LT5568-2 Datasheet, PDF (1/16 Pages) Linear Technology – GSM/EDGE Optimized, High Linearity Direct Quadrature Modulator

FEATURES
■ _{Optimized Image Rejection for 850MHz to 965MHz}
■ _{High OIP3: +22.9dBm at 900MHz}
■ _{Low Output Noise Floor at 5MHz Offset:}
No RF: –159.4dBm/Hz
P_OUT = 4dBm: –153dBm/Hz
■ _{Integrated LO Buffer and LO Quadrature Phase}
Generator
■ _{50Ω AC-Coupled Single-Ended LO and RF Ports}
■ _{50Ω DC Interface to Baseband Inputs}
■ _{Low Carrier Leakage: –43dBm at 900MHz}
■ _{High Image Rejection: –52dBc at 900MHz}
■ _{16-Lead 4mm × 4mm QFN Package}
U
APPLICATIO S
■ _{Infrastructure Tx for GSM/Cellular Bands}
■ _{Image Reject Up-Converters for Cellular Bands}
■ _{Low-Noise Variable Phase-Shifter for 700MHz to}
1050MHz Local Oscillator Signals
■ _{RFID Reader}
LT5568-2
GSM/EDGE Optimized,
High Linearity Direct
Quadrature Modulator
DESCRIPTIO
The LT^®5568-2 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
GSM, EDGE, CDMA, CDMA2000 and other systems that
operate in the 850MHz to 965MHz band. It may be config-
ured as an image reject upconverting mixer, by applying
90° phase-shifted signals to the I and Q inputs. The 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 four balanced I and Q
baseband input ports are intended for DC coupling from a
source with a common mode voltage level of about 0.5V.
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.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
850MHz to 965MHz Direct Conversion Transmitter Application
I-DAC
EN
Q-DAC
V_CC
V-I
I-CHANNEL
0°
90°
Q-CHANNEL
V-I
LT5568-2
BALUN
5V
100nF
x 2 _{RF = 850MHz}
TO 965MHz
PA
BASEBAND
GENERATOR
VCO/SYNTHESIZER
55682 TA01
GSM EVM and Noise
vs RF Output Power at 900MHz
5
–96
4
–98
3
NOISE
–100
2
–102
EVM
1
–104
0
–10
–106
–8 –6 –4 –2 0 2 4 6
GSM RF OUTPUT POWER (dBm)
55682 TA02
55682f
1