This document describes the Illinois Scan Architecture, a technique for reducing test costs for chips with scan designs. It works by dividing the main scan chain into multiple parallel internal chains, with a single scan input pin. This allows test vectors to be broadcast to all chains simultaneously, reducing test time and data volume by the number of chains with little impact on fault coverage. The document provides experimental data showing reductions in test vectors, cycles, and data volume for several ISCAS circuits using Illinois Scan. It also discusses techniques for further optimizing the technique, such as grouping chains intelligently to minimize the number of scan input pins needed.
Vlsi Design of Low Transition Low Power Test Pattern Generator Using Fault Co...iosrjce
Now a day’s highly integrated multi layer board with IC’s is virtually impossible to be accessed
physically for testing. The major problem detected during testing a circuit includes test generation and gate to
I/O pin problems. In design of any circuit, consuming low power and less hardware utilization is an important
design parameter. Therefore reliable testing methods are introduced which reduces the cost of the hardware
required and also power consumed by the device. In this project a new fault coverage test pattern generator is
generated using a linear feedback shift register called FC-LFSR which can perform fault analysis and reduces
the total power of the circuit. In this test, it generates three intermediate patterns between the random patterns
which reduces the transitional activities of primary inputs so that the switching activities inside the circuit under
test will be reduced. The test patterns generated are applied to c17 benchmark circuit, whose results with fault
coverage of the circuit being tested. The simulation for this design is performed using Xilinx ISE software using
Verilog hardware description language
Mixed Scanning and DFT Techniques for Arithmetic CoreIJERA Editor
Elliptic curve Cryptosystem used in cryptography chips undergoes side channel threats, where the attackers deciphered the secret key from the scan path. The usage of extra electronic components in scan path architecture will protect the secret key from threats. This work presents a new scan based flip flop for secure cryptographic application. By adding more sensitive internal nets along with the scan enable the testing team can find out the bugs in chip after post-silicon and even after chip fabrication. Also present a new mixed technique by adding DFT(design for testing or Dfx unit) unit and scan unit in same chip unit without affecting the normal critical path ,i.e. without affecting speed of operation of chip, latency in normal mode. Both Scan unit and DFT unit are used for testing the sequential and combinational circuits present in 32 Bit Arithmetic core. Here a proposed PN code generation unit as scan in port to increase the code coverage and scan out port efficiency. The proposed system will written in verilog code and simulated using Xilinx Tool. The hardware module core is synthesized using Xilinx Vertex 5 Field Programmable Gated Array (FPGA) kit. The performance utilization is reported with the help of generated synthesis result
Design for Testability in Timely Testing of Vlsi CircuitsIJERA Editor
Even though a circuit is designed error-free, manufactured circuits may not function correctly. Since the manufacturing process is not perfect, some defects such as short-circuits, open-circuits, open interconnections, pin shorts, etc., may be introduced. Points out that the cost of detecting a faulty component increases ten times at each step between prepackage component test and system warranty repair. It is important to identify a faulty component as early in the manufacturing process as possible. Therefore, testing has become a very important aspect of any VLSI manufacturing system.Two main issues related to test and security domain are scan-based attacks and misuse of JTAG interface. Design for testability presents effective and timely testing of VLSI circuits. The project is to test the circuits after design and then reduce the area, power, delay and security of misuse. BIST architecture is used to test the circuits effectively compared to scan based testing. In built-in self-test (BIST), on-chip circuitry is added to generate test vectors or analyze output responses or both. BIST is usually performed using pseudorandom pattern generators (PRPGs). Among the advantages of pseudorandom BIST are: (1) the low cost compared to testing from automatic test equipment (ATE). (2) The speed of the test, which is much faster than when it is applied from ATE. (3) The applicability of the test while the circuit is in the field, and (4) the potential for high quality of test.
Electrical & functional testing challenges in your company.
BOX ICT. B BOX X1149: Boundary Scan Solution. VIPER: How to take advantage of modular test systems.
