reliability improving approach with opto-based voting system
DESCRIPTION
Reliability Improving Approach with Opto-Based Voting System. Y.Yanagawa A , T.Takahara B , T.Mizuno BC , H.Saito C A The University of Tokyo B The Graduate University for Advanced Studies C The Institute of Space and Astronautical Science, JAXA. - PowerPoint PPT PresentationTRANSCRIPT
Yanagawa 1 P155/MAPLD 2004
Reliability Improving Approach with Opto-Based Voting System
Y.Yanagawa A , T.Takahara B, T.Mizuno BC, H.Saito C
A The University of Tokyo
B The Graduate University for Advanced Studies
C The Institute of Space and Astronautical Science, JAXA
Yanagawa 2 P155/MAPLD 2004
Our strategy for improving performance and reliability
Abstract
We propose new high-speed voting system based on optical signal. Majority voting is major approach to boost system reliability in computers. It has been used for many space applications. In such redundant system, signals are usually voted by logical synchronous circuits. However, such circuits often limits operating frequency of the whole system because voter should run at least twice as fast as system. System operating frequency is naturally limited by the voting speed. On the other hand, in these days, traditional parallel buses in commercial computers are going to be serial. This is because, the faster bus operating speed becomes to increase band width, the more difficult to decrease clock or signal skew to synchronize signals in them. The same thing can be said to FPGA. Many FPGAs provide ultra high-speed serial port to achieve both high speed data rate and simple wiring. In general, serial connection requires to be operated at very high frequency to keep bandwidth wide enough. In this paper, we introduce two types of analog voting scheme: electrical signal based voting system and optical signal based one. The latter one is new type of voting system based on optical signal, that is fast enough to be used in redundant high-speed serial connection. Then, these two voting system is evaluated their feasibility.
Yanagawa 3 P155/MAPLD 2004
Our strategy for improving performance and reliability
Outline
• Backgrounds
– Trend of computer systems
– FPGA Interface
– Redundant computing system
• Our Approach for Improving Reliability and Performance
– Electrical signal based Voting System
– Opto-Based Voting System
• Discussion
• Summary and Future Work
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Trend of Computer Systems
High Speed Serial Bus in COTS Computers
• COTS (Commercial Off The Shelf) Computers are going to use serial bus
– Difficult to synchronize signals in the parallel bus
– To improve bandwidth, every data bus is going to be serial
• PCI Express
• Serial ATA
• Serial memory
• Now several Gbps per channel is achieved on the serial bus
Yanagawa 5 P155/MAPLD 2004
FPGA Interface
High Speed Serial interfaces in FPGAs
• Some FPGAs begin to provide embedded high speed serial interface
• Save many I/O pins with keeping high I/O bandwidth
• Built-in high speed serial interface• 10Gbps ether net
• Fiber channel
• Etc…
– Low jitter
– Easy to implement
Txp
Txn
Rxp
Rxn
Txp
Txn
Rxp
RxnSerializer
Deserializer
Deserializer
Serializer
N bit N bit
N bitN bit
FPGA/ Other DevicesFPGA
Yanagawa 6 P155/MAPLD 2004
Redundant computing system
Triple Voting System
• Improve system reliability
• Utilize multiple module redundancy
• Mitigate radiation effect for space application
• Performance is limited by the speed of voting module
Triple Voting System Overview
Yanagawa 7 P155/MAPLD 2004
Our Approach for improving Reliability and Performance
Reliability Improving Approach
• Motivation– Improving system performance and memory access band width– Simplify system configuration for resource reduction– Serial interface is already available in some FPGAs– Easier to manage signal synchronization – Remove performance limitation caused by traditional voting circuits in the re
dundant system
• System Requirement– Compared to traditional parallel bus (eg. 32bit 100MHz), more than 3Gbps d
ata rate is desirable for serial bus
• Strategy– Propose very high speed voting circuit
• Fast enough to be used for memory bus• Improving voter performance up to several GHz
Yanagawa 8 P155/MAPLD 2004
Our Approach for improving Reliability and Performance
Performance Improving Approach
• Improving approach
– Electrical signal based voting system (Voltage averaging)
– Opto-Based voting system (Newly proposed in this paper)
R
R
R
Vo
V1
V3
V2
Vref
Vo=(V1+V2+V3)/ 3
P2
Light waves
Po+O->E
conversionVo
VrefPo=(P1+P2+P3)
Electrical signal based voting Opto-Based voting
Both types of voting are evaluated
Yanagawa 9 P155/MAPLD 2004
Electrical signal based Voting System
Scheme of Electrical signal based Voting System
• Design high-speed voting system with traditional voltage voting scheme to estimate its speed limit
• Serial communication often uses differential signal
• Voltage Averaging System for differential signal
– Positive signals and negative signals are averaged using registers, respectively
+
-
Ap
Bp
Cp
An
Bn
Cn
Z0
X
X
X
X
X
X
Op
On
ToSerial Receiver
(Differential Output)
Voter
FromSerial Transmitter(Differential Input)
Outline of voltage averaging system for differential signal
Yanagawa 10 P155/MAPLD 2004
Electrical signal based Voting System
Experimental Setup
• Voltage Averaging System for differential signal is built with chip register and microstrip line on the glass epoxy board
• Validate system functionality by using low frequency LVDS signal (120Mbps) and evaluate transmission characteristic at high frequency
DataGenerator
LVDSTransmitter
Ap
Bp
Cp
An
Bn
Cn
25
Op
On
Voter
25
LVDSReceiver
IN1
IN2
IN3TTL- Input
TTL-Output
LVDS transceiver spec.
Magnified view of voter moduleOverall Experiment system
Transmission characteristic design
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Electrical signal based Voting System
Evaluation Result
• The signals are voted properly at 60MHz (120Mbps)
– Observe signal TTL-Input and TTL-Output by digital storage oscilloscope and logic analyzer
Signal of TTL-Input (IN1,IN2,IN3) and
TTL-Output (5V/Div, 50ns/Div, 2GSample)
Signal “IN2” simulates error
Logical signal of TTL-Input (IN1,IN2,IN3) and TTL-Output
Signal “IN2” simulates error
IN1
IN2
IN3
OUT
Yanagawa 12 P155/MAPLD 2004
Electrical signal based Voting System
Evaluation of transmission characteristic at high frequency
• Transmission characteristic is evaluated by the evaluation board below.
• Target frequency 2GHz( = 15 [cm] )• Voting region is designed as concentrated const
ant circuit
(6.4[mm] x 6.4[mm] < /20)• Microstrip Line is designed
• Zdiff=100.7 [, Z1,Z2=58.87 [
• Glass epoxy board– Dielectric Constant = 4.7– Hight h = 1.6 [mm]– Dielectric dissipation factor tan = 0.0175
To NetworkAnalyzer
Microstrip LineZdiff=100Ω
Voter
50ΩTermination
50ΩTermination
3dBCoupler
π / 2 phaseshift Output
π / 2 phaseshift cable
6.4mm
6.4m
m
27ΩChip register
Glass epoxyboard
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Loss in3dB coupler
Loss inSMA cable
+Microstrip line+Connection
Loss inVoter
Loss inMicrostrip Line+SMA cable+ConnectionA B C D
Electrical signal based Voting System
Evaluation Result - Transmission Characteristic
ComponentLoss [dB]
Note
A : 3dB coupler -3.437 Measured value
B+D : Transmission path -0.956 -13.933 – (A + C)
C : Voter -9.54 Theoretical value
Total (A + B + C + D) -13.933
Total loss is -13.933 [dB]
Detail of the loss
Transmission Characteristic (S21) of evaluation board (Start:1GHz, Stop:3GHz,5dB/Div)
• Transmission Characteristic of the voting system
Yanagawa 14 P155/MAPLD 2004
Electrical signal based Voting System
Evaluation Result - Discussion
• As the digital signal has wide frequency spectrum, the voting circuit is built with chip register (lumped parameter circuit ) and microstrip line
• This design results in large transmission loss of -13.9[dB]
• -13.9[dB] loss is critical to the signal transmission
– Increase noise susceptibility
• On the other hand, if it is built with pure microstrip line (distributed constant circuit) , its characteristic varies largely with the input signal frequency
– Unable to operate with wide spectrum signal
Electrical signal based voting system is not suitable for high frequency signal
Yanagawa 15 P155/MAPLD 2004
Opto-Based Voting System
Scheme of Opto-Based Voting System
• This system utilizes optical power to decide majority
• Electrical signals are modulated into AM optical signals.
• Each signals are mixed together to sum up the power of every optical signal at photo detector.
• Proper threshold is set at the photo detector to determine logical output
Majority Vote by Amplitude Modulated Optical Signals
Time
1 0 1 1
Time
1 0 1 1
Time
ModuleA
1011
Modulated Lights
・・・・・・
・・・・・・
・・・・・・
PhotoDetector Time
1 0 1 1 ・・・・・・Module
B
Module Cw/ Error
Electrical Output
Time
Threshold
Mixture of three light waves
Yanagawa 16 P155/MAPLD 2004
Opto-Based Voting System
Fundamental evaluation
• Many optical transceivers use laser diode to modulate optical wave by high speed input signal
• Check if such “coherent” optical signals can be summed up without interfering each other for majority voting
LASER DiodePhotoDiode
I VConversion
+
-
2.2k10k+9V
Vout
3 LDs PD
Experimental System
Yanagawa 17 P155/MAPLD 2004
Opto-Based Voting System
Evaluation Result
• Measure the output voltage of photo detector with turning each LD ON/OFF
• Output voltage increases linearly as the number of ON LD increases
• This result shows that even coherent light wave can be summed up
• It is possible to determine how many modules are ON by comparing the output voltage
Output Voltage of Photo Detector
Yanagawa 18 P155/MAPLD 2004
Our strategy for improving performance and reliability
Summary
• Optical voting method have many advantages
– No parasitic capacitance on the transmission line
– Easy to transmit high speed signal
– Many high speed optical devices are available on the market
– Electromagnetic Compatibility (EMC)
• The evaluation result shows that optical voting system is feasible for majority voting
Electrical Optical
Frequency Response
Poor Good
Circuit Design
Difficult Easy
System Complexity
Simple Complex
Performance Comparison of each method
Yanagawa 19 P155/MAPLD 2004
Future work
Triple Voting System with Serial Memory
• Application of this voting system– Triple voting system with serial memory
• Simple wiring, Save resource for voter, Easy to synchronize
CPUA
LASER PD
ModulatorOpticalIN
OpticalOUT
CPUB
CPU
ModulatorOpticalIN
OpticalOUT
CPUC
CPU
ModulatorOpticalIN
OpticalOUT
Serial Out
Serial Out
Serial Out
SerialMemory
Serial In
Serial In
Serial In
Optical connection
Electrical connection
Yanagawa 20 P155/MAPLD 2004
Future work
Vector based Optical Error Detection
• Vector based optical error detection and error correction system• Map each input signal from redundant modules to optical wave vectors by using phase modulati
on• These optical signals are mixed at the detector• Error module detection and majority voting can be achieved all at once by checking vectorial sum
mation of the mixed optical signals
InputVector
GeneratedVector
(1,0,1)
Input Value from “A”Input Value from “B”
Input Value from “C”(0,1,1)
(1,0,1)
(1,1,0)
(0,1,0)
(1,0,0)
(0,0,1)
(1,1,1)(0,0,0) A = 1
B = 1
C = 1
C = 0
A = 0
B = 0
r
Generated Vector (r
VotedOutput
Error module
(1, 0) 1 B
(1, /3) 1 C
(1, 2/3) 0 A
(1, ) 0 B
(1, 4/3) 0 C
(1, 5/3) 1 A
(2, 0) 1 -
(2, ) 0 -
Correspondence between vector and voting result