Analog Devices Inc. LTC6948IUFD-1#PBF

Overview

LTC6948IUFD-1#PBF from Analog Devices is an ultralow-noise fractional-N PLL synthesizer with integrated VCO, operating from 0.373GHz to 3.74GHz (O_DIV = 6 to 1). It features a 4th-order ΔΣ modulator, –226 dBc/Hz normalized in-band phase noise floor, 18-bit fractional denominator, and supports reference inputs up to 425MHz. It is used in high-performance wireless basestations for LTE and W-CDMA local oscillator generation.

For engineers reviewing the LTC6948IUFD-1#PBF datasheet, LTC6948IUFD-1#PBF pinout, LTC6948IUFD-1#PBF application, or LTC6948IUFD-1#PBF equivalent, key selection criteria include output frequency range coverage (0.373–3.74GHz), integrated VCO tuning sensitivity (4.7–7.2 %/V), RF output power programmability (–9 to +3 dBm), and fast frequency switching with <20 µs calibration time for 126MHz steps.

Technical Context

The LTC6948IUFD-1#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 (Numerator = 1–262143), and programmable VCO output divider (O = 1–6). Its VCO core covers 2.24–3.74 GHz, extended downward via integer division.

It supports SPI-based configuration with status reporting via STAT pin, RF output muting with 110 ns enable time, and dual-supply operation: 3.3V for digital/RF sections (VD+, VREF+, VRF+) and 5V for VCO/charge pump (VVCO+, VCP+). The device operates across –40°C to +105°C junction temperature.

Key Specifications

Pinout & Package

Package: 28-lead (4 mm × 5 mm) plastic QFN (UFD), exposed pad (Pin 29) soldered to PCB ground plane for thermal and electrical integrity. Operating junction temperature: –40°C to +105°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with HMC830LP6GE and ADF4371BCPZ, the LTC6948IUFD-1#PBF delivers the lowest normalized in-band phase noise floor (–226 dBc/Hz) and fastest verified frequency step response (<20 µs), making it optimal for high-order QAM wireless infrastructure where spectral purity and agility are primary constraints.

Availability

LTC6948IUFD-1#PBF is available at Aetrix Electronics and suitable for wireless basestation LO generation, microwave data link transceivers, military secure radio, and test & measurement signal sources requiring stable component supply across industrial temperature ranges.

Supply support for LTC6948IUFD-1#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. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving communications, industrial, automotive, and instrumentation markets.

The LTC6948 product line delivers ultralow-noise, wideband fractional-N synthesizers with integrated VCOs for demanding RF applications including 4G/5G infrastructure, defense EW systems, and precision test equipment.

FAQ

What is the output frequency range of the LTC6948IUFD-1#PBF?

The LTC6948IUFD-1#PBF provides an output frequency range of 0.373 GHz to 3.74 GHz, achieved via its integrated VCO (2.24–3.74 GHz) and programmable output divider (O_DIV = 1 to 6). This range is specific to the -1 variant and confirmed in the "Output Frequency Range vs Output Divider Setting" table. The device maintains 50% duty cycle across all divider settings, supporting direct interface to balanced mixers.

How does the LTC6948IUFD-1#PBF achieve ultralow phase noise performance?

The LTC6948IUFD-1#PBF achieves ultralow phase noise through a combination of architectural features: a 4th-order ΔΣ modulator that suppresses fractional spurs, an optimized VCO core with –157 dBc/Hz wideband output phase noise floor, and a –226 dBc/Hz normalized in-band phase noise floor. These values are measured under specified conditions (e.g., INTN = 1, ICP = 5.6 mA) and validated per Analog Devices' characterization data in the LTC6948 datasheet Rev. FA.

What are the supply voltage requirements for the LTC6948IUFD-1#PBF?

The LTC6948IUFD-1#PBF requires three distinct supply domains: 3.15–3.45 V for VD+, VREF+, and VRF+ (digital, reference, and RF buffers); 4.75–5.25 V for VVCO+ (VCO core); and 4.0–5.25 V for VCP+ (charge pump). Each supply must be bypassed per datasheet recommendations-e.g., 0.1 µF ceramic for VD+/VCP+, 0.01 µF for VRF+, and 1 µF for VVCO+-to ensure stable operation and phase noise performance.

Can the LTC6948IUFD-1#PBF be used with a single-ended reference input?

Yes, the LTC6948IUFD-1#PBF supports single-ended reference inputs on REF+ (Pin 1) with REF– (Pin 28) bypassed to GND. For signals ≤2.7 VP-P, use a 1 µF AC-coupling capacitor; for >2.7 VP-P, use a 47 pF capacitor. The internal self-bias circuitry sets the common-mode voltage to ~1.85 V, and input resistance is 5.8–11.6 kΩ differential, ensuring compatibility with standard CMOS or clipped sine wave references.

What is the purpose of the MUTE pin on the LTC6948IUFD-1#PBF?

The MUTE pin (Pin 9) is an active-low CMOS input that disables the RF+ and RF– differential outputs while preserving internal VCO and PLL bias states. When asserted, RF output power drops to –80 dBm; deassertion restores full output within 170 ns. This enables fast TDD switching in FDD/TDD basestation architectures without requiring full PLL relock or VCO recalibration.