worst case thermal situation
occurs when the MGA-725M4 is
operated at its Maximum Operat-
ing Conditions in an effort to
maximize output power or to
achieve minimum distortion. A
similar calculation for the
Maximum Operating bias of
4.2 volts and 60 mA yields a
maximum allowable case tempera-
ture of 100
°
C. This calculation
further assumes the worst case of
no RF power being extracted from
the device. When operated in a
saturated mode, both power
added efficiency and the maxi-
mum allowable case temperature
will increase.
Note “Case” temperature for
surface mount packages such as
the SOT-343 refers to the interface
between the package pins and the
mounting surface, i.e., the tem-
perature at the PCB mounting pad.
The primary heat path from the
RFIC chip to the system heat sink
is by means of conduction through
the package leads and ground vias
to the ground plane of the PCB.
PCB Layout and Grounding
When laying out a printed circuit
board for the MGA-725M4, several
points should be considered. Of
primary concern is the RF bypass-
ing of the ground terminals when
the device is biased using the
source resistor method.
Package Footprint
A suggested PCB pad print for the
miniature, Minipak 1412 package
used by the MGA-725M4 is shown
in Figure 10.
0.5
0.020
0.4
0.016
0.4
0.016
1.1
0.043
0.3
0.012
0.5
0.020
0.3
0.012
Figure 10. PCB Pad Print for Minipak 1412
Package (mm [inches]).
This pad print provides allowance
for package placement by auto-
mated assembly equipment
without adding excessive
parasitics that could impair the
high frequency performance of the
MGA-725M4. The layout is shown
with a footprint of the MGA-725M4
superimposed on the PCB pads for
reference.
RF Bypass
For layouts using the source
resistor method of biasing, both of
the ground terminals of the
MGA-725M4 must be well
by-passed to maintain device
stability.
Beginning with the package pad
print in Figure 10, a RF layout
similar to the one shown in
Figure 11 is a good starting point
for using the MGA-725M4 with
capacitor-bypassed ground
terminals. It is a best practice to
use multiple vias to minimize
overall ground path inductance.
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