4 bit cmos full adder in submicron technology with low leakage and ground bounce noise...
TRANSCRIPT
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4-BIT CMOS FULL ADDER IN SUB MICRON TECHNOLOGY FOR LOW LEAKAGE AND GROUND BOUNCE NOISE REDUCTION
PROJECT GUIDE :
Mr. Y.CHANDRA SEKHAR
ASSOCIATE PROFESSOR
BY