Vlsi Design of Low Transition Low Power Test Pattern Generator Using Fault Co...iosrjce
Now a day’s highly integrated multi layer board with IC’s is virtually impossible to be accessed
physically for testing. The major problem detected during testing a circuit includes test generation and gate to
I/O pin problems. In design of any circuit, consuming low power and less hardware utilization is an important
design parameter. Therefore reliable testing methods are introduced which reduces the cost of the hardware
required and also power consumed by the device. In this project a new fault coverage test pattern generator is
generated using a linear feedback shift register called FC-LFSR which can perform fault analysis and reduces
the total power of the circuit. In this test, it generates three intermediate patterns between the random patterns
which reduces the transitional activities of primary inputs so that the switching activities inside the circuit under
test will be reduced. The test patterns generated are applied to c17 benchmark circuit, whose results with fault
coverage of the circuit being tested. The simulation for this design is performed using Xilinx ISE software using
Verilog hardware description language
Mixed Scanning and DFT Techniques for Arithmetic CoreIJERA Editor
Elliptic curve Cryptosystem used in cryptography chips undergoes side channel threats, where the attackers deciphered the secret key from the scan path. The usage of extra electronic components in scan path architecture will protect the secret key from threats. This work presents a new scan based flip flop for secure cryptographic application. By adding more sensitive internal nets along with the scan enable the testing team can find out the bugs in chip after post-silicon and even after chip fabrication. Also present a new mixed technique by adding DFT(design for testing or Dfx unit) unit and scan unit in same chip unit without affecting the normal critical path ,i.e. without affecting speed of operation of chip, latency in normal mode. Both Scan unit and DFT unit are used for testing the sequential and combinational circuits present in 32 Bit Arithmetic core. Here a proposed PN code generation unit as scan in port to increase the code coverage and scan out port efficiency. The proposed system will written in verilog code and simulated using Xilinx Tool. The hardware module core is synthesized using Xilinx Vertex 5 Field Programmable Gated Array (FPGA) kit. The performance utilization is reported with the help of generated synthesis result
Design for Testability in Timely Testing of Vlsi CircuitsIJERA Editor
Even though a circuit is designed error-free, manufactured circuits may not function correctly. Since the manufacturing process is not perfect, some defects such as short-circuits, open-circuits, open interconnections, pin shorts, etc., may be introduced. Points out that the cost of detecting a faulty component increases ten times at each step between prepackage component test and system warranty repair. It is important to identify a faulty component as early in the manufacturing process as possible. Therefore, testing has become a very important aspect of any VLSI manufacturing system.Two main issues related to test and security domain are scan-based attacks and misuse of JTAG interface. Design for testability presents effective and timely testing of VLSI circuits. The project is to test the circuits after design and then reduce the area, power, delay and security of misuse. BIST architecture is used to test the circuits effectively compared to scan based testing. In built-in self-test (BIST), on-chip circuitry is added to generate test vectors or analyze output responses or both. BIST is usually performed using pseudorandom pattern generators (PRPGs). Among the advantages of pseudorandom BIST are: (1) the low cost compared to testing from automatic test equipment (ATE). (2) The speed of the test, which is much faster than when it is applied from ATE. (3) The applicability of the test while the circuit is in the field, and (4) the potential for high quality of test.
Electrical & functional testing challenges in your company.
BOX ICT. B BOX X1149: Boundary Scan Solution. VIPER: How to take advantage of modular test systems.
Online and Offline Testing Of C-Bist Using Sramiosrjce
Built-in self test techniques constitute a class of schemes that provide the capability of performing atspeed
testing with high fault coverage hence; they constitute an attractive solution to the problem of testing
VLSI devices. Concurrent BIST schemes perform testing during the circuit normal operation without imposing a
need to set the circuit offline to perform the test; therefore they can circumvent problems appearing in offline
BIST techniques. In this brief, a novel input vector monitoring concurrent BIST architecture has been presented,
based on the use of a SRAM-cell like register for storing the information of whether an input vector has
appeared or not during normal operation. The evaluation criteria for this class of schemes are the hardware
overhead and the CTL, i.e., the time required for the test to complete, while the circuit operates normally. The
simulation results shown to be more efficient than previously proposed Concurrent BIST techniques in terms of
hardware overhead and CTL.
