DESCRIPTION
The LT®5558 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. It may also be configured as an image reject upconverting 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 doublebalanced mixers. The outputs of these mixers are summed and applied to an on-chip RF transformer, which converts the differential mixer signals to a 50Ωsingle-ended output.

FEATURES
■ Direct Conversion from Baseband to RF
■ High OIP3: + 22.4dBm at 900MHz
■ Low Output Noise Floor at 20MHz Offset:
   No RF: –158dBm/Hz
   POUT = 4dBm: –152.7dBm/Hz
■ Low Carrier Leakage: –43.7dBm at 900MHz
■ High Image Rejection: –49dBc at 900MHz
■ 3 Channel CDMA2000 ACPR: –70.4dBc at 900MHz
■ Integrated LO Buffer and LO Quadrature Phase Generator
■ 50Ω AC-Coupled Single-ended LO and RF Ports
■ High Impedance Interface to Baseband Inputs
   with 2.1V Common Mode Voltage
■ 16-Lead QFN 4mm × 4mm Package

APPLICATION
■ RFID Single-Sideband Transmitters
■ Infrastructure TX for Cellular and ISM Bands
■ Image Reject Up-Converters for Cellular Bands
■ Low-Noise Variable Phase-Shifter for 600MHz to 1100MHz Local Oscillator Signals
■ Microwave Links