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What is hold time violation?

Author

Christopher Snyder

Updated on March 04, 2026

What is hold time violation?

Hold time is defined as the minimum amount of time after the clock's active edge during which data must be stable. Violation in this case may cause incorrect data to be latched, which is known as a hold violation. Note that setup and hold time is measured with respect to the active clock edge only.

Similarly, it is asked, which of the following can cause timing violations?

Violations can be caused by routing paths that are too long, insufficient constraint definitions, clock skew, and a number of other causes.

Additionally, why is hold time required? This duration is known as hold time. The data that was launched at the current edge should not travel to the capturing flop before hold time has passed after the clock edge. Adherence to hold time ensures that the data launched at current clock edge does not get captured at the same edge.

Accordingly, how do you fix FPGA setup and hold violations?

For hold time violations:

Skew the clock to the start/endpoint (reverse of how to fix setup) to make the endpoint clock arrive earlier.
Insert cells along the path to increase the propogation time (insert chains of buffers)
Reduce the drive strength of cells on the path to make the transition time increase.

How is setup and hold time calculated?

Calculation of Setup Violation Check: Consider above circuit of 2 FF connected to each other.

Setup Slack = Required time - Arrival time (since we want data to arrive before it is required)
Where:
Arrival time (max) = clock delay FF1 (max) +clock-to-Q delay FF1 (max) + comb.

Can setup and hold violation on same path?

Same path has Setup and Hold violation at the Same Time.

That's the reason we do the Timing analysis several time during the whole design Cycle. As we move forward, we get more clarity about the inputs/condition, we feed those inputs to timing analysis tool and try to fix setup and hold violation incrementally.

Which is hard to fix -- setup violation or hold violation and why?

We can emphasis on Setup before as well as after CTS also because setup can be slacked because of delay in Data path so even if your clock is ideal i.e. not propagated then also your setup can be violated because tool will have to check that data which is launched will be captured properly or not and the propagation of

How do you solve a clock skew problem?

How to Identify and Solve Clock Skew Problems with NTP.
Simple Test.
Check if the Windows Time Service is running.
Windows Time Service (W32TM) Status.
Windows Time Service (W32TM) Configuration.
Fixing Issues in NTP Clients.
Configure a Computer to Sync with the Domain Time Source.
Disable the Hyper-V Time Sync Service.

What is setup time and hold time?

Setup time is defined as the minimum amount of time before the clock's active edge that the data must be stable for it to be latched correctly. Hold time is defined as the minimum amount of time after the clock's active edge during which data must be stable.

Why global skew is important?

Significance of Global Skew is it finds out the delay of the clock tree in such a way that it removes the setup violation as well as Hold violation. In this context, we have to use skew balancing to get the required slack.

What is setup time and hold time in flip flop?

? Setup Time: the amount of time the data at the synchronous input (D) must be stable before. the active edge of clock. ? Hold Time: the amount of time the data at the synchronous input (D) must be stable after the active edge of clock. Both setup and hold time for a flip-flop is specified in the library.

What is meant by clock skew?

Clock skew (sometimes called timing skew) is a phenomenon in synchronous digital circuit systems (such as computer systems) in which the same sourced clock signal arrives at different components at different times. The instantaneous difference between the readings of any two clocks is called their skew.

How does the jitter affect the setup and hold paths?

In other words, jitter in clock period makes the setup timing more tight. Or it decreases setup slack for single cycle timing paths. Effect of clock jitter on hold slack for single cycle paths: Going on the same grounds as setup slack, hold check will be from edge 1 -> edge 1 only.

What are the steps required to solve setup and hold violations in VLSI?

8 Ways To Fix Setup violation:

Adding inverter decreases the transition time 2 times then the existing buffer gate.
As such cell delay of 1 buffer gate ≈ cell delay of 2 Inverter gate.
So stage delay (cell delay + wire delay) in case of single buffer < stage delay in case of 2 inverter in the same path.

How do you solve Metastability?

The most common way to tolerate metastability is to add one or more successive synchronizing flip-flops to the synchronizer. This approach allows for an entire clock period (except for the setup time of the second flip-flop) for metastable events in the first synchronizing flip-flop to resolve themselves.

How do you fix the hold time violation after the chip was fabricated?

There is no way to fix setup or hold violation after fabrication. One thing generally industry does is to sell the chip at lower operating frequency if there is setup violation. If there is a hold violation, chip will be thrown into garbage.

How can we prevent metastability in digital circuits?

