Op amps are available for almost every design need you have. Design engineers tend to take them for granted because they expect that there will be one for just the design they are building. However, no matter what op amp suppliers provide engineers always want it tweaked a little bit so it works just right for their application. Suppliers are always scurrying to keep up with customer needs but it seems like their customers are always saying about the last op amp iteration “Yes, that's nice, but what can you do for my newest design?”
For most designers, the three most basic features are price, power and board space. So the manufacturer is always looking to be competitive and provide value for those three aspects. Getting the right balance between speed and supply voltage is an issue for every supplier.
Additionally, many end products are pushing for smaller packages, lower power and faster speeds to help meet the demands for portable equipment. That portable equipment includes the consumer market and items such as MP3 players, cell phones, PDAs, and digital cameras. “However, a similar but quieter revolution has been taking place in the industrial, medical and test and measurement markets,” said Erik Soule, Signal Conditioning Market Manager for Linear Technology Corporation. Equipment suppliers are finding strong demand for portable versions of their traditionally wall-powered products. Applications include portable gas monitors, ultrasound equipment, oscilloscopes, military radios and weigh scales.
What these devices have in common is the need for analog ICs that can provide the same high (or higher) performance specifications as silicon in their existing equipment, but in smaller, lower power versions.
The LT6010/1/2 family from Linear Technology is an example of this new generation of amplifiers designed to meet this need. Operating from 2.7 V up to +/-18 V, they consume only 135 uA, yet offer input offset voltage guaranteed less than 35 uV, less than 110 pA input bias current and rail-to-rail outputs. For space-constrained applications, these rugged, fully specified industrial temperature range devices are available in a tiny, thermally enhanced 3 mm x 3 mm x 0.8 mm dual flat no-lead (DFN) package.
Offering similar capabilities is the TS187x amplifier family from STMicroelectronics that operates with voltages as low as 1.8V and features both input and output rail-to-rail capabilities. The common mode input voltage extends 200mV beyond the supply voltages while the output voltage swing is within 100mV of each rail. The TS187X family is ideal for sensor interface, battery-supplied and portable applications.
Another product, for similar applications is the MAX4091 from Maxim Integrated Products. It combines DC accuracy with rail-to-rail operation at the input and output. It can operate from either a single supply (2.7 V to 6 V) or split supplies (1.35V to 3V). It requires less than 130 uA of supply current and can drive loads in excess of 2000 pF. The precision performance of the MAX4091 combined with its wide input and output dynamic range, makes it an ideal choice for battery-operated equipment, industrial, and data acquisition and control applications.
“The trends include smaller packaging and rail-to-rail inputs,” agreed Steve Sockolov Director of Precision Analog Amps. However, ADI doesn't see a voltage trend. “Customers are not necessarily just trying to get lower voltages. They are trying to get lower and higher voltages. Customers want it all, and that keeps ADI on its toes to always have the best process development technology,” he said.
To get smaller packages, better speed to power ratios, and lower cost, it takes improved process development. ADI has done a lot of op amps at 5 V but now many designers are looking for +/-5 V. “The reason designers want +/-5 V is because it's easier for them to put on two supplies and have the ground as zero than to have a pseudo ground in the middle. Many signals and sensors put out +/-5V and that's what they are used to,” said Sockolov.
“Single 5V systems are tricky and annoying to deal with in precision front-end circuitry,” added Bruce Trump, Strategic Marketing Manager for Precision Amps at the company. “The +/-5V design is a beautiful thing,” he said. “You can use a true ground reference signal and if you're doing precision analog processing then there's nothing like the comfort of having a real ground to reference signals.” To support the designers that need +/-5V, TI introduced the OPA335 about 6 months ago and will introduce the OPA735, a higher voltage version of the 335, in early December 2003.
To meet the requirements of today's design engineers improvements are constantly needed. Customers want faster parts and they don't want to burn more power, so the manufacturer's challenge is to push more performance, offer higher speed, drive the power down, and of course provide it at a lower price. If you compare current products to those released 5 and 10 years ago you see that the new products are much cheaper, faster, smaller, and with lower power. How is that possible? “It's related to process technology,” said Simon Prutton, Director of Applications and Marketing for Intersil Corp, “you need to have a high-speed process technology. For example, the high speed process has allowed the supply voltage to go down. Most of the products 10 years ago were 30-V and 28-V processes, but today most are 10-V.”
“However, having said that, continued Mr. Prutton, “the market these products served needed the entire voltage swing in the 5-V area to be extremely linear, and that was possible only if you stayed away from the supply edges, because early high-speed op amps, would give you significant linearity problems as you swung close to the supply.” Now, according to Mr. Prutton, you can buy a 10-V rail-to-rail op amp like Intersil's EL8102 that provides frequencies to 500 MHz and slews at 600 V/us, all on 6mA. That's important to the medical imaging customers. They are very concerned about power and they have a goal to run from the power outlet in the hospital.
Specialized process technology also is needed to help amplifiers attain high gain with few stages, or get lower parasitics with smaller capacitances on the internal gain nodes. “The unique process technologies such as SiGe give performance advantages for the amplifier products,” observed Erroll Dietz, Product Line Director for the Amplifiers Group at National Semiconductor. “SiGe can get lower noise transistors because you can dope the base of the transistors much higher,” he said.” Dietz also thinks these more exotic processes will be used where they can provide lower noise and distortion with better output swings, while maintaining the frequency performance and bandwidth for a given power consumption.
