Latches And Flip Flop Research Paper

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Chapter 3

Latches and Flip-Flops

3.1 Introduction

Latches and flip-flops are the fundamental elements for storing information.A latch or flip-flop stores one bit of information[38]. The main difference between latches and flip-flops is that in the case of latches, outputs are constantly affected by their inputs when the enable signal is high.. Flip-flops output changes at the rising or falling edge of the enable signal. This enable signal is the controlling clock signal. After the rising or falling edge of the clock, the flip-flop content remains constant even if the input changes.
There are basically four main types of latches and flip-flops: SR, D, JK, and T. The major differences in these
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Clock-to-Q delay

Propagation delay from the clock input to the output Q terminal. On Assumption that the data input D is set early enough with respect to the effective edge of the clock input signal.

3.4.2. Setup time
The minimum time needed between the D input signal change and the triggering clock signal edge on the clock input. This parameter ensures that the output will follow the input in worst case conditions of process, voltage and temperature (PVT) and assumes that the clock triggering edge and pulse have enough time to capture the data input change.

3.4.3. Hold time
The minimum time needed for the D input to stay stable after the occurrence of the triggering edge of the clock signal. This metric guarantees that the output Q stays stable after the triggeringedge of the clock signal takes place, under worst PVT situations. This metric assumes that the D input change happened at least after a minimum delay from the previous D input change.

3.4.4. Data-to-Q delay
The sum of setup of data to the D input of flip-flop and the Clock-to-Q delay as defined above. It is desirable to minimize the setup time requirement of flip-flops and the Clock-to-Q delay to target the highest possible frequency for the design at

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