Flip FlopChapter 15

Subject : Digital SystemYear : 2009

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Overview• Latch and Flip Flop• Propagation Delay, Set-up time, Hold time in the

application of flip flop• Apply flip flop in basic operation

Flip Flop• Flip-flops are synchronous bistable devices, also

known as bistable multivibrators. In this case, the term synchronous means that the output changes state only at a specified point on the triggering input called the clock (CLK), which is designated as a control input, C; that is, changes in the output occur in synchronization with the clock.

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Edge-triggered Flip-Flop logic Symbol

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The Edge-Triggered S-R Flip-Flop

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The Edge-Triggered S-R Flip-Flop

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The Edge-Triggered S-R Flip-Flop

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The Edge-Triggered D Flip-Flop

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The Edge-Triggered J-K Flip-Flop

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The Edge-Triggered J-K Flip-Flop

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FLIP-FLOP OPERATING CHARACTERISTICS

• A propagation delay time is the interval of time required after an input signal has been applied for the resulting output change to occur. Four categories of propagation delay times are important in the operation of a flip-flop: – Propagation delay t PLH as measured from the triggering edge

of the clock pulse to the LOW-to-HIGH transition of the output.

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FLIP-FLOP OPERATING CHARACTERISTICS

– Propagation delay t PHL as measured from the triggering edge of the clock pulse to the HIGH-to-LOW transition of the output.

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Set-up Time

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• The set-up time is the minimum interval required for the logic levels to be maintained constantly on the inputs (J and K, or Sand R, or D) prior to the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip-flop.

Hold Time • The hold time is the minimum interval required

for the logic levels to remain on the inputs after the triggering edge of the clock pulse in order for the levels to be reliably clocked into the flip-flop.

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Flip Flop Application

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