Designing Non-Uniform Distributed PA MMICs for Decade Bandwidth

mmTron’s Michael Roberg, Engineering Fellow, recently presented a tutorial on designing non-uniform distributed power amplifiers at the IEEE MTT-S World Microwave Conference. Watch a replay of his presentation below — a very detailed tutorial from one of the best MMIC power amplifier designers.

This presentation was one of six in the GaN MMIC Power Amplifier Design session. You’ll find the others here.

mmTron’s Disruptive Value Proposition for FWA

Photo of a tower holding multiple radio antennas. Text next to the photo reads Improving the ROI of Fixed Wireless Access

The global demand for broadband access to the internet is fueling rapid growth of fixed wireless access (FWA) and satellite communications, with mmWave spectrum at 24 GHz and above increasingly being tapped to add network capacity.

What is the spec limiting the performance of a mmWave communications system?

Linear power is the key parameter for achieving high data rate mmWave communication. Linearity determines the highest modulation usable for a given channel bandwidth, which sets the maximum data rate of the system. The output power determines the range of a wireless link. The greater the power and linearity, the longer the range and higher data rate for transmission. Power and linearity go hand-in-hand to enable long-reach high data rate systems. High power alone is useless without linearity, because the data rate will not be high enough for demanding internet applications such as high-definition video and emerging VR and AI devices.

mmTron’s power amplifier (PA) products are designed to simultaneously provide high power and linearity while also maintaining excellent efficiency. For example, mmTron’s TMC2111, a GaN PA covering 24.5 to 29 GHz, delivered a record-setting 10 W output power at 3.5% EVM with 30 dBc ACLR, using a 5G NR signal at 29 GHz — to our knowledge the highest linear output power for a MMIC PA at mmWave frequencies.

TMC2111 EVM vs. output power
TMC2111 ACLR vs. output power

Why is the TMC2111’s performance notable?

FCC regulations allow an EIRP of 75 dBm from a FWA base station operating at 28 or 39 GHz. [1] Yet most FWA systems today operate well below that maximum because the EIRP is limited by the output power of the semiconductors and the gain of the antenna array. As the linear output power of a silicon PA is much less than that of GaN — approximately 10x — a silicon-based transmitter requires a larger array than one using GaN to achieve the same EIRP. [1]

Alternatively, the system designer can use an mmTron GaN-based transmitter to increase the EIRP, resulting in a longer distance between antennas. This significantly reduces the number of base stations required and the overall cost of the network, since fewer base stations are needed to cover the same geographical area.

What’s the business case for mmTron?

FWA has emerged as the predominant use for mmWave 5G. Mobile operators are currently tapping unused capacity in their sub-6 GHz (FR1) bands, yet this spectrum won’t support the increasing demand for both FWA and mobile users. Operators must turn to the mmWave (FR2) bands to support this demand.

Ericsson forecasts that global FWA connections will reach 330 million by the end of 2029, up from 130 million at the end of 2023. They forecast the associated data traffic to grow by more than 5x from 2023 to 2029, reaching 159 EB or almost 30% of the total mobile network data traffic. [2]

What’s the take-away?

mmTron has developed a differentiated design and manufacturing expertise for high power, highly linear PAs, as illustrated by the performance achieved by the TMC2111. This unique value proposition is enabling operators to not only reduce the cost of their FWA networks, but also deliver the high data rates users are demanding.

References

[1] “5G Fixed Wireless Access Array and RF Front-End Trade-Offs,” Bror Peterson and David Schnaufer, Microwave Journal, February 2018

[2] “Fixed wireless access outlook,” Ericsson Mobility Report, November 2023, web: www.ericsson.com/en/reports-and-papers/mobility-report/dataforecasts/fwa-outlook

Driving 5G Forward: The Technology of mmTron’s MMICs

Under the title Driving 5G Forward is a street light with an antenna mounted on top of the arm between the post and light

mmTron was started in 2020 to provide disruptive MMICs for mmWave applications. By disruptive, we mean significantly extending the performance of those key parameters that improve system performance.

