J V R Ravindra

K S Sainarayanan

M B Srinivas

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Minimizing Simultaneous Switching Noise (SSN) using Modified Odd/Even 
Bus Invert Method 
K.S.Sainarayanan, J.V.R.Ravindra and M.B. Srinivas 
Center for VLSI and Embedded Systems, 
International Institute of Information Technology (IIIT), Hyderabad. 
{kssai, ravindra}@research.iiit.ac.in, srinivas@iiit.net
Abstract
In high speed digital circuits, the inductive effect is 
more dominant compared to capacitive effect. In 
particular, as the technology is shrinking, the spacing 
between interconnects becomes less which increases 
Simultaneous Switching Noise (SSN) or 
dt
di
M noise. 
So earlier methods proposed which concentrate on 
reducing capacitive effect do not hold good. This 
paper proposes a modified Odd/Even Bus Invert 
scheme, which reduces the simultaneous switching 
activity, thereby improving the signal integrity. The 
performance of the proposed coding scheme has been 
tested on various benchmarks and it is found that SSN 
or
dt
di
M is reduced by 28% compared to data 
transmitted unencoded The proposed Codec has been 
designed and it has been found that power overhead is 
3.3%. 
Keywords 
Simultaneous Switching Noise (SSN), Odd 
Simultaneous Transitions (OST), Even Simultaneous 
Transitions (EST), Coding, VLSI, Low power. 
1. Introduction 
The need for higher processing speeds has driven 
VLSI circuitry to operate in GHz range. As the speed 
of VLSI circuits are increasing rapidly, the effect of 
inductive crosstalk in IC packaging is becoming a 
significant bottleneck in inter chip communications. 
International Roadmap for Semiconductors (ITRS) has 
predicted that IC performance is continuing to be 
doubled every 18 months whereas the package 
performance is doubling over the next decade [1]. This 
imbalance is due to the effect of parasitic inductance in 
packaging. Furthermore, as we approach DSM 
technology, the spacing between interconnects 
becomes less, which leads to crosstalk, and thereby 
deteriorating the signal integrity [7]. To overcome this 
issue, several methods like shielding, buffer insertion, 
crosstalk aware routing and differential signaling have 
been proposed. Even though the aforementioned 
methods reduce cross talk effectively, the higher power 
consumption due to the complex nature of their drivers 
and buffers, limits their usability. Bus Coding is yet 
another approach to solve the above mentioned 
problem. Although previous coding techniques aim at 
reducing the capacitive crosstalk [4, 7, 8], the crosstalk 
due to inductive effects become more dominant in 
VLSI connectors. Hence, this paper proposes a 
modified Odd/Even Bus Invert scheme, which reduces 
the simultaneous switching Noise. 
2. Theory 
2.1. Crosstalk noise 
 Mutual inductance and capacitance are mechanisms 
that cause crosstalk. Especially in high speed digital 
design and packaging the effect of mutual inductance 
is more dominant compared to that of the mutual 
capacitance.
This paper focuses on reducing the mutual 
inductance. Mutual inductance mL induces current 
from an aggressor line onto a quiet line by means of 
magnetic field thereby degrading the signal integrity 
[3]. Especially in DSM the spacing between the lines 
increases the effect of mutual inductance leading to 
increasing crosstalk.
A crosstalk may be induced in the voltage of a pin 
‘ i ’ in which the signal is static, by the adjacent pins in 
which the signal is varying [5]. This is given by the 
expression  
Proceedings of the Third IEEE International Workshop on Electronic Design, Test and Applications (DELTA’06) 
0-7695-2500-8/05 $20.00 © 2005 IEEE 
p
p
ip
i
glitch
dt
di
MV                                      (1) 
Where, ipM is the mutual inductance between the 
thi pin and the thp pin and pi is the current in the 
thp
pin. The sign of the coupled voltage is positive or 
negative depending on whether the 
thp neighboring 
pin undergoes a rising or falling transition. 
Furthermore, the crosstalk noise or 
dt
di
M noise is 
data-pattern dependent. This dependency is exploited 
by coding the data in such a way that crosstalk is 
reduced. A two line model showing the various 
inductance and capacitance is shown in Figure 1. We 
shall prove the dependency of data pattern on 
crosstalk.
Figure1. Equivalent circuit model for two wire 
bus
2.1. Odd Mode 
 Odd-mode propagation mode occurs when two 
coupled lines are driven with equal magnitude and 
180 out of phase with one another. Let us assume 
that 02211 LLL . Thus in Odd mode propagation 
the current will be of equal amplitude but flow in 
opposite direction [2]. The effective Inductance 
oddL due to odd mode of propagation is given in Eq 
(2).
)2(1211 LLLodd
The pattern of magnetic field of two conductors in 
odd mode is shown in Fig 2(a). 
2.2. Even Mode 
 Even mode propagation mode occurs when the 
coupled transmission lines are driven with equal 
magnitude and are in phase with one another. Thus in 
even mode propagation the current will be of equal 
magnitude and flow in the same direction [2]. The 
effective Inductance evenL due to even mode 
propagation is shown in Eq (3). 
)3(1211 LLLeven
The pattern of magnetic field for a two wire model 
propagating in even mode is shown in Fig 2(b). 
     Figure 2(A). Odd Mode 
     Figure 2(B). Even Mode 
Thus the Inductive Crosstalk in bus lines is 
significantly lower, when propagating in odd mode 
rather then even mode. 
3. Propose Coding scheme 
Let the input to the proposed coding scheme at time 
)1(K be 1kA and let 1kE  be the output at that 
time. The proposed Coding Scheme is as follows. 
1. Calculate the number of Simultaneous 
Switching Transitions (SST)  of 
1kA  at odd 
position and denote it by OST (Odd 
Simultaneous Transitions) 
2. Calculate the number of Simultaneous 
Switching Transitions (SST) of 
1kA  at even 
position and denote it by EST (Even 
Simultaneous Transitions) 
3. if (OST>EST)   
begin
flip odd positioned bits of the data & 
append with 01 and transmit. 
I1
I2
Proceedings of the Third IEEE International Workshop on Electronic Design, Test and Applications (DELTA’06) 
0-7695-2500-8/05 $20.00 © 2005 IEEE 
              end 
   else 
   if (OST<EST ) 
            begin 
                 flip even positioned bits of the data &
                 append with 00 and transmit 
            end 
           else 
            begin 
        Send as it is with 10 appended
           end
4. Illustration of the Proposed Coding 
Scheme
4.1. Example 1 
Let the present data on the bus be 
1kA =
{11111111} or { }. The number of OST is 4 
& EST is 3. Since OST is greater than EST, hence flip 
the odd positioned bits & append with 01. Thus the 
data to be transmitted after encoding is 
1kE  = {0l 
0l0l 0l}{0l} { }{ }. Thus the Simultaneous 
transition is reduced from 7 to 0 which reduces the 
SSN.
4.2. Example 2 
Let the present data on the bus be 
1kA =
{10101010} or { }. The number of OST & 
EST is 0. Since OST is equal to EST, the data is 
transmitted with encoding appending 10. Thus the data 
to be transmitted after encoding is 
1kE = {10101010} 
{10} { } { }. Thus the best case is 
transmitted as it is without increasing the crosstalk. 
5. Hardware Implementation 
The Hardware implementation of the proposed 
CODEC is shown in Figure 3 (a) and Figure 3 (b). 
OST and EST estimator is a 3-bit ADDER-COUNTER 
which counts number of even and odd simultaneous 
transitions respectively. The output of the comparator 
indicate if OST>EST or OST<EST or OST=EST. If 
OST >EST then the odd position bits are flipped and 
bits “01” are appended and transmitted. If OST <EST 
then the even position bits are flipped and bits “00” are 
appended and transmitted. If both are equal then the 
data is sent without encoding by appending “10”. A 2 
to 4 decoder Figure3 (b) is used to decode the 
transmitted data. 
n            n+2  
 01
00
10
Figure3 (a) Hardware implementation of the 
proposed Encoder 
kE
n+1
      n+2
Figure3 (b) Hardware implementation of the 
decoder
6. Simulation Results 
The comparison of the proposed coding scheme 
with various other coding schemes, with respect to 
Inductive crosstalk is shown in Table1. It has been 
found that the proposed method reduces the 
Simultaneous Switching Noise by 28% on an average, 
when compared to transmitting the data without 
encoding. 
Percentage Of Cross Talk Bus
Coding
Methods
mpeg vortex go gcc compress 
Unencoded 100 100 100 100 100 
BI [4] 85 84 83.5 84 83 
CBI [8] 80 78.25 79 80 78.12 
MBI [6] 76 75.52 74.2 75 75.26 
Proposed
Method
72 73.08 70.2 74.6 72.05 
Table1. Comparison of Crosstalk Noise of 
Various Coding Schemes Tested On SPEC’95 
Benchmarks
OST
Estimator 
EST
Estimator 
C
O
M
P
A
R
A
T
O
R
Flip Odd 
position bits
Flip Even 
position bits
Buffer
00
2 to 4
Decoder
             01
             10
Flip Even 
Flip Odd 
Buffer
Proceedings of the Third IEEE International Workshop on Electronic Design, Test and Applications (DELTA’06) 
0-7695-2500-8/05 $20.00 © 2005 IEEE 
Power analysis of the various Codecs has been 
performed using MAGMA tools. The comparison of 
the relative power overhead of the various coding 
scheme is shown in Table 2. 
Bus Coding 
Technique
% Relative 
power
BI [4] 3% 
CBI [8] 3.6% 
MBI [6] 3.4% 
Proposed Coding 
Method 
3.3% 
Table2. Percent Power Overhead of the 
Various Coding Schemes With Respect To 
Unencoded
The proposed codec has been designed using 
Magma tools and it is shown in Figure5 
Figure 5: Layout of the proposed CODEC 
using MAGMA tools 
7. Conclusions
The inductive effect in IC packaging is well 
pronounced in high speed digital circuit which 
degrades the signal integrity. Addressing this issue 
with aggressive package design is slow and often too 
expensive for a majority of applications. This paper 
proposed a Modified Odd/Even Bus Invert coding and 
it has been found that SSN or glitching is reduced by 
28%. The Codec was designed using Magma and the 
overhead has been found to be 5%. 
8.  Acknowledgements 
Authors wish to thank Magma® Design Automation 
(India) Pvt. Ltd, Bangalore for sponsoring Magma® tools 
used in this work.
9. References 
[1] International Technology Roadmap For Semiconductors. 
Website: http://public.itrs.net 
[2] Stephen H. Hall, Garrett W. Hall and James A. McCall, 
High-Speed Digital System Design. John Wiley and Sons 
Inc., 2000 
[3] A. P. Chandrakasan and R. W. Brodersen, Low Power 
Digital CMOS Design, Kluwer Academic Publisher, 1995. 
[4] Mircea R. Stan and Wayne P. Burleson, Bus Invert 
Coding For Low Power I/O. IEEE Transaction on VLSI 
Systems, pp. 49-58, March 1995. 
[5] B.J. LamMeres and S.P. Khatri. Encoding-Based
Minimization of Inductive Cross-talk For Off-chip Data 
Transmission. Proceedings of DATE, pp. 1318–1323, March 
2005.
[6] M. Lampropoulos et al., Minimization of Crosstalk Noise, 
Delay and Power Using a Modified Bus Invert Technique.
Proceedings of DATE, pp. 1372-1373, Feb 2004. 
[7] B. Victor & K. Keutzer, Bus encoding to prevent 
crosstalk delay. Proceedings of IEEE ICCAD, pp. 57–63, 
Nov 2001
[8] K.-W. Kim and et al., Coupling-driven signal encoding 
scheme for low-power interface design. Proceedings of IEEE 
ICCAD, pp. 318 –321, Nov. 2000.
Proceedings of the Third IEEE International Workshop on Electronic Design, Test and Applications (DELTA’06) 
0-7695-2500-8/05 $20.00 © 2005 IEEE 


Minimizing Simultaneous Switching Noise (SSN) using Modified Odd/Even Bus Invert Method

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Minimizing Simultaneous Switching Noise (SSN) using Modified Odd/Even Bus Invert Method

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