Clock tree synthesis basics pdf

Jan 10, 2014 clock tree synthesis is a process which makes sure that the clock gets distributed evenly to all sequential elements in a design. Normal clock gating circuit consists of an and gate in the clock path with one input as enable. Power aware clock tree synthesis part 2 hello while trying to build a clock tree which is power aware, lets go back a step ahead and look, what are the top observations for a clock network, and below image covers the same. A detailed explanation on the above is present in my clock tree synthesis course on udemy now, thats important thing we jumped into. Physically placing the standard cells and macros what.

Sep 30, 2016 clock tree synthesis clock tree synthesis is a process which makes sure that the clock gets distributed evenly to all sequential elements in a design. Cts clock tree synthesis december 18, 2012 by arunodayanjohn. Clock tree synthesis cts plays an important role in building wellbalanced clock tree, fixing timing violations and reducing the extra unnecessary pessimism in the design. Apr 26, 2018 clock trees are now the single largest source of dynamic power consumption, which makes clock tree synthesis cts and optimization an important task for achieving overall power savings. At each stage in the design cycle, it is imperative to check for timing violations by carrying out static timing analysis and do course correction, if required. Clock buffers and clock inverter with equal rise and fall times are used. From graph partitioning to timing closure handbook of algorithms for physical design automation. I think the position of page topic is too low such that the content space is limited. Introduction to multisource clock tree systems electronic. Went through clock tree synthesis course and found. Basics of setup and hold part 3 vlsi design overview and. First estimation of power dissipation of the design is carried out by calculation or using power analysis tools. The goal of cts is to minimize the skew and latency.

The goal during building a clock tree is to reduce the skew, maintain symmetrical clock tree structure and to cover all the registers in the design. Dec 18, 2012 cts clock tree synthesis december 18, 2012 by arunodayanjohn cts is the process of insertion of buffers or inverters along the clock paths of asic design in order to achieve zerominimum skew or balanced skew. Backend physical design interview questions and answers. Clock tree synthesis clock tree synthesis cts is the process of inserting buffersinverters along the clock paths of the asic design to balance the clock delay to all clock inputs. Whereas hfns uses buffers and inverters with a relaxed rise and fall times. After cts, the routing process determines the precise path for interconnection.

This blog provides an overview of various practical concepts related to synthesis, sta, low power, fpga which are used in industry. Clock tree synthesis cts cts quality checks skew, power, latency, etc. Mar 22, 2018 clock tree synthesis is very important in pd flow. Dec 04, 2017 clock tree synthesis is a part of physical design. The videos will develop an analytical approach to tackle technical challenges while building clock. Fanout buffers are the most basic type of clock and they are used to distribute an input frequency. We also try to cover the practical questionnaires related to these topics which are asked in the interviews of productservice based semiconductor companies. Sanity checks in physical design flow vlsi basics and. Violations are seen only after clock tree synthesis. Single clock normal synthesis and optimizationmultiple clocks synthesis each clock seperatelymultiple clocks with domain crossing synthesis each clock seperately and balance the skew. The complexity of the clock tree and the number of clocking components used depends on the hardware design. Clock tree synthesis under aggressive buffer insertion. Clock trees are now the single largest source of dynamic power consumption, which makes clock tree synthesis cts and optimization an important task for achieving overall power savings. Hfns are used mostly for reset, scan enable and other static signals having high fanouts.

There are two types of stop pins known as ignore pins and sync pins. What are the good books for learning clock tree synthesis. Once the netlist has successfully been placed and routed, you should be. There are two books which are really good to learn about cts vlsi physical design. The original clock root is partitioned into several pseudo clock. It is specific to your projectmore the clocks more challenging. Pdf an efficient clock tree synthesis method in physical design. With this series of lectures, we have explored onsite concepts applied in the vlsi industry.

A renewed emphasis on highfrequency clock design has heightened interest in multisource clocktree synthesis cts. Some clock synthesis works generate unbuffered clock networks that require a separate buffer. This paper aims to share practical experience regarding building a poweroptimized clock tree, determining the optimum targets for clock tree synthesis cts and monitoring the quality of results qor along the way. The placement data will be given as input for cts, along with the clock tree constraints. In this lecture, we are going to discuss why we usually do cts. Htree quality check of htree clock tree buffering buffered htree htree with uneven spread of flops advanced htree for million flops power aware cts clock gating static timing analysis with. Minimizing clock latency range in robust clock tree synthesis wenhao liu yihlang li huichi chen you have to enlarge your font. Clock tree synthesis requires accurate timing analysis in order to control clock skews among different parts of the clock tree.

