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Share: Analog: Back to the future, part two  

2012-08-30 16:59:31|  分类: Reading notes |  标签: |举报 |字号 订阅

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Analog: Back to the future, part two

Steve Taranovich - July 16, 2012


Part one of this series covered op amp history from National SemiconductorThis second part of the series covers Philbrick Nexus, Burr-Brown, Analog Devices and Linear Technology history and contributions in op amp history up to the 21st century offerings from these companies

Philbrick Nexus


Figure 1: George Arthur Philbrick, Founder of GAP/R George A Philbrick Researches

Philbrick Nexus was the company that launched the commercial use of the Operational Amplifier in 1952.

The first commercial Operational amplifier was the K2-W op-amp. It was based on the amplifier used in the Philbrick K3 modular Analog-Computer "black boxes ". 

That amplifier's basic circuit architecture, in turn, was probably inspired by an earlier amplifier designed by Loebe Juliehttp://www.philbrickarchive.org/lj.htm   The K2-W Operational Amplifierentered the commercial market in 1952, and was last manufactured in 1971. It performed mathematical Operations in analog computers. Soon after, the K2-W and its successors saw wide application in industry. See Figure 2. The Analog Computer was the educational vehicle to familiarize the engineer and the engineering student, with Operational Amplifier techniques.

 

Figure 2: The K2-W direct-current operational amplifier “for use in electronic computers” circa 1947 (From the Proceedings of the I.R.E. in a paper entitled “Analysis of problems in dynamics by electronic circuits” by J.R. Ragazzini, R.H. Randall, and F.A. Russell)

Editor’s note: John R. Ragazzini was dean of the School of Engineering and Science at New York University in the Bronx when I went there from 1968 to 1972---great guy and brilliant engineer.

Burr-Brown (BB) Op-Amp History Review

The term “Op-Amp” was first coined around 1947, but the concept of a DC coupled feedback amplifier was understood in the 1920s.  The need for analog computers during World War II brought the op-amp into wide use.  Of course, these amplifiers were all made with vacuum tubes.

It was not until 1956 when Burr-Brown introduced the first commercial transistorized amplifiers and it was 1958 when they introduced the model 130, the world’s first transistorized op-amp.

Looking at the big picture, one clear evolutionary path was from “boxes” to sub-micron integrated circuits with “no” packages (chip-scale). 

Figure 3: The big picture of the evolution of the Burr-Brown op amp (Courtesy of Howard Skolnik, one of the great analog designers at Burr-Brown in the early days)

1956    BB started with “instruments” in wooden boxes.  The 1st product was the model 100 AC Decade Amplifier (See Figure 4).  This was not an op-amp.  Other early products, in wooden boxes, included a Differential AC Amp, Square Wave generator, Variable Gain Preamp and AC Millivolt Meter.

Figure 4: The Model 100 was the first product that Burr-Brown made in 1956

1957    Tom Brown visited several major customers including MIT to see how they were using BB products.  To his surprise he found that they were removing the circuits and discarding his beloved boxes!  He learned two important lessons:  Smaller is better and making “components” is better business than making “end products.”

The model 130, the world’s 1st transistorized op-amp was introduced.  This was a completely discrete design using just 8 transistors on a PC-board in a 3 ?” long aluminum shell.

The desire for “smaller” led BB to the potted module concept.  While still using PCBs and all discrete components, innovative techniques greatly increased density.  The 1501 was the first modular op-amp and is now part of the Smithsonian collection.

The 1st monolithic (IC) op-amp was introduced by Fairchild (uA702 Bob Widlar). It was not very useful and was later superseded by the uA709 (1965).

1965   The 1538 module was the 1st transistorized chopper stabilized op-amp.
           
The 1552 module was the 1st FET-input op-amp.
           The 1553 module was the 1st transistorized chopper stabilized op-amp. MOSFET-input op-amp.

1966   The 3051 was BB’s 1st monolithic op-amp (Jerry Graeme on outside Fab).

The uA741 was introduced by Fairchild (Dave Fullagar).

The move to hybrids was well underway. The ability to mix and match chip-level along with discrete components on a thick-film substrate opened the door to complex circuits with very high performance.

  Trimming of thick-film resistors allows higher precision in both modular & hybrid designs.
  1st monolithic op-amp produced on BB Fab (3051).

  Trimming of thin-film resistors provides improved stability and smaller size in hybrids.

1st two-chip hybrid op-amp (OPA102) combined a bipolar monolithic chip with a dual FET chip to produce high performance at lower cost than before.

