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Have your cake and eat it too with these precision amps

Norwood, Mass. — Analog Devices, Inc. (ADI) is introducing a suite of amplifiers designed to meet the demanding signal conditioning requirements of high-voltage industrial and instrumentation equipment.

ADI's AD8677: Tiny version of ADI's popular OP07 op amp

This operational amplifier is one-quarter the size of competitive offerings while providing improved accuracy compared to high-performance, ultra-low-offset-voltage op amps like ADI's own industry-standard OP07. Addressing the needs of applications such as industrial programmable logic controllers (PLCs), automated test equipment (ATE) platforms, and machine monitoring systems, ADI's new manufacturing process (see link below to EET story) enabled a 40 percent power consumption reduction, while maintaining a 75μV (maximum) voltage offset and 1.3μV/°C (maximum) drift. This device is packed into a tiny 3mm x 3mm TSOT-23 package. The increased accuracy, small package size and lower power consumption make the AD8677 suited for precision thermal and current sensing and precision filtering applications that require the high performance of an op amp like the OP07, but also need a reduction in system size.

The AD8677 provides greater accuracy than the OP07. Performance enhancements include higher common-mode rejection ratio (CMRR) of 130dB, an enhanced power supply rejection ratio (PSRR) of 110dB and a wider output swing of ±14 V.

The 1.2-mA power consumption of the AD8677 lowers thermal output relative to competing devices and reduces the need for additional cooling with heat sinks or fans. The new amp's low input bias current of ±2 nA and high open-loop gain further reduce system errors. High open-loop gain insures linearity and gain accuracy over the wide input signal range of ±13 V, even at high closed-loop gains. With very high 80 degree phase margin, AD8677 is extremely tolerant of both parasitic capacitance caused by printed-circuit board layout and external load and filtering capacitances, making it supremely easy to use.

ADI's ADA4004-4: Quietest quad precision amp

The ADA4004-4 is said to be the industry's lowest-noise quad precision amp, dramatically reducing power consumption and package size. The amplifier reduces signal interference and eliminates heat sinks in high-voltage industrial environments by shrinking package size and power consumption.

This device is intended for the demanding requirements of multichannel data acquisition, analytical instruments, automated test equipment and other industrial and medical systems that operate from ±18-V power supplies. ADI's iPolar process enabled the device to reduce power consumption by 50 percent compared with competing devices while fitting into a chip-scale package that is up to 70 percent smaller. The combination of reduced power and size allows the ADA4004-4 to maintain excellent dynamic range without the cooling fans or heat sinks required by other quad low-noise amps, making it ideal for applications that demand high-voltage precision performance at extended industrial temperature ranges.

The ADA4004-4 achieves voltage noise of 2 nV/√ Hz while consuming just 1.7 mA of supply current. Despite the much smaller chip-scale package, the lower power consumption enables the part to operate over the extended industrial temperature range of -40°C to +125°C without de-rating.

ADI's AD8675: 36-V low-noise amp with rail-to-rail output

For industrial applications such as automated test equipment (ATE), analytical instruments and industrial controls that require high signal voltages and low noise, ADI introduced the AD8675, the industry's only 36-V, low-noise precision amplifier with a voltage noise density of 2.5 V/√ Hz and rail-to-rail output. The dual-supply AD8675 is only half the cost of competing amplifiers while reducing power 30 percent, lowering input bias current 75 percent, and providing 65 percent less drift over temperature. The new device also achieves three times the bandwidth and ships in a 3mm x 5mm 8-lead MSOP, just half the size of other amplifiers designed for high-voltage industrial applications, which meets the requirements of industrial systems developers for improved system performance and smaller equipment. By incorporating rail-to-rail output, the AD8675 increases signal-to-noise ratio (SNR) and dynamic range by 30 percent and improves system resolution.

