Issued Date：2024/10/09AI High Speed Signal
Issued By：iST
As AI technology advances, ensuring stable and interference-free high-speed signal transmission in AI application devices has become a significant challenge for engineers. How to ensure products meet high-speed specification requirements and maintain market leadership?
AI High Speed Signal
In today’s technological landscape, whether it’s AI servers, accelerators, switches, or AI edge computing devices like PCs, gaming consoles, graphic cards, set-top boxes, monitors, and TVs, all these devices face the challenge of high-speed signal transmission. Every design aspect, from eliminating signal interference to material selection, can impact the product’s final performance and market success. Especially with the widespread adoption of high-speed specifications like PCIe Gen 6 and Ethernet 400/800G, product testing and verification have become indispensable steps in the design process. Many companies, particularly developers involved in AI applications, urgently need efficient testing solutions to address potential issues in high-speed transmission and ensure their products pass market verification.
In this article, iST’s Signal Testing Lab will share practical cases on how the latest comprehensive AI high-speed signal solutions, covering Front-end SI/PI Simulation & Design Evaluation, PCB (Printed Circuit Board) Substrate Characteristic Test Analysis, Port Physical Layer (PHY) Conformance Verification, and High-Speed Signal Test Custom Fixture Design, can provide one-stop assistance to keep you ahead during this wave of technological innovation.
AI High Speed Signal
AI High Speed Signal
The iST Signal Testing Lab has identified new technical challenges posed by faster computing environments in AI applications, including signal transmission stability, debugging needs, and thermal management. The introduction of high-speed signal repeater ICs (Re-drivers) for signal compensation and the need for upgraded PCB materials and connectors add complexity to both product design and testing. Below, we present four core AI high-speed signal solutions:
1. Front-end SI/PI Simulation & Design Evaluation
Signal Integrity (SI) and Power Integrity (PI) simulations are critical in ensuring the competitiveness of high-speed transmission systems. As electronics evolve, especially in high-bandwidth AI applications, impedance mismatch, poor structural design, or improper via layout can cause signal distortion and interference, degrading overall performance. Higher computational speeds and densities increase the risks of voltage fluctuations and noise, affecting both power integrity and system performance. SI and PI assessments are crucial for maintaining stability in these high-speed environments.
iST offers Signal Integrity and Power Integrity Simulation Services. Clients need only to provide relevant files, such as schematic and board files, to utilize Ansys and Cadence simulation software. These simulations assist customers in evaluating front-end designs during the product development phase and conduct signal simulations prior to trial production, helping to mitigate cost risks associated with design defects.
(1) Key services provided by iST include:
a. Signal Integrity (SI):
- (a) S-parameters:Return loss, Insertion loss, Crosstalk
- (b) Time Domain Reflectometry (TDR)
- (c) Eye Diagram Analysis
b. Power Integrity (PI):
- (a) DC IR-drop Analysis: This analysis evaluates the voltage drop across the Power Net to ensure it remains within acceptable limits, preventing system anomalies. Key testing metrics include voltage drop distribution, current density, DCR (Direct Current Resistance), and power loss.
- (b) AC PDN (Power Delivery Network) Analysis: This process examines the impedance at the device end, ensuring that low AC (Alternating Current) impedance is maintained. High impedance can lead to abnormal IC operation and power noise, adversely affecting system stability
(2) iST’s Case Sharing：
a. Case Sharing 1 – Layout Optimization:
After completing the layout design, Signal Integrity (SI) analysis was conducted to confirm the signal quality. During the simulation process, we discovered that the signal exhibited a high reflection coefficient in the operating frequency band (base frequency of 8 GHz), particularly around the areas where the traces entered and exited vias, as well as near capacitors. We optimized these areas by ensuring symmetrical routing for the vias and improving the anti-pad routing beneath the capacitors, thereby resolving impedance discontinuity caused by oversized capacitors. Following these adjustments, the reflection coefficients for both the base frequency and harmonics were significantly reduced, ensuring signal integrity.
Figure 1: Comparison of signal reflection coefficients (S11) before and after optimization. (source: iST)
b. Case Sharing 2 – DC IR-Drop Improvement:
The customer experienced voltage loss as the transmission distance increased when designing their board. Through analysis of Power DC simulation results, we observed that the voltage drop on the Power Plane was too high. Further investigation revealed that excessive fragmentation of the Power Plane was the primary cause. To address this issue, we adjusted the integrity and distribution of the Power Plane, reducing the overall voltage drop and optimizing the placement and method of the Sense compensation. Ultimately, we met the customer’s requirements regarding voltage drop variations at different sites.
