Power Supply Induced Jitter on Clocks: Risks, Mitigation, and the Importance of Accurate Verification

In the realm of digital systems, clocks play a crucial role in synchronizing various components and ensuring smooth flow of logic propagation. However, the accuracy of clocks can be significantly affected by power supply induced jitter. Jitter refers to the deviation in the timing of clock signals with PDN noise compared to ideal periodic timing. This essay explores the risks associated with power supply induced jitter on clocks, strategies to mitigate its impact, and the crucial role of accurate verification in maintaining reliable clock performance.

Infinisim JitterEdge is a specialized jitter analytics solution, designed to compute power supply induced jitter of clock domains containing millions of gates at SPICE accuracy. It computes both period and cycle-to-cycle jitter at all clock nets, for all transitions using large milli-second power-supply noise profiles. Customers use Infinisim jitter analysis during physical design iterations and before final tape-out to ensure timing closure.

Understanding Power Supply Induced Jitter

Power supply induced jitter occurs when fluctuations or noise in the power supply voltage affect the timing of a clock signal. In digital systems, clock signals are typically generated by phase-locked loops (PLLs) or delay-locked loops (DLLs). PLL jitter is added to the PDN jitter to compute total clock jitter.

Risks of Power Supply Induced Jitter

1. Timing Errors: The primary risk associated with power supply induced jitter is the introduction of timing errors. These errors can lead to setup and hold violations resulting in synchronization errors between different components
2. Increased Bit Error Rates (BER): Jitter-induced timing errors can result in data transmission issues, leading to a higher BER in communication channels. This can degrade the overall system’s reliability and performance.
3. Reduced Signal Integrity: Jitter can cause signal integrity problems, leading to crosstalk, data corruption, and other noise-related issues, especially in high-speed digital systems.
4. Frequency Synthesizer Instability: In systems that rely on frequency synthesizers for clock generation, power supply induced jitter can cause the synthesizer to become unstable, leading to unpredictable system behavior.

Mitigating Power Supply Induced Jitter

To minimize the impact of power supply induced jitter on clocks, several mitigation strategies can be employed:

1. Quality Power Supply Design: Implementing a robust and well-designed power supply system is crucial. This includes the use of decoupling capacitors, voltage regulators, and power planes to reduce noise and fluctuations in the supply voltage.
2. Filtering and Isolation: Incorporate filtering mechanisms to remove high-frequency noise from the power supply. Additionally, isolate sensitive clock generation circuits from noisy power sources to limit the propagation of jitter.
3. Clock Buffering and Distribution: Utilize clock buffers to distribute the clock signal efficiently and accurately. Proper buffering helps to isolate the clock signal from the original source, reducing the impact of jitter.
4. Clock Synchronization Techniques: Implement clock synchronization techniques that enable multiple components to share a common reference clock, mitigating potential timing discrepancies.
5. Minimize Load and Crosstalk: Reduce the capacitive load on clock distribution networks and minimize crosstalk between clock and data signals to maintain signal integrity.

Importance of Accurate Verification

Accurate verification of power supply induced jitter is essential for several reasons:

1. System Reliability: Accurate verification ensures that the system meets timing requirements, reducing the risk of errors and malfunctions caused by jitter-induced timing variations.
2. Performance Optimization: By understanding the extent of jitter in the system, designers can optimize clock generation and distribution, maximizing performance without compromising reliability.
3. Compliance with Standards: Many industries and applications have specific timing requirements, such as in telecommunications or safety-critical systems. Accurate verification ensures compliance with these standards.
4. Cost and Time Savings: Early identification and mitigation of power supply induced jitter during the verification process save time and resources, preventing potential issues during product deployment.

Conclusion

Power supply induced jitter on clocks poses significant risks to the accurate operation of digital systems. Mitigation strategies, including quality power supply design, filtering, and proper clock distribution, are essential for reducing jitter’s impact. Accurate verification of power supply induced jitter is crucial to maintaining system reliability, optimizing performance, and ensuring compliance with industry standards. By understanding and addressing this challenge, designers can create more robust and dependable digital systems capable of meeting the demands of modern technology.

Characterization is a common technique used in the analysis of clock jitter and involves measuring and quantifying the variations in a clock signal’s timing. Characterization is often used to describe the process of measuring and analyzing the behavior of a signal or component to understand its performance characteristics. In the context of clock jitter, characterization-based tools measure the statistical distribution of jitter values, determine key metrics such as RMS jitter and peak-to-peak jitter, and analyzing how different factors in the design contribute to jitter.

For designs at 7nm and below nodes, where a sub-pico-second level of jitter needs to be identified, a more accurate approach is needed. Running a full circuit simulation at the transistor-level along with parasitic interconnect can provide SPICE accurate Jitter analysis and help identify sources of jitter and their impact. Infinisim’s ClockEdge’s jitter capability provides the accuracy needed to model clock jitter and its effects.

If you have questions feel free to contact the clock experts at Infinisim here: https://infinisim.com/contact/

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