Load Pull: The Measure of Performance
Prior to his current role, Greg held several key executive posts at Maury Microwave including Director of Sales and Marketing, Director of Quality Assurance, and Director of Calibration and Repair Services. Prior to joining the Maury team in June of 1996, Greg held responsibilities in Master Scheduling, Process Analysis, and Quality Engineering at McDonnell Douglas in Long Beach, CA and two years as a Manufacturing Analyst for General Dynamics, Pomona Division. Under Greg's leadership, the company has reorganized its two major business units (Precision Microwave Components and Device Characterization Solutions) to better serve the needs of its customers. Greg received a BS degree from California State Polytechnic University, Pomona in the field of Operations Management and Business Administration. Greg is the son of former president Marc A. Maury and the grandson of Maury Microwave founder, Mario A. Maury, Sr.
MWJ: Greg, thanks for taking the time to speak with us today. First - I’d like to first congratulate Maury Microwave on its 50th anniversary. That puts Maury Microwave and Microwave Journal at the same age. Can you tell us about how your company formed?
GM: David, first I would like to wish the Microwave Journal a ‘Happy 50th Anniversary, too!’ That puts us both in the company of our colleagues at Rosenberger, Disneyland, and the Dodgers move to Los Angeles!
My Grandfather, Mario Maury Sr., an Electronics Engineering Graduate of Columbia University, in 2006 named one of the ‘Legends of the Microwave Measurement Industry,' was with Motorola, Phoenix, when he conceived the company. He asked my uncle Mario A. Maury Jr., and my father Marc A. Maury, both with General Dynamics Corp., Pomona Division, to join the endeavor, and in October 1957, in Montclair, California, Maury & Associates was formed.
Since the passing of my uncle Mario in 1995, I have to say, one of the key reasons for our longevity has been the unwavering principles of honesty and integrity held by my father, Marc Maury.
MWJ: We were sorry to hear about Mario’s passing. He was well known throughout the industry. How many people were with Maury when it started and how many employees are there today?
GM: The three founders slowly added part time help and then full-time help. In 1966 the third brother, my uncle Richard Maury, joined the company as a Design Engineer. Today we have 140 outstanding employees, and I am surrounded by an excellent management team!
MWJ: What were your first products? Were these unique to the industry at the time?
GM: David, our first products were Low Pass and Band Pass Filters designed by Mario Sr. What made them unique was that our customers demanded custom requirements, as opposed to standard product. Early customers included Hughes Aircraft and Jet Propulsion Laboratories (JPL).
MWJ: Connectors and various microwave components have certainly evolved over the years. What are some of the leading concerns with today’s precision components for measurement?
GM: A lot of new engineers have ‘grown up’ in an environment where software bears the load in regards to the precision work, but the practices of connector usage and connector care have quite often been overlooked. ‘Precision is, as precision does’ there is a clear regimen to accurate connectivity in order to be able to verify the integrity of your test system and therefore the accuracy and repeatability your test results.
MWJ: Maury was around during the advent of the Network Analyzer and clearly benefitted from the need for calibration components. Do you have a close relationship with test and measurement equipment manufacturers - then and today?
GM: In the 1970’s we provided many of the calibration kits and components for the HP 8542 and HP 8409 series of Network Analyzers, then in 1983 we were selected by HP to be the principal supplier of Cal Kits for the new HP8510 VNA which revolutionized the industry. We continue to work closely with Agilent as a Channel Partner. Today we do support all major network analyzer manufacturer’s Analyzers with our cal kits, cal standards and precision components as well as our device characterization solutions.
MWJ: How knowledgeable is the engineering community today with regard to measurement precision and accuracy? Is training and support a big part of your company’s focus beyond components and test systems?
GM: The knowledge within the industry has been expanding exponentially, however the validity of modeling and design still rests on measurement precision and measurement accuracy. Training and support are a big part of our mission, helping our customers to remember and address each of these basics is a primary objective at Maury Microwave. Diligence to excellence in Installation, Training and Support are critical to our customers’ success this is where we have built a strong reputation in the industry.
MWJ: How would you categorize the various groups of engineers requiring device characterization, i.e. process engineers, device developers, circuit designers, etc.
GM: Different groups of engineers have different requirements. Process engineers and device developers need quick feedback on the effect of device or process changes. Circuit designers often will use the load pull system to determine impedances that meet their requirements, and then synthesize matching networks directly to finish an amplifier design. Modeling engineers typically take more data to characterize a device over a range of operation. They use the measured data to improve their device models so that circuit designers can simulate more complex circuits. Production engineers require tuners that are fast and can run continuously without wear or maintenance requirements. They try to minimize measurement time, so may just test devices on-wafer at a single impedance as a go/no go test, or check stability over a constant VSWR circle, for example.
MWJ: As Silicon CMOS process nodes drop to 45 nm and below, what is a growing concern in terms of device characterization?
GM: Silicon CMOS brings high reflections, a growing concern is the ability to match these high impedances making High Gamma Tuners even more important. This is also an area where we are seeing an increasing interest in Noise Parameter Measurements.
MWJ: Do devices targeting broadband wireless applications require unique characterization?
