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LT5518

1.5GHz–2.4GHz High Linearity Direct Quadrature Modulator

Linear Technology 

LT5518

1.5GHz–2.4GHz

High Linearity Direct

Quadrature Modulator

FEATURES

■ High Input Impedance Version of the LT5528

■ Direct Conversion to 1.5GHz – 2.4GHz

■ High OIP3: 22.8dBm at 2GHz

■ Low Output Noise Floor at 20MHz Offset:

No RF: –158.2dBm/Hz

POUT = 4dBm: –152.5dBm/Hz

■ 4-Ch W-CDMA ACPR: –64dBc at 2.14GHz

■ Integrated LO Buffer and LO Quadrature Phase

Generator

■ 50Ω AC-Coupled Single-Ended LO and RF Ports

■ Low Carrier Leakage: –49dBm at 2GHz

■ High Image Rejection: 40dB at 2GHz

■ 16-Lead QFN 4mm × 4mm Package

U

APPLICATIO S

■ Infrastructure Tx for DCS, PCS and UMTS Bands

■ Image Reject Up-Converters for DCS, PCS and UMTS

Bands

■ Low Noise Variable Phase-Shifter for 1.5GHz to

2.4GHz Local Oscillator Signals

DESCRIPTIO

The LT®5518 is a direct I/Q modulator designed for high

performance wireless applications, including wireless

infrastructure. It allows direct modulation of an RF signal

using differential baseband I and Q signals. It supports PHS,

GSM, EDGE, TD-SCDMA, CDMA, CDMA2000, W-CDMA

and other systems. It may also be configured as an image

reject up-converting mixer, by applying 90° phase-shifted

signals to the I and Q inputs. The high impedance I/Q

baseband inputs consist of voltage-to-current converters

that in turn drive double-balanced mixers. The outputs of

these mixers are summed and applied to an on-chip RF

transformer, which converts the differential mixer signals

to a 50Ω single-ended output. The balanced I and Q

baseband input ports are intended for DC coupling from a

source with a common mode voltage level of about 2.1V.

The LO path consists of an LO buffer with single-ended

input, and precision quadrature generators that produce

the LO drive for the mixers. The supply voltage range is

4.5V to 5.25V.

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

TYPICAL APPLICATIO

1.5GHz to 2.4GHz Direct Conversion Transmitter Application

with LO Feedthrough and Image Calibration Loop

W-CDMA ACPR, AltCPR and Noise vs RF Output

Power at 2140MHz for 1 and 4 Channels

I-DAC

EN

Q-DAC

14

16 V-I

VCC 8, 13

LT5518

5V

100nF

×2 RF = 1.5GHz

TO 2.4GHz

I-CHANNEL

1

0°

90°

7 Q-CHANNEL

5 V-I

BALUN

11

PA

LO FEEDTHROUGH

CAL OUT

IMAGE CAL OUT

CAL

BASEBAND

GENERATOR

2, 4, 6, 9, 10, 12, 15, 17

3

VCO/SYNTHESIZER

ADC

5518 TA01a

–55

4-CH ACPR

–135

–60

–140

4-CH ALTCPR

–65

–145

1-CH ACPR

–70

–150

–75

1-CH ALTCPR

–80 4-CH NOISE

–155

1-CH NOISE

–160

DOWNLINK TEST MODEL 64 DPCH

–85

–34 –30 –26 –22 –18 –14 –10

RF OUTPUT POWER PER CARRIER (dBm)

–165

5518 TA01b

5518f

1

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