Scan-Based Delay Measurement Technique Using Signature RegistersIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
Scan design is currently the most popular structured DFT approach. It is implemented by Connecting selected storage elements present in the design into multiple shift registers, called Scan chains.
Scannability Rules -->
The tool perform basic two check
1) It ensures all the defined clocks including set/Reset are at their off-states, the sequential element remain stable and inactive. (S1)
2) It ensures for each defined clocks can capture data when all other defined clocks are off. (S2)
Boundary scan for support engineers and techniciansInterlatin
Boundary scan in one of the most important electronic tests in the actual automotive, medical and consumer electronic manufacturing. Keysight Technologies electronic test systems have the capability to do this test - systems such as i3070 and the x1149 which provides boundary scan in a box. This training focuses on this test used by support engineers and technicians.
Level sensitive scan design(LSSD) and Boundry scan(BS)Praveen Kumar
This presentation contains,
Introduction,design for testability, scan chain, operation, scan structure, test vectors, Boundry scan, test logic, operation, BS cell, states of TAP controller, Boundry scan instructions.
Design Verification and Test Vector Minimization Using Heuristic Method of a ...ijcisjournal
The reduction in feature size increases the probability of manufacturing defect in the IC will result in a
faulty chip. A very small defect can easily result in a faulty transistor or interconnecting wire when the
feature size is less. Testing is required to guarantee fault-free products, regardless of whether the product
is a VLSI device or an electronic system. Simulation is used to verify the correctness of the design. To test n
input circuit we required 2n
test vectors. As the number inputs of a circuit are more, the exponential growth
of the required number of vectors takes much time to test the circuit. It is necessary to find testing methods
to reduce test vectors . So here designed an heuristic approach to test the ripple carry adder. Modelsim and
Xilinx tools are used to verify and synthesize the design.
COMPARATIVE ANALYSIS OF SIMULATION TECHNIQUES: SCAN COMPRESSION AND INTERNAL ...IJCI JOURNAL
With advancement in technology, the feature size of transistors is shrinking and the transistor count in a circuit design is exponentially increasing. As a result, it is hard to control and observe internal nodes leading to complexity in locating and debugging faults specially for sequential circuits. Design for Testability (DFT) provides a way for fault detection of the circuit under test in less simulation duration with little increase in area. Many techniques are proposed under DFT for pattern simulation. In this paper, we have compared two such pattern simulation techniques namely scan compression and internal scan. The experiment is performed on different benchmark circuits, it is observed the simulation time is significantly reduced with increased coverage and a little area overhead.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Online and Offline Testing Of C-Bist Using Sramiosrjce
Built-in self test techniques constitute a class of schemes that provide the capability of performing atspeed
testing with high fault coverage hence; they constitute an attractive solution to the problem of testing
VLSI devices. Concurrent BIST schemes perform testing during the circuit normal operation without imposing a
need to set the circuit offline to perform the test; therefore they can circumvent problems appearing in offline
BIST techniques. In this brief, a novel input vector monitoring concurrent BIST architecture has been presented,
based on the use of a SRAM-cell like register for storing the information of whether an input vector has
appeared or not during normal operation. The evaluation criteria for this class of schemes are the hardware
overhead and the CTL, i.e., the time required for the test to complete, while the circuit operates normally. The
simulation results shown to be more efficient than previously proposed Concurrent BIST techniques in terms of
hardware overhead and CTL.
Scan-Based Delay Measurement Technique Using Signature RegistersIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
Scan design is currently the most popular structured DFT approach. It is implemented by Connecting selected storage elements present in the design into multiple shift registers, called Scan chains.
