Bipolar RAM

DEPARTMENT OF TECHNICAL EDUCATION ANDHRA PRADESH Name Designation Branch Institute Year/semester Subject Subject code Topic Duration Sub Topic Teaching Aids

: C.V.S.B.UMA VANI : Lecturer : ECE : GPW ,Palamaner. : III semester : Digital Electronics : CM-305 : Semiconductor Memories (4/10) : 50 Mts : Bipolar RAM Cell : ppt , Diagrams CM305.69

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OBJECTIVES

On completion of this period you would be able to • Define the Memory cell. • Explain the working of basic bipolar RAM cell.

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Recap

In the last class we have studied about • Static and Dynamic Memories • Different types of ROM’s.

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Do You Know ? • What is meant by Static Memory ? • What is meant by Dynamic Memory?

• What is meant by Sequential Access Memory? • What is meant by Random Access Memory?

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Memory Cell: • A memory Cell is the basic unit for storing a Single bit of information.

• The cells used to construct semiconductor memories are usually Flip-Flops designed by using either bipolar or MOS transistors.

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Fig:1 Basic bipolar RAM Storage Cell CM305.69

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• The basic bipolar RAM storage cell is shown in Fig.1 • In this Flip-Flop one Transistor is ON and the other is

OFF. • The OFF transistor is forced into ON by an external trigger pulse, the transistor that was initially ON turns OFF. • It has two stable states which are used to store information in the form of logic 0 & 1. CM305.69

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Fig:2 Bipolar RAM Cell CM305.69

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• The bipolar RAM cell with required facilities is shown in Fig.2. • The Flip – Flop consists of two transistors T1 and T2 with additional emitters for addressing. • The remaining circuitry for writing &reading the data. • Signals Ax and Ay are used to address the cell. CM305.69

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• Let Ax, Ay &W/R inputs at logic 0 the O/P’s of G1 & G2 will be 1, Transistors T3 &T4 ON. D1& D2 are nonconducting. • The state of Flip-Flop is T1 is ON T2 is OFF. • Let Ax, Ay &W/R inputs at logic 1.If the data input is at logic 1 the O/P’s of G1 will be 1& G2 will be 0.T3 is ON T4 is OFF. Hence, the logic level at the collector of T2 will become the logic level of the data input.

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Summary

We have discussed about • The working of a Basic Memory Cell. • The working of a Basic bipolar RAM Cell.

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QUIZ (1) A Memory Cell stores (a) One bit of information (b) One byte of information (c) One Nibble of information (d) None of the above

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(2) A Bipolar RAM Cell is constructed by using (a) MOSFET’ s (b) CMOSFET’ s

(c) Bipolar Transistors (d) None of the above

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QUESTIONS (1) What is meant by Memory Cell ?

(2) Explain the working of Bipolar RAM Cell.

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