620MHz - 1100MHz High Linearity Direct Quadrature Modulator

The LT5571 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 RFID, 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 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 at 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.

Applications

* RFID Interrogators

* GSM, CDMA, CDMA2000 Transmitters

* Point-to-Point Wireless Infrastructure Tx

* Image Reject Up-Converters for Cellular Bands

* Low-Noise Variable Phase-Shifter for 620MHz to 1100MHz Local Oscillator Signals

* Direct Conversion from Baseband to RF

* High Output: –4.2dB Conversion Gain

* High OIP3: 21.7dBm at 900MHz

* Low Output Noise Floor at 20MHz Offset:

* No RF: –159dBm/Hz

* POUT = 4dBm: –153.3dBm/Hz

* Low Carrier Leakage: –42dBm at 900MHz

* High Image Rejection: –53dBc at 900MHz

* 3-Ch 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 DC Interface to Baseband Input with 0.5V Common Mode Voltage

* 16-Lead QFN 4mm × 4mm Package