Analog Devices Inc. LTC6948IUFD-3#PBF

Overview

LTC6948IUFD-3#PBF from Analog Devices is an ultralow-noise fractional-N PLL synthesizer with integrated VCO, operating from 3.84GHz to 5.79GHz (O_DIV = 1) or 0.64GHz to 1.93GHz (O_DIV = 6), featuring –225 dBc/Hz normalized in-band phase noise floor, 18-bit fractional denominator, and 4th-order ΔΣ modulator for spurious suppression. It serves as the local oscillator core in microwave receivers and wireless basestations.

For engineers reviewing the LTC6948IUFD-3#PBF datasheet, LTC6948IUFD-3#PBF pinout, LTC6948IUFD-3#PBF application, or LTC6948IUFD-3#PBF equivalent, key selection criteria include output frequency coverage (3.84–5.79 GHz), VCO tuning sensitivity (4.0–6.0 %/V), integrated phase noise (0.14° RMS, 100 Hz–40 MHz), RF output power (–2.9 to 3 dBm, programmable), and SPI-controlled divider configuration (R = 1–31, N = 35–1019, O = 1–6).

Technical Context

The LTC6948IUFD-3#PBF implements a fully integrated PLL architecture with reference divider (R = 1–31), phase-frequency detector, ultralow-noise charge pump (ICP = 1–11.2 mA), 4th-order fractional-N ΔΣ modulator (18-bit denominator), and VCO output divider (O = 1–6). Its VCO covers 3.84–5.79 GHz, enabling direct synthesis of LTE/WiMAX/PCS bands without external multipliers.

It supports fast frequency switching via SPI interface (SCLK ≥ 25 ns high/low time), includes RF output muting (<170 ns disable time), and integrates LDO regulation for the ΔΣ modulator (selectable 1.7–2.6 V). The device operates across –40°C to +105°C junction temperature with three independent supply domains: 3.3 V (digital/RF/ref), 5 V (VCO/charge pump), and configurable LDO voltage.

Key Specifications

Pinout & Package

28-lead (4 mm × 5 mm) plastic QFN (UFD package) with exposed thermal pad (Pin 29 = GND). Requires soldering of exposed pad to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fractional-N PLL synthesizer applications.

Compared with HMC703LP4E and ADF4372BCPZ, the LTC6948IUFD-3#PBF offers the widest native output range (3.84–5.79 GHz) among its variant group, best-in-class 1/f noise (–274 dBc/Hz), and fastest RF mute disable time (170 ns), making it optimal for TDD wireless infrastructure where spectral purity, agility, and reliability are co-prioritized.

Availability

LTC6948IUFD-3#PBF is available at Aetrix Electronics and suitable for wireless basestation transceivers, microwave point-to-point links, military secure radios, and test & measurement instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC6948IUFD-3#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 is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving precision instrumentation, communications, and industrial markets.

The LTC6948 product line delivers ultralow-noise, wideband fractional-N PLL synthesizers with integrated VCOs for demanding RF signal generation in wireless infrastructure, defense, and test equipment-designed to replace discrete PLL/VCO solutions with superior phase noise, integration, and ease of use.

FAQ

What is the output frequency range of the LTC6948IUFD-3#PBF?

The LTC6948IUFD-3#PBF provides a native VCO frequency range of 3.84 GHz to 5.79 GHz. With its programmable output divider (O_DIV = 1 to 6), the effective RF output frequency extends from 0.64 GHz (3.84 GHz ÷ 6) to 5.79 GHz (O_DIV = 1). This range is specifically optimized for PCS, W-CDMA, and 5 GHz WiMAX bands, and is confirmed in the "Output Frequency Range vs Output Divider Setting" table for the -3 variant.

Does the LTC6948IUFD-3#PBF support SPI communication, and what are the timing requirements?

Yes, the LTC6948IUFD-3#PBF supports full-duplex SPI communication via CS, SCLK, SDI, and SDO pins. Minimum SCLK high/low times are 25 ns each, setup/hold times for SDI relative to SCLK are 6 ns, and CS high time must be ≥10 ns. These specifications ensure reliable register access at up to 20 MHz SCLK rates, enabling fast frequency reconfiguration in TDD systems.

How does the LTC6948IUFD-3#PBF achieve ultralow phase noise performance?

The LTC6948IUFD-3#PBF achieves ultralow phase noise through a combination of architectural features: a 4th-order ΔΣ modulator suppressing fractional spurs, a high-performance integrated VCO with –274 dBc/Hz normalized 1/f noise, and an ultralow-noise charge pump with ±2% current matching. Measured data shows –225 dBc/Hz normalized in-band floor and 0.14° RMS integrated phase noise (100 Hz–40 MHz), directly validated in the Electrical Characteristics table and Typical Performance plots.

What is the purpose of the MUTE pin on the LTC6948IUFD-3#PBF, and how fast does it respond?

The MUTE pin (Pin 9) is an active-low CMOS input that disables the RF± differential outputs while preserving internal VCO and bias circuitry. This enables rapid RF gating without VCO recalibration. The device specifies 110 ns mute enable time and 170 ns mute disable time, verified in the Electrical Characteristics table under "Mute Enable/Disable Time", making it suitable for time-division duplex (TDD) operation in LTE and 5G NR base stations.

What are the supply voltage requirements for the LTC6948IUFD-3#PBF?

The LTC6948IUFD-3#PBF requires three distinct supply domains: VREF+/VD+/VRF+ = 3.15–3.45 V (3.3 V nominal), VVCO+ = 4.75–5.25 V (5 V nominal), and VCP+ = 4.0–5.25 V. The LDO pin supports optional internal regulation (1.7–2.6 V) for the ΔΣ modulator. All supplies must be bypassed per datasheet recommendations (e.g., 0.1 µF ceramic for VD+, 0.01 µF for VRF+), and the exposed pad (Pin 29) must be soldered to GND for thermal and electrical integrity.