会社ブログについて ADI AD8138 Low-Distortion Differential ADC Driver: 320 MHz Bandwidth, -94 dBc SFDR—A Key Component in High-Speed Signal Chains

In the design of high-speed data acquisition and communication systems, the performance of the differential signal processing stage often directly determines the upper limit of the entire signal chain. As ADC sampling rates and resolutions continue to increase, if the differential amplifier driving the ADC has insufficient rise time or high distortion, even the highest-spec converters will struggle to deliver their rated performance. ADI’s AD8138 is a low-distortion differential ADC driver specifically designed to address this challenge. With a 320 MHz bandwidth and excellent harmonic distortion performance, it has become a highly competitive component in mid- to high-end signal chains.

Product Overview

The AD8138 is manufactured using ADI’s proprietary XFCB bipolar process, achieving significant advancements in differential signal processing compared to traditional operational amplifiers. It can function as either a single-ended-to-differential amplifier or be configured as a differential-to-differential amplifier, offering the same ease of use as a standard op-amp and greatly simplifying the design of differential signal amplification and driving circuits. Its unique internal feedback structure provides balanced output gain and phase matching, thereby suppressing even-order harmonics and minimizing gain errors caused by mismatches in external gain-setting resistors.

Key Specifications

The core specifications of the AD8138 at 25°C, with a ±5 V supply voltage and G = +1 are as follows:

−3 dB bandwidth: 320 MHz (G = +1)

Slew rate: 1150 V/μs (typical)

0.01% settling time: 16 ns

Overshoot recovery time: 4 ns

SFDR (5 MHz): −94 dBc

SFDR (20 MHz): −85 dBc

Input Voltage Noise: 5 nV/√Hz

Offset Voltage: 1 mV (typical)

Common-Mode Rejection Ratio (CMRR): 77 dB

Supply Voltage Range: +3 V to ±5 V

Power Dissipation at 5 V: 90 mW

0.1 dB gain flatness: up to 40 MHz

Operating temperature range: −40°C to +85°C

Package: 8-pin SOIC / MSOP

The common-mode level of the differential output can be independently adjusted via the VOCM pin, making level conversion simple and straightforward when driving a single-supply ADC.

Key Features

A combination of low distortion and high bandwidth. With an SFDR of −94 dBc at 5 MHz and −85 dBc at 20 MHz, the AD8138 is capable of driving 10- to 16-bit high-speed ADCs under high-frequency conditions, helping to preserve signal integrity in communication receive chains. A 320 MHz bandwidth and a slew rate of 1150 V/μs ensure that the driver’s own response speed does not become a bottleneck for the ADC’s sampling accuracy.

Transformer-less, DC-coupled differential drive. In traditional solutions, single-ended-to-differential conversion often relies on transformers, but transformers cannot pass low-frequency and DC components. The AD8138’s differential output can directly balance the inputs of a differential ADC, eliminating the need for a transformer stage. This preserves the full low-frequency and DC components, enabling a true DC-coupled signal chain.

Easy-to-use architecture. The external gain is adjustable, and the VOCM pin provides independent control of the output common-mode voltage, allowing a single device to flexibly adapt to the input common-mode requirements of different ADCs and reducing the complexity of signal chain design.

Typical Applications

The AD8138 is specifically designed for signal chain stages requiring differential drive, with primary applications covering the following areas:

Differential ADC drivers. This is its core application. Successive Approximation Register (SAR) ADCs and pipelined ADCs can only achieve their full performance potential with differential drive. The AD8138 precisely balances the ADC inputs, eliminating the need for transformers while preserving DC information. ADI’s application notes include a complete solution using the AD8138 in conjunction with the 14-bit, 4.2 MSPS SAR ADC (AD7357) to achieve a DC-coupled single-ended-to-differential conversion. Its 16 ns settling time meets the fast response requirements of high-speed sampling.

Single-ended-to-differential converters. Sensor signal conditioning and receiver front ends typically output single-ended signals, while ADCs require differential inputs. The AD8138 can losslessly convert single-ended signals into high-quality differential signals and provides common-mode level shifting.

Intermediate Frequency (IF) and Baseband Gain Modules. With its high bandwidth and third-order intermodulation point (IP3) characteristics, the AD8138 is well-suited for gain amplification and signal conditioning tasks in intermediate frequency (IF) and baseband signal chains, making it ideal for communication receivers, software-defined radio, and radar signal processing systems.

Differential Buffers and Line Drivers. In applications requiring differential signal transmission or driving differential loads in subsequent stages, the AD8138 can function as a buffer or line driver, providing sufficient drive capability while maintaining signal quality.

Furthermore, its offset and dynamic performance make it suitable for data acquisition systems with stringent accuracy and distortion requirements, such as industrial automation test equipment, medical imaging front-ends, and ultrasound signal acquisition.

Availability Information

Shenzhen Mingjiada Electronics Co., Ltd. consistently supplies the full range of AD8138 models, covering SOIC-8 and MSOP-8 packages, and supports the supply of AD8138-EP enhanced products (meeting AQEC standards for defense and aerospace applications). Founded in 1996, Mingjiada is a professional, authorized independent distributor of electronic components. The company is ISO 9001 certified and maintains a well-established distribution network and inventory system for the full range of ADI products. The standard AD8138 model, AD8138ARMZ, and its tape-and-reel formats are available, supporting flexible procurement from R&D samples to mass production. To request samples or receive bulk quotes for the AD8138, please submit an inquiry through Mingjiada Electronics’ official channels.

Contact Information: Mobile +86 13410018555; Email sales@hkmjd.com; Website www.integrated-ic.com.

Tags: AD8138ARMZ, AD8138ARM, AD8138AR, AD8138A, AD8138