Communications Care-Abouts

For communication systems, the parameters are data rate, link distance, and the attendant cost of the radio network. At the component level, the combined output power and linearity of the power amplifier in the transmitter drive the data rate and link distance. Longer links reduce the number of transmitters and repeaters and the resulting cost of the network.

Brute power, however, is not the goal, as saturating a semiconductor device to get higher power generates harmonics and intermodulation products. Power at a specified error vector magnitude (EVM) is the key metric, with the required EVM set by the modulation used by the communications system. The output power at this EVM becomes the metric for judging the quality of the power amplifier or transmitter.

The power consumption of the transmitter is also important, as it determines the heat sinking required to channel heat from the semiconductor devices. This thermal design is a major contributor to the weight and size of the transmitter, important because it can limit where the transmitter can be mounted and whether it can be carried and installed by one person. At the component level, the power-added efficiency of the power amplifier is the key metric for judging power consumption.

Historically, power amplifier designers focused on just two of these three metrics: output power, linearity, and power-added efficiency. Optimize the two most important parameters and accept the third, which was largely determined by the semiconductor technology, bias point, and matching circuits.

Market Need Meets Opportunity

Seeing the need to optimize all three became the goal for mmTron’s designers. They start with the choice of semiconductor technology for the application, then optimize the process, device bias points, matching circuit topology and element values. To achieve precision in the simulation — the goal is always first-pass design success — they had to improve their circuit and electromagnetic analysis tools and design flow. (Keysight published a case study on the electronic design automation (EDA) stack we used for the design of the TMC211, a 26 to 29.5 GHz power amplifier MMIC with 50 watts saturated output, which you can download here.)

Disruptive Performance

mmTron’s 37 to 41 GHz GaN power amplifier MMIC illustrates how this design philosophy and approach achieve disruptive performance. The first MMIC developed by mmTron, the TMC212 power amplifier was designed for the n260 5G band. With a 400 MHz 5GNR signal, it provides 27 dBm output power with just 1.8% EVM, truly state-of-the-art.

The three-stage MMIC has 23 dB small-signal gain and is matched to 50 Ω. It is nominally biased at +24 V on the drain, with a negative gate voltage adjusted to set the drain current to 400 mA. The TMC212 is offered in a 6 mm x 6 mm laminate QFN package. At 85°C ambient, the junction temperature of the GaN MMIC is below 140°C, which supports more than 10 million hours of reliable operation.

With its high linear power, the TMC212 is being used in fixed wireless access and “smart” repeaters. It’s one of a family of mmTron MMICs developed for the 5G NR bands (n257, n258, n259, and n261). Performance information on all mmTron’s devices are available on the Products page of our website.

Active Baluns: Bridging the Microwave and Digital Worlds

Among the innovative products mmTron introduced last year, the active balun created a new product category. It serves as a bridge between the high-speed digital and microwave worlds, a key element as systems adopt direct RF sampling.

Functionally, the active balun is an interface for high-speed A/D and D/A converters. It preserves the digital converter’s dynamic range by providing low noise, high linearity, and wide bandwidth amplification.

A tutorial on active baluns written by Seyed Tabatabaei, mmTron’s founder, was recently published by 5G Technology World. Seyed discusses the performance requirements driving the designs and choosing the best semiconductor technology for implementation.

mmTron has introduced four initial products in the active balun family. Click on the links below to see the technical specs for each product:

TMC160-16 — Single Channel D/A Converter Interface
TMC161-16 — Single Channel A/D Converter Interface
TMC180-16 — Dual-Channel D/A Converter Interface
TMC181-16 — Dual-Channel A/D Converter Interface

2023: An Amazing Year for mmTron

2023 has been an incredible year for mmTron, as we announced our product-market strategy and unveiled more than 20 innovative products that extend the industry’s output power, linearity, efficiency, and bandwidth for Satcom, 5G, instrumentation, and aerospace/defense applications.

mmTron’s family of 5 W GaN power amplifiers (TMC152, TMC253, and TMC212) provide the highest linear power for the 5G FR2 bands from 22 to 41 GHz. The TMC211, TMC2111, and TMC2112 provide even higher linear power across 24.5 to 29.5 GHz: 40 to 50 W saturated power and >20 W linear power with an NPR of 19 dBc.

