ATF-331M4-TR2 View Datasheet(PDF) - Avago Technologies
Part Name
Description
MFG CO.
'ATF-331M4-TR2' PDF : 14 Pages View PDF
S and Noise Parameter Measurements
The position of the reference planes used for the mea-
surement of both S and Noise Parameter measurements is
shown in Figure 23. The reference plane can be described
as being at the center of both the gate and drain pads.
S and noise parameters are measured with a 50 ohm
microstrip test fixture made with a 0.010” thickness
aluminum substrate. Both source pads are connected
directly to ground via a 0.010” thickness metal rib which
provides a very low inductance path to ground for both
source pads. The inductance associated with the addition
of printed circuit board plated through holes and source
bypass capacitors must be added to the computer circuit
simulation to properly model the effect of grounding the
source leads in a typical amplifier design.
Reference
Plane
Source
Pin 3
Gate
Pin 2
Px
Drain
Pin 4
Source
Pin 1
Microstrip
Transmission Lines
Figure 23. Position of the Reference Planes.
Noise Parameter Applications Information
The Fmin values are based on a set of 16 noise figure mea-
surements made at 16 different impedances using an ATN
NP5 test system. From these measurements, a true Fmin
is calculated. Fmin represents the true minimum noise
figure of the device when the device is presented with an
impedance matching network that transforms the source
impedance, typically 50, 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 Fmin
only when the device is presented with o. If the reflection
coefficient of the matching network is other than o, then
the noise figure of the device will be greater than Fmin
based on the following equation.
NF = Fmin + 4 Rn |s – o | 2
Zo (|1 + o| 2)(1- |s|2)
Where Rn/Zo is the normalized noise resistance, o is the
optimum reflection coefficient required to produce Fmin
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 asso-
ciated 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. Typically for
FETs, the higher o usually infers that an impedance much
higher than 50 is required for the device to produce Fmin.
At VHF frequencies and even 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 air wound 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 air
wound coil. Losses as high as 0.5 dB or greater add to the
typical 0.15 dB Fmin of the device creating an amplifier
noise figure of nearly 0.65 dB.
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