MGA-83563-TR1 Просмотр технического описания (PDF) - HP => Agilent Technologies
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MGA-83563-TR1 Datasheet PDF : 24 Pages
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11
Operating life tests [1] for the
MGA-83563 have established that
a MTTF of 106 hours will be met
for channel temperatures ≤ 150°C.
To achieve the 106 hour MTTF
goal, the circuit to which the
device is mounted (i.e., the case
temperature) should therefore
not exceed 150° – 46°C, or 104°C.
Repeating the reliability calcula-
tion using the worst case maxi-
mum device current of 200 mA,
the DC power dissipation is
552 mW. Summing the RF input
and output powers, Pdiss is
397 mW which results in a
channel-to-case temperature rise
of 69°C. The maximum case
temperature for the MTTF goal of
106 hours is then 150°– 69°C, or
81°C.
For other MTTF goals, power
dissipation, or operating tempera-
tures, Agilent publishes reliability
data sheets based on operating
life tests to enable designers to
arrive at a thermal design for
their particular operating environ-
ment. For a reliability data sheet
covering the MGA-83563, request
Agilent publication number 5964-
4128E, titled “GaAs MMIC Ampli-
fier Reliability Data.” This reliabil-
ity data sheet covers the Agilent
family of PHEMT GaAs RFICs.
Linear Amplifier Thermal
Example
If the MGA-83563 is used in a
linear application, the total power
dissipation is significantly higher
than for the saturated mode. The
dissipated power is greater due to
higher device current (not as
efficient as the saturated mode)
and also because no signal power
is being removed.
The maximum power dissipation
for reliable linear operation is
calculated in the same manner as
was done for the saturated
amplifier example. For linear
circuits, the RF input and output
power are negligible and assumed
to be zero. All of the DC power is
thus dissipated as heat. For
purposes of comparison to the
saturated mode example, this
calculation will use the same
MTTF goal of 106 hours and
supply voltage of 3 volts.
Calculations are again made for
both nominal and worst case
conditions.
From the data of Figure 10, the
typical 3-volt, small signal device
current for the MGA-83563 at
elevated temperatures is 156 mA.
The total device power dissipa-
tion, Pdiss, is then 3.0 volts *
156 mA, or 468 mW. The tempera-
ture increment from the RFIC
channel to case is 0.468 watt *
175°C/watt, or 82°C.
Commensurate with the MTTF
goal of 106 hours, the circuit to
which the device is mounted
should therefore not exceed
150°– 82°C, or 68°C.
For the worst case calculation, a
guard band of 40% is added to the
typical current to arrive at a
maximum DC current of 218 mA.
The Pdiss is 655 mW and the
channel-to-case temperature rise
is 115°C. The maximum case
temperature for worst case
current condition is 35°C.
A case temperature of 68°C for
nominal operation, or 35°C in the
worst case, is unacceptably low
for most applications. In order to
use the MGA-83562 reliably for
linear applications, the Pdiss must
be lowered by reducing the
supply voltage.
The implication on RF output
power performance for amplifiers
operating with a reduced Vd is
covered later in this application
note in the section subtitled “Use
of the MGA-83563 for Linear
Applications”.
Design Example for
2.5 GHz
The design of a 2.5 GHz amplifier
will be used to illustrate the
approach for using the
MGA-83563. The basic design
procedure outlined earlier will be
used, in which the interstage
inductor (L2) is chosen first,
followed by the design of an
initial small signal, output match.
The output match will then be
empirically optimized for large
signal conditions after which an
input match will be added.
The printed circuit layout in
Figure 21 is used as the starting
place. The circuit is designed for
fabrication on 0.031-inch thick
FR-4 dielectric material.
Interstage Inductor L2
The first step is to choose a value
for the interstage inductor, L2.
Referring to Figure 19, a value of
1.5 nH corresponds to the design
frequency of 2.5 GHz. A chip
inductor is chosen for L2 in this
example. However, for small
inductance values such as this,
the interstage inductor could also
be realized with a length of high
impedance transmission line.
The interstage inductor is by-
passed with a 62 pF capacitor,
which has a reactance of 1 Ω at
2.5 GHz. Connecting the supply
voltage to the bypassed side of
the inductor completes the
interstage part of the amplifier.
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