New SerDes standard reduces power loss

The Power of ASA

13. April 2022, 14:38 Uhr | Irina Hübner
Für Assistenzsysteme und deren Kommunikation benötigten Strombedarfs hat insbesondere bei E-Fahrzeugenunschätzbare Vorteile: Die Reichweite steigt mit dem SerDes-Standard ASA Motion Link, die Verlustleistung deutlich reduziert
© Tierney/

Reducing the power required for assistance systems and their communication has invaluable benefits, especially for e-vehicles: The range increases. With the SerDes standard ASA Motion Link, the power dissipation for asymmetrical high-speed SerDes can be significantly reduced.

The transition to electric vehicles (EVs) is a key part of solving global challenges such as climate change. However, a limiting factor around their adoption is the range they can drive on a single charge. At the same time, to improve road safety, vehicles are taking on ever greater amounts of microelectronic-processing power. Cameras, displays, radars, leading-edge microprocessors, and all the links that connect them consume enormous amount of power, which is counterproductive to a large EV range. Reducing power consumption in cars is important, for reasons of environmental protection as well as customer satisfaction.

Taking this on as an opportunity to innovate, the Automotive SerDes Alliance (ASA) has recently defined a new standard, the ASA Motion Link, that drastically reduces power dissipation for high speed asymmetric SerDes. These links connect displays, cameras, and high-speed sensors such as radars to the central processing elements – dozens of instances per vehicle. As image sensors development continuously trends towards higher resolution and bit depth, this requires larger data rates in the transmission technologies connecting them. With so many factors increasing the power dissipation, it becomes important to look to the future and identify opportunities to lower the power consumption.

ASA offers several inherent advantages to improve the overall system power consumption:

1) ASA's transmission mechanism and protocol stacks are optimized for lowest power consumption

ASA Motion Link uses Time Division Duplexing (TDD) to transmit high bandwidth downstream data and low bandwidth upstream data traffic (see Figure 1). This technique greatly reduces the size and complexity of the receiver implementations. The reduction in complexity is achieved due to the non-overlap of signals in the forward and reverse directions at any given point in time. This in turn eases the recovery of signal on the receiver side. Legacy SerDes technologies typically use Frequency Division Duplexing which involves overlapping of signals and requires filtering techniques to separate the signals.

ASA-based products can meet the requirements of the target applications with lower power consumption – in some cases power dissipation can be reduced by 50%! Additionally, ASA defines a Light Sleep mode that further optimizes the power consumption based on the exact use case and link utilization. For example, when the actually used data rate is lower than what is available with the ASA link, Light Sleep can be used to reduce the power consumption further, even for the high data rate downstream transmission.

TDD-basiertes Übertragungsschema von ASA-Standards
Figure 1. ASA TDD-based transfer scheme.

2) ASA’s TDD based transmission enables enhanced Power over Cable (PoC) implementation at reduced costs.

The TDD based transmission scheme leads to significantly relaxed Return Loss (RL)/echo limits on the nodes compared with existing SerDes solutions (see Figure 2). Because a unit either transmits or receives data, the received data is not impacted by echoes of the transmitted data. A reduced RL allows for the use of smaller and cheaper inductors with lower saturation currents, while still meeting the power delivery and link performance requirements. In addition, the combination of lower power consumption and better RL, also enables the use of power over cable for future display applications.

 ASA-Motion-Link-MDI-Rückflussdämpfungsgrenzlinien im Vergleich zu denen von FDD-basierten SerDes-Systeme
Figure 2. ASA Motion Link MDI return loss limit lines compared with those of FDD-based SerDes systems.

3) ASA-based SerDes integration into the imagers will optimize the system attributes even further for future applications. In a typical application, this can reduce power dissipation of the SerDes communication in this application by 75%!

For automotive cameras, which often use SerDes as a communication technology, there is an additional component in respect to power. Many automotive cameras are placed in locations with very limited space, like the side mirrors. A small camera form factor is therefore essential for being able to offer the respective customer functions. At the same time, the small form factor limits the maximum power dissipation acceptable for cameras; typically to values around 2 Watts per camera sensor module. When this maximum is reached, no further functionality can be added. Any additional heat would significantly impair the quality of the image sensor and potentially render the images useless for the application. This is the reason why meeting low power consumption for the camera sensor modules is particularly important.

Additional to the low power consumption to start with, ASA’s simpler architecture and protocol stack enables easy integration into the future sensor products. By eliminating the high-speed interfaces between the sensor and Serializer, as well as the protocol adaptation layers involved, this enables the most competitive chip area, cost, and power efficient solution.

All these features help to save power in the camera modules and other systems using SerDes. Freed up space and energy in cameras can simply be saved or spent on higher resolutions, frame rates, or Artificial Intelligence (AI) processing features for next generation ADAS sensors. In the display applications, all these advantages will be turned into the ability to deliver the power required by higher resolution panels with a single data line.



The authors

Kirsten Matheus, Senior Expert Communication Technologies, BMW
Claude Gauthier, Director of Strategic Innovation, NXP
Nik Dimitrakopoulos, E/E & Infotainment, Rohde & Schwarz
Samay Kapoor, Senior Director of Business Management, Aviva Links
Conrad Zerna, Senior Mixed-Signal ASIC Designer, Fraunhofer IIS
Kamal Dalmia, COO, Aviva Links
Ajeya Gupta, Advanced Networking & Electrical Architecture, Ford Motor Company

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BMW AG, NXP Semiconductors Germany, NXP Semiconductor Netherlands B.V.