Scannability Rules -->
The tool perform basic two check
1) It ensures all the defined clocks including set/Reset are at their off-states, the sequential element remain stable and inactive. (S1)
2) It ensures for each defined clocks can capture data when all other defined clocks are off. (S2)
Boundary scan for support engineers and techniciansInterlatin
Boundary scan in one of the most important electronic tests in the actual automotive, medical and consumer electronic manufacturing. Keysight Technologies electronic test systems have the capability to do this test - systems such as i3070 and the x1149 which provides boundary scan in a box. This training focuses on this test used by support engineers and technicians.
Level sensitive scan design(LSSD) and Boundry scan(BS)Praveen Kumar
This presentation contains,
Introduction,design for testability, scan chain, operation, scan structure, test vectors, Boundry scan, test logic, operation, BS cell, states of TAP controller, Boundry scan instructions.
Design Verification and Test Vector Minimization Using Heuristic Method of a ...ijcisjournal
The reduction in feature size increases the probability of manufacturing defect in the IC will result in a
faulty chip. A very small defect can easily result in a faulty transistor or interconnecting wire when the
feature size is less. Testing is required to guarantee fault-free products, regardless of whether the product
is a VLSI device or an electronic system. Simulation is used to verify the correctness of the design. To test n
input circuit we required 2n
test vectors. As the number inputs of a circuit are more, the exponential growth
of the required number of vectors takes much time to test the circuit. It is necessary to find testing methods
to reduce test vectors . So here designed an heuristic approach to test the ripple carry adder. Modelsim and
Xilinx tools are used to verify and synthesize the design.
COMPARATIVE ANALYSIS OF SIMULATION TECHNIQUES: SCAN COMPRESSION AND INTERNAL ...IJCI JOURNAL
With advancement in technology, the feature size of transistors is shrinking and the transistor count in a circuit design is exponentially increasing. As a result, it is hard to control and observe internal nodes leading to complexity in locating and debugging faults specially for sequential circuits. Design for Testability (DFT) provides a way for fault detection of the circuit under test in less simulation duration with little increase in area. Many techniques are proposed under DFT for pattern simulation. In this paper, we have compared two such pattern simulation techniques namely scan compression and internal scan. The experiment is performed on different benchmark circuits, it is observed the simulation time is significantly reduced with increased coverage and a little area overhead.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
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1. Illinois Scan Architecture
Janak H. Patel
Department of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign
jhpatel@illinois.edu
2. 2
Cost of a Chip
300mm wafer will give 700 ~1cm2 chips
Material Costs (wafer, copper etc) ~5%
Fab amortization cost ($3B/fab) plus
Fab operational cost ~25%
Personnel cost ~20%
Package Cost ~10%
Testing Cost ~40% !!!
Semiconductor Wafer
Manufacturing test is done
at wafer level without cutting
out the chips.
3. 3
Cost of Testing Semiconductor Chips
Three main variable components
Test Application Time
When amortizing the cost of a tester over all chips,
higher test time results in to higher actual cost
Rule of thumb: 1 second per chip!
Test Data Volume
Low and medium cost testers have limited storage
Tester Pins
Cost of a tester is directly proportional to the number
of pins it supports
4. 4
Example: An IBM chip
7million gates (logic only, RAM not included)
250k Flip-Flops
Full Scan design, all FFs connected as shift
register
7000 Test Vectors
Test Application Time: 7000x250k = 1.75G cycles
at 100MHz scan speed it takes 17.5 Seconds!
at 500MHz scan speed it takes 3.5 Seconds
Tester memory required: 7000x250k = 1.75G bits
250,000 ffs
Scan
in
Scan
out
5. 5
Parallel Scan
Scan-in
1000 Parallel Scan Chains by 250 FFs
Scan Channels on most Testers range from 10 to 200
Scan-out
Reduces Test Vector Load time by a factor of 1000!
1000
scan-in pins!
1000
scan-out pins!
