Broadcom Design Tip: W-CDMA application using MGA-71543, Noise Amplifier User guide

Brand: Broadcom

Model: Design Tip: W-CDMA application using MGA-71543, Noise Amplifier

Category: TV signal amplifiers

Type: User guide

Revision 07/13/01 @ 4:56 PM Page 1

W-CDMA application using MGA-71543, a Low

Noise Amplifier with Bypass Switch.

_________________________

INTRODUCTION:

The MGA-71543 is a single stage GaAs RFIC

low noise amplifier with an integrated bypass

switch (Figure 1).

Figure 1. MGA-71543. Functional Diagram

The purpose of the switch feature is to prevent

distortion of high signal levels in receiver

applications by bypassing the amplifier.

Furthermore it saves current thus improving

battery life.

One of the two ground leads of the amplifier is

tied to the control leads of the switch to allow

simple control of the bias. Therefore, using one

of the ground leads, it is possible to vary the bias

current (including completely shutting down the

amplifier) by varying the resistor to ground that

is attached to it.

In short, the MGA-71543 is a small LNA/Bypass

Switch MMIC that provides a low Noise figure,

a high gain and high third order input intercept

point (IIP3) especially suitable for the LNA stage

for W-CDMA application.

This application note describes a W-CDMA Low

noise amplifier design using Agilent

Technologies’ MGA-71543.

Design overview and summary:

The board used for this design is shown in

figure2. The schematic of this board is shown

in figure 3. The number of components used

can be reduced in a real application circuit

because some jumpers (0 Ω resistors), and

bypass capacitors could be eliminated without

performance degradation (some are only used

for ease, if tuning is necessary and also as a

safety to avoid any possible oscillations).

Matching and biasing

A simple series-shunt network of 1.5nH and

4.7nH at the input provides the noise matching

and the necessary DC grounding (of the input

pin). Because the main active device is a

depletion mode FET, source-biasing technique is

used so that only one positive DC supply is

required at the output. The input (gate) is DC

grounded and the source is RF bypassed, while

current setting resistors (R20 or R21) are

attached to ground.

A simple shunt-series network of 3.9nH and

1.8pF at the output does the required matching

for linearity while providing the RF choking and

DC blocking. The output-matching network does

not affect the noise figure, which was already set

by the input matching.

R38 and R25 provide some resistor loading at

low frequency and help stabilize the device at

low frequency. The rest of the components used,

including bypass capacitors (C8, C36, C37, C44,

C47), current setting resistors (R20 or R21),

voltage drop resistor (R24), DC block capacitors,

are all listed in table 1.

Performance Results

It is possible to achieve 3.7dBm of input Third

order intercept Point (IIP3) at 2.1GHz with a

device current of 11mA.

Conclusion

The MGA-71543 can be used for W-CDMA

application with the following typical

performance summary data:

NF Gain IIP3 S11 S22

1.2 15 3.7 13 8

Current = 11mA

Frequency: 2.1GHz

RF IN

RF OUT

SW & Bias Control

Description4 layer Board

Designation B

WCDMA-2100

Part Number Package

U2 or 71

DUT

MGA-71543 SOT-343 (SC-70) / Switch LNA

U4 or 03 Switch b/n Gnd resistors FDG6303N Dual N-channel, Digital FET

C12 1.8 pF

Size 0402/Output match, DC block

0.033 µ

µµ

µF

Size 0402 / Bypass capacitor

C9 5.6 pF

Size 0402 / DC block capacitor

C38 Not used

C36, C37, C44 82, 82, 27 pF

Size 0402 / Bypass capacitors

C47

0.033 µ

µµ

µF

Size 0402 / Bypass capacitor

L5 3.9 nH

TOK LL1005 0402/Out match/RF choke,DC feed

L6 4.7 nH

TOK LL1005 Size 0402 / input noise matching

L7 1.5 nH

TOK LL1005 Size 0402 / input noise matching

L25 Not used For tuning / Not used here

R38

51 Ω

ΩΩ

Ω

Size 0402

R20

36 Ω

Size 0402 / set Id for 16mA Bias

R21

56 Ω

ΩΩ

Ω

Size 0402 / set Id for 10.5mA Bias

R24, R25

6.2 Ω

ΩΩ

Ω

R24Drop voltage,R25resistive load

R16,R17

0 Ω

ΩΩ

Ω

Size 0402 (Jumper)

R37

0 Ω

ΩΩ

Ω

0402 Jumper or replace with a stub

R18,R28 Not Used Used for other current setting

Table 1. Component Values for 2100 MHz amplifier on smaller board

Figure 2. Test board layout

Software

controlling the

switch

Manual switch

control

U4 = FDG6303N

Dual N-channel, Digital

FET

R38

C37

R20

R21

R38

R25

R24

C47

C44

C12

R16 (0 Ω Jumper)

R17 (0 Ω Jumper)

OUTIN

MGA-71543

FDG6303N

Vd=3 Volt

Selects current

set by R20

Selects current

set by R21

Figure 3. Test board layout and

schematic

Broadcom Design Tip: W-CDMA application using MGA-71543, Noise Amplifier User guide

Brand: Broadcom

Model: Design Tip: W-CDMA application using MGA-71543, Noise Amplifier

Category: TV signal amplifiers

Type: User guide

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Broadcom Design Tip: W-CDMA application using MGA-71543, Noise Amplifier User guide

Broadcom Design Tip: W-CDMA application using MGA-71543, Noise Amplifier User guide

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