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Op amps amplify low-level analog signals simply

Austin, Texas — Cirrus Logic Inc. claims to have simplified the task of amplifying low-level analog signals within scientific and industrial measurement applications with its latest operational amplifiers.

The dual-channel CS3004 and CS3014 and single-channel CS3003 and CS3013 ICs deliver performance that results in dramatically higher accuracy than competing op amps, said John Paulos, vice president and general manager of Cirrus Logic's Industrial Products Division.

The CS3013 and CS3014 also offer low power consumption for battery-powered portable instruments and personal monitoring applications such as gas safety detectors.

“Often within the signal path of many industrial and scientific instrument applications the operational amplifier is what limits the overall performance of the circuit,” Paulos said. “The CS300X family offers a superior combination of high gain and low errors that yields exceptional accuracy, making these integrated circuits ideal for applications performing the highest-precision measurements.”

Applications such as temperature and safety monitoring and industrial process controllers require not only minimal errors due to noise, leakage and drift but also extremely high gain to preserve measurement accuracy, according to Paulos.

The CS300X family is said to fulfill these requirements; with input leakage of 100 picoamps and an input offset voltage of 5 microvolts (CS3003/CS3013; 10 uV in the CS3004/CS3014) with drift of 0.05 uV per degree. Critical noise errors are limited to 17 nanovolts √ Hertz in the CS3003 and CS3004 (22 nV √ Hertz in the CS3013/CS3014), which is held flat above 2-kHz bandwidth.

Accuracy in high-resolution measurement applications is ensured with open-loop gain performance of 150 dB in the CS3003/CS3004, while the low-power CS3013/14 provides 135 dB.

Operating from single or bipolar power supplies of 2.7 volts to 5 V (± 1.35 V to ± 2.5 V), consumption is 1,000 microamps per amplifier in the CS3003/CS3004 and 500 uA each in the CS3013/CS3014. In addition to the small-outline eight-pin SO package, these devices will also be available in the new 4 x 4-mm leadless QFN package.

The dual-amplifier CS3004 and CS3014 are priced at $1.52 in quantities of 1,000-piece quantities. The CS3003 and CS3013, which are both single amplifiers, are scheduled for release in June of 2006 and will be priced at 99 cents each in same quantities. Click here for the CS3004/CS3014 and CS3003/CS3013 data sheets.

Cirrus Logic Inc. , 1-800-625-4084, www.Cirrus.com.

Cirrus is launching this family of op amps with four parts — two single and two dual versions. The op amps are a result of the company's effort to develop amps that can support their own A/D converters, which are the highest resolution, and lowest noise in the industry, according to Rich Wegner, senior marketing manager of Cirrus' industrial product division. “We want the amplifier to contribute as little error as possible — but it has to be able to provide enough gain to preserve measurement accuracy,” he said.

Typically, the A/D converter always performs better than the amplifier so you end up chasing your tail to find an op amp that can maintain the A/D converter's specs, Wegner said. These latest amplifiers originated from the front end of Cirrus' six-year-old CS5532 A/D converter family.

When comparing these devices to competing devices, designers need to look at the whole picture for total accuracy instead of doing a spec to spec comparison, Wegner said. “You need a combination of gain, low voltage noise, and low offset drift to achieve low total error for high resolution A/D converters,” he said. “Otherwise, you'll need additional parts to correct certain parameters,” he added.

Three years ago, Cirrus rolled out its last generation family (CS3001/3002, CS3011/3012) of precision amps. The devices are similar to the new ones with the exception of two key specs — power consumption, which has been lowered significantly from 1,400 microamps to 500 uA, and noise performance, which has increased a bit in the newer family, according to Wegner. “There is a slight tradeoff since we lowered power consumption — noise performance has increased from 11 nV to 17 nV in the newer family. Essentially, noise is up by a factor of two and power consumption is down by a factor of two, which is a reasonable tradeoff in portable applications,” he said.

Although the package size of the new and older op amps is the same right now (SO8), the company plans to roll the devices out in the new leadless QFN package size in June (4 x 4 mm). “This represents a 50 percentage reduction in acreage,” Wegner said.

The diagram below shows typical noise at 17 nV, which is significantly better than what is available in the market today, according to Wegner. “The real significance here is that noise is plotted down to 0.01 Hz, which no competitor wants you to see. A fast Fourier transform (FFT) showing noise this low in frequency requires 17 hours of data collection,” he said.

 
 
See related frequency chart

The teeny tiny input offset voltage is another indicator of how well behaved these op amps are, Wegner said. A histogram of offset voltage to 3.2 Hz shows impressive stability over an hour. “In other words, this error voltage stays very close to 25 nV, while similar devices might be all over the map. This is a very stable part,” he said.

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