ATF-55143-TR2G View Datasheet(PDF) - Avago Technologies
Part Name
Description
MFG CO.
ATF-55143-TR2G
Avago Technologies
'ATF-55143-TR2G' PDF : 20 Pages View PDF
Noise Parameter Applications Information
F values at 2 GHz and higher are based on measure-
min
ments while the F below 2 GHz have been extrapo-
mins
lated. The F values are based on a set of 16 noise
min
figure measurements made at 16 different impedances
using an ATN NP5 test system. From these measure-
ments, a true F is calculated. F represents the true
min
min
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 o.
The designer must design a matching network that will
present o to the device with 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
min
is presented with o. If the reflection coefficient of the
matching network is other than o, then the noise fig-
ure of the device will be greater than F based on the
min
following equation.
4R
NF = F + n
|s – o | 2
min Zo (|1 + o| 2)(1 -|s|2)
Typically for FETs, the higher o usually infers that an
impedance much higher than 50Ω is required for the
device to produce F . At VHF frequencies and even
min
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 compo-
nents 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 multilayer 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 typi-
cal 0.15 dB F of the device creating an amplifier noise
min
figure of nearly 0.65 dB. A discussion concerning cal-
culated and measured circuit losses and their effect on
amplifier noise figure is covered in Avago Technologies
Application 1085.
Where
R /Z
no
is
the
normalized
noise
resistance,
o
is
the optimum reflection coefficient required to produce
F
min
and
s
is
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. o is typically fairly
low at higher frequencies and increases as frequency is
lowered. Larger gate width devices will typically have a
lower o as compared to narrower gate width devices.
18
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