Our portfolio of eight distributed amplifiers addresses broadband applications from 20 to 160 GHz, achieving the highest gain-bandwidth products.

We also created a new product category: data converter interfaces for high-speed A/D and D/A converters. These interfaces provide a low noise, high linearity transition from the differential ports of the converters to the 50 Ω RF world. To get the best performance, we designed our own baluns and have released them as standalone products (TMC810, TMC811, TMC812, and TMC813).

mmTron exhibited at IMS in San Diego and EuMW in Berlin, and our capabilities have been featured by Microwave Journal, Microwave Product Digest, and everythingRF.

Thank you for your interest and contributions to making this an incredible year for mmTron.

Highlights from the 2023 BCICTS in Monterey

Photo of Fisherman's Wharf in Monterey, Calif. with the text "mmTron at BCICTS" in the bottom foreground.

The IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS) just completed its sixth annual conference, 15–18 October, in Monterey, Calif. BCICTS is the marriage of the Compound Semiconductor IC Symposium (CSICS) and the Bipolar/BiCMOS Circuit and Technology Meeting (BCTM), which ran for 42 and 35 years, respectively, before joining to start BCICTS.

mmTron was one of seven companies exhibiting this year, along with five sponsors, to help underwrite the event. Co-founders Seyed Tabatabaei and Mona Molaasgari and Mike Roberg, Engineering Fellow, attended to take in the conference papers and share mmTron’s differentiated strategy for serving the mmWave market.

Mike has long served on the conference technical program committee (TPC) and served as the BCICTS publications chair this year. Next year, he’ll chair the TPC. His association with BCICTS gives him a good perspective on the technology and industry, so we asked Mike to share his impressions of the event:

“BCICTS attendees were greeted by beautiful weather and a fantastic technical program in Monterey.

The three excellent plenary talks highlighted the future directions of compound semiconductor technology. Tom Kazior (DARPA) gave an excellent talk on how 3D heterogeneous integration will be a key enabler for next generation RF systems. Building on this concept, Shahriar Shahramian (Bell Labs) discussed Bell Labs’ research efforts in E- and D-Band phased array development, which is enabled by glass interposer technology. Umesh Mishra (UCSB) wrapped up the plenary session with an excellent talk discussing how N-polar GaN offers significant promise for improving mmWave power density, which is becoming a bottleneck for many applications.

The exhibitor reception, held Monday evening, enabled the attendees to have substantive technical conversations with one another, so was well attended. With some 170 attendees, BCICTS is a smaller conference, which makes the engagement opportunities unique for exhibitors. Most attendees are directly involved with IC design, so the discussions are typically technical and detailed, which often identifies unique business opportunities for the exhibitors.

It was clear from the conference that mmWave systems are a hot topic. The challenges seemed to consistent across all the presented papers: consumed and dissipated power needs to be reduced while linearity and output power are increased. Oh, and don’t forget the integration challenges at mmWave, making a phased array, for example!

While these challenges are quite difficult, they are favorable for mmTron’s future due to our mmWave IC design expertise, which leads to products with world class power, power-added efficiency, and linearity. As GaN nodes continue being developed for mmWave (e.g., STARRY NITE, a program on the microelectronics roadmap of the Office of Undersecretary of Defense Research & Engineering), mmTron is well-positioned to offer GaN MMIC products exceeding 100 GHz with output power not previously achievable.

Fraunhofer’s presentation on advanced mHEMT technologies was one of the papers that was particularly impressive. It achieved MMIC amplifier performance beyond 700 GHz, which is astounding. They presented an integrated module for a synthetic aperture radar, with performance at 400 GHz, also impressive.

