SEMINAR ON OUTPUT RESPONSE ANALYSIS

BYTEJASHREE PATIL1DS15LVS12

CONTENTS

Introduction

Transistor count

Syndrome checking

Signature analysis

Conclusion

1. INTRODUCTION

As complexity increases the length of response data produced by CUT also increases. Hence we

need to compress the data to reduce the length.

BIST technique usually combine a built-in binary pattern generator with circuitry for compressing

the corresponding response data produced by a Circuit Under Test(CUT).

There are three compression techniques.

:- Transition count

:- Syndrome checking

:- Signature analysis

2. TRANSITION COUNT It is defined as the total number of transitions from 1 to 0 and 0 to 1 in a response sequence for a

given input sequence.

Example: Z =10011010 then transition count c(Z) = 5

Fig. 2.1 response to test sequence of length 5

Fig 2.2 change in number of transition due to fault s-a-0

3. SYNDROME CHECKING

The syndrome of a given Boolean function is defined as S

Where K is the number of min terms realized by the function

n is the number of input lines Example : syndrome of 3 input AND gate is = 1/8, syndrome of 2 input OR gate is = 3/4 Basic syndrome relations:

Continued…

Fig 2.1 a fan out free circuit

S1 = ¾

S2 = ¼

S3 = 1- (S1)(S2)

= 1- (3/4)(1/4)

= 13/16

continued…

x1 x2 x3 Fault free α (s-a-1) β (s-a-0)000 1 1 1

001 1 1 1

010 1 0 0

011 0 0 0

100 1 0 0

101 0 0 0

110 1 0 0

111 0 0 0

syndrome 5/8 2/8 2/8

Inputs Output response

Fig 2.2 circuit under test

4. SIGNATURE ANALYSIS

It is pioneered by Hewlett- Packard ltd that deletes error data streams caused by hardware faults. It is used as a data compression technique to reduce long data streams into a unique code called

the signature. Signature creating and analysing:

Fig 3.1 signature analyser

Continued…..

Fig 3.2 four bit signature generator

Fig 3.3 the state diagram of signature generator

‘n’ stage signature generator can generate signatures.

If the length of the sequence is ‘m’ and signature generator has ‘n’ stages, then sequences map into signatures.

Here only one of the possible input is error free and produces correct signature.

There is an occurrence of aliasing which means, the signature generated from faulty output response of a circuit

may be identical to the signature obtained from fault free response. In other words, presence of fault is masked.

The probability P that an input sequence has deteriorated into another having the same signature itself is ,

P = - 1) / -1)

For m >> n , P = 1/ ,thus aliasing will be low if the signature generator has many stages. And it will be capable of

generating large number of signatures.

The 16 bit signature generator can generate up to 65536 signatures.

Fig 3.4 16 bit signature generator

Fig 3.5 multiple input signature generator

5. CONCLUSION

This presentation is mainly focused on compression techniques which are used for output response

analysis in a BIST environment.

These techniques normally involve binary test pattern as an input to the compressors. The

compressed data is compared with fault free response.

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