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Digital Transmission System Design Using ADS and Genesys

Case Studies

Keysight Technologies

Minimizing Design Risk, Shortening Development Time of a Digital Transmission System

Case Study

Powerful design and simulation software provides valuable insights to help uncover and solve difficult design challenges at every stage of the design process

Shaping the audio world of tomorrow is no easy challenge. That’s because professional audio digital transmission systems for use in broadcast studios, theaters and live performances demand uncompromised audio performance and quality, and that means artifact free sound and exceptional dynamics. More and more, they also require the ability to operate in multichannel environments over a large switching environment.

These were the challenges facing Sennheiser electronic GmbH & Co KG—a private German audio company specializing in the design and production of a wide range of consumer and high fidelity products—when it set out to develop the world’s first digital transmission system without a compounder system. The work was arduous, spanning a decade.

Those efforts paid off in September 2012 when Sennheiser launched its flagship product, the Digital 9000 system (Figure 1). This professional audio, 8-channel, wireless digital transmission system features a large switching bandwidth (470- to 798-MHz), unique uncompressed digital audio transmission, and outstanding intermodulation safety and RF sensitivity. It is the industry’s first professional digital transmission system to conform to European ETSI guidelines without using audio codes. At each step of the Digital 9000 system’s development,the Keysight EEsof EDA Advanced Design System (ADS) and Genesys design and simulation software from Keysight Technologies, Inc. played a crucial and pivotal role.

Sketching the Situation

Creating a digital transmission system that could operate in multichannel environments over a large switching bandwidth was a difficult task for the Sennheiser design team. The Digital 9000 system was an extremely complicated design. To even make its design possible, communication theory had to be extended and Voltage-Controlled Oscillators (VCOs) with a large tuning range had to be developed. Moreover, achieving suitable phase noise performance over the entire tuning range was difficult, as was just meeting all of the specified requirements for the system. Once the digital transmission system design was complete, its validation presented an entirely new set of challenges.

Eying a Solution

To overcome these challenges, Sennheiser’s lead RF design engineer on the project and Keysight Certified Expert, Roger Drees, knew he had to find the right tools with the right capabilities. For that, he turned to a trusted source—Keysight.

Drees had previously used Keysight EDA’s software with much success and realized its value in developing the Digital 9000 system. As he explains, “I was first introduced to Keysight products in school and became convinced of their value. When starting our Digital 9000 system project, it was clear to me that these same solutions had the capabilities we needed and could prove extremely helpful. I approached my company about the prospect and Keysight EDA’s design and simulation software was quickly adopted.”

Throughout the process, Sennheiser made use of a number of different Keysight EDA solutions, including: Advanced Design System (ADS) electronic design automation software for RF, microwave, and high-speed digital applications, Genesys, and the Momentum and Ptolemy simulators.

ADS provided the Sennheiser team access to full, standards-based design and verification with Wireless Libraries (e.g., the Modelithics Component Libraries) and circuit-system-EM co-simulation in an integrated platform (Figure 2). It also enabled the team to use a range of simulation engines (e.g., S-parameter, Harmonic Balance, Circuit Envelope, Transient, and Optimization), as well as Momentum 3D Planar EM simulation.

The ADS Momentum simulator provided Sennheiser with the ideal electromagnetic tool for analyzing signal integrity effects in PCBs; offering not only high accuracy but fast simulation times as well (Figure 3). Commonly used to model and analyze passive circuits, Momentum is also integrated in Keysight EDA’s Genesys software. Genesys is affordable, accurate, easy-to-use RF and microwave simulation software for circuit board and subsystem designers. For the Sennheiser team, it provided key capabilities for their RF and microwave filter, matching and circuit synthesis efforts.

Eying the Results

The use of the ADS and Genesys software proved pivotal for the Sennheiser team, providing valuable insight that helped it uncover and solve difficult design challenges at every stage of the design process.

During system simulation, the ADS RF Budget simulation software allowed Sennheiser to model the Digital 9000’s complete RF system with accurate block-level models and perform an RF budget analysis. EVM simulation with ADS/Circuit Envelope/Ptolemy was used to simulate the influence of active and passive RF modules and surface acoustic wave filters for a proprietary digital modulation. EVM/BER simulation also proved an invaluable capability.

For circuit simulation, ADS was used to design passive and active RF modules. The ADS Modelithics Component Libraries provided easy access to accurate, measurement-based passive and active models that take parasitic and substrate effects into account. Using the Layout Components feature in the Momentum EM simulator, Sennheiser was able to create components from a layout page in ADS and insert them into a schematic page just like any other component would be, with the symbols representing these components in the schematic designated as either a black box or layout look-alike symbol. The ADS RF-circuit co-simulation capability then allowed the team to simulate its RF and circuit design together.

Looking to the Future

Over the past decade or so, Sennheiser invested substantial time and effort in the development of its flagship product, the Digital 9000 system. While a complicated and challenging undertaking, those efforts were greatly aided by the use of Keysight EDA’s ADS and Genesys. For the Sennheiser team, the benefit of their use on the Digital 9000 system project was clear; it was able to successfully meet its system requirements with minimized PCB design risk, fewer PCB design cycles, and reduced overall development time.

 

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