If you’ve read either (or hopefully both) of my previous blog posts (here and here), you’ll know I’m in the process of telling the story of an in-house smart speaker design project. It was undertaken last summer by a team of talented Altairians, with the aim of demonstrating the practical benefits of a simulation-driven approach to development. In particular, in a world increasingly dominated by multi-physics product design, we were keen to show how Altair solutions can help overcome the costs, delays and compromises that are associated with physical prototyping and testing.
Last time out, I looked at the structural and acoustic questions posed by our nascent smart speaker design. This time round, attention turns to the printed circuit board (PCB). I’ll be drawing on another excellent webinar, this time delivered by Aniket Hedge, project engineer, with the support of Jaehoon Kim, EM Application Engineer. I’m pleased to report you’ll find a view-on-demand version here, along with the entire smart speaker series. The aim in this post is to provide a flavor of their presentation. However, if you’d like to learn more about the virtual alternatives to physical testing and prototyping, I thoroughly recommend watching it in full.
As Aniket explains, the PCB represents the heart of our wireless speaker. It hosts all the functional modules, with the main elements comprising wireless, audio, power supply and charging. Aniket also reminds us of the tough commercial environment in which many PCB designers now operate. The demands for cost reduction, miniaturization and faster time to market are near-universal in the consumer electronics domain. In addition, for a wireless speaker, the challenges include reliable, standards-based connectivity, seamless audio streaming, and clear audio output to deliver that all-important perceived quality.
The components of our PCB design include a USB connection, charging IC, Bluetooth IC and antenna, audio amp, control IC, memory, LCD driver IC and speaker output. For this stage of the project, the focus was on two design considerations: audio quality and high-speed performance. For the former, Aniket demonstrates how differential audio lines, shielded audio lines and the thermal behavior of the main ICs are critical to achieving the desired results. For the latter, he emphasizes that designers need to ensure the satisfaction of specific impedance and the safe use of high-speed bus lines.
As you may recall from my earlier posts, the overriding theme of our project is the value of adopting a unified and integrated design environment for all the physics embraced by smart products. To this end, Aniket and Jaehoon’s tool of choice is Altair PollEx. This comprehensive PCB level EDA software suite covers design review, analysis and manufacturing. Designed to significantly reduce development cycles, its main features include the PCB Modeler with ECAD connectivity, the Unified Part Editor (UPE), PCB solvers (including signal, power integrity, and thermal analysis), PCB verification (including Design for Electrical (DFE)) and Logic/CAM.
To verify the differential audio lines and shielded audio lines, DFE checks were identified as the most appropriate methodology. This reflects the fact that DFE is becoming more and more important in consumer electronics, due to the increased operating speeds and complexity of products. The trends towards small volume production, shorter product lifecycles and rapid technology change are also driving the requirement for DFE.
All these factors mean that DFE checks at the development stage have become a necessity for electronics companies. By saving time and resources, they reduce both cost and time to market. What’s more, with PollEx, the DFE workflow couldn’t be easier. First, we import the design files, then apply the company design rules and ODM client rules. An actionable DFE check result is generated, enabling the engineer to evaluate and modify their design easily.
In our project, audio quality was verified via the strength of the differential pair, defined by its line separation and coupling ratio criteria. The second process that Aniket undertook is verification of the shielding of the audio lines by the ground plane, again via DFE check.
The flexibility of the DFE checking process is emphasized, with DFE rules customized easily. Moreover, any failures exposed by the checks can be linked back to the original ECAD drawing for fast rectification. Bear in mind also that Altair’s DFE tool can address many other attributes, such as electrical high speed, power, component separation and EMI ring stability, for example.
Next up is signal integrity (SI). Why? Quite simply, at higher bit rates and over longer distances, electrical signals can become degraded to the point at which errors occur, and the system or device fails. With the benefit of SI analysis, it is possible to mitigate any such impairments well before investment in physical prototyping and manufacture. Moreover, with PollEx, SI is very much part of the one-stop-shop philosophy. Designers can choose from numerous solvers – both 2.5D and 3D – to enable rapid feedback and any necessary changes.
The SI workflow demonstrated is the now familiar process of importing existing design files, this time via an I/O buffer model. After inputting all these files into the SI tool, the Altair proprietary SPICE engine generates results in the shape of waveforms, S-parameters, eye diagrams, and net topology, for example.
Aniket used SI to verify our smart speaker’s high-speed performance, demonstrating how we can employ it to achieve seamless connectivity quickly and efficiently via the USB data lines. In this case, that meant meeting the USB 2.0 specification. Impedance requirements had to be matched across the entire frequency. Aniket shows how PollEx’s SI tool facilitates not only network analysis of the USB lines, but also network topology analysis. And it’s a straightforward process. Net structures between components on the board can be reviewed, and ‘what if’ studies conducted quickly and easily by creating and modifying topologies. Analyzing the results via the waveform viewer, Aniket shows how easy it is for users to compare the results of any such adjustments. Similarly, SI analysis is performed on the high-speed memory bus lines, to verify they meet DDR requirements.
This latest step in our design journey is concluded by using PollEx to address thermal analysis. Once again, this is a critical issue in numerous consumer electronics products. By detecting and correcting thermal problems at this stage, it’s possible to prevent costly over-design and identify thermal requirements for the entire system.
In the case of our smart speaker, the charging IC and audio amp represented the main heating sources. They needed to be carefully assessed in terms of their impact on audio performance. As before, PollEx does all the leg work in terms of calculating the junction and board temperatures of various components, and then displaying the results in the form of a heat map of our board. Aniket virtually introduces forced convection, before re-running the thermal analysis and watching the changes to the heat map unfold on screen. Spoiler alert: there’s a lot more blue on it.
Mechanical design and validation of the PCB in the smart speaker is another important parameter in terms of ensuring system reliability and the overall success of our design. Any kind of inappropriate functioning in respect of the electrical, electronic, mechanical or circuitry elements might lead to the failure of these systems. Mechanical reliability is therefore of paramount importance.
Once accurate material mechanical data is obtained from the PCB design from PollEx, and fluid flow simulation conducted to obtain heat transfer from heating and cooling on the speaker, this data can be considered in terms of the conduction of mechanical thermal stress.
Including these thermal stresses as preloading to conduct dynamics analysis is a very important step for obtaining accurate mechanical validation of the PCB. To conduct dynamics simulation, dynamics loading of the full speaker model is needed. This can be obtained from either the test lab or a virtual test lab to simulate random vibration-based fatigue that confirms the reliability of the PCB design. Crucially, these simulations provide the insight that identifies critical points, and enables ‘what if’ studies and exploration of different mount configurations. It also speeds up the product development process.
As with the entire smart speaker journey, Altair’s approach here is all about the speed and flexibility of a unified solution that addresses the full array of challenges faced by the designer or engineer. In my next and final post in this series, we’ll be looking at two other vital design considerations for our speaker. Specifically, how can we apply all the benefits we’ve seen so far in our simulation-driven process to the demands of antenna design and EMI? But as I mentioned at the outset, there’s no need to wait for me to put pen to paper. You can find the whole story of the smart speaker project, told by the people who made it happen, here.