Linear Technology LT5572 Quick Start Manual

DESCRIPTION
Demonstration circuit 945 is an I/Q modulator
®
featuring the LT
2.5GHz direct I/Q modulator designed for high
performance wireless applications, including wireless
infrastructure. It may also be configured as an image
reject upconverting mixer, by applying 90° phase-
shifted signals to the I and Q inputs.
A high-speed, internally matched LO amplifier drives
two double-balanced mixer cores, allowing the use of
a low power, single-ended LO source. It allows direct
modulation of an RF signal using differential
baseband I and Q signals. The LT 5572 supports
GSM, EDGE, CDMA, CDMA2000, W-CDMA, 64-QAM,
OFDM and other modulation formats.
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
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 945
5572. The LT 5572 is a 1.5GHz to
HIGH LINEARITY DIRECT QUADRATURE MODULATOR
output. The four balanced I and Q base-band input
ports are intended for DC coupling from a source with
a common-mode voltage level of about 0.5V. The
differential input impedance of the baseband inputs is
approximately 90KΩ.
impedance is easily set for a specific application
using external
demonstration circuit, this is set to 100Ω differential,
making it ideally suited for current drive applications.
The LO path consists of an LO buffer with single-
ended input, and precision quadrature generators
which produce the LO drive for the mixers.
Demonstration circuit 945 is designed for an RF
output frequency range from 1.5GHz to 2.5GHz.
Design files for this circuit board are available. Call
the LTC factory.
LT is a registered trademark of Linear Technology Corporation.
LT5572
The input termination
resistors. On the DC945
1