National has been focusing on low-voltage, low-power op amps in developing products for the battery powered market, and with the smaller packaging. For example, National offers the LMC7101 low voltage, low power op amp in the small footprint SOT-23 package, as well as the LMV family of low voltage, low power amps in the SC-70 small footprint package.
However, National also sees a need for higher voltage products because in the real world there are signals that need to move tens of volts. If you look at the flat panel displays or laser diodes where you need 5V or the blue light diodes that are 7V, these can't be supplied by deep sub-micron CMOS technology. “So, as we go forward, those things that are analog, where performance is not critical, and can be done in CMOS, will be integrated,” said Dietz. “For applications that are performance critical, customers can use the more exotic processes that have the higher real estate costs, because they only consume a small amount of real estate.”
Other companies also look to their processes to keep up with the demands by customers using op amps. For example, “TI has process technologies that span the whole range of high-speed and precision,” said Michael Steffes, Strategic Marketing Manager for High-Speed Amplifiers for TI. The company has its BiCom-1.5 process, which is a 36-V process with transistors speeds in the 3 to 4 GHz range for high-voltage products. Products from that process have +/-15 V supply capabilities and a bandwidth in excess of 300 to 400 MHz. One of the op amp products from that process is the THS3061. Another process technology, developed in Tucson, is the CBC10 process which is a 13-V process that provides 12-V products with internal frequency in the 9 to 10 GHz region, and yields products with 1 to 1.3 GHz capability. The CBC10 process was specifically targeted for DSL, video, and communications applications. The next step in the continuum is the BiCom-III process which is a silicon-germanium (SiGe) complementary bipolar-CMOS manufacturing process, developed in Freising Germany, that provides speed increases up to 3x more than previous processes. It's a 5-V process with a 20-GHz transistor speed. Products from that process have 2 – 3 GHz capabilities. Steffes says that using the right process can help you get the balance between the speed and supply voltage.
So manufacturers of op amps can feel secure that if they have all the right processes that they have the engineers nice and safe in their back pockets, right? Wrong. Having a lot of processes leads to a plethora of products and that leads to problems for engineers who need to make a quick decision. The answer flowing from some innovative companies is to offer a selection tool.
ADI's Sockolov says that because there are lots of amplifiers it is very hard for a designer to choose the appropriate one. So ADI decided that they have to provide more support for the customer to choose the right amplifier and to use it correctly. That means both technical and sales support is required. ADI has done some market surveys and company found out that the amplifier design usually needs to be done within a week. The survey also indicated that designers work very hard on specifying the correct processor, central converter and the system architecture ideas, but they leave the amplifier design for the end because they see it as very easy. Typically, engineers are stuck to do the designs in analog, something they weren't trained to do. ADI took this information and decided to develop some tools to help make the decision process easier for the designer. The company will roll out three to four web-based design tools over the next month, and even more next year. These tools are very broad based and can help users find high- and low-voltage op amps made in a variety of processes.
ADI also developed products to help designers meet their precision needs. The company uses a technology they call DigiTrim. Both ADI's AD8607 and its new AD8555 offer low microvolt offsets using the DigiTrim technology. It enables very accurate CMOS but it still needs help to compensate for amplifier drift over temperature. The company uses chopper technology to compensate for the temperature drift. ADI's third generation of chopper technology offers low noise and almost zero drift and zero offset for op amp designs. The company combines DigiTrim and chopper technologies on the 8555. It gives the user the capability to change the offset and gain. Without this technology designers would have to make an amplifier with a circuit to adjust the gain, and another circuit to adjust the offset. That would require several components and even more importantly it would require individual adjustments to get the right balance. The AD8555 has those two technologies and the user can adjust the gain and offset of the system under computer control. ADI has used it internally and now they are offering it to customers. “I could imagine this part being used in a current sense application where you have a sense resistor that has a very specific resistance (e.g., 0.01 ohms or even 0.013 ohms) and needs to be adjustable,” said Sockolov.
National Semi is no stranger to offering help to design engineers, having introduced Webench a couple years ago. Now, National has taken on the challenge of devising Webench for Amplifiers.
It's an intelligent application tool designed for those engineers who have historically used the data book and the application book, it will let them do this online and simulate with results. National understands that designers don't design their systems around op amps. “It's not like a microprocessor that has parts wrapping around it, but it is an important piece that provides differentiation for end products, it's a necessary signal conditioning part. Webench for Amplifiers is for people that don't deal with op amps all the time. It makes it much easier to figure out which op amp is the best one to use.
Fortunately, with the development of these tools, manufacturers can help you zero in on what you need and even show you what they have done for you today.
Analog Devices, Inc.
Tel: 800-ANALOGD (262-5643)
Linear Technology Corp.
Maxim Integrated Products, Inc.
Tel: 408-737-7600 or 800-998-8800
National Semiconductor Corp.
Texas Instruments Inc.
Tel: 800-477-8924, ext. 4500