ATF55143 HP [Agilent(Hewlett-Packard)], ATF55143 Datasheet - Page 18

• Manufacturer Part Number: ATF55143
• Description: Agilent ATF-55143 Low Noise Enhancement Mode Pseudomorphic HEMT in a Surface Mount Plastic Package
• Manufacturer: HP [Agilent(Hewlett-Packard)]

made at 16 different impedances
From these measurements, a true
Noise Parameter Applications
Information
F
are based on measurements
while t he F
been extrapolated. The F
values are based on a set of
16 noise f igure measurements
using an ATN NP5 test system.
F
sents the true minimum noise
figure of the device when the
device is presented wit h an
impedance matching network
that transforms the source
impedance, typically 50 , to an
impedance represented by the
reflection coefficient
designer must design a matching
network that will present
the device with minimal associ-
ated circuit losses. The noise
figure of the completed amplifier
is equal to the noise f igure of the
device plus the losses of the
matching netw ork preceding the
device. The noise figure of the
device is equal to F
min
min
values at 2 GHz and higher
is calculated. F
mins
below 2 GHz ha ve
min
min
only when
o
repre-
. The
min
o
to
the device is present ed with
the ref lection coefficient of the
matching network is other than
device will be g reater than F
based on t he following equation.
NF = F
Where R
noise resistance,
mum reflection coefficient
required to produce F
the reflection coefficient of the
source impedance actually
presented to the device. The
losses of the matching networks
are non-zero and they will also
add to the noise figure of the
device creating a higher amplifier
noise figure. The losses of the
matching networks are related to
the Q of the components and
associated printed circuit board
loss.
higher frequencies and increases
as frequency is lowered. Larger
gate width devices will typically
have a lower
narrower gate width devices.
o
, then the noise figure of the
min
o
is typically fairly low at
n
/Z
+ 4 R
o
Zo (|1 +
is the normalized
n
o
as compared to
18
o
is the opti-
|
min
s
o
|
–
2
) (1 - |
and
o
|
2
min
o
. If
s
s
|
is
2
)
Typically for FETs, the higher
usually infers that an impedance
much higher than 50 is required
for the device to produce F
VHF frequencies and even lower
L Band frequencies, the required
impedance can be in the vicinity
of several thousand ohms. Match-
ing to such a high impedance
requires very hi-Q components in
order to minimize circuit losses.
As an example at 900 MHz, when
airwound coils (Q > 100) are used
for matching networks, the loss
can still be up to 0.25 dB which
will add directly to the noise
figure of the device. Using multi-
layer molded inductors with Qs in
the 30 to 50 range results in
additional loss over the airwound
coil. Losses as high as 0.5 dB or
greater add to the typical 0.15 dB
F
amplifier noise figure of nearly
0.65 dB. A discussion concerning
calculated and measured circuit
losses and their effect on ampli-
fier noise figure is covered in
Agilent Technologies Application
1085.
min
of the device creating an
min
. At
o