Clock Tree Synthesis (CTS) is a critical phase in the physical design flow of integrated circuits, aimed at distributing the clock signal with minimal skew and jitter across the chip. This blog explores advanced CTS methodologies, specific case studies, and the latest cutting-edge technologies in digital design.
Importance of CTS in IC Design
1. Designing the Clock TreeClock tree design involves planning the distribution of the clock signal to various parts of the chip. This process must balance the need for low skew and jitter with other design constraints like area and power consumption.
Case Study:
A team at Vitesse used Synopsys' Clock Tree Compiler (CTC) in their design flow to manage complex clock trees. They achieved significant improvements in clock skew management by using a hierarchical approach where sub-clock trees were driven by a top-level clock. This method allowed them to meet their stringent timing requirements efficiently.
Implementation:
Hierarchical Clock Trees: Divide the clock tree into manageable sub-trees driven by a top-level clock.
Optimization Tools: Use tools like Synopsys CTC to automate and optimize clock tree design.
2. Utilizing Clock Buffers and Inverters
Clock buffers and inverters are used to strengthen the clock signal and ensure it reaches all parts of the chip without degradation. The placement and sizing of these components are crucial for maintaining signal integrity.
Case Study:
Cadence’s CTgen tool was employed to optimize the placement of clock buffers and inverters in a design with high fanout networks. The tool helped in reducing skew and maintaining signal integrity by using high drive strength buffers and optimizing the number of driver-receiver segments.
Implementation:
High Drive Strength Buffers: Use buffers with high drive strength to maintain signal integrity over long distances.
Segment Optimization: Minimize the number of driver-receiver segments to reduce potential skew and jitter.
Innovative Methods in CTS
1. Managing Skew and JitterManaging skew and jitter is critical for ensuring synchronous operation across the chip. Tools that support physically aware CTS can help in achieving better results by considering physical design constraints.
Case Study:
A semiconductor company integrated physically aware CTS using Synopsys tools. This integration allowed them to better manage skew and jitter by accounting for physical layout constraints during the synthesis process. As a result, they achieved more accurate timing closure and improved overall performance.
Implementation:
Physically Aware Tools:Utilize CTS tools that integrate physical constraints into the synthesis process.
Skew Optimization:Employ strategies to balance clock skew, such as adjusting buffer placement and using clock tree balancing techniques.
2. Implementing Advanced Clock Gating
Clock gating is used to reduce dynamic power consumption by disabling the clock signal to certain parts of the circuit when they are not in use. Effective clock gating can also help in managing clock tree complexity.
Case Study:
The Dolphin integration with Cadence tools was used to implement advanced clock gating techniques. The team defined specific gating schemes and adjusted the clock tree to accommodate these gates, resulting in significant power savings without compromising performance.
Implementation:
Define Gating Schemes:Plan and implement clock gating schemes during the early stages of clock tree design.
Tool Integration:Use tools that support advanced clock gating and integrate these gates into the CTS process.