atf-35143 Avago Technologies, atf-35143 Datasheet - Page 15

• Manufacturer Part Number: atf-35143
• Description: Low Noise Pseudomorphic Hemt In A Surface Mount Plastic Package
• Manufacturer: Avago Technologies

Noise Parameter Applications Information
F
measurements while the F
extrapolated. The F
16 noise figure measurements made at 16 different
impedances using an ATN NP5 test system. From these
measurements, a true F
the true minimum noise figure of the device when the
device is presented with an impedance matching network
that transforms the source impedance, typically 50Ω, to
an impedance represented by the reflection coefficient
Γ
will present Γ
circuit losses. The noise figure of the completed amplifier
is equal to the noise figure of the device plus the losses
of the matching network preceding the device. The
noise figure of the device is equal to F
device is presented with Γ
of the matching network is other than Γ
figure of the device will be greater than F
following equation.
NF = F
Zo (|1 + Γ
Where R
15
min
o
. The designer must design a matching network that
values at 2 GHz and higher are based on
min
n
+ 4 R
/Z
o
is the normalized noise resistance, Γ
o
to the device with minimal associated
n
|Γ
min
values are based on a set of
min
s
– Γ
o
is calculated. F
o
mins
|
. If the reflection coefficient
2
)(1 - Γ
o
|
below 2 GHz have been
2
s
|
2
)
min
o
min
, then the noise
only when the
min
based on the
represents
o
is
the optimum reflection coefficient required to produce
F
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. Γ
low at higher frequencies and increases as frequency is
lowered. Larger gate width devices will typically have a
lower Γ
Typically for FETs, the higher Γ
impedance much higher than 50Ω is required for the
device to produce F
lower L Band frequencies, the required impedance can
be in the vicinity of several thousand ohms. Matching to
such a high impedance requires very hi-Q components
in order to minimize circuit losses. As an example at
900 MHz, when airwwound 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 muiltilayer 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
of nearly 0.65 dB. A discussion concerning calculated
and measured circuit losses and their effect on amplifier
noise figure is covered in Avago Application 1085.
min
and Γ
min
of the device creating an amplifier noise figure
o
as compared to narrower gate width devices.
s
is the reflection coefficient of the source
min
. At VHF frequencies and even
o
usually infers that an
o
is typically fairly