1. Thought of the Day To be what we are, and to become
what we are capable of becoming,
is the only purpose of life.
रविवार, 24 फरवरी 2019
LOgic Circuits -1

2. Flip-Flops - 1
D.C. Kulshreshtha

3. Introduction Arithmetic and logic circuits consists of
Logic gates,
Flip-flops.
Used for adding, subtracting, multiplying and dividing binary numbers.
Operations performed in less than a microsecond.
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4. Two types :
Combinational logic circuits.
Sequential logic circuits.
The output at any time depends upon the combination of the input signals at that instant only.
The output depends on the present input values as well as the past output values.
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LOgic Circuits -1

5. Combinational Circuits
The output is not fed back to the input.
For a change in the input, the output appears immediately, except the propagation delay.
Examples :
Half-adder, Full-adder, Subtractor, Comparators, Decoders and Encoders, Multiplexers or Data Selectors (Many into one), Demultiplexers or Data Distributors (One into many), Parity Generators or Checkers, Code Converters, etc.
रविवार, 24 फरवरी 2019
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6. Block Diagram of Combinational Circuit
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7. Sequential Circuits Memory elements form feedback paths.
An output signal is a functional of the present input signals and a sequence of the past input signals (i.e., the past output signals).
Needs a storage device to know what has happened in the past. (Flip-Flop)
Two types :
Synchronous or clocked.
Asynchronous or unclocked.
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8. Block Diagram of Sequential Circuit
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Block Diagram of Sequential Circuit
LOgic Circuits -1

9. Synchronization is achieved by master-clock generator.
Clock pulses are applied to various AND gates.
The clock pulses should be slow enough to permit the slowest circuit to respond.
This limits the speed.
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LOgic Circuits -1

10. No need to wait for the clock pulse. Hence considerably faster.
In Asynchronous circuits, events can occur after one event is completed.
No need to wait for the clock pulse.
Hence considerably faster.
However, the system may become unstable.
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LOgic Circuits -1

11. FLIP-FLOPS Simplest memory cell having two states (0 and 1).
It flips from one state to the other and then flops back.
Also called bistable multivibrator, latch, or toggle.
It has one or more inputs, and two outputs
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12. Block Diagram of a Flip-Flop.
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13. Flip-Flop (Bistable Multivibrator) Circuit.
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14. It has only two stable states.
There are two cross-coupled inverting amplifiers, having positive feedback.
It has only two stable states.
Q1 is turned ON by applying positive signal through the SET input at its base.
Its collector will be at VCE(sat) = 0.2 to 0.4 V.
Hence Q(bar) is zero.
Then Q has to be 1.
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LOgic Circuits -1

15. Types of Flip-Flops
Different types depend on how their inputs and clock pulses cause the transition between two states.
S-R, J-K, D, and T flip-flops.
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16. S-R Flip Flop
It has two inputs and two outputs (complement to each other).
Can be implemented by using NOR or NAND gates.
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17. Cross-coupled connections form the feedback path.
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19. रविवार, 24 फरवरी 2019
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20. रविवार, 24 फरवरी 2019
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21. Difference between NOR-based and NAND-based S-R Flip Flops
The NOR flip-flop inputs are normally 0 and must be pulsed to the 1 state. That is, it is active HIGH.
The NAND flip-flop inputs are normally 1 and must be pulsed to the 0 state. That is, it is active LOW.
Can convert NAND flip-flop into NOR type, by placing an inverter at each input.
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22. रविवार, 24 फरवरी 2019
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23. रविवार, 24 फरवरी 2019
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24. Clocked S-R Flip-Flop
Additional control input that determines when the state of the flip-flop is to be changed.
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25. The clock pulse input acts as an enable signal for the other two inputs.
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26. रविवार, 24 फरवरी 2019
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27. Symbol of Clocked S-R Flip-Flop
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28. What is the output waveform ?
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29. The End
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LOgic Circuits -1