Why do we need 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. The goal of CTS is to minimize the skew and latency. … Less clock tree inverters and buffers should be used to meet the area and power constraints.

What is clock tree synthesis in physical design?


CTS is the process of connecting the clocks to all clock pin of sequential circuits by using inverters/buffers in order to balance the skew and to minimize the insertion delay. All the clock pins are driven by a single clock source.

What is clock tree design?

A clock tree is a clock distribution network within a system or hardware design. It includes the clocking circuitry and devices from clock source to destination. The complexity of the clock tree and the number of clocking components used. depends on the hardware design.

What is difference between HFN synthesis and CTS?

HFN synthesis is performed on reset/scan enable/test enable, etc… The requirement is usually max_tran , max_cap, and max_fanout. CTS is for the clocks where you specify the clock tree slew and skew as the requirements, and depending on the tool, you also specify insertion delay.

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Why do we check setup before CTS?

Short answer: Setup violation depends on the data path delay while hold violation depends on the clock path delay. Before CTS, clock path is taken as ideal because we don’t have skew and transition numbers of the clock path, but this information is sufficient to perform Setup Analysis .

What is clock pulling in VLSI?

Clock pulling refers to making the clock late at the launch stage to fix the hold violations. ( Negative Skewing)

Why clock inverters are preferred over clock buffer?

In most of the library files, a buffer is the combination of two inverters so we can say that inverter will be having lesser delay than buffer with the same drive strength. Also inverters having more driving capacity than a buffer that’s why most of the libraries preferred inverter over buffer for CTS.

Why do we need clock buffer?

Clock buffer is typically used to fan out clock signal and isolate the source from the loads.

What are clock tree types?

Up to now, there have been two main methods of clock distribution for large, high-performance designs: conventional clock-tree synthesis (CTS) and clock mesh. Multisource CTS has emerged as a new method that is a hybrid of these two.

What is clock offset in VLSI?

Clock Offset – offset of the clock is a delay of a given clock source, it might be known, or unknown. Offset can be measured in time units or phase degree.

What is high fan out synthesis?

High Fanout Net Synthesis (HFNS) is the process of buffering the high fanout nets to balance the load. High Fanout Net is the net which drives more number of loads. … The nets which more than these limit are known as High Fanout Nets. Clock nets, reset, scan enable nets are generally considered as High Fanout Nets.

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What constraints you add in CTS clock tree synthesis for clock gates?

The clock tree constraints will be Latency, Skew, Maximum transition, Maximum capacitance, Maximum fan-out, list of buffers and inverters etc.

What is latency in VLSI?

When describing a digital circuit there are two other important factors: latency and throughput. Latency is the time needed for an input change to produce an output change; latency can be expressed as a length of time or, in synchronous circuits, as a certain number of clock cycles.

What is jitter in VLSI?

Jitter: Jitter is the short term variations of a signal with respect to its ideal position in time. It is the variation of the clock period from edge to edge.it can vary +/- jitter value. From cycle to cycle the period and duty cycle can change slightly due to the clock generation circuitry.