NOISE IMMUNE CONVOLUTIONAL ENCODER DESIGN AND ITS IMPLEMENTATIONIN TANNER

International Journal on Cybernetics & Informatics (IJCI) Vol. 5, No. 4, August 2016
DOI: 10.5121/ijci.2016.5429 271
NOISE IMMUNE CONVOLUTIONAL ENCODER
DESIGN AND ITS IMPLEMENTATIONIN TANNER
P.Koti Lakshmi1
and Prof. Rameshwar Rao2
1
Assistant Professor, Dept. of ECE, UCE, Osmania University, Hyderabad.
2
Professor(Retd), Dept. of ECE, UCE,Osmania University, Hyderabad.
ABSTRACT
With the rapid advances in integrated circuit(IC) technologies, number of functions on a chip was
increasing at a very fast rate, with which interconnect density is increasing especially in functional logic
chips. The on-chip noise affects are increasing and needs to be addressed. In this paper we have
implemented a convolution encoder using a technique that provides higher noise immunity. The encoder
circuit is simulated in Tanner 15.0 with data rate of 25Mbps and a clock frequency of 250MHz
KEY WORDS
Noise immune design, Convolutional encoder design.
1. INTRODUCTION
Due to the rapid advances in integrated circuit technologies,with the advent of VLSI,The
electronics industry has achieved a phenomenal growth over the last few decades,The number of
applications of been rising steadily, and at a very fast pace. Typically, the required computational
power (or, in other words, the intelligence) of these applications is the driving force for the fast
development of this field.
The design complexity of logic chips increases almost exponentially with the number of
transistors to be integrated. As the technology aggressively scales down, the density on the chip
have increased and hence the interconnection density, leading to increased interaction among the
connections and thereby increasing crosstalk and system failures.
On the other hand with the decrease in supply, the gate threshold is decreased to preserve system
throughput and so leakage currents have increased. And therefore the noise margins have greatly
reduced. The noise immunity is of more concern in high fan-in circuits as they have larger
leakage due to more parallel evaluation paths. As the number of parallel paths(fan-in) increase in
the design, the noise immunity of the design decreases. The circuits with wide fan-in include
coding and decoding circuits in communications, address decoding and encoding, data
sequencing and timing control in computational applications.

272
PROBLEM STATEMENT
The basic digital communication system employs various encoding and decoding circuits as
shown in Fig. 1. Forward error correction schemes are generally used in transmitter to encode the
data or information and in receiver to detect and correct errors.
Fig.1 Basic Digital Communication System
Forward Error Correction (FEC) in digital communication system improves the error detection as
well as error correction capability of the system at the cost of increased bandwidth and system
complexity. Using FEC the need for retransmission of data can be avoided hence it is applied in
situations where retransmissions are relatively costly or impossible. FEC codes can be classified
in two categories namely block codes and convolution codes. Block codes operate on fixed size
data blockswhere as convolution codes operate on arbitrary length data blocks. A convolution
coder is often used in digital communication systems where the signal to noise ratio is very low.
Error detection and correction or error control arethe techniques that enable reliable delivery of
digital data over an unreliable (noisy) communication channel. Many communication channels
are subject to channel noise, and thus errors may be introduced during transmission from the
source to a receiver. Error detection techniques allow detecting such errors, where aserror
correction techniques allow for the reconstruction of the original data.
As the encoder circuits comprise of high fan-in gates, when implemented in nano-metric
technologies, are prone to noise effects. In the chips which realize logic, most of the chip area is
used in providing interconnections and because of their high density; interaction among them
would be more. This large inter coupling among the wires introduces noise in the nearby wires
which in turn may result in errors in function realization, especially when the encoder input gets
corrupted, it results in unrecoverable error at the output of the encoder. Thus we have designed a
convolution encoder with a technique which is more noise immune and simulated the design.
In section II we discussed the noise immune technique, Section III deals with Convolution
encoder design ,in section IV, simulation results and in section V conclusion were presented.
2. NOISE IMMUNE GATE DESIGN
Dynamic logiccircuits find their wide application in high speed, low power areas such as
microprocessors, digital signal processing, dynamic memories etc., because of their low device
count, high speed, short circuit power free and glitch free operation [2]. On the other hand it is
also possible to design a dynamic logic unit that is smaller than its static counterpart. Dynamic
logic consists of pull down network realizing the logic.

