Subject
Year
: Digital System
: 2009
Flip Flop
Chapter 15
Overview
• Latch and Flip Flop
• Propagation Delay, Set-up time, Hold time in the application of flip flop
• Apply flip flop in basic operation
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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
• 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.
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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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