CMOS Voltage Comparator Touts 50,000:1 Improvement in Sensor Input Signal Detection

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Advanced Linear's Signal Power Draw Comparison

Sunnyvale, Calif. — Advanced Linear Devices, Inc. announced an ultra-sensitive, high-performance electrically programmable analog device (EPAD) analog voltage comparator. Designated the ALD2321, the first in this family of products is destined to revolutionize the field of small signal detection for practical sensor applications in defense, security, process control and a wide range of other industries.

Designed to reduce input loading effects that cause linearity errors and typically limit the resolution and sensitivity of many critical sensors, ALD's voltage comparator features a unique front-end stage with an input-signal power specification of only 0.004 pW (0.2 mV x 20 pA). Compared to current technology, which ranges from 200 to 1000 pW, circuit designers can realize a 50,000:1 improvement in small signal threshold detection, thereby expanding the useful range of many existing and new analog sensors that generate very low, sub-millivolt output signals.

The low input power design is achieved through the use of EPAD technology for electronically minimizing the input offset voltage and high impedance, insulated gate metal-oxide semiconductor field-effect transistor (MOSFET) transistors, which subsequently drive the input amplifier stage by controlling the input gate voltage. Other pertinent features include low power supply current — 110μA, 3 to 11-Vdc power supply, dual complementary (push-pull) outputs, 50 mA output sink current, and 30 transistor-transistor logic (TTL) load fanout.

For mission-critical applications that depend on highly advanced sensors with signals that are difficult to detect, ALD delivers the only voltage comparator capable of providing the signal detection to complete the mission. This makes them ideal for sensitive instrumentation in mobile platforms and the increasing need to detect trace molecular amounts of chemical, biological and radioactive elements. Other applications include power supply voltage monitors, photodiode sensors, and relay or LED drivers.

As sensors have become more sophisticated, signal amplification is usually required to take advantage of their full output range. Historically, sensor advancements have exceeded the capacity of supporting analog circuitry to render the full range of their sensitivity unattainable — until now. ALD has reinvented the analog voltage comparator to capture and process the faintest signals for high performance applications. ALD voltage comparators can now directly process signals that previously required preprocessing and amplification.

“ALD has taken a standard component and turbo-charged it to make it a state-of-the-art analog device,” said Robert L. Chao, president and CEO of Advanced Linear Devices. “By doing so, ALD has taken a fresh look at the basic functions that these devices perform and breathed new life into them, enabling voltage comparators to meet the wide range of signal detection demands from a new generation of sensors.”

Although voltage comparators aren't new technology, ALD has taken a creative approach to improving these important analog components. ALD has embedded several discrete functions into a single CMOS chip — the resulting circuit is unmatched in its precision. The ALD dual voltage comparator simultaneously delivers the lowest input bias current and lowest input/offset voltage available in a single chip. The chip supports applications demanding low level signal detection with high source impedance.

The ALD2321 EPAD voltage comparator is available now in sample quantities from Mouser Electronics. Pricing is $1.78 to $2.69 in quantities of 100, depending on the grade required. The ALD2321 is available in JEDEC standard 16 lead PDIP, SOIC and CERDIP packages.

Richard Reid, the infamous shoe bomber who allegedly tried to ignite explosives hidden in his shoes on an American Airlines flight in December 2001, probably never would have made it to the plane if ALD's new voltage comparator was designed into a sensor that was used by airport security.

There is a perceived need for more sensitive portable instruments, especially since 9/11, Chao said. Using ALD's EPAD voltage comparator, an entire benchtop system could be condensed into a portable system, like a handheld device that could be used at an airport security gate, he said. ALD's EPAD voltage comparator is so sensitive that it can be used with appropriate sensors or detectors to detect trace biological, chemical or environmental molecules.

Today, there are sensors sitting on shelves in R&D labs because manufacturers don't have the necessary electronics, such as ALD's EPAD voltage comparator, to detect signals that were previously undetectable, Chao said.

The thumbnail slide above, entitled “Signal Power Draw Comparison,” shows a dramatic reduction in signal power — from 200 pW for the industry standard comparator (LM393A), down to 0.4 pW for Advanced Linear's ALD2301A, to 0.004 pW for ALD's latest EPAD comparator. The ALD2321 voltage comparator requires signal power that is 50,000 times less than what its competitors are offering, Chao said.

There are a number of companies manufacturing the industry standard LM383A comparator or a similar device, including Advanced Micro Devices, Fairchild Semiconductor, National Semiconductor, On Semiconductor and Texas Instruments.

The comparator market is a relatively small market, representing under $100 million in annual sales worldwide, said Gary Grandbois, principal analyst at iSuppli Corp., El Segundo, Calif. The market for precision comparators would be even smaller, he said.

The ALD2321 is the first device in an upcoming family of devices that will utilize Advanced Linear's patented EPAD technology. Other products will follow in the coming year, Chao said.

Because the ALD2321 voltage comparator was designed as a direct sensory interface, signal-conditioning circuits aren't needed, or are much simplified. It is so precise, that it can actually work with a lot of sensors directly, Chao said. It's also a departure from the standard voltage comparator, in the sense that it's a whole analog subsystem on a chip. The comparator includes the preamplifier stage, internal amplifier stage, a level translation stage and an output driver stage, which would have previously been performed by up to four different chips, Chao said.

While the basic physics of this technology was conceived almost 20 years, the application is new and the technology is still evolving. It's so sensitive, that it took ALD two years, instead of two weeks, to design a test system for the new device, Chao said.

ALD's patented EPAD technology utilizes a monolithic MOSFET in which the threshold voltage can be precisely controlled via a stored non-volatile charge. E-TRIM basically describes the process or how Advanced Linear is applying the EPAD technology. “Using this technology, we can actually do electronic trimming. It's sort of like the trimmer part people use, except that it is electronic,” Chao explained. “It's integrated right onto the chip so the footprint, compared to an actual trimmer part, is much smaller,” he added.

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