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National navigates upstream into precision op amps

Posted: 12 Jan 2005 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? operational amplifier. op amp? lmp? linear technology? maxim integrated products?

National Semiconductor Corp. will announce a series of operational amplifiers in a bid to position itself more completely within the precision-amp market. The LMP parts have controlled offsets and gain specifications over automotive and industrial temperature ranges, National said. Though premium-priced, the op amps are intended to compete with precision offerings from such competitors as Linear Technology, Maxim Integrated Products, Texas Instruments and Analog Devices.

The products, which depend on BiCMOS manufacturing controls as well as extended-temperature testing and a die sort from the wafer, target high-precision applications that require devices with carefully controlled gain and offset values.

The input offset voltage (Vos) of an op ampa measure of how faithfully a precision amplifier can capture a low-level signalhas shifted from 1mV to hundreds of microvolts over the years, thanks to improvements in process technology, said Carlos Sanchez, marketing manager for National's amplifier group. (The lower the Vos, the more precise the part is considered.)

"These days, tens of microvolts is almost standard," Sanchez said. "The trick is to guarantee this over temperature."

National's introductions include the LMP2011, -12 and -14 amplifiers, with ultralow (60?V) offset and zero drift from -40C to 125C, and the LMP8270, -71 and -72 high-common-mode, voltage-difference amps.

Manufacturers of test-and-measurement instruments have been the typical users of such amps, said National senior design manager Huibert Verhoeven. But automotive engine controls are increasingly using precision amps to measure and control emissions, and consumer handhelds are using them as regulators (error amps) for sub-1V supplies, he said.

These new drivers could push the precision-amp market to $1 billion by 2009, according to analog-industry tracker DataBeans Inc.

National has previously offered precision op amps: Its LMC2001, for example, has an input offset guaranteed not to drift more than 5?V over a 10-year period. But with generic parts dominating amplifier shipments, the company has been best-known for commodity parts. The LMP introductions position National in the higher-priced arena now dominated by the likes of Linear Technology Corp.

National ships more than 500 million amplifiers per year, Sanchez said. Through October, he said, the company grew its amplifier business 24.7 percent, double the industry's rate. The company's amplifier group now comprises two segments: one covering multimarket building blocks and the other application-specific standard products for targeted markets. The former includes high-speed amps, low-power and low-voltage products, and the precision line. The ASSP segment includes products for displays, cellular handsets and optical comms.

Stringent screening

Supporting the precision-amp effort will require that every part be tested and screened over temperature; as a result, guaranteeing performance over temperature will add to the amplifiers' costs. But to keep the costs of test from making the parts inaccessible, the tested parts will not be run through hot-and-cold cycles. Rather, Sanchez said, they will be tested at three temperatures: 25C (the likely ambient), -40C and 85C. National experts would then use carefully calibrated process models and statistics to fill in the area under the temperature curves that are not specifically tested.

"Testing is not cheap for anybody," Sanchez acknowledged. While a general-purpose op amp sells for 20 cents in volume, the LMP parts will likely be priced at more than $1-especially if the buyer wants precision thin-film resistors on-chip. Still, National is confident it can compete.

In addition to its guaranteed low (60&microV) Vos, the LMP2011 has no 1/f noise, a high common-mode rejection ratio (130 dB), a wide gain-bandwidth product (3MHz) and a low supply current (930?A).

The LMP8270 voltage-difference amp extracts its input signal from a -2V to 27V input common-mode source. Its Vos temperature drift is less than 15?V/C, tested over a -40C to 150C range.

- Stephan Ohr

EE Times

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