To minimize the failures due to metastability in asynchronous signal transfers, circuit designers typically use a sequence of registers (a synchronization register chain or synchronizer) in the destination clock domain to resynchronize the signal to the new clock domain.

How do you stop clocks from skewing?

The simplest method to help prevent the short data path problem is to minimize the clock skew by using the low-skew global routing resources for clock signals. Microsemi devices provide various types of global routing resources that significantly reduce skew.

What is STA in VLSI?

Definition. Static timing analysis (STA) is a method of validating the timing performance of a design by checking all possible paths for timing violations. Compared to dynamic simulation, static timing analysis is much faster because it is not necessary to simulate the logical operation of the circuit.

What's a flip flop?

A flip-flop is a device which stores a single bit (binary digit) of data; one of its two states represents a "one" and the other represents a "zero". Such data storage can be used for storage of state, and such a circuit is described as sequential logic in electronics.

Why is hold time negative?

Hold time is the time for which data should be stable after the triggering edge of the clock to get latched properly by the flop. When a flop has a negative hold time the data can change even before the triggering edge of the clock and get latched properly.

How is hold time calculated?

The AHT is calculated by adding up all inbound customer call and message hold times divided by the number of inbound customer calls answered by the agent or interactive voice response (IVR) system. To reduce the Average Hold Time, companies can: Increase their customer handling agents to meet the demand.

Which violation is more crucial setup or hold Why?

A hold violation is more serious than a setup violation because it cannot be fixed by increasing the clock period. It can be intentionally introduced to decrease the clock period at which the circuit will operate correctly, and/or to increase the setup or hold safety margins.

Can holding time be negative?

Depending upon the times of arrival of clock and data, hold time can be positive or negative.

What is propagation delay in flip flop?

The amount of time it takes for the output of the first Flip-Flop to travel to the input of the second Flip-Flop is the Propagation Delay. The further apart those two Flip-Flops are or the more combinational logic in the middle, the longer the propagation delay between the two of them.

What is difference between latch and flip flop?

Both latches and flip-flops are circuit elements whose output depends not only on the current inputs, but also on previous inputs and outputs. The difference between a latch and a flip-flop is that a latch does not have a clock signal, whereas a flip-flop always does.

How is set time of flip flop measured?

Setup time for Flip Flop:

Take a clock of pulse width 10ns i.e. a frequency of 100MHz.
Consider data transition from 0 → 1 at infinite setup time say 10ns before the active clock edge.
Calculate the C-Q delay from 50% of clock to 50% of Output.
Keep on bringing the data closer to the active edge of the clock.

What is required time?

The required time represents when the data is required to be present at the same pin FF2:D. Assume in this example that in the presence of an FF with the same polarity, the capturing edge is simply one cycle following the launch edge.

Why is hold time on same clock edge?

Hold time is basically the minimum required propagation delay. The level must be stable for some hold time after each edge in order to be captured correctly. This is independent of clock period and hence is measured off of the same edge, except with parameters that are the opposite of that for the setup time.

Does latch have setup and hold time?

The time before the clock falling edge that Data should remain stable is known as latch setup time. Similarly, the time after the clock falling edge that Data should remain stable is called latch hold time. So, setup time of the latch involves the delay of input transmission gate and the two inverters.

What is propagation delay time?

Propagation delay is defined as the flight time of packets over the transmission link and is limited by the speed of light. For example, if the source and destination are in the same building at the distance of 200 m, the propagation delay will be ∼ 1 μsec.

What is manufacturing setup time?

Machine setup time refers to the period of time that is required to prepare a machine for its next run after it has completed producing the last part of the previous run.

Why is hold time frequency independent?

than answer is no, because hold time is independent of frequency. As shown in figure, in the window of Tsetup and Thold, data must remain stable. Figure explain that there is hold violation due to data change in the Thold timing window which result into hold violation.

What is the setup required time in NS?

INPUT DATA

Digital designers define the set-up time as the minimum amount of time before the latching edge that the data must become stable. As an example, a set-up time of 1 ns (min) implies that the data must be stable at least 1 ns before the clock latching edge.

What is hold slack?

Setup and hold slack is defined as the difference between data required time and data arrival time. setup slack= Data Required Time- Data Arrival Time. hold slack= Data Arrival Time- Data Required Time. A +ve setup slack means design is working at the specified frequency and it has some more margin as well.

What is hold time in digital electronics?

Hold time may refer to: In digital electronics, the minimum amount of time the data input should be held steady after the clock event for reliable sampling; see Flip-flop (electronics)#Timing considerations. The amount of time spent in a phone queue on hold (telephone)

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