6. 6
Parallel Scan Output Compaction
Scan-in
100 Parallel Scan Chains by 2500 FFs output
compactor
A Combinational Compactor is a tree of XOR gates
A Sequential Compactor is a Linear Feedback Shift Register with
multiple parallel inputs XORed. Also called a Multiple Input
Signature Analyzer (MISR)
7. 7
Parallel Scan - Summary
Scan loading time can be reduced by dividing the
single scan chain in to parallel scan chains
Some Observations
Output Compaction is well established
Number of scan chains is limited by the availability
of pins on a chip and tester scan channels
Additional “pins” on an embedded core require
more routing in the SOC
Parallel Scan has no impact on test data volume
8. 8
Test Vector Compaction
For example, all 40 ISCAS 85 and
ISCAS89 (full scan) circuits, sizes
of the test sets generated by
MinTest (Hamzaoglu and Patel, ICCAD
1998, pp. 283-289) meets Lower
bounds for 31 out of 40 ISCAS
circuits.
This shows that Compaction
has already reached theoretical
lower bounds in many
instances
Need solutions beyond vector
compaction
Test Vectors
Circuit
Lower
Bound
Min
Test
C432 27 27
C5315 37 37
C7552 65 73
S1196 113 113
S1423 20 20
S5378 97 97
S38714 62 68
9. 9
BIST: STUMPS Architecture
P. H. Bardell and W. H. McAnney, “Self-Testing of Multichip Logic Modules,”
Proc. Of Int. Test Conf., pp. 200-204, Nov. 1982. (used by IBM for multi-chip-modules)
L
F
S
R
Scan Chain
Scan Chain
Scan Chain
Scan Chain
Phase
Shifter
M
I
S
R
Circuit Under Test
This has the same limitations as any other BIST based scheme
Linear
Feedback
Shift
Register
Multiple
Input
Signature
Register
10. 10
Limitations of Logic BIST
BIST is excellent for Data Volume Reduction, But
Lower Fault Coverage. Test Point insertion and/or
additional logic in test generator is required to
cover Random Resistant Faults
Design Modification needed to permit any arbitrary
test pattern
Tri-State logic must be fully decoded
No floating bus is permitted, since unknown values
can corrupt the signature
Switching activities of various modules, and hence
the power, cannot be easily controlled
Will almost always increase the tester time!
Failure Diagnosis becomes extremely difficult
11. 11
Proposed New Method
Illinois Scan Architecture
Applicable to full-scan embedded cores and full-
scan stand-alone chips
Addresses all issues raised earlier –
Low test application time, low pin overhead, and
low test data volume
Does not have any of the limitations of the BIST
No test point insertions and No design
modifications!
Undesirable test vectors can be filtered, e.g.,
Vectors that produce Tri-State Conflicts, Unknown
value generation, or High switching activity
12. 12
Illinois Scan Architecture
Take a Serial Scan
1. Divide it up into several chains
keeping the same Scan-in pin
2. Add a MISR to compact the outputs
Scan
in
Scan
out
MISR
Scan
in
Scan
out
14. 14
Untestable Faults in Illinois Scan
In the figure shown on left,
all three scan chains will
have identical test vectors
Therefore, only applicable
test vectors are 000 and
111 for the AND gate
Test vectors 110, 011 and
101 cannot be applied due
to Broadcast constraint
This makes three faults on
the AND gate Untestable
scan in
1
1
1
0
0
0
In practice, how serious is this problem?
How many faults become untestable?
15. 15
Additional Untestable Faults
Illinois Scan puts constraints
on inputs
Cannot generate tests for
some of the faults that
are testable
The number of such
“Additional Untestable
Faults” is surprisingly
small
Experimental Data for
Scan Chain divided into 16
chains (arbitrary partition),
with a single scan input.
0
200
400
600
800
1000
1200
ILS-13207
ILS-15850
ILS-35932
ILS-38417
ILS-38584
Untestable
Faults
16. 16
Two Test Modes of Illinois Scan
Scan Out
Scan Chain 1
Scan Chain 2
Scan Chain n
Scan In
1. Broadcast Test Mode
1. Reduces Scan Time by a factor of n
2. Reduces Scan Data by a factor of n
But may require many more vectors
and may reduce fault-coverage!