Monolithic dielectric isolation (DI) process available to BB designers greatly increasing their capabilities.

INA101 is BB’s 1st monolithic instrumentation amplifier.

OPA100 ultra-low bias current op-amp is 1st produced using the BB DiFET (DI BiFET) process.

OPA111 Low noise, low drift op-amp built on BB DiFET process.

1986   INA110 is BB’s 1st monolithic BiFET instrumentation amplifier.

OPA445  Hi-Voltage BiFET op-amp. +/-45V.

OPA627 Near “ideal” op-amp built on BB DiFET process.  250uV Vos, 5pA Ibias, 5nv Noise, 16MHz BW, 55V/us SR, +/-18V supplies.

1996   OPA237    1st op-amp in SOT-23 package.
           OPA2237 1st dual op-amp in MSOP-8 package.

           OPA336  1st BB op-amp on 0.6u CMOS.

           OPA2652 1st op-amp on BB’s CBC-10 process.

Comparing the first transistorized op-amp to a modern chip-scale device. 

Table 1: A Comparison of the first transistorized op-amp to a modern chip-scale device.


Analog Devices Inc. (ADI)

EDN directed some pertinent questions to Barry Gilbert, ADI Technology Fellow (Figure 5) and Bob Adams, ADI Fellow (Figure 7):

Figure 5: Barry Gilbert in his early days circa 1951

Barrie Gilbert

Background: Gilbert is one of the industry’s foremost experts in the development and application of analog circuitry. He now directs engineering at the Northwest Labs in Beaverton, Oregon, ADI’s first remote design center.

Gilbert’s 40-year affiliation with Analog Devices Inc. – dating back to 1972 – saw the company go from being principally a module maker to a producer of high-volume IC parts and digital signal processors.

One of the circuit cells that bears his name has for decades been used in all forms of communication systems, including ordinary radios, cell phones, microwave TV links, data modems, satellite communications and even radio telescopes.

The Gilbert cell—actually an entire class of versatile cell topologies used as basic analog function blocks—has served as the foundational design for products used everywhere in today’s electronic systems.  All invoke the now famous Translinear Principle. This fundamental theory in circuit design was discovered, formalized, refined and popularized by Gilbert. Translinear circuits perform pure-current-mode signal processing, a fundamental insight. Today, these ideas, whether in the original bipolar form or in CMOS embodiments, are found throughout analog design.

Figure 6: A schematic of the two-quadrant Gilbert Cell

Since its invention in 1967, what has become known as the Gilbert Mixer is now ubiquitous in radio transmitters and receivers. The compact nature and precise commutation properties of this mixer opened one of many important doors to the integration of radios in monolithic form, leading to the proliferation of modern indispensable communications devices. A closely related circuit, known as the Gilbert multiplier, overnight revolutionized the implementation of this important mathematical analog function. The 1968 Journal of Solid-State Circuits paper describing it became the first paper to be cited 100 times. Today, more than 40 years later, it remains one of the most-cited JSSC papers.

Gilbert believes that childhood hardships—including at age three losing his father in World War II, leaving his mother and three other children penniless—force one to be resourceful. Before and during his teenage years, he had access to a plethora of inexpensive military surplus gear which greatly helped to make him inventive. Gilbert laments that today's aspiring engineers are lacking the visceral experience of handling and hefting large coils and tuning capacitors, transformers and vacuum tubes, and such. Today’s surplus circuit boards are all but useless as a source of inspiration, or even “spare parts” to tinker with.

1. What initial analog developments from ADI’s past have helped shape ICs in the 21st century industry?

In 1971-72, Analog Devices worked with and funded a start-up called Nova Devices to begin fabrication of linear integrated circuits. This collaboration carried through to become Analog Devices Semiconductor (ADS) division and started to deliver high-performance linear in 1972. Much of the early revenue came from op amps, including the AD741 – a near-copy of the historic precursor, but with stronger emphasis on precision and quality. And Analog Devices began making laser-trimmed FET op amps with much better performance than the industry standards of the day. This emphasis on providing high accuracy and advanced performance arose from the very earliest days. With the advent of nonlinear functions, such as the first high accuracy laser-trimmed analog multiplier, the AD534, the first monolithic RMS-DC converter, the AD536, and the first complete monolithic V/F converter, the AD537 – all using translinear techniques – another seminal emphasis came to the fore, namely the provision of precise calibration of nonlinear functions. Undoubtedly, it was the development of wafer-laser-trimming of ADI’s proprietary thin-film resistors that gave the company a considerable edge, in this regard.

