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DEPARTMENT OF TECHNICAL EDUCATIONANDHRA PRADESH

Name : C.V.S.B.UMA VANIDesignation : LecturerBranch : ECEInstitute : GPW ,Palamaner.Year/semester : III semesterSubject : Digital Electronics Subject code : CM-305Topic : Semiconductor Memories (4/10)Duration : 50 MtsSub Topic : Bipolar RAM CellTeaching Aids : ppt , Diagrams

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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

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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.

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Fig:2 Bipolar RAM Cell

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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.

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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 non- conducting.

• 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.