GSM/EDGE Optimized, High Linearity Direct Quadrature Modulator

The LT5568-2 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 configured 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.

Applications

* 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

* 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

* POUT = 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