ELEC 5970-001/6970-001(Fall 2005)
Special Topics in Electrical Engineering
Low-Power Design of Electronic Circuits
Test Power
Vishwani D. Agrawal
James J. Danaher Professor
Department of Electrical and Computer Engineering
Auburn University
http://www.eng.auburn.edu/~vagrawal
vagrawal@eng.auburn.edu
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Test Power Problem
• A circuit is designed for certain function. Its
design must allow the power consumption
necessary to execute that function.
• Power buses are laid out to carry the maximum
current necessary for the function.
• Heat dissipation of package conforms to the
average power consumption during the intended
function.
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Testing Differs from Function
Other chips
System
inputs
System
outputs
VLSI chip
system
Functional inputs
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Functional outputs
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Basic Mode of Testing
Packaged or unpackaged
device under test (DUT)
DUT output for
comparison with
expected response
stored in ATE
VLSI chip
Test vectors:
Pre-generated
and stored in
ATE
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Clock
Power
Automatic Test Equipment (ATE):
Control processor, vector memory,
timing generators, power module,
response comparator
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Functional Inputs vs. Test Vectors
• Functional inputs:
• Functionally meaningful
signals
• Generated by circuitry
• Restricted set of inputs
• May have been
optimized to reduce
logic activity and power
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• Test vectors:
• Functionally irrelevant
signals
• Generated by software
to test faults
• Can be random or
pseudorandom
• May be optimized to
reduce test time; can
have high logic activity
• May use testability logic
for test application
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An Example
VLSI chip in system operation
3-bit random
vectors
Binary to
decimal
converter
8-bit
1-hot
VLSI chip
vectors
system
VLSI chip under test
High activity
8-bit
test vectors
from ATE
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VLSI chip
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Reducing Comb. Test Power
1
V1 V2 V3 V4 V5
1 1 0 0 0
1 0 1 0 0
1 0 1 0 1
1 0 1 1 1
10 input transitions
V1
3
4
V2
3
3
2
V4
2
1
V3
1
V5
2
Traveling salesperson problem (TSP): Find the shortest distance
closed path (or cycle) to visit all nodes exactly once.
V1 V3 V5 V4 V2
1 0 0 0 1
5 input transitions
1 1 0 0 0
1 1 1 0 0
1 1 1 1 0
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Traveling Salesperson Problem
• A. V. Aho, J. E. Hopcroft anf J. D. Ullman,
Data Structures and Algorithms, Reading,
Massachusetts: Addison-Wesley, 1983.
• E. Horowitz and S. Sahni, Fundamentals
of Computer Algorithms, Computer
Science Press, 1984.
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Scan Testing
Primary
inputs
Primary
outputs
Combinational
logic
Scan-out
SO
Scan enable
SE
Scan-in
SI
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Scan
flipflops
D
D
SI
ELEC 5970-001/6970-001 Lecture 20
1
0
SO
mux
D’
SE
DFF
D’
9
Example: State Machine
Functional transitions
S1
S5
S4
S2
S3
Reduced power state encoding
S1 = 000
S2 = 011
S3 = 001
S4 = 010
S5 = 100
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State transition
Comb. Input
changes
000 → 001
1
000 → 100
1
011 → 010
1
001 → 011
1
010 → 000
1
100 → 010
2
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Scan Testing of State Machine
Primary
inputs
Combinational
logic
Primary
outputs
Test transitions
State
transition
Comb.
Input
changes
FF=0
100 → 010
2
FF=0
010 → 101
3
FF=1
101 → 010
3
Scan-out
100
Scan-in
010
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Low Power Scan Flip-Flop
SO
SI
D
DFF
1
D’
SI
0
mux
D
mux
SO
DFF
D’
SE
SE
Scan FF cell
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Low power scan FF cell
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Built-In Self-Test (BIST)
Linear feedback shift register (LFSR)
BIST
Controller
Pseudo-random patterns
Circuit under test (CUT)
Circuit responses
Multiple input signature register (MISR)
Clock
C. E. Stroud, A Designer’s Guide to Built-In Self-Test, Boston: Kluwer
Academic Publishers, 2002.