Later, Analog Devices and the ADS division made further progress in the fabrication of linear ICs. Process 1 was optimized principally for op amp use; Process 2 was a little faster, and was used in I2L modes in the earliest ADCs. Further advances in speed came with Process 3. I felt the need for, and defined, a complementary bipolar process, which became “CB.” A radical later departure was the early adoption of silicon-on-insulator (SOI) processes, the “XF” series.

2. How did your innovation or an older architecture specifically set us up to achieve today’s 21stcentury performance?

The growth to maturity of ADS, which rapidly became the largest revenue generator of ADI, and is no longer a separate division, came out of the seminal contributions of numerous talented people. It’s hard to identify crucial product developments that shaped the company at large. Each of these people would have a unique perspective on that issue.

But if I am to speak of from my own viewpoint, I believe it was my personal interest in “radio” – going back to childhood days – that drove me to push hard to provide the tools and ideas to develop chips for this sector of the business, at a time when the company was predominantly a provider of industrial and, to a lesser extent, military components. No one was using the word “gigahertz” at that time! One key development was of the first five-stage RF logarithmic amplifier, the AD640, sometime in the 1980s. Since that time, my team and I have development numerous multistage log amps for use in RF power measurement. We can boast that practically every cell phone and base station in the world uses these ADI products.

As for “older architecture,” products developed in the 1970s using translinear techniques – such as the AD534 multiplier, and other developments of that kind – remain in the catalog and continue to generate significant revenue.

Beyond that, I believe my insistence that we needed at least one scientific computer – and eventually a CAD team of our own – eventually yielded fruit. We initially purchased one VAX780 and time-shared it.

3.   What advice do you have for today’s 21st century designer? What analog know-how does today’s designer need to create successful designs?

These are crucial questions, but they would need the wisdom of Solomon to provide adequate answers!

First, I would say this. Before any young person enters into a life of microelectronic design, he or she should be quite sure that this is going to be the beginning of a life full of joyous discovery and invention. There are many fields that can provide this sort of joy, so self-examination as to a career is essential at a very early age.

Second set out to be the best in your field. As an IC designer, you will need to wear many assorted hats. Yes, often you will be wearing your Circuit Designer’s Cap and Cape, but at other times, you will need to don your Pragmatist’s Hat, your Economist’s Hat, your Physicist’s Hat and many more. Deliberation over difficult trade-offs will frequently arise. In short, IC product design is not simply about transistors.

Third, beyond being “best in class” you must aspire to becoming Master of the Dance. By that, I mean that you will develop a deep sense of being in control of all that your mischievous little transistors do.

They will often want to sing, when you just need them to do a jig from left to right across your stage. When you choreograph your circuit on the screen, you must think like a transistor thinks. You must actually become a transistor!

Fourth, ask “What IF?” a thousand times a day. This question is the quintessential fountain of invention.


Bob Adams


Figure 7: Bob Adams at his desk at DBX, an early competitor to Dolby circa 1982. DBX made noise-reduction systems and analog processing gear, largely based on novel log/antilog-based voltage-controlled amplifiers and RMS detectors. Adams got a good expertise here in analog signal processing.

Background: Adams graduated with a BSEE from Tufts University in 1976, and after spending several years as a musician, he began a career in the consumer/professional audio equipment market. In the late 1970s, he published the first paper on log-domain filtering and then began working extensively in the brand new area of sigma-delta A/D converters, producing the first audio converter with greater than 16-bit resolution.

In 1988, Adams joined the ADI Converter Group as a Senior Staff Designer. Together with Paul Ferguson, he developed ADI's first sigma-delta converters. During the past 20 years, Adams has pioneered many important architectural advances in sigma-delta converters including mismatch-shaping, multi-bit quantization, and continuous-time architectures.

Adams also has a passion for digital signal processing and produced the world’s first monolithic asynchronous sample rate converters—the AD1890 family—using patented ideas and design techniques. After getting a taste of digital design, Adams founded the sigmaDSP line of audio-specific DSP cores.

Questions

1 What initial analog developments from ADI’s past have helped shape ICs in the 21st century industry?

There are many such developments, and it’s hard to come up with only a few. The obvious ones are a variety of improvements to the basic band-gap cell, done by engineers such as Paul Brokaw and Barrie Gilbert; a variety of circuits based on the translinear principle that are now used extensively in RF circuits such as VGAs and RF power monitoring; and many different innovations used in A/D and D/A converters of all types that have survived to the present day.