273
From the basic theory of dynamic logic, large amount of noise gets induced and power
consumption increases. Dynamic logic suffers from charge sharing and cascading. To overcome
these problems domino logic was proposed. When a dynamic gate is cascaded by a static inverter,
it is called Domino logic. For the same output current and a lower switching threshold, aDomino
gate runs faster thanits static counterpart as they present much lower input capacitance.
The proposed domino circuit is shown in the Fig.2 [3]. Transistor M3 and M5 are connected
between the dynamic- node and ground, gate ofM3 transistor is connected to the OUT terminal
and M3 is stacked with M5. During evaluation phase when PDN is on with one or more inputs
connected to logic one, the transistor M4 discharges the dynamic-node and the Out terminal goes
to logic „1‟ and M3 becomes on which aids in faster discharge of any accumulated charge on
dyn_node along with PDN and M4. The rate of discharge can be controlled by varying the W/L
ratio of M4. When all the inputs are at logic „0‟, output stay at logic „0‟ and M3 remains off and
thus dyn_node retains its charge. If any input changes from logic „0‟ to logic „1‟ , PDN becomes
conducting and during evaluation phase when clock is high, dyn_node discharges below Vt of the
inverter turning its output to logic „1‟. When output becomes logic „1‟, M3 turns on providing a
path to discharge dyn_node quickly as M5 is also ON during evaluation phase. At the same time
as the source node of M6 being connected to N-foot, effect of noise in the circuit can also be
reduced. An Ex-or gate of the proposed technique is implemented and simulated.
Fig.2 Proposed noise immune technique. Fig.3 Two inputs Ex-OR gate of the proposed technique.
3. CONVOLUTIONAL ENCODER DESIGN:
Convolution codes operate on arbitrary length data blocks. The convolution coder is often used in
digital communication systems where the signal to noise ratio is very low. In this, the encoding
operation may be viewed as discrete time convolution of input sequence with the impulse
response of the encoder.
Convolutional codes are commonly specified by three parameters, (n,k,and m),Where n
represents the number of output bits,krepresents number of input bits andm, the number of
registers. [4] Code rate k/n is measure of efficiency of the code. Generally k and n range from 1
to 8, m from 2 to 10 and code rate from 1/8 to 7/8 except for deep space applications where code
rates as low as 1/100 or even longer will be used[4]. Convolutional code chip manufacturers often
specify the code by parameters (n,k,L), where L is constraint length, defined by L = k(m-1), and

274
represents the number of bits in the encoder memory that effect the generation of the n output
bits[4].
As a bit is shifted along the register it becomes part of other output symbols sent. Thus the
present output bit that is observed has information about previous input bits. A convolution
encoder used shown in Fig.4. It is assumed here that the shift register shifts in one bit at a time
and outputs three bits, though other combinations of input to output bits are also possible.
Table 1. Encoder Transition tableFig.4. Convolutional Encoder
Here the present input bit is shifted intoS1,S2 and S3 holds the previous bits thus defining the
state of the encoder. For every input bit there are three output bits (O1, O2,O3), thus code rate is
1/3. The transition tabledefines the output of the encoder for given state and input (Table.1).
It is the code generation polynomial which gives a unique error detection quality for a
generator.For example a list of Generator polynomials found by Busgang for good rate 1 /2 codes
is shown in Table.2, as can be seen from the table that fan-in of summing circuit (here EX-OR) is
increasing with constraint length. Thus as the fan-in increases the effect of on chip noise at will
be more and thus can cause errors in the coded output, and cannot be recovered at the receiver as
the encoder output itself is erroneous. Thus to eliminate such type of error, Ex-or gate should
have high noise immunity.
Constraint
Length
G1 G2
3
4
5
6
7
8
9
10
110
1101
11010
110101
110101
110111
110111
110111001
111
1110
11101
111011
110101
1110011
111001101
1110011001
Table.2 Generator Polynomials found by Busgang for good rate ½ codes
Input[S1] [S2 S3] [O1 O2 O3]
0 0 0 0 0 0
1 0 0 1 1 0
0 1 0 1 1 0
1 1 0 0 1 1
0 1 1 0 1 1
1 1 1 1 1 0
0 0 1 1 0 1
1 0 1 0 0 0

