Analog Devices Inc. DC678A

Overview

DC678A from Analog Devices (formerly Linear Technology) is a fully populated evaluation board for the LT5517 40MHz–900MHz high-linearity quadrature demodulator IC. It implements a transformer-coupled RF input, 2XLO interface with DC blocking, and differential I/Q baseband outputs with on-board decoupling and termination options. Designed for wireless infrastructure receiver validation, it supports direct-conversion receiver characterization at 800MHz with measured IIP3 = 21dBm and NF = 12.4dB.

For engineers reviewing the DC678A datasheet, DC678A pinout, DC678A application, or DC678A equivalent, this page delivers verified board-level specifications, layout-validated RF performance data, supply sequencing guidance, thermal management notes for continuous operation, and interoperability details with common signal generators and baseband ADCs.

Technical Context

The DC678A implements the reference design from LT5517 datasheet Figure 2, using a M/A-COM MABAES0054 1:4 broadband transformer for 50Ω RF input matching across 40–900MHz. It routes all LT5517 pins-including EN, VCC (pins 6/7/8/12), GNDRF (pins 1/4), and exposed pad (pin 17)-to accessible test points and edge-mount SMA connectors.

Baseband outputs (IOUT±, QOUT±) are brought out to SMA jacks with optional 10pF shunt capacitors (C13–C16) for harmonic filtering, while the 2XLO input (pin 10) includes a 1nF DC-blocking capacitor (C5) and series resistor (R2) for level adjustment. Power delivery uses parallel 0.1µF and 2.2µF ceramic capacitors per VCC net.

Key Specifications

Availability

DC678A is available at Aetrix Electronics and suitable for wireless infrastructure receiver development, high-linearity I/Q demodulator validation, and 450MHz/800MHz/900MHz base station front-end prototyping requiring stable component supply and traceable evaluation hardware.

Supply support for DC678A 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 for precision signal processing applications.

The DC678A belongs to Analog Devices' Linear Technology evaluation board portfolio, engineered specifically to accelerate RF receiver design verification for high-dynamic-range communications infrastructure equipment.

FAQ

What is the primary function of the DC678A evaluation board?

The DC678A evaluation board is a fully assembled and tested platform for characterizing the LT5517 quadrature demodulator IC. It provides validated RF input matching, 2XLO interface conditioning, differential I/Q baseband output access, and power delivery-enabling immediate measurement of conversion gain, noise figure, IIP2/IIP3, and I/Q mismatch without custom PCB design. The DC678A directly implements the test circuit shown in LT5517 datasheet Figure 2.

Which RF frequency bands does the DC678A support with its transformer-based input?

The DC678A uses a M/A-COM MABAES0054 1:4 broadband transformer that maintains impedance match and phase balance from 40MHz to 900MHz. This allows the DC678A to validate LT5517 performance across key wireless infrastructure bands including 450MHz TDD-LTE, 700MHz FDD-LTE, 800MHz GSM/UMTS, and 900MHz PHS-matching the full RF input range specified for the LT5517 IC itself.

How is the 2XLO signal interfaced on the DC678A, and what drive level is required?

The DC678A routes the 2XLO signal to pin 10 of the LT5517 through a 1nF DC-blocking capacitor (C5) and optional 0Ω jumper (R2) for level tuning. It accepts –15dBm to 0dBm 2XLO input power, as confirmed by LT5517 AC electrical specs. The board's 2XLO port achieves >20dB return loss up to 1.8GHz due to internal 50Ω matching-eliminating external matching networks for most signal generator sources.

Can the DC678A be used for production-level testing, or is it strictly for lab evaluation?

The DC678A is qualified for production-level RF testing: its 4-layer PCB includes controlled-impedance traces, solid ground plane coupling to the LT5517's exposed pad, and thermal vias under power pins. It has been used in manufacturing test fixtures for LTE base station receivers where repeatable IIP3 and NF measurements are required. However, long-term continuous operation requires forced-air cooling above 70°C ambient due to 550mW typical dissipation.

Does the DC678A include provisions for enabling or disabling the LT5517 during operation?

Yes-the DC678A brings the LT5517's EN pin (pin 5) to a test point (TP5) and includes a 100kΩ pull-up resistor (R1) to VCC. Applying 0V to TP5 disables the LT5517, reducing supply current to ≤20µA; applying ≥1.6V enables full operation with 200ns turn-on time. This allows dynamic power cycling during automated test sequences without reprogramming host controllers.