•
•
•
M
I
S
R
Scan Chain 1
Scan Chain 2
Scan Chain n
2. Serial Test Mode
Mode 2 for covering the loss of
fault-coverage in the Broadcast Mode
Generates “top-off vectors”.
Note: Most industrial circuits do
not use Mode 2.
•
•
•
Scan In
Scan Out
M
I
S
R
17. 17
Number of Test Vectors
0
50
100
150
200
250
300
350
400
fs13207
ILS-13207
fs15850
ILS-15850
fs35932
ILS-35932
fs38417
ILS-38417
fs38584
ILS-38584
Circuit
Vectors
scan vectors
broadcast vectors
Circuit Versions: fs = full scan, and ILS = Illinois Scan, DIV16
18. 18
Number of Test Cycles
0
25,000
50,000
75,000
100,000
125,000
150,000
175,000
200,000 fs13207
ILS-13207
fs15850
ILS-15850
fs35932
ILS-35932
fs38417
ILS-38417
fs38584
ILS-38584
C
i
r
cui
t
C
ycl
e
s
scan cycles
broadcast cycles
Circuit Versions: fs = full scan, and ILS = Illinois Scan, DIV16
19. 19
Illinois Scan Data Volume
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
450,000
fs13207
ILS-arb
fs15850
ILS-arb
fs35932
ILS-arb
fs38417
ILS-arb
fs38584
ILS-arb
Circuit
Data
Bits
Scan Test Data
Broadcast Test Data
Circuit Versions: fs = full scan, and ILS = Illinois Scan, DIV16
22. 22
Case Study at Texas Instruments
Illinois
Scan
Version
Broadcast
Vectors
Broadcast
Fault
Coverage
Additional
Untestable
Faults
Serial
Scan
Vectors
needed
Serial
Scan
Fault
Coverage
Broadcast
Vectors
needed
Data
Volume
Reduction
Factor
DIV16 15,000 94.08% 733 53 70% 9700 1.4
DIV24 14,000 94.09% 692 38 67% 9500 2
DIV32 12,000 93.87% 1565 59 73% 8000 3
Original Circuit : 150K logic gates, 9300 scan flip-flops
910 Scan Vectors, 94.25% stuck-at fault coverage
Similar reduction was also found in Transition Fault Data
Frank Hsu, Ken Butler and Janak Patel, “A Case Study on the Implementation of the
Illinois Scan Architecture,” Int. Test Conf. Oct. 2001
23. 23
IBM Data using Illinois Scan (OPMISR+)
Design
Gate
Count
Scan
flip-flops
Test Time
Reduction
Test Volume
Reduction
Chip1 1.7M 230k 130x 200x
Chip2 2.1M 31k 38x 54x
Chip3* 715k 41k 7x 21x
Chip4* 1.2M 65k 8x 12x
“….scan fan-out, which is sometimes informally referred to as Illinois Scan [ix].
In the Cadence ATPG tools we refer to this as OPMISR+.”
Data and quote From: Test Compression Methods in Cadence Encounter Test Design Edition,
Technology Application Note, December 2003
* These chips already had their scan divided by customer
24. 24
Intel Data on Illinois Scan
From a Paper by D. Wu et. al. of Intel, published in 2003 Int.
Test Conf.
“The first test chip has 81 scan-in and 81 scan-out channels, we
use Illinois Scan with 4 scan-in and 81 scan-out. The results are
quite surprising: both methods got the same test coverage.”
“We have implemented Illinois scan into one of the
microprocessors, but the silicon results will not be ready for the
timing of this year’s ITC.”
25. 25
More Data on Illinois Scan
7M Gates, 250k flip-flops, 7000 test vectors
Source: V. Chickermane, B. Fautz and B. Keller,
Channel-Masking Synthesis for Efficient On-Chip Test Compression, Int. Test Conf., 2004.
