Analog Devices Inc. LT5568-2EUF#TRPBF

Overview

LT5568-2EUF#TRPBF from Analog Devices (formerly Linear Technology) is a high-linearity direct quadrature I/Q modulator for cellular infrastructure transmitters operating from 700MHz to 1050MHz. It delivers +22.9dBm OIP3 at 850MHz, –46dBc image rejection, –43dBm carrier leakage, –154dBm/Hz noise floor at 5MHz offset (POUT = 4dBm), and supports W-CDMA, CDMA2000, LTE, and TD-SCDMA base station uplink paths.

For engineers reviewing the LT5568-2EUF#TRPBF datasheet, LT5568-2EUF#TRPBF pinout, LT5568-2EUF#TRPBF application, or LT5568-2EUF#TRPBF equivalent, key selection criteria include RF output linearity (OIP3/OIP2), image rejection stability across LO frequency, baseband input common-mode voltage tolerance (0.54V), enable-controlled power-down (50μA sleep current), and 16-lead 4mm × 4mm QFN package thermal performance (θJA = 37°C/W).

Technical Context

The LT5568-2EUF#TRPBF integrates differential voltage-to-current converters for I/Q baseband inputs (BBPI/BBMI/BBPQ/BBMQ), double-balanced up-conversion mixers, an on-chip 50Ω RF balun, and a precision LO quadrature phase generator with integrated buffer. Its architecture enables true direct-conversion modulation without external phase-shifting components.

LO path operation is fully self-contained: single-ended 50Ω AC-coupled LO input (–10dBm to +5dBm) drives internal quadrature splitters that deliver matched in-phase and 90°-shifted signals to both mixers. Baseband interface requires DC-coupled 0.54V common-mode bias and differential drive to suppress even-order distortion and maintain >63dBm OIP2.

Key Specifications

Pinout & Package

LT5568-2EUF#TRPBF uses a 16-lead 4mm × 4mm plastic QFN package (UF) with exposed thermal pad (Pin 17) requiring PCB soldering for thermal and RF grounding. Pin assignment is validated per Linear Technology datasheet DS5568F.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar direct-conversion modulator applications.

Compared with ADL5375-05ACPZ-R7 and TRF3705IRGZT, the LT5568-2EUF#TRPBF uniquely integrates the LO quadrature generator and RF balun in a compact 4mm × 4mm QFN, delivering optimal balance of integration, linearity (+22.9dBm OIP3), and image rejection (–46dBc) for 700–1050MHz infrastructure transmitters.

Availability

LT5568-2EUF#TRPBF is available at Aetrix Electronics and suitable for cellular infrastructure transmitters, CDMA2000 base stations, and TD-SCDMA radio units requiring stable component supply, long-term lifecycle support, and traceable sourcing for telecom OEMs.

Supply support for LT5568-2EUF#TRPBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and RF ICs for communications, industrial, and automotive markets.

The LT5568 product line was designed specifically for high-linearity, direct-conversion wireless infrastructure transmitters-emphasizing image rejection, wide dynamic range, and integration of critical RF functions into a single QFN package.

FAQ

What is the recommended LO input power for optimal performance of the LT5568-2EUF#TRPBF?

The LT5568-2EUF#TRPBF achieves best linearity and noise performance at 0dBm LO input power. Lower LO power (e.g., –5dBm) improves image rejection but degrades noise floor by ~1.5dB at POUT = 4dBm. Higher LO power (e.g., +5dBm) increases carrier leakage without improving OIP3 or gain, so 0dBm is the design target specified in the datasheet for LT5568-2EUF#TRPBF characterization.

Does the LT5568-2EUF#TRPBF require external filtering on its baseband inputs?

Yes, the LT5568-2EUF#TRPBF requires external reconstruction filtering between the DAC and baseband inputs to suppress DAC images and harmonics. The internal baseband RC filter (25Ω + 12pF) provides only ~330MHz –1dB bandwidth; for W-CDMA or LTE, a 5th-order passive ladder filter (as shown in Figure 3 of the LT5568-2EUF#TRPBF datasheet) is recommended to meet spectral mask requirements before the LT5568-2EUF#TRPBF input stage.

How does the LT5568-2EUF#TRPBF handle DC offset and I/Q imbalance in practical designs?

The LT5568-2EUF#TRPBF has inherent tolerance to moderate I/Q gain/phase errors (0.07dB/0.45° typical), but system-level DC offset must be managed externally. Baseband DACs must be calibrated to match differential amplitudes and common-mode voltage (0.54V) precisely; mismatch directly impacts LO feedthrough (–43dBm typ.) and image rejection. The LT5568-2EUF#TRPBF itself does not include digital calibration or trimming circuits.

Can the LT5568-2EUF#TRPBF be used outside its specified 700–1050MHz RF range?

The LT5568-2EUF#TRPBF is characterized and guaranteed for 700–1050MHz RF operation. While usable down to 600MHz or up to 1200MHz per absolute max ratings, image rejection degrades significantly beyond 1050MHz due to quadrature phase error in the internal LO splitter, and conversion gain drops outside the specified band. For reliable performance, LT5568-2EUF#TRPBF should be operated strictly within 700–1050MHz unless validated per application-specific testing.

What is the role of the exposed thermal pad (Pin 17) on the LT5568-2EUF#TRPBF package?

The exposed thermal pad (Pin 17) on the LT5568-2EUF#TRPBF is electrically connected to ground and serves dual purposes: it provides critical RF grounding for all internal GND pins (2,4,6,9,10,12,15) and acts as the primary thermal dissipation path. Per Linear Technology's layout guidelines, this pad must be soldered to a large PCB copper pour with multiple thermal vias to minimize θJA (37°C/W) and prevent junction temperature exceedance during continuous 117mA operation.