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Test Scheduling Example
R1
R2
M1
M2
R3
R4
A datapath
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BIST Configuration 1: Test Time
M1
MISR1
LFSR2
M2
Test power
LFSR1
T2: test for M2
T1: test for M1
MISR2
Test time
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BIST Configuration 2: Test Power
M1
MISR1
LFSR2
M2
Test power
R1
T1: test for M1
T2: test for M2
MISR2
Test time
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Testing of MCM and SOC
• Test resources: Typically registers and
multiplexers that can be reconfigured as test
pattern generators (e.g., LFSR) or as output
response analyzers (e.g., MISR).
• Test resources (R1, . . . ) and tests (T1, . . . )
are identified for the system to be tested.
• Each test is characterized for test time,
power dissipation and resources it requires.
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Resource Allocation Graph
T1
R1
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R2
T2
R3
T3
R4
T4
R5
T5
R6
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R7
T6
R8
R9
18
Test Compatibility Graph (TCG)
T1
(2, 100)
T6
(1, 100)
T2
(1,10)
T5
(2, 10)
T3
(1, 10)
Power
Pmax = 4
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Test time
T4
(1, 5)
Tests that form a
clique can be performed
concurrently.
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Test Scheduling Algorithm
• Identify all possible cliques in TCG:
•
•
•
•
•
C1 = {T1, T3, T5}
C2 = {T1, T3, T4}
C3 = {T1, T6}
C4 = {T2, T5}
C5 = {T2, T6}
• Break up clique sets into power
compatible sets (PCS), that satisfy the
power constraint.
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Test Scheduling Algorithm . . .
• PCS (Pmax = 4), tests within a set are ordered
for decreasing test length:
•
•
•
•
•
C1 = {T1, T3, T5} → (T1, T3), (T1, T5), (T3, T5)
C2 = {T1, T3, T4} → (T1, T3, T4)
C3 = {T1, T6} → (T1, T6)
C4 = {T2, T5} → (T2, T5)
C5 = {T2, T6} → (T2, T6)
• Expand PCS into subsets of decreasing test
lengths. Each subset is an independent test
session, consisting of tests that can be
concurrently applied.
• Select test sessions to cover all tests such that
the added time of selected sessions is minimum.
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TS Algorithm: Cover Table
Test sessions
T1
(T1, T3, T4)
X
(T1, T5)
X
(T1, T6)
X
(T2, T6)
T2
(T3, T4)
T4
X
X
T6
X
X
X
100
X
100
X
100
X
10
X
10
X
10
X
X
Length
100
X
(T5)
(T4)
T5
X
(T3, T5)
(T2, T5)
T3
10
5
Selected sessions are (T3,T4), (T2, T5) and (T1, T6). Test time = 120.
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A System Example: ASIC Z*
RAM 2
Time=61
Power=241
ROM 1
Time=102
Power=279
RAM 3
Time=38
Power=213
ROM 2
Time=102
Power=279
Random logic 1, time=134, power=295
Random logic 2, time=160, power=352
RAM 4
Time=23
Power=96
RAM 1
Time=69
Power=282
Reg. file
Time = 10
Power=95
*Y. Zorian, “A Distributed Control Scheme for Complex VLSI Devices,”
Proc. VLSI Test Symp., April 1993, pp. 4-9.
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Test Scheduling for ASIC Z
1200
Reg. file
Power limit = 900
Power
900
600
RAM 2
RAM 3
Random logic 1
ROM 1
300
RAM 1
Random logic 2
ROM 2
RAM 4
0
200
300
400
Test time
331
•R. M. Chou, K. K. Saluja and V. D. Agrawal, “Scheduling Tests for VLSI
Systems under Power Constraints,” IEEE Trans. VLSI Systems, vol. 5,
no. 2, pp. 175-185, June 1997.
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References
• N. Nicolici and B. M. Al-Hashimi, PowerConstrained Testing of VLSI Circuits,
Boston: Kluwer Academic Publishers,
2003.
• E. Larsson, Introduction to Advanced
System-on-Chip Test Design and
Optimization, Springer 2005.
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