Analog Devices Inc. DC844D

Overview

DC844D from Analog Devices (formerly Linear Technology) is a demonstration circuit built around the LT5515 1.5–2.5GHz direct-conversion quadrature demodulator, delivering I/Q baseband outputs with 260MHz bandwidth, 20dBm IIP3, and 16.8dB noise figure at 1900MHz-designed for PCS-band receiver evaluation and PA linearization loop applications.

For engineers reviewing the DC844D datasheet, DC844D pinout, DC844D application, or DC844D equivalent, this page provides verified performance data, frequency-band optimization details (1.7–2.2GHz), supply current behavior under EN control, output impedance (120Ω differential), and design guidance for external matching transformers outside the native band.

Technical Context

The DC844D implements a fully populated RF front-end for the LT5515 IC, featuring optimized 1.7–2.2GHz balun-based RF and LO interfaces, differential I/Q baseband outputs with shunt capacitor filtering provisions, and EN-controlled power sequencing (125mA active / 20µA shutdown). It operates with ±0.3dB gain mismatch and ±1° phase mismatch across 1MHz baseband signals.

Its architecture eliminates IF stages by enabling direct RF-to-baseband conversion, supporting channel-select filtering at baseband outputs and reducing system-level image/IF filtering requirements-critical for compact, high-dynamic-range wireless receivers in PCS and LTE infrastructure.

Key Specifications

Availability

DC844D is available at Aetrix Electronics and suitable for RF receiver evaluation, PA linearization loop prototyping, and 1900MHz PCS-band transceiver development requiring stable component supply and traceable reference design validation.

Supply support for DC844D 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 acquired Linear Technology in 2017 and maintains full technical and manufacturing continuity for legacy LTC/LT products including the DC844D platform.

The DC844D belongs to Linear's demonstration circuit family targeting RF signal chain validation; it was designed to accelerate adoption of the LT5515 in high-linearity, direct-conversion receiver architectures for cellular infrastructure and test equipment.

FAQ

What is the primary function of the DC844D demonstration circuit?

The DC844D demonstration circuit implements a complete 1.7–2.2GHz RF front-end for the LT5515 quadrature demodulator, enabling direct RF-to-I/Q baseband conversion without intermediate frequency stages. It serves as a validated hardware reference for evaluating receiver linearity, image rejection, and baseband interface compatibility in PCS-band systems. The DC844D includes matched transformers, biasing, and filtering to reflect real-world deployment conditions for the DC844D.

Does the DC844D require external power regulation or level-shifting?

No-the DC844D accepts a single 5V DC supply (current-limited to 170mA per quick-start guide) and uses internal bias networks compatible with standard 5V logic for the EN pin. No external LDOs, level shifters, or voltage translators are needed to operate the DC844D in its specified configuration.

Can the DC844D be used outside the 1.7–2.2GHz range?

Yes-but only with external RF and LO matching transformers designed for the target frequency. The onboard transformers limit optimal performance to 1.7–2.2GHz; operation outside that band requires replacing those components to maintain impedance match, LO-RF isolation (>46dB), and conversion gain stability. The DC844D documentation explicitly states this requirement.

How is baseband output filtering implemented on the DC844D?

The DC844D provides solder pads for shunt capacitors at each differential I and Q output to suppress high-frequency mixing products. Capacitor values must be optimized per operating frequency-larger values improve harmonic suppression but reduce usable baseband bandwidth below the native 260MHz. This filtering method avoids active components while preserving LT5515 linearity. The DC844D schematic confirms these provisions.

Is the DC844D pin-compatible with other Linear demo boards like DC844B or DC844C?

No-DC844D is not pin-compatible with earlier variants such as DC844B or DC844C. Each revision targets different demodulator ICs (e.g., LT5515 vs. LT5516) and features distinct RF/LO transformer layouts, power routing, and baseband termination schemes. Interchangeability is not supported; the DC844D must be used as a standalone evaluation platform per its documented setup procedure.