GM: Wireless Applications are a big part of the commercial output of this industry and most device characterization is done with modulated signals. Because of their commercial target market, ruggedness and stability testing, such as measuring over a constant VSWR circle has become very important.
MWJ: What are the challenges of measuring high-power devices with very low impedances such as LDMOS?
GM: Very low impedance devices require tuners with very high gammas such as our series of High Gamma Tuners which can provide 200:1 VSWR. The tuner must also have excellent repeatability and power handling capability at those high gamma states.
MWJ: Your High Gamma Tuner, which provides Gammas of .97, is quite an impressive accomplishment. You must have worked very hard to eliminate tuner losses. Are there patentable technologies behind these tuners or is it a case of superb design and manufacturing?
GM: All of our tuners take advantage of our core strength of precision manufacturing and all of them use proprietary techniques to produce the lowest possible losses. The High Gamma Tuner itself uses some unique patent pending technology in order to produce high gammas over their full bandwidth.
MWJ: LDMOS transistors can be very unstable and seem to oscillate quite easily, how do test systems and specifically variable impedance tests such as load pull, address this stability issue?
GM: Measuring unstable devices is a case where the test system components must all work together. The Tuners have to provide high gamma ranges in-band but must also provide low gamma at frequencies out of band. Measurement software must allow for current and power limit setting as well as be able to identify oscillation points. In addition, the test fixturing and bias networks are also critical.
MWJ: Are GaN devices with higher output impedances easier to characterize?
GM: Maury Microwave Tuner systems are easily adaptable to devices such as GaN.
MWJ: Designers are trying to squeeze every last bit of performance such as linearity or efficiency out of their devices. What are the challenges for developing optimum output matching structures for Doherty amplifiers, or those operating as Class E or F? Does your staff include circuit designers with power amplifier experience?
GM: To optimize linearity and efficiency it is important to include impedance matching at the harmonic as well as at the fundamental frequency. Some of the major tools to accomplish this are harmonic tuners and Large Signal Network Analyzer (LSNA) measurements. Maury Microwave has partnered with NMDG NV to introduce a commercial LSNA in 2004 and continues to offer solutions such as the VNA+ in order to allow our customers to look at their device in real time. We are also working closely with Agilent as a Channel Partner as they introduce new capabilities with their PNA-X.
MWJ: Are your customers strictly in the microwave space or are you seeing any customers with a high-speed digital focus?
GM: The majority of Load Pull power measurements are concentrated in the microwave space however many of our customers need to mix hi-speed digital signals with microwave. A growing scenario uses devices with digital baseband inputs and microwave/RF outputs or vice versa.
MWJ: Are load pull techniques used strictly in CW or two-tone measurements or are they being applied to digitally modulated devices?
GM:When automated Load Pull was introduced in 1987 it was just CW measurements, 2-tone wasn’t added until the early 90s. But digitally modulated systems became the main emphasis shortly after with the expansion of the wireless and cell-phone industry.
MWJ: Could you walk us through the various parts of a typical load-pull system including the controlling software and how tuner control and data acquisition are all integrated into the VNA measurement system?
GM: Traditional Load Pull systems added impedance tuners and software to a test bench that otherwise would have measured only in the 50 ohm environment. The test bench would include primarily RF Sources, power meters, spectrum analyzers, LSNA’s, noise figure analyzers, VNA’s and RF switches. Historically, VNA’s were used for just S-parameter measurements while a Load Pull or Noise parameter measurement would use switches to connect to the VNA. Some of the newer VNA’s are evolving into more comprehensive measurement. In the future I expect instruments such as the Agilent PNA-X to play a bigger and more central role.
MWJ: How is your load-pull measurement data incorporated into various simulation and circuit design software?
GM: Bringing the measured data back into the simulation software is an important step in the total circuit design process. S-Parameter and Noise Parameter results are saved into Touchstone files which can be used by many simulation programs. Load Pull files can be input directly into Agilent’s ADS software simulation package or into (AWR’s) Microwave Office. All of the power measurement data can be exported into mdif files for use in these simulation programs.
MWJ: As RF components become ubiquitous in consumer electronics, they are required to be less expensive, consume less power and be more reliable. How does this impact characterization?
GM: These factors increase the need for device characterization in the design stages in order to guarantee that the device will be stable and robust in the presence of manufacturing variations.
MWJ: Complexity often means more testing over an ever-increasing range of operating conditions. The need for more data points is pushing the T&M manufacturers to develop faster test equipment. How does this challenge affect your products and development efforts?
GM: As a part of recognizing this paradigm shift, Maury Microwave and NMDG NV share the vision of fast component characterization tools under realistic conditions where the characterization engineer can tune different parameters on the fly, see the complete component behavior, monitor specifications and go right to the optimal performance point. Maury Microwave and NMDG can bundle their expertise and strengths to offer tools to allow this paradigm shift as well as to anticipate the needs of tomorrow. At Maury we are there for our partners and for our customers.
Maury is uniquely qualified to insure our customer’s success through our extensive interactions with our Channel partners, Agilent Technologies and Cascade Microtech.
MWJ: Thanks, Greg. Maury Microwave is clearly a company with a high standard for quality, technical knowledge and customer satisfaction. It’s been a pleasure speaking with you and we wish you continued success over your next 50 years.