The AD8675 achieves its precision in part due to an offset voltage of 20μV, a drift less that 0.2μV/°C, and noise of only 100 nV peak to peak (from 0.1 Hz to 10 Hz), making it suited for applications where both AC and DC error sources cannot be tolerated. For applications with even lower error tolerances, the AD8675 has a proprietary offset nulling capability that allows a combination of both device and system offset errors up to 1 mV to be compensated externally. Unlike previous nulling schemes, the new technique does not degrade CMRR or offset drift performance of the amplifier.

Pricing and Availability

The AD8677 is sampling now and will be available in production quantities in September. Fully specified to operate over an extended industrial temperature range of “40°C to + 125°C, the device is available in a 5-lead TSOT-23, as well as 8-lead narrow SOIC package.

The AD8677 is priced at 75 cents per unit in 1,000-unit quantities. Click here for the AD8677 data sheet.

The ADA4004-4 is currently sampling and will be available in production quantities in October. The device is available in a 4mm x 4mm 16-lead LFCSP and a 14-lead narrow SOIC package.

Pricing for the ADA4004-4 is $3.04 per unit in 1,000-piece quantities. Click here for the ADA4004-4 data sheet.

The AD8675 is currently sampling and will be available in production quantities in September. Fully specified to operate over a temperature range of -40°C to +125°C, the device is available in an 8-lead MSOP and 8-lead narrow SOIC package.

Pricing for the AD8675 is $1.17 per unit in 1,000-piece quantities. Click here for the AD8675 data sheet.

About Analog Devices' iPolar High-Voltage Trench Isolation Process Technology
The ±18-V iPolar process from ADI improves upon the best characteristics of precision bipolar and JFET processes by using a lateral dielectric isolation technique and completely redesigned transistors that are optimized for speed, noise, matching, linearity and stability.Click here for more information about ADI’s iPolar process in EET.

Analog Devices , 1-800-262-5643, www.analog.com.


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Competitive view of ADI's ADA4004-4

While reviewing these amplifiers, the old adage about having your cake and eating it too came to mind. In many instances, designers are often forced to choose between different electronic specs. If you want fast amplifiers, for example, then be prepared to deal with additional noise. If you want quiet amps, then you will have to use larger package sizes — this is not so with ADI's new amplifiers.

These bipolar amplifier families tout many performance improvements, package and power advantages over amplifiers utilizing other processes, according to Steve Sockolov, ADI's product line director for precision amplifiers in the analog semiconductor components division.

Today ADI is kicking off three new amplifier families with a flagship device from each family, which will be expanding shortly, Sockolov said. The current offering consists of three precision amps — one with rail-to-rail outputs.

The family trio is aimed at signal-conditioning applications. Like many semiconductor makers, the company's roots are entrenched in the industrial and instrumentation markets. Lately, customers in this sector have been complaining that they are being ignored by semiconductor makers in favor of the communications and consumer markets, Sockolov said. These markets are evolving and customers need new products to reflect these changes, he explained.

These amps offer the high-voltage capability for industrial output ranges that customers require today, said Eric Nolan, ADI's product marketing manager for precision amps.

The AD8675 single amp is one of the few 36-V precision amps in the market with rail-to- rail output, Nolan said. Basically, designers have been using the 36-V supply for many years, even though the performance requirements for systems are getting higher and tighter. One way to get better resolution and dynamic range is to make more use of the supply range. “Typically, the output swing for a 36-V amplifier is only in the 20- to 22-V range. With rail-to-rail output, however, you can use the full 30-V supply,” Nolan said. The voltage swings within roughly 100 mV of the rail.

With the majority of precision amps, 36 V seems to be the maximum range that parts are specified at. Typically, they are specified at ±15 V. “The 36-V rating gives you extra headroom over the supply for regulation tolerances — it's a safety margin for operating the parts,” Nolan said.

While there are a few competing devices with rail-to-rail outputs, none offer such low noise characteristics, Nolan said. “There are very few precision 30-V parts with R-R output and only one with input voltage noise that comes close to this part,” he said.

