DEMO-ATF-5X1P8 Datasheet, PDF(17/23 Page) Broadcom Corporation. – High Linearity Enhancement Mode[ Pseudomorphic HEMT in 2x2 mm2 LPCC[3] Package

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DEMO-ATF-5X1P8 Datasheet, PDF (17/23 Pages) Broadcom Corporation. – High Linearity Enhancement Mode[ Pseudomorphic HEMT in 2x2 mm2 LPCC[3] Package

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PCB Layout

A recommended PCB pad layout for the Leadless Plastic

Chip Carrier (LPCC) package used by the ATF-521P8 is

shown in Figure 10. This layout provides plenty of plated

through hole vias for good thermal and RF grounding. It

also provides a good transition from microstrip to the

device package. For more detailed dimensions refer to

Section 9 of the data sheet.

Figure 10. Microstripline Layout.

RF Grounding

Unlike SOT packages, ATF-521P8 is housed in a leadless

package with the die mounted directly to the lead

frame or the belly of the package shown in Figure 11.

Pin 8

Pin 7 (Drain)

Pin 6

Pin 5

Pin 1 (Source)

Pin 2 (Gate)

Pin 3

Pin 4 (Source)

Bottom View

Figure 11. LPCC Package for ATF-521P8.

This simplifies RF grounding by reducing the amount

of inductance from the source to ground. It is also

recommended to ground pins 1 and 4 since they are

also connected to the device source. Pins 3, 5, 6, and 8

are not connected, but may be used to help dissipate

heat from the package or for better alignment when

soldering the device.

This three-layer board (Figure 12) contains a 10-mil layer

and a 52-mil layer separated by a ground plane. The first

layer is Getek RG200D material with dielectric constant

of 3.8. The second layer is for mechanical rigidity and

consists of FR4 with dielectric constant of 4.2.

High Linearity Tx Driver

The need for higher data rates and increased voice

capacity gave rise to a new third generation standard

know as Wideband CDMA or UMTS. This new standard

requires higher performance from radio components

such as higher dynamic range and better linearity. For

example, a WCDMA waveform has a very high peak to

average ratio which forces amplifiers in a transmit chain

to have very good Adjacent Channel Leakage power

Ratio or ACLR, or else operate in a backed off mode.

If the amplifier is not backed off then the waveform is

compressed and the signal becomes very nonlinear.

This application example presents a highly linear

transmit drive for use in the 2.14GHz frequency range.

Using the RF matching techniques described earlier,

ATF-521P8 is matched to the following input and output

impedances:

short

Figure 12. ATF-521P8 demoboard.

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