But when enable becomes one in between positive level of the clock a glitch is obtained. Clock tree synthesis and soc clock distribution strategies. While we are trying to modify the above clock tree to be power aware, we need to make sure the above observations are retained. Smart vlsi is wellpositioned to support customers at any point and any level of semiconductor product life cycle. Algorithms for vlsi physical design automation naveed shervani, kluwer academic publisher, second edition. Paper special section on vlsi design and cad algorithms a. Its often the case that a single reference clock will be cascaded and. It is a onestopshop to understand industrial vlsi circuits. Based upon this estimation the width of the power ring and width and number of power straps are calculated.

Ic compiler ii is the industry leading place and route solution that delivers bestinclass qualityofresults qor for nextgeneration designs across all market verticals and process technologies while enabling unprecedented productivity. Clock tree synthesis in eda 1 implications of clocking 2 clock distribution 3 clock tree synthesis 4 additional subjects. This paper proposes a method aiding in low clock skew applicable to the mainstream industry clock tree synthesis cts design flow. Clock tree synthesis is a process which makes sure that the clock gets distributed evenly to all sequential elements in a design. Place and route stage pnr flow what is physical design.

Clock tree synthesis clock tree synthesis is a process which makes sure that the clock gets distributed evenly to all sequential elements in a design. Three basic routing structures for global clock h tree low skew, smallest routing capacitance, low power floorplan flexibility is poor. Why double spacing and multiple vias are used related to clock. But clock switches continuously, increasing the dynamic power consumption. So in order to balance the skew and minimize insertion delay cts is performed. Multisource clocktree synthesis is a relatively new option for clock distribution, joining conventional clocktree synthesis. We will discuss about skew and insertion delay in upcoming posts. For this tutorial we will generate layout for the gatelevel netlist of the greatest common divisor gcd circuit synthesized in tutorial 2. The clock distribution network or clock tree, when this network forms a tree distributes the clock signals from a common point to all the elements that need it. Ic compiler ii is the industry leading place and route solution that delivers bestinclass qualityofresults qor for nextgeneration designs across all market verticals and.

Cts is the process of insertion of buffers or inverters along the clock paths of asic design in order to achieve zerominimum skew or balanced skew. Since systems can have several ics with different clock performance requirements and frequencies, a clock tree refers to the various clocks feeding those ics. Minimizing clock latency range in robust clock tree synthesis. Clock is not propagated before cts as shown in the picture. Power aware clock tree synthesis part 2 vlsi system design. Vlsi academy clock tree synthesis clock tree networks are pillars and columns of a chip. What are the difference between high fanout synthesis and clock tree synthesis. Cts clock tree synthesis december 18, 2012 by arunodayanjohn cts is the process of insertion of buffers or inverters along the clock paths of asic design in order to achieve zerominimum skew or balanced skew. Static timing analysis sta interview questions static timing analysis interview questions static timing analysis plays major role in physical designpd flow.

Aug 08, 2015 the goal of clock tree synthesis cts is to minimize skew and insertion delay. Since this function is vital to the operation of a synchronous system, much attention has been given to the characteristics of these clock signals and the electrical networks used. Whats the difference between cts, multisource cts, and clock. We have captured some problematic scenarios and the problem solving. Whats the difference between cts, multisource cts, and clock mesh. Apart from these, useful skew is also added in the design by means of. Single clocknormal synthesis and optimizationmultiple clockssynthesis each clock seperatelymultiple clocks with domain crossingsynthesis each clock seperately and balance the skew. Timing is important because just designing the chip is not enough. Also, buffer insertion is an essential part in practical clock networks, since it helps reduce delay and slew. What are some good vlsi physical design books for beginner. Here are some of the standard vlsi physical design books that are helping me. In which layer do you prefer for clock routing and why. Building a wellbalanced clock tree and effectively managing clock skew has been a challenge since the first. Our team exposure to various processes, foundries and eda tools as an added advantage for shorter turnaround time for customers production release and time to market.

Power aware clock tree synthesis vlsi system design. Power aware clock tree synthesis part 2 hello while trying to build a clock tree which is power aware, lets go back a step ahead and look, what are the top observations for a. Download as ppt, pdf, txt or read online from scribd. Clock distribution and balancing methodology for large and. The goal of cts is to minimize skew and insertion delay. Clock tree synthesis clock tree synthesis cts is the process of inserting buffersinverters along the clock paths of the asic design to. A renewed emphasis on highfrequency clock design has heightened interest in multisource clock tree synthesis cts. A typical physical design cycle involves logic synthesis followed by test insertion, placement, clock tree synthesis and data routing. I took this course for understanding the basics of clock tree analysis. The goal of clock tree synthesis cts is to minimize skew and insertion delay. This tutorial covers how to implement a multisource cts design.