Analog Devices Inc. LT5568EUF#PBF

Overview

LT5568EUF#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 CDMA2000, W-CDMA, LTE, and TD-SCDMA baseband upconversion.

For engineers reviewing the LT5568EUF#PBF datasheet, LT5568EUF#PBF pinout, LT5568EUF#PBF application, or LT5568EUF#PBF equivalent, key selection criteria include RF output linearity (OIP3/OIP2), image/carrier suppression, baseband interface common-mode voltage (0.54V), LO input power sensitivity (0dBm typical), and thermal performance in 4mm × 4mm QFN packages for dense RF front-end layouts.

Technical Context

The LT5568EUF#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 LO buffer. Its architecture enables true direct-conversion modulation without external image-reject filtering.

Baseband inputs are DC-coupled with 50Ω single-ended impedance and fixed 0.54V common-mode bias; the LO path accepts –10dBm to +5dBm at 50Ω, while RF output is AC-coupled 50Ω single-ended. Enable control (EN) provides 0.3μs turn-on and 1.4μs turn-off with 50μA sleep current.

Key Specifications

Pinout & Package

The LT5568EUF#PBF is housed in a 16-lead 4mm × 4mm plastic QFN package (UF) with exposed pad (Pin 17) that must be soldered to PCB ground for optimal 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 TRF3705IRGZT, the LT5568EUF#PBF offers superior integration (on-chip LO quadrature + balun) and optimized linearity/noise for 700–1050MHz cellular infrastructure, trading off frequency flexibility for reduced bill-of-materials and improved phase accuracy.

Availability

LT5568EUF#PBF is available at Aetrix Electronics and suitable for cellular base station transmitters, CDMA2000 multi-carrier test equipment, and RFID reader front-ends requiring stable component supply, high-volume manufacturability, and long-term lifecycle support.

Supply support for LT5568EUF#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. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and RF ICs, serving communications, industrial, automotive, and healthcare markets with precision signal processing solutions.

The LT5568EUF#PBF belongs to Linear's high-linearity RF modulator product line, designed specifically for cellular infrastructure transmitters demanding exceptional image/carrier suppression, wide dynamic range, and compact integration in macro/micro base stations.

FAQ

What is the recommended LO input power for optimal performance of the LT5568EUF#PBF?

The LT5568EUF#PBF achieves best linearity (OIP3), noise floor, and gain 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. The datasheet specifies –10dBm to +5dBm operational range.

How does the LT5568EUF#PBF handle baseband input common-mode voltage?

The LT5568EUF#PBF internally biases all four baseband inputs (BBPI, BBMI, BBPQ, BBMQ) to 0.54V DC, requiring external sources to match this level. For DACs with adjustable common-mode output, set to 0.27V (due to internal voltage division); mismatch causes increased LO feedthrough and degraded OIP2. This 0.54V bias is stable over –40°C to 85°C.

Can the LT5568EUF#PBF be used as an image-reject upconverting mixer?

Yes - the LT5568EUF#PBF can be configured as an image-reject upconverting mixer by applying 90° phase-shifted signals to the I and Q inputs instead of differential baseband. This leverages its internal quadrature LO path and balanced mixer topology to suppress the unwanted sideband, achieving –46dBc image rejection at 850MHz without external filtering.

What is the purpose of the exposed pad (Pin 17) on the LT5568EUF#PBF package?

The exposed pad (Pin 17) on the LT5568EUF#PBF is internally connected to all ground pins and serves dual functions: (1) low-inductance RF grounding critical for minimizing LO/RF port return loss degradation, and (2) thermal dissipation path achieving θJA = 37°C/W. It must be soldered to a solid PCB ground plane; floating or undersized connections severely degrade RF performance and thermal reliability.

Does the LT5568EUF#PBF support DC-coupled baseband inputs?

Yes - the LT5568EUF#PBF features true DC-coupled baseband inputs with 50Ω single-ended impedance and fixed 0.54V internal common-mode bias. This allows direct connection to current-output DACs without AC-coupling capacitors, enabling precise control of DC offset to minimize LO feedthrough and optimize OIP2 performance in static or low-frequency I/Q applications.