When the advancement of autonomous driving was introduced to the automotive industry, designers looked for proven, industry-standard interfaces for improved data transfer. Previously the Mobile Industry Processor Interface (MIPI) had been widely used in the mobile industry; however, it became the optimal choice for data transmission in autonomous driving as the benefits greatly outweighed those seen by the traditional automative CAN and I2C buses. MIPI is predominantly used in automotive ADAS design (Autonomous Driving) to adhere to specific design requirements as seen below.
| Design Requirement | MIPI Benefit |
| Battery Powered | Low Energy Transport Solution
|
| Surround View Cameras | High Bandwidth |
| Minimal Interference | EMI Mitigation
|
| Dynamic Driving Conditions | Vibration Resistance |
| Functional Safety | ISO26262 Adherence |
| Reliability | Proven Implementation
|
While the implementation of MIPI interfaces in automotive applications has improved data transfer it has also introduced signal integrity concerns which must be addressed for successful implementation. This is where ZF Automotive turned towards simulation with Sigrity Aurora.
Background
ZF Automotive is a major automotive supplier producing driveline and chassis systems as well as active and passive safety technologies. For over 10 years, ZF Automotive has been combining electrical engineering expertise with advanced PCB, signal integrity, and power integrity knowledge to address complex challenges seen in the automotive industry.
Problems & Challenges
The increasing use of MIPI standards in automotive applications requires additional attention be given to the signal quality for data transmission. This is due to the unique challenges posed by automotive environments which can degrade the quality of MIPI signals. These challenges include:
- Electromagnetic Interference (EMI)
- Temperature Variations
- Power Fluctuations
- PCB Design Constraints
To address these challenges, designers must evaluate and improve signal integrity for reliable performance in high-speed data transmission.
Goals & Objectives
The overall objective of ZF Automotive is to ensure long-term performance stability and compliance with automotive industry standards for their products. For their autonomous driving (ADAS) devices, this can be achieved by anticipating and preventing SI problems for MIPI interfaces as well as improving overall system robustness through:
- Minimizing signal losses
- Reducing crosstalk
- Improving data reliability
Additionally, ZF Automotive strived to develop best practices for MIPI implementation to maximize MIPI signal integrity in automotive applications and accelerate future designs. These best practices should include an emphasis on crucial elements such as:
- Trace routing strategies
- Impedance control
- Differential pair design
- Termination tactics
- Power integrity considerations
Approach & Solution
To perform realistic signal integrity analysis, ZF Automotive turned to Cadence’s Sigrity X Aurora. Sigrity Aurora was leveraged to perform realistic signal integrity analysis due to features which increase automation and integration, including:
- Scripting Support to Reduce Setup Time
- Easy to Follow Workflows
- Auto Cropping Functionality to Reduce Database Size
- Unified Design Environment for PCB and Simulation
- No Detailed Models Required
- No Data Migration or Third-Party Tools
- Constraint-Driven Flow
- Synchronization Between PCB and Simulation
These features enhanced analysis, streamlined collaboration between designers and SI/PI engineers, and accelerated the design and analysis process.
Implementation
ZF Automotive incorporated signal integrity analysis throughout the layout process to address SI concerns and improve MIPI performance when change was easiest. The following analyses were performed to create a robust MIPI design which adhered to industry and safety standards.
1. Impedance Analysis
Ensuring consistent trace impedance for single-ended and differential nets is the foundation of signal integrity, especially in high-speed designs. Sigrity X Aurora helped ZF Automotive perform impedance analysis through two different methods:
In-Design Impedance Analysis
The impedance analysis workflow was used in Sigrity X Aurora throughout the layout process, incorporating the stackup definition, simulation models, and impedance target of 100 ohms to identify and fix impedance discontinuities. This identified any deviations early in the design process before layout completion.
TDR Plot
The interconnect model extraction workflow in Sigrity X Aurora was used to automatically generate the TDR plot. The S-parameter plotted TDR report allowed designers to compare MIPI signal performance to MIPI specifications and verify the impedance of the differential signals.
2. Crosstalk Analysis
MIPI crosstalk analysis was performed to ensure crosstalk remained within the acceptable levels. Sigrity X Aurora enabled ZF Automotive to perform crosstalk analysis through:
In-Design Crosstalk Analysis
The crosstalk analysis workflow was used in Sigrity X Aurora throughout the layout process to analyze crosstalk between traces on the PCB. This enabled ZF Automotive to evaluate crosstalk at the board level and identify if crosstalk exceeded the defined limit of 50mV.
Crosstalk Plot
The interconnect model extraction workflow in Sigrity X Aurora was used to automatically generate the crosstalk plot. The S-Parameter plotted crosstalk report enabled ZF Automotive to quickly identify if crosstalk exceeded -40dB at 500MHz per MIPI specifications.
3. Insertion and Return Loss Analysis
Once again, using the interconnect model extraction workflow, ZF Automotive automatically generated the required insertion loss and return loss plots. This allowed them to evaluate the insertion loss was below -1dB and the return loss was below -10dB.
Since Sigrity X Aurora is CAD and layout aware the setup required to run these simulations was minimal. This enabled ZF Automotive to efficiently perform in-design analysis for impedance and crosstalk as well as analysis of critical plots to verify and improve MIPI performance.
Results & Outcomes
“Design smarter, simulate earlier, fix faster- that’s Aurora.”
Sigrity X Aurora was able to create a realistic digital twin for efficient analysis of ZF Automotive’s autonomous driving devices containing MIPI interfaces 10x faster compared to traditional methods. This enabled the designers to quickly verify proper MIPI operation and signal integrity including:
- 100 Ω continuous trace impedance
- Less than 50mV crosstalk for MIPI signals on the PCB
- Adherence to MIPI performance standards
- Minimal Insertion Loss and Return Loss
Performing simulation and analysis with Sigrity X Aurora provided a unified environment to identify, correct, and verify common signal integrity issues facing MIPI interfaces. Additionally, the Sigrity X Aurora flow reduced the time required for integration and collaboration between the design engineer and SI/PI engineer.
Insights & Lessons Learned
Sigrity X Aurora provided an ideal environment to produce and analyze a digital twin, enabling ZF automotive to quickly identify signal integrity issues and improve MIPI interface performance. Sigrity Aurora improved their PCB design and analysis flow with:
- Reduced Setup Time
- User-Friendly Interface
- Native Environment for In-Design Analysis and Results
- Early Detection of Issues
- Reduced Database Size
- Desktop Simulations
- Faster Simulation Time
- Streamlined Communication
- Enhanced Engineering Efficiency
- Constraint-Driven Flow and Synchronization
ZF Automative proved Sigrity X Aurora provides engineering teams with a powerful environment that anticipates and prevents SI problems, offering engineers a framework for effectively analyzing and improving MIPI interfaces. Simulating your high-speed designs in Sigrity X Aurora, gives engineers early in-context access to realistic, reliable results that will ensure long-term performance stability and compliance with Automotive industry standards. Learn more about Sigrity X Aurora and get a free trial to test out impedance analysis, crosstalk analysis, coupling analysis, IR drop analysis, and more on your designs.
