Analog Devices Inc. LT5568-2EUF#PBF

Overview

LT5568-2EUF#PBF from Analog Devices (formerly Linear Technology) is a high-linearity direct-conversion 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 baseband upconversion.

For engineers reviewing the LT5568-2EUF#PBF datasheet, LT5568-2EUF#PBF pinout, LT5568-2EUF#PBF application, or LT5568-2EUF#PBF equivalent, key selection criteria include RF output linearity (OIP3/OIP2), image rejection stability across frequency, LO feedthrough suppression, baseband common-mode voltage tolerance (0.54V), and QFN-16 thermal performance with exposed pad grounding.

Technical Context

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

It operates with 4.5V–5.25V supply, draws 80–165mA active current, features EN-controlled shutdown (50μA), and maintains <0.45° I/Q phase imbalance and <0.07dB gain imbalance across 700–1050MHz - critical for maintaining EVM in multi-carrier CDMA2000 and W-CDMA systems.

Key Specifications

Pinout & Package

LT5568-2EUF#PBF is housed in a 16-lead 4mm × 4mm plastic QFN package with exposed thermal pad (Pin 17), requiring soldering to PCB ground plane for RF performance and thermal management.

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 TRF372017IRGZT, the LT5568-2EUF#PBF offers superior image rejection (–46dBc vs –38dBc/–40dBc) and lower noise floor in its native 700–1050MHz band, making it optimal for high-density cellular infrastructure where spectral purity is non-negotiable.

Availability

LT5568-2EUF#PBF is available at Aetrix Electronics and suitable for cellular infrastructure transmitters, CDMA2000 base stations, and W-CDMA Node B equipment requiring stable component supply, long-term lifecycle support, and traceable sourcing for Class B RF applications.

Supply support for LT5568-2EUF#PBF 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. (ADI) is a global leader in high-performance analog, mixed-signal, and RF ICs, formed through the acquisition of Linear Technology in 2017.

The LT5568-2EUF#PBF belongs to ADI's high-linearity RF modulator product line, engineered specifically for cellular infrastructure transmitters demanding ultra-low distortion, precise I/Q balance, and robust thermal performance in continuous-duty base station environments.

FAQ

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

The LT5568-2EUF#PBF achieves best linearity and noise performance at 0dBm LO input power. At –5dBm, image rejection improves slightly but noise floor degrades by 1.5dB at POUT = 4dBm; at +5dBm, LO feedthrough increases with no OIP3 gain. The datasheet specifies –10dBm to +5dBm operational range, with 0dBm as the design center point for LT5568-2EUF#PBF.

How does the LT5568-2EUF#PBF handle baseband common-mode voltage, and why is it critical?

The LT5568-2EUF#PBF internally biases all four baseband inputs (BBPI/BBMI/BBPQ/BBMQ) to 0.54V DC. Driving these pins with mismatched common-mode voltage causes severe even-order distortion and degraded OIP2. DAC sources must be configured for 0.27V common-mode if using standard 50Ω source termination, because the LT5568-2EUF#PBF's internal bias forms a 2:1 voltage divider - correct biasing is essential for achieving the specified –46dBc image rejection and +22.9dBm OIP3.

Can the LT5568-2EUF#PBF be used as an image-reject upconverting mixer, and what configuration is required?

Yes, the LT5568-2EUF#PBF can operate as an image-reject upconverting mixer by applying 90° phase-shifted signals to the I and Q baseband inputs instead of differential I/Q data. This exploits the same quadrature architecture used in direct modulation mode. The internal LO quadrature generator remains active, and the RF output contains only the desired sideband - confirmed by –46dBc image rejection at 850MHz. No hardware reconfiguration is needed; only the baseband signal phasing changes.

What is the role of the exposed thermal pad (Pin 17) on the LT5568-2EUF#PBF, and how must it be implemented?

The exposed pad (Pin 17) on the LT5568-2EUF#PBF serves as both primary thermal dissipation path and RF ground reference for the on-chip balun. It must be soldered to a solid copper ground plane using ≥6 thermal vias (0.3mm diameter) spaced ≤2mm apart. Inadequate pad connection degrades RF output return loss (S22), increases junction temperature beyond 125°C max, and reduces image rejection by up to 8dB - all verified in LT5568-2EUF#PBF evaluation board testing (DC966A).

Does the LT5568-2EUF#PBF support DC-coupled baseband inputs, and what are the design implications?

Yes, the LT5568-2EUF#PBF supports true DC-coupled baseband inputs with 50Ω single-ended impedance and 0.54V internal common-mode bias. This eliminates AC coupling capacitors and level-shifting circuitry, reducing component count and phase skew. However, DAC output common-mode must be precisely set (0.27V for 50Ω sources) to avoid I/Q imbalance; any DC offset >±20mV degrades image rejection below –40dBc - a critical constraint explicitly validated in LT5568-2EUF#PBF characterization data.