2 How did your innovation or an older architecture specifically set us up to achieve today’s 21stcentury performance?

When I first began playing around with delta-sigma converters back in the early 1980s, I did not have much IC design experience and therefore was drawn to topologies that could be tested on a breadboard. This led me to use a continuous-time architecture that used conventional op-amps, R’s and C’s. This choice leads to a number of performance issues that I had to tackle, including sensitivity to clock jitter which was solved by the use of multi-bit quantization.

Integrated delta-sigma converters really took off in the 1990s, and most of the designs were based on switched-capacitor circuits that were easier to integrate. However, in the last five years or so, there has been a swing back to continuous-time/multi-bit designs, partly as a result of the introduction of mismatch-shaping techniques. Most of the lessons I learned back in the ’80s are still relevant today.

3 What advice do you have for today’s 21st century designer? (What analog know-how does today’s designer need to create successful designs?)

It’s really important for today’s designers to be as “broad” as possible. Most of today’s most successful ICs require a blend of analog, digital, and system-level know-how.  In many cases, analog problems can now be solved with a combination of analog and digital techniques. For example, if you are designing an A/D converter, the problem of precision matching can often be overcome by a background digital calibration loop. On the other hand, if your circuit is too noisy, no amount of digital logic can fix it.

The Linear Technology op amp story

Bob Dobkin discusses some of the history and his experiences in the early days of op amps.  Before founding Linear Technology in 1981, Mr. Dobkin was Director of Advanced Circuit Development at National Semiconductor for eleven years. He was with Philbrick/Nexus before that.

Linear Technology introduced its first product in 1983, the LT1001 precision op amp. Dobkin said, “We’re going to do it an order of magnitude better than anyone else has done.”

In the early days, IC trimming was done using “Zener zaps” at the wafer level and later on they were able to trim after packaging.

The tools at that time were breadboards made from transistor pairs, a favorite of Jim Williams. If the breadboard worked, then the IC would work. SPICE was not very reliable; models were not very good.

Figure 8: Classic Jim Williams at his best in the lab

In 1983 there were many +5v logic ICs, so the company developed the LT1013, a single-supply, dual precision op amp for operation from 5V to 36 V.

Later came the super-gain amplifiers like the LM108 by National; Linear Technology’s solution was the improved LT1008. Later the chopper LT1050 was developed.

In the mid-to-late 80s, processes were improved and the 3 to 4 inch wafers went to 6 inch. Fabs were cleaner; relatively small geometries of 2 micron from digital processes helped op amp speeds to increase.

At that time IC design went from less than 10 masks to 20 or 30 masks and bipolar processes became fully complementary with PNP transistors being as fast as NPNs, so transistor bandwidths were able to begin moving up in the 300 MHz to 1 GHz regions. This brought about op amp speeds in the order of 30 to 50 MHz with higher slew rates than previously possible.

Today, complementary processes have transistors in the 10 GHz region, giving op amps bandwidth capabilities of 1 GHz and much higher slew rates to drive high speed ADCs.

Dobkin commented that analog companies like Linear need their own special proprietary processes to differentiate themselves from competitors; he said that the Chinese and Taiwanese semiconductor companies do not have this. Standard processes and outside foundries are also used, but Linear has two fabs that make 95% of their products.

Dobkin’s philosophy at Linear is to “minimize the phone calls,” do it right and customers will not have to call with problems that the IC is having in their designs. When he developed the LM318 at National, the decision was to make the speed 15 MHz without great phase margin, since the goal was speed with this product. (See Analog: Back to the Future Part 1.) Well, when the op amp oscillated in customers’ circuits, they would call him and he would tell them how to compensate the device.

Linear’s 21st century solutions now include the LTC6417, a differential ADC driver amplifier that is an improvement over the previous LTC6416 buffer amp. The design gets the best performance in the 20 to 140 MHz region at lowest power dissipation. The data sheet speaks well to RF designers with specs like OIP3, P1dB and noise figure. The 50 ohm drive capability is what RF engineers like in an IF amp. Linear’s design capabilities, combined with an advanced SiGe process, results in some superb fully differential amplifiers (FDAs).

Another excellent new amplifier is the LTC6431-15 for 600 MHz to 1 GHz signals with excellent OIP3 and great ADC drive capability, which can even move a step closer to the antenna in a receiver. The test capabilities in production are challenged with these types of super speed devices. Testing needs to be done accurately and quickly and Linear even specifies more guaranteed min and max specs on their data sheets, something that designers love!



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