16
As a guideline for operation at
higher bias levels, the Maximum
Operating conditions shown in the
data sheet table of Absolute
Maximum Ratings should be
followed. This set of conditions is
the maximum combination of bias
voltage, bias current, and device
temperature that is recommended
for reliable operation. Note: In
contrast to Absolute Maximum
ratings, in which exceeding any
one parameter may result in
LNA applications, the power
dissipation is 3.0 volts x20 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.
Subtracting the channel-to-case
temperature rise from the
suggested maximum junction
temperature of 150°C, the result-
ing maximum allowable case
temperature is 138°C.
3
2
1
4
R
bias
Bypass Switch
Enable
Figure 9. MGA-72543 Amplifier/
Bypass State Switching.
damage to the device, all of the
Maximum Operating conditions
may reliably be applied to the
MGA-72543 simultaneously.
The worst case thermal situation
occurs when the MGA-72543 is
operated at its Maximum Operat-
ing conditions in an effort to
maximize output power or
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.
achieve minimum distortion. A
similar calculation for the Maxi-
mum Operating bias of 4.2 volts
and 60 mA yields a maximum
allowable case temperature 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.
Controlling the Switch
The state of the MGA-72543
(amplifier or bypass mode) is
controlled by the device current.
For device currents greater than
5 mA, the MGA-72543 functions
as an amplifier. If the device
current is set to zero, the MGA-
72543 is switched into a bypass
mode in which the amplifier is
turned off and the signal is routed
around the amplifier with a loss
of approximately 2.5 dB.
The speed at which the MGA-
72543 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 blocking capacitors.
The input and output of the
MGA-72543 while in the bypass
state are internally matched to
50 Ω. The input return loss can be
further improved at 1900 MHz by
adding a 2.7 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-72543
is in the amplifier state.
Note: “Case” temperature for
surface mount packages such as
the SOT-343 refers to the inter-
face between the package pins
and the mounting surface, i.e., the
temperature at the PCB mounting
pads. The primary heat path from
the RFIC chip to the system
heatsink is by means of conduc-
tion through the package leads
and ground vias to the
The bypass state is normally
engaged in the presence of high
input levels to prevent distortion
of the signal that might occur in
the amplifier. In the bypass state,
the input TOI is very high,
typically +39 dBm at 1900 MHz.
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 simplest method of placing
the MGA-72543 into the bypass
mode is to open-circuit the
ground terminals at Pins 1 and 4.
With the ground connection open,
the internal control circuit of the
MGA-72543 auto-switches from
the amplifier mode into a bypass
state and the device current
groundplane of the PCB.
PCB Layout and Grounding
When laying out a printed circuit
board for the MGA-72543, several
points should be considered. Of
primary concern is the RF
bypassing of the ground terminals
when the device is biased using
the source resistor method.
The MGA-72543 is a compara-
tively low power dissipation
device and, as such, operates at
conservative temperatures. When
biased at 3 volts and 20 mA for
drops to near zero. Nominal
current in the bypass state is 2 µA
with a maximum of 15 µA.
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
