atf-34143 Avago Technologies, atf-34143 Datasheet - Page 11

• Manufacturer Part Number: atf-34143
• Description: Low Noise Pseudomorphic Hemt In A Surface Mount Plastic Package
• Manufacturer: Avago Technologies

Noise Parameter Applications Information
F
ments while the F
lated. The F
measurements made at 16 different impedances using an
ATN NP5 test system. From these measurements, a true
F
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
a matching network that will present Γ
minimal associated 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
only when the device is presented with Γ
coefficient of the matching network is other than Γ
the noise figure of the device will be greater than F
based on the following equation.
NF = F
Zo (|1 + Γ
Where R
optimum reflection coefficient required to produce F
and Γ
ance actually presented to the device. The losses of the
matching networks are non-zero and they will also add
11
min
min
values at 2 GHz and higher are based on measure-
is calculated. F
min
s
is the reflection coefficient of the source imped-
n
+ 4 R
/Z
min
o
is the normalized noise resistance, Γ
values are based on a set of 16 noise figure
n
|Γ
mins
min
s
represents the true minimum noise
o
– Γ
below 2 GHz have been extrapo-
|
2
)(1 – Γ
o
|
2
o
s
|
. The designer must design
2
)
o
to the device with
o
. If the reflection
o
o
is the
, then
min
min
min
to the noise figure of the device creating a higher ampli-
fier noise figure. The losses of the matching networks
are related to the Q of the components and associated
printed circuit board loss. Γ
frequencies and increases as frequency is lowered. Larger
gate width devices will typically have a lower Γ
pared to narrower gate width devices.
Typically for FETs, the higher Γ
pedance much higher than 50Ω is required for the device
to produce F
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
device creating an amplifier noise figure 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
. At VHF frequencies and even lower L
o
is typically fairly low at higher
o
usually infers that an im-
o
min
as com-
of the