Illinois
Scan
26. 26
Illinois Scan in CAD Tools
Cadence (formerly IBM)
Illinois Scan on their patented “OPMISR” is called
OPMISR+
Syntest
Illinois Scan is called “Virtual Scan”
Synopsis
ATPG Tools understand and support Illinois Scan
Mentor Graphics
No Illinois Scan!
Proprietary tool called TestCompress
27. 27
Illinois Scan with multiple pins
Large Industrial Circuits have used Illinois Scan
with multiple pins
IBM ASIC-4 chip (Design and Test, Sept. 2002, pp. 65-72)
1.14 million gates, 46 pins, 269 internal chains
Intel chips (Int. Test Conf., Sept. 2003, pp. 1229-1238)
ASIC-1, 4 pins, 81 internal chains
ASIC-2, 4 pins, 96 internal chains
Next generation microprocessor (no data given)
All of the above scan-chain groupings are ad-hoc!
Can we do better with intelligent grouping?
28. 28
Optimal Grouping of Chains
scan chains
scan-in
pins
Objective:
Minimize number of Scan-In Pins without loss in fault coverage.
29. 29
Compatibility among Chains
Compatibility between two scan cells
Two inputs (scan cells) are compatible if and only if
no fault becomes untestable as a result of tying the
two cells to a single input (Chen&Gupta, ITC 1995)
Compatibility between two scan chains
Two chains are compatible if and only if every pair
of scan-cells that receive the same broadcast
value are compatible (Hamzaoglu&Patel, FTCS 1999)
Determination of all pairwise compatibilities is
computationally very expensive
Resort to an inexpensive algorithm which gives a
subset of all compatible pairs
30. 30
Incompatibilities from a Test Set
A Partially Specified Test Vector, 20-bits long folded on to 5 chains
Vector 1
001x 0xx1 x01x 0011 xx11 0 0 1 x a
0 x x 1 b
x 0 1 x c
0 0 1 1 d
x x 1 1 e
0 0 1 x a
0 x x 1 b
x 1 1 x c
0 0 1 1 d
x x 1 1 e
Vector 2
001x 0xx1 x11x 0011 xx11
Chains a and c are incompatible,
so are chains c and d
No conflicting values found
Chain
31. 31
Example of Chain Grouping
A B C
D E F
G H
Given Incompatible Pairs:
AB, AD, AG, BD, BE, BF, CE, CF, EF, EG, EH, FH
Construct a Graph with Nodes=Chains and Edges=Incompatibility
Perform Graph Coloring Algorithm
A
B
C
D
E
F
G
H
Conflict-free Chain Grouping
34. 34
Illinois Scan: Summary
A simple DFT technique, ideal for reducing test
costs for large chips
Significant reduction in test application time, test
data and test pins without loss in fault coverage
Even a “dumb” partition is very effective!
For large chips, 400 factor reduction is likely!
“Things should be made as simple as possible,
but not any simpler” Albert Einstein
35. 35
More information on Illinois Scan
1. I. Hamzaoglu and J.H. Patel, “Reducing test application time for full-scan
embedded cores,” Proc. 29th Int. Symp. On Fault-Tolerant Computing
(FTCS-29), pp.260-267, June 1999
2. F. Hsu, K. Butler and J.H. Patel, “A case study on the implementation of
Illinois Scan Architecture,” Proc. Int. Test Conf. pp. 538-547, October 2001
3. A.R. Pandey and J.H. Patel, “An incremental algorithm for test generation
in Illinois Scan Architecture based designs,” Proc. Of Design Automation and
Test in Europe (DATE), pp. 368-375, March 2002.
4. A.R. Pandey and J.H. Patel, “Reconfiguration techniques for reducing test
time and test data volume in Illinois Scan Architecture based designs,” IEEE
VLSI Test Symp. (VTS), pp. 9-15, April 2002.
5. M.A. Shah and J.H. Patel, “Enhancement of the Illinois Scan Architecture
for Use with Multiple Scan Inputs,” IEEE Computer Society Annual
Symposium on VLSI, pp. 167-172, Feb. 2004.