ATF-38143 Ver la hoja de datos (PDF) - HP => Agilent Technologies

Número de pieza

componentes Descripción

Fabricante

ATF-38143

Low Noise 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 represents the

true minimum noise figure of the

device when the device is pre-

sented with an impedance

matching network that trans-

forms the source impedance,

typically 50Ω, to an impedance

represented by the reflection

coefficient Γo. The designer must

design a matching network that

will present Γo 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 Γo. If the reflec-

tion coefficient of the matching

network is other than Γo, then the

noise figure of the 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.

Matching to such a high imped-

ance requires very hi-Q compo-

nents 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

muilti-layer 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. A discussion

concerning calculated and

measured circuit losses and their

effect on amplifier noise figure is

covered in Agilent Application

1085.

9

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