The AD8675 provides 30 percent less noise (2.5 nV/√ Hz) than the closest competing amps — most of which don't have a rail-to-rail output stage, Nolan said. The most similar device offers noise that is just over 3 nV/√ range — but achieving low noise involves other design compromises in speed, bias current, power consumption and package size, Nolan said. “A 1 or 2-nV/√ Hz part on other bipolar processes, for instance, even one that doesn't have rail-to-rail output will have higher input bias current, consume a great deal more power and require a larger package than our device,” he said.

Typically, you have to make input devices quite large or increase power consumption in order to reduce noise. This fact of life generally forces compromises. “The die and package sizes on lower noise parts (under 5nV/√ Hz) are generally much larger, and result in higher power levels and higher input bias currents,” Nolan said.

The AD8675 touts low input bias current at 5 nA maximum for a 2.5 nV/√ Hz amplifier. “It's important to preserve dc accuracy because input bias current leads to input offset errors with unbalanced source impedance,” Nolan said.

Designers aren't forced to choose between lower noise and larger package sizes with ADI's AD8675 because this device combines all of these elements — low noise, low power consumption and tiny packaging with 3x the bandwidth of competing parts, Nolan said.

These days' people are cramming more circuitry onto their boards — adding channels and power consumption is becoming more important. Also, managing the heat generated by these components is difficult, especially when everyone wants smaller boxes at the same time.

Way back when, industrial amps were specified at up to 70°C and typically customers only cared about parts working in the 40°C to 50°C range, Nolan said.

Today, however, temperature requirements have evolved and customers want parts specified to 105° C to 115°C typically. Automotive apps have always demanded higher temperature parts, but this has also become more important in the industrial sector over the past five years, Nolan said.

One of the biggest achievements that ADI has realized with these amplifiers is their tiny package sizes. This AD8675 amplifiers, for instance, come in a MSOP, whereas competitive parts are offering lower performance in a 8-lead SOIC, Nolan said. “That's half the size. If you are using a lot of these parts on one board, this represents a significant savings when you are trying to shrink the size of the board.”

Increasing amounts of electronic circuitry and high-current electrical devices generate more noise and interfere with system accuracy. Many times, filters are used on printed-circuit boards to reduce the effects of these external noise sources, Nolan said. “Putting these capacitive filters around the sensitive inputs of low noise amps to reduce electromagnetic interference (EMI) can be tricky since they can impact the stability of the circuit, often causing oscillation issues,” he said.

A favorite trick of designers to reduce the EMI impact, for instance, is to hang large capacitance on the input of the amplifier across the two input terminals. Doing this works to reduce differential noise but putting the large capacitance on the amplifier input can lead to oscillation in the circuit, Nolan said. “With more than 80 degrees of phase margin, the AD8677 essentially prevents oscillation when using this technique,” he said.

The ADA4004-4 is the lowest noise quad amplifier in the 30-V arena for industrial and instrumentation apps, Nolan said. Usually, four amps generate quite a bit of power internally. At just 2.5 mA per amplifier the internal temperature of a quad amplifier rises by 40 degrees in an SOIC package and many low noise amplifiers consume considerably more current than this. But, the ADA4004-4 generates only 20 to 25 degrees of heat internally, less than 10 degrees in the more thermally efficient LFCSP package — so you can use them over a wider operating temperature range, Nolan said. The 4×4 mm LFCSP package also represents a large reduction in package size, versus competing amplifiers in SOIC packages.

The single version of this device (ADA4004-1), will be offered in a SOT23 package (2.9mm x 3.0mm), compared to the industry standard SOIC-8 package size. Unlike many low noise amplifiers, ADA4004 has high open loop gain (140 dB typical). This is key for precision in the ac and dc realm, where many others are closer to 120 dB, Nolan said. The higher the open-loop gain, the higher the precision and lower the gain error in the application, he explained.

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