— Mike Roberg

Photo of Mike Roberg, Seyed Tabatabaei, and Jim Sowers at the mmTron exhibit at the 2023 BCICTS conference in Monterey, Calif.
Mike Roberg, Seyed Tabatabaei, and mmTron technical advisor Jim Sowers
at the mmTron exhibit at the 2023 BCICTS conference in Monterey.

To Support Growth, mmTron Moves to New Office, Expanded Lab

A photo of the multl-story office building and mmTron's door sign. The text reads "mmTron Expands Offices and Lab"

To support the market’s interest in our mmWave products, we moved into larger offices during the summer. Our new space has an expanded lab for development and production testing, with the following capabilities:

— Keysight 4-port PNA-X,
— Keysight spectrum analyzer,
— Rohde & Schwarz 20 giga-sample-per-second (GSPS) oscilloscope,
— Keysight transistor modeling system,
— power meters, and
— programmable power supplies.

Two probe stations from FormFactor enable on-wafer testing. One is capable of interfacing with frequency extenders for measurements to THz.

The new space also includes wire bond assembly, incoming and outgoing inspection, and inventory storage with N2 desiccators, as well as offices for team members.

We’re still in Redwood City, less than ½ mile from our previous location.

A photo of Michael Roberg, Engineering Fellow, in the lab at mmTron's new office.
Michael Roberg, Engineering Fellow, in the lab at mmTron’s new office.

Download mmTron’s IMS 2023 MicroApps Presentation

Title slide from mmTron's MicroApps presentation at IMS 2023

If you missed this year’s IMS in San Diego — or perhaps you were there but too busy to see everything — you can still download and review the slides from our MicroApps presentation.

Our CEO, Seyed Tabatabaei, gave an overview of the challenges when simultaneously designing MMICs for high output power, linearity, and power-added efficiency at mmWave frequencies. Optimizing all three is the motivating mission for mmTron.

Download here: mmWave PAs — Why Sacrifice High Power for Linearity?

A View of the mmWave Landscape

A photo of mmTron's founder, Seyed Tabatabaei with the title of his article published in MPD: "Today’s Palette of Semiconductor Technologies: A Millimeter-wave MMIC Designer’s Dream"

Seyed Tabatabaei, mmTron’s founder, president, and CEO, shares his view of the mmWave semiconductor landscape in the July 2023 issue of Microwave Product Digest.

“After almost 40 years, I find this the most fulfilling time to be working in millimeter-wave. No longer relegated to lab or niche applications, our pallet of millimeter-wave semiconductor technologies is truly enabling global communications.”

Read the full article online at MPD.

mmTron’s 50 W, Ka-Band GaN PA Design Featured by Keysight

Simulation layout of a GaN MMIC power amplifier

Keysight Technologies recently published a case study describing how mmTron’s 28 GHz, 50 watt power amplifier (PA) MMIC was developed using the Keysight RF EDA environment.

The TMC211 was designed to provide 50 watts saturated output power across 27 to 31 GHz, with 53 dBm OIP3 and 28% power-aided efficiency. The design is the highest power, single die, GaN MMIC commercially announced. The unique single die PA eliminates the combining losses from a multiple die design; however, the power density requires careful thermal design.

mmTron designers used ADS as the center of the TMC211 workflow. After initial simulations using sinusoidal stimulation, ADS enabled application waveforms to be used.

“There are many PA subtleties that only appear under modulated signals,” says Seyed Tabatabaei, mmTron’s CEO. “How the signal phase changes between stages, memory effects, interactions with capacitor values and placements, and power consumption all depend on modulation.”

Circuit simulation was only part of the workflow. mmTron employed the other EDA tools in Keysight PathWave, including ADS Electro-Thermal Simulator. ADS combines the native EM simulator and the electro-thermal extension in a single interface without layout conversions.

Listing of Keysight EDA tools used my mmTron in the design of the TMC211

mmTron’s design was one of three examples shown in Keysight’s video highlighting its RF EDA environment.

Download Keysight’s case study.