ATF-54143 Ver la hoja de datos (PDF) - HP => Agilent Technologies

Número de pieza

componentes Descripción

Fabricante

ATF-54143

Low Noise Enhancement Mode Pseudomorphic HEMT in a Surface Mount Plastic Package

HP => Agilent Technologies 

Noise Parameter Applications

Information

Fmin values at 2 GHz and higher

are based on measurements

while the Fmins below 2 GHz have

been extrapolated. The Fmin

values are based on a set of

16 noise figure measurements

made at 16 different impedances

using an ATN NP5 test system.

From these measurements, a true

Fmin is calculated. Fmin repre-

sents 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 Go. The

designer must design a matching

network that will present Go to

the device with minimal associ-

ated 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 Go.

If the reflection coefficient of the

matching network is other than

G , then the noise figure of the

o

device will be greater than Fmin

based on the following equation.

NF = Fmin + 4 Rn

|Γs – Γo | 2

Zo (|1 + Γo| 2) (1 - |Γs|2)

Where Rn/Zo is the normalized

noise resistance, Γo is the opti-

mum reflection coefficient

required to produce Fmin and Γs 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. Γo is typically fairly low at

higher frequencies and increases

as frequency is lowered. Larger

gate width devices will typically

have a lower Γo as compared to

narrower gate width devices.

Typically for FETs, the higher Γo

usually infers that an impedance

much higher than 50Ω 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. 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

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

Fmin of the device creating an

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 Application 1085.

14

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