Figure 2: After iST‘s modifications,
all IR-drop results for the Power Plane passed successfully. (source: iST)2. PCB Substrate Characteristic Test
In high-speed signal transmission, increasing losses make PCB material quality crucial for maintaining signal integrity. To ensure the quality of PCBs, it’s essential to evaluate the materials not only during the design phase but also through actual testing to validate their performance.
(1) iST offers comprehensive testing services for both PCBs and PCB assemblies (PCBAs) to support these needs:
a. Impedance Measurement: Testing the impedance characteristics of PCB materials to ensure stable signal transmission.
b. S-parameter Measurement: Analyzing signal transmission quality at high speeds to identify any performance issues.
c. Intel Delta-3.0/4.0 Testing: Verifying PCB performance under both normal and varying temperature conditions, ensuring reliability across environments.
d. Board-Level Debug Testing: Performing end-to-end channel loss tests to detect and resolve signal transmission issues in the PCB.
(2) iST’s Case Sharing：
a. Case Sharing 1 – TDR / S-parameter:
When a client’s product failed association standards, iST recommended TDR and S-parameter tests to ensure PCB impedance and production alignment with design requirements.
Figure 3: Testing on PCB using a network analyzer, including results for impedance (TDR), insertion loss (IL), and return loss (RL). (source: iST)
b. Case Sharing 2 – Fixture De-embedding:
During PCB characteristic testing, probes or fixtures may introduce extra losses. We utilized software-based de-embedding to eliminate these effects, providing more accurate results.
Figure 4: Utilizing software post-processing to eliminate the influence of probes or fixtures on test results. (source: iST)
3. PHY Conformance
PHY (Port Physical Layer) is responsible for data transmission between devices and networks. PHY Conformance tests ensure that physical layer performance meets specific protocol standards, enabling stable and efficient data transmission without signal distortion or interference.
Clients only need to provide semi-finished boards and interface data for test validation. This service helps clients ensure compliance with specific standards at the hardware or system level, guaranteeing proper operation and adherence to regulatory requirements. Additionally, we offer troubleshooting and debugging services to ensure smooth product performance.
(1) iST’s services include compliance and debugging support for PCIe and Ethernet standards:
a. PCIe 5.0/6.0 Pre-Conformance Testing（Tx/Rx/100M Clock）:This testing evaluates the transmission performance of PCIe 5.0 and 6.0, ensuring compliance with predefined timing and signal integrity requirements. It includes assessments of PCIe Electrical Characteristics Test and PCIe Protocol Test.
b. Ethernet 400/800G Conformance Testing (IEEE 802.3bj/bs/ck):验证Ethernet This testing verifies the performance of Ethernet 400G and 800G to ensure conformity with high-performance fiber module standards such as QSFP-DD and OSFP, guaranteeing reliability in high-speed data transmission.
Figure 5: 100G BaseE CR / KR Ethernet Rx testing solution.(source: Anritsu / edited: iST)
Figure 6: PCIe5.0/6.0 Rx testing solution.(source: Anritsu / edited: iST)
4. Custom Test Fixture Design
In the process of high-speed signal testing, customized testing fixtures not only enhance testing efficiency and shorten development cycles but also prevent testing errors caused by unsuitable fixtures, ensuring high performance and reliability of the products. iST offers tailored testing fixture designs based on customer needs and provides a comprehensive service from planning, design, verification and production, ensuring that the testing equipment meets specific requirements.
The rise of generative AI has accelerated the growth of the high-speed signal market. With years of accumulated experience in high-speed signal testing, iST Signal Testing Laboratory has established close collaborations with global standard organizations such as USB-IF, HDMI Forum, and VESA, leveraging industry-leading equipment to provide you with the most accurate testing and analysis. Whether you are involved in the design and development of servers, switches, AI acceleration cards, or edge computing devices such as PCs, gaming consoles, graphics cards, set-top boxes, monitors, and TVs, we can assist you in swiftly entering the market.
If you would like to further understand the details, please feel free to contact Mr. Chen at +886-2-2792-2890 ext. 2715 or via email at [email protected]；[email protected]。