However,lock tree synthesis tools can recognise the clock gates, and also do a power aware cts. Design and layout guidelines for the cdcvf2505 clock driver. It offers lower skew and better onchip variation ocv performance than a. Pdf an efficient clock tree synthesis method in physical design. A practical clock tree synthesis for semisynchronous circuits. The cts engines of these tools support most of the soc requirements to design a robust clock tree. Htrees zero low skew only in the absence of pvt variations two types of approaches to handle this. We have captured some problematic scenarios and the problem solving. The methodology presented here resulted in clock tree power savings of. Easy design uses a lot of wiring resources power and area implications.
This work presents a clock tree insertion and timing verification methodology for three dimensional integrated circuits 3dic. How to use an hclock tree in a pipelined adder electrical. The complexity of the clock tree and the number of clocking components used depends on the hardware design. Current methodology fig 1 shows a typical implementation of clock tree being currently followed. This paper proposes a method aiding in low clock skew applicable to the mainstream industry clock tree synthesis cts design flow. To deal with sparklecode issue in asynchronous sar subadcs, a new backend metastability correction technique is employed. Issues such as power, signal integrity, clock tree. Second, designing a hierarchical clock tree and harden it inside the silago logic. Standard cell asic to fpga design methodology and guidelines introduction the cost of designing traditional standard cell asics is increasing every year. Addressing clock tree synthesis cts challenges in soc. A hardware design methodology or platform is complete if it has the capabilities to. The skew between the leaves of the h tree on tiers a and c i. Cip cataloginginpublication wilke, gustavo reis analysis and optimization of meshbased clock distribution architectures gustavo reis wilke.
During cts, the tool isolates exclude pins from the clock tree by inserting a guide buffer before the pin. In a synchronous clock distribution network with zero latencies, digital circuits switch simultaneously on the clock edge, therefore they generate substrate noise due to the sharp peaks on the supply current. Clock tree insertion and verification for 3d integrated. Differential signaling, skew control, careful transmission line design, and other techniques can be used to ensure that a centralized clock source provides similar.
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. Clock network costs the most power for a synchronous design and directly affects circuit. Clock tree power reduction by clock latency reduction. Designing a clock tree 5 questions to ask symmetry blog. Finally, some conclusions are presented in section v. A clock waveform acquired from the topology combining an h tree and global rings, shown in fig. The integration of these techniques offers the maximum bene. Our approach can be seamlessly integrated into a typical design flow, and its effectiveness is demonstrated with experimental results obtained. A survey on buffered clock tree synthesis for skew. Mar 14, 2019 clock gating can occur at the leaf level at the register or higher up in the clock tree.
Clock tree insertion and verification for 3d integrated circuits. When clock gating is done at the block level, the entire clock tree for the block can be disabled. Highspeed clock network design is a collection of design concepts, techniques and research works from the author for clock distribution in microprocessors and. The 3dic verification methodology serves as an efficient means to perform all setup and. Aug 07, 20 the goal of clock tree synthesis is to get the skew in the design to be close to zero. Clock trees vs clock grids there are 2 two kinds of clock skews. Increasingly, structured approaches to clock tree design are seen in practice.
Thus, clock trees are still of interest and great practical relevance for reasons of cost ef. Buffered clock tree synthesis has become increasingly critical in an attempt to generate a high performance synchronous chip design. Robust chiplevel clock tree synthesis for soc designs. Such non tree methods typically have large overheads in terms of power, area, wirelength and signoff analysis complexity. Addressing clock tree synthesis challenges design and reuse.
If possible, route data and clock in opposite directions. Exact zero skew in terms of distance here we are ignoring parasitic delay due to the symmetry of the h tree. The ability to construct multiple clock trees effectively is very important. Shield clock wires route power lines vdd or gnd next to clock lines to minimizeeliminate coupling with neighboring. Each branch of clock tree can be represented by a distributed resistance capacitance segment by b uffer insertion. The proposed methodology relies on designing a hybrid clock network that provides predictability and robustness to the design ow. Clocktree is easy and your clients will love the convenience. We present a method to build leaf cells at lesser latencies.
Switching activity is high, since clock toggles constantly. Its often the case that a single reference clock will be cascaded and. A multisource clock tree is a hybrid containing the best aspects of a conventional clock tree and a pure clock mesh. It uses a single resistor at the load end of the trace, as shown in figure 7 and, like the thevenin and ac methods, it acts by preventing signal reflection from the load end.
Once the clock inventory has been completed, determine. Mar 14, 2012 multisource clock tree synthesis is a relatively new option for clock distribution, joining conventional clock tree synthesis and clock mesh. Dec 03, 2012 method of mean and median follows the strategy similar to h tree algorithm, provided the h tree shape is achieved by proper partitioning of the module. Design methodology concept the most crucial effect of the uncertainty introduced in the clock signal delay is the increased delay uncertainty between the. Design and layout guidelines for the cdcvf2505 clock. Clock tree optimization we now explain the toplevel clock tree optimization problem and our approach. Cluster clock nodes and build a local tree by the load balance based cts methods create a buffered rc network from the local clock tree minimize clock skew by wire sizing and snake routing zadvantages. 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. Cheng li 5 the higher the clock tree ct latency, the more this helps us meet any setup time requirement for the design. Optimal generalized htree topology and buffering for high. Clock tree optimization in synchronous cmos digital circuits. Pdf this paper proposes a method aiding in low clock skew applicable to the mainstream industry clock tree synthesis cts design flow.
The use of gated clocks to help with dynamic power consumption make jitter worse. C is effectively the delay of a stacked 3d via traversing the three tiers to transfer the clock signal from the. Since systems can have several ics with different clock performance requirements and frequencies, a clock tree refers to the various clocks feeding those ics. A survey on buffered clock tree synthesis for skew optimization anju rose tom1, k. Lisa parker clock tree of life design clock by lisa parker new home gift housewarming gift silver clock panachehomeware 4. Clock tree synthesis for timing convergence and timing. Clock tree synthesis part 1 digital design analog design. These tools even generate clock spec definitions from sdctiming constraint files. Clock tree optimization in synchronous cmos digital. H tree do not produce corner sharper than 900 and no clock terminals in the h tree approach in close proximity like x tree. Clock distribution network an overview sciencedirect topics. Clock trees vs clock grids there are 2 two kinds of clock skews structural layout skew capacitive load mismatch wire length mismatch skew due to pvt variations handled by balanced clock trees eg. It continuously partitions the system into two equal parts fig3 and connects the center of the whole circuit module to center of the two subcircuits submodule and thus produces a non.
Check if any cell has big transition times, capacitance, or high fanout. Popular in high speed mpu design, but not suitable for asic. It has been designed in the context of and incorporated into the 3dic design methodology also developed within our research group. Power clock is a major power consumer in your design. In this paper, we propose a new clock tree synthesis method for semisynchronous circuits. The resulting reduction in clock network switching becomes extremely valuable in reducing dynamic power. This dissertation provides a comprehensive study on four clock design techniques. Clock power consumption depends on switching activity and wire length. Clock tree is an important terminology in the physical design process which takes place after placement. Stinson ee 371 lecture 1 7 clock distribution examples h tree binary difficult to get low skew complex design least number of wiring resources global local semicustom custom local dist.
The tool considers exclude pins only in calculation and optimizations for design rule constraints. Clock tree synthesis for timing convergence and timing yield. Cluster clock nodes and build a local tree by the load. Global clock routing in presence of obstacles is a new domain of research in recent days. Firstly, we conducted many clock tree synthesis experiments, which. Oct 16, 2017 exclude pin are clock tree endpoints that are excluded from clock tree timing calculation and optimization. Weak cells with high fanout produce huge transition times. Clock power minimization using structured latch templates. Both of these clock gating methods will eventually introduce physical gates in the clock paths which control their downstream clocks. Whats the difference between cts, multisource cts, and clock. Standard cell asic to fpga design methodology and guidelines. The tree is essentially a way to distribute the clock to different places on the layout at approximately the same time i. Notes8 sta and clock tree faculty of engineering and.
You can choose either to shield clock nets before routing signal nets or vice versa. An e cient timing and clock tree aware placement flow with. With technology advancement happened over the past one and half decade, clock tree robustness has become an even more critical factor affecting soc performance. There are techniques using clock latencies in order to. In this work, a novel low swing clock tree synthesis methodology is combined with a custom low swing clockaware d flipflop dff design. The methodology presented here resulted in clock tree power savings of up to 20% according to simulation results. The original clock root is partitioned into several pseudo clock. The clock skew between the tiers of each block is listed in table 16. In addition to nonrecurring engineering nre and mask costs, development costs are increasing due to design complexity.
Robust chiplevel clock tree synthesis computer engineering. Pdf an efficient clock tree synthesis method in physical. Analysis and optimization of meshbased clock distribution. Design techniques for ultrahighspeed timeinterleaved. For the h tree topology, the clock signal delay is measured from the root to a leaf of the tree on each tier, with no other load connected to these leaves. A clock tree obtained by the proposed method is a multilevel multiway clock tree such that a clock input timing of each register is a multiple of a predefined unit delay and the length of interconnection from a parent node to its child is upper bounded. Clock tree synthesis in asic backend design atlantis press. Pdf clocktree synthesis for lowemi design researchgate. A reliable clock tree design methodology for asic designs.
High performance low swing clock tree synthesis with custom d. In section iv, we summarize our work and outline directions for future research. Clock tree layout design for reduced delay uncertainty. Clock distribution network an overview sciencedirect. Clock distribution techniques matching gates and wires skew keep transistors oriented in same direction keep transistor environment identical keep wire lengthwidthspacing identical use fully shielded wires minimize clock distribution depth skew, jitter more buffers means more chance for mismatch p, v, or t. These gates could introduce clock skew and lead to setup and holdtime violations even when mapped into the soc, however, this is compensated for by the clock tree synthesis and layout tools. Popular clock tree construction algorithms are h tree or mms algorithms that construct global clock trees with uniform node distributions 4. The way i understand it now, you essentially have to overlay your clock tree onto the design itself and put the flipflops at the ends of your tree. Regional clock tree generation by abutment in synchoros. Telehealth appointments in a secure, hipaacompliant platform.
High performance ic clock networks with grid and tree. A survey on buffered clock tree synthesis for skew optimization. Shielding clock nets icc implements clock shielding using nondefault routing rules. Clock tree synthesis cts is at the heart of asic design and clock tree network robustness is one of the most important quality metrics of soc design. At first we conducted many clock tree synthesis experiments. We propose a new clock driven design methodology that tackles the design of the clock network early in the design cycle before the implementation of the logic.
Clock tree routing algorithms vlsi physical design for. As a result, the higher the ct latency, the more buffering that may be. Characterization, clock tree synthesis and power grid. The synthesis and optimization methods for the two most commonly used clock topologies in ic design the grid topology and the tree topologyare primarily. We present a novel methodology optimizing the clock tree for less substrate generation by using statistical single cycle supply. In this paper we present a novel methodology for substrate noise reduction, which is based on an errordriven optimization of the clock tree latencies using supply current profiles taking timing constraints and the clock skew into account.
All flops are built at the same latency number, which is decided by the maximum latency in the design, which is c in this case. Clock power minimization using structured latch templates and. Clock distribution and balancing methodology for large and. Synchronizing every sequential element in the design. Power gating is a common method to reduce the static power consumption. Refine the current clock tree repeat timing optimization on datapaths if design timing is not met, loop back to step 1 prects cts postcts clock tree opt offsets, refine final opt functional skew driven cts flow. An e cient timing and clock tree aware placement flow with multibit flipflops for power reduction by jasmine kaur gulati mt14081 under the supervision of. Clock gating is a common technique for reducing clock power by shutting off the clock to unused sinks. Section iii describes experimental setup and our experimental results. However, the more it hurts us meet any hold time requirement for the design. Gnana sheela2 1, 2electronics and communication department, toc h institute of science and technology, kerala, india abstract. Clock tree synthesis 15 define clock clock definition is done on the cell or port just behind the flip flop cloud.
590 574 1045 681 1065 921 485 829 33 688 1360 1640 676 1214 937 583 99 744 771 505 614 685 1700 1729 636 1481 1671 1106 1243 1544 1316 102 330 662