275
The encoder circuit is thus implemented with a gate having high noise immunity as reported in
[4]. Two input and three input ex-or gates were implemented and simulated with the proposed
technique.
4. SIMULATION AND RESULTS
Simulations were done on Tanner T-spice 15.0 with 16nm technology PTM files with 1V supply.
The encoder circuit is implemented in three design techniques namely footless domino gate with
keeper (FLDG Keeper), Scheme [8] technique and Noise immune proposed technique. All the
circuits were simulated with 250MHz clock and data rate of 25Mbps.
Fig.5. Simulation results of convolutional encoder using three different techniques
From the simulation result we have observed that the proposed technique has less- ripple in the
output and more noise immune as EX-OR gates are implemented with noise immune design
technique.

276
Fig.6. Simulation result of two input Ex-OR gate.
Fig. 6 shows the simulation output of two inputs Ex-OR gate with noise immune technique.
Fig.7 Simulation result of three input Ex-OR gate.
Fig. 7 shows the simulation output of a three input Ex-OR gate with noise immune technique.

277
CONCLUSION
In this paper we have presented theimplementation results of a rate 1/3 convolutional encoder
with input data rate of 25Mbps and Clock rate of 250MHz. The circuit is implemented in three
different techniques and their simulation results were presented, and found that the proposed
technique has fewer ripples in the output and is more noise immune.
ACKNOWLEDGEMENTS:
We would like to thank TEQIP-II grants for the facilities provided to carry out the work in the
department.
REFERENCES
[1] John P. Uyemura “CMOS Logic circuit Design” Springer International Edition, 2005.
[2] H.L. Yeager et al, “Domino Circuit Topology”, U. S. Patent 6784695, Aug. 31, 2004.
[3] P. Koti Lakshmi and Prof Rameshwar Rao, “A Technique for designing high speed noise immune
CMOS domino high fan-in circuits in 16nm technology”, International Journal of VLSI design &
Communication systems (VLSICS) vol.6, No.5, Oct 2015.
[4] Charan Langton, Editor “coding and decoding with Convolutional Codes” Tutorial 12,
www.complextoreal.com.
AUTHORS
Mrs. P. KotiLakshmi is working as Assistant Professor in the department of ECE at
Osmania University, Hyderabad. She has 15 years of teaching experience. She obtained
her AMIETE Degree from IETE, New Delhi in 1999, M.E in Digital systems from
Osmania University, Hyderabad in 2004, and currently pursuing PhD in VLSI
Design from Osmania University , Hyderabad, Andhra Pradesh . Her areas of interest
include VLSI Design and Wireless Communications.
rof. Rameshwar Rao is Professor (Retd.) of department of ECE, University college of
Engineering, Osmania University, Hyderabad. During his tenure he held many positions
as Vice Chancellor of JNTUH, Hyderabad, Andhra Pradesh., Dean, Faculty of
Engineering, Osmania University (OU)., Convener, PGECET. He obtained B.E. degree
in ECE from OU, M.Tech. and PhD degree from prestigious IIT Bombay.His work
experience spans across 35 years as R&D engineer at Avionics Design Bureau,
Hindustan Aeronautics Ltd., Hyderabad and as an eminent teacher at Osmania
University, Hyderabad. His research interests include VHDL Modeling & Synthesis,
(During last three years), Data and Computer Communications, Detection and Estimation Theory,
Information and Coding Theory, Microprocessor based applications and VLSI Design. He has to his credit
more than 60 conference/ journal publications.

NOISE IMMUNE CONVOLUTIONAL ENCODER DESIGN AND ITS IMPLEMENTATIONIN TANNER

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