Analog Devices Inc. (NYSE: ADI), a global leader in high-performance semiconductors for signal processing applications and market leader in amplifier ICs, continued its long history of meeting the design needs of industrial and instrumentation equipment customers with the introduction of a zero-drift, programmable-gain instrumentation amplifier (in-amp). Zero-drift in-amps are often used in harsh industrial environments such as power plants to cancel, or reject, large common-mode voltages that would otherwise drown out smaller system-critical signals.
The AD8231 zero-drift in-amp is designed for industrial sensors, where, despite the presence of “noise” resulting from much larger background voltages, signals generated by resistance temperature detectors, thermocouplers, automotive pressure sensors and other devices must be measured precisely. Featuring software gain-programmability and 80 percent lower input noise than competing devices, the AD8231 enables designers of industrial sensors to maintain dc precision while easily adjusting gain values. The new in-amp also offers rail-to-rail inputs and outputs at up to 1-MHz bandwidth—five times the throughput of the nearest competing zero-drift in-amp. The AD8231 is the only zero-drift in-amp to integrate an uncommitted op-amp, which eases system design and reduces cost and board space requirements by at least 50 percent.
“Zero-drift instrumentation amplifiers can have high noise at high gains for a variety of reasons, including the presence of chopping noise,” said Steve Sockolov, product line director, Precision Signal Processing, Analog Devices. “However, the trade-off between offset drift and noise becomes untenable as the gain increases to the level demanded by today’s industrial equipment manufacturers. Analog Devices addressed this challenge using a proprietary auto-zero technique that dramatically lowers the in-amp’s noise profile while eliminating the need for external components, such as switched capacitors.”
Rugged Design Is Ideal for Demanding Industrial Applications
Using a three-operational amplifier (op-amp) instrumentation architecture, the AD8231 enhances reliability by integrating auto-zero amplifiers to maintain a voltage offset of only 50 nV/° C across temperature and over years of operation. The AD8231 also features internal gain-setting resistors, which limit gain coefficient temperature drift to 10 ppm/° C. The device’s LFCSP (lead-frame chip-scale package) material was chosen for its reliability and robustness over temperature, which results in a part that is specified for the extended industrial temperature range of –40° C to 125° C. The package comes with a center paddle, which keeps the part securely soldered to the printed-circuit board in high-vibration environments.
Software Programmability Makes Gain Adjustment Easy
The AD8231 features software programmable gains of 1, 2, 4, 8, 16, 32, 64, or 128, which are programmed through an easy-to-use three-pin interface. The gain can be set using digital logic, which allows users to repeatedly adjust gain once the in-amp has been designed into the system. A pin-strapping gain setting option is also included. The new device operates on a single supply from 3.3 V to 5 V and has rail-to-rail outputs, making it easy to interface to an analog-to-digital converter (ADC). The AD8231 has high impedance inputs of 10 gigaohms, and unlike competing parts, does not suffer performance degradation when using higher impedance sensors.
Flexibility of Design Yields Cost, Space Savings
The AD8231 includes an additional on-chip op-amp, which further extends performance. The op-amp can be used to create a differential output to drive today’s high performance ADCs, or to add or customize gains. The integrated op-amp also provides a tool for additional error correction, level shifting, or filtering. Using the same low-noise auto-zero techniques as the in-amp, the on-chip op-amp also has rail-to-rail inputs and outputs. The ability of the AD8231 to eliminate noise-prone discrete components, such as switched capacitors, combined with the added on-chip signal conditioning of the integrated op-amp, cuts cost by 60 percent and reduces board space requirements by 50 percent compared to other zero-drift in-amps.
Manufactured using Analog Devices’ highly efficient iCMOS(TM) (industrial CMOS) process technology, the AD8231 achieves a noise level of 32 nV/rt-Hz, five times lower than competitive zero-drift in-amps. The AD8231 also features 122-dB CMR (common-mode rejection), allowing the in-amp to detect very low-amplitude signals in noisy environments.
Compatible with High-Performance ADCs
Ideally suited for industrial controls and sensors requiring a single 3.3-V to 5-V power supply, ADI’s new single-supply in-amp easily interfaces to ADCs and microcontrollers by using the same power supply as digital components. The AD8231 is designed to work well with Analog Devices’ data converters (including the AD7942, AD7685 and AD7980 PulSAR(R) ADCs), the ADuC702x family of precision analog microcontrollers and ADI’s ADR121, ADR43x and ADR44x voltage reference.
Pricing and Availability
The AD8231 zero-drift, digitally-programmable, gain in-amp is sampling now in a 16-lead LFCSP package with production quantities available in April 2007. The AD8231 is priced at $1.69 in 1,000-unit quantities.
Analog Devices in Industrial
Analog Devices has a more than 40-year heritage of working in concert with its industrial customers to define, develop and deploy complete signal chain solutions that are optimized for their applications. ADI’s legacy of supporting the sector’s long product life cycles with multi-year manufacturing commitments is augmented by the company’s educated sales force, knowledgeable field applications engineers and advanced design support tools that include evaluation boards and SPICE models.
About Analog Devices
Innovation, performance, and excellence are the cultural pillars on which Analog Devices has built one of the most long-standing, high-growth companies within the technology sector. Acknowledged industry-wide as the world leader in data conversion and signal conditioning technology, Analog Devices serves over 60,000 customers around the world, representing virtually all types of electronics equipment. Celebrating more than 40 years as a leading global manufacturer of high-performance integrated circuits used in analog and digital signal processing applications, Analog Devices, Inc. is headquartered in Norwood, Massachusetts, and employs approximately 8,900 people worldwide. It has manufacturing facilities in Massachusetts, California, North Carolina, Ireland, and the Philippines. Analog Devices’ common stock is listed on the New York Stock Exchange and ADI is included in the S&P 500 Index.
iCMOS is a trademark and PulSAR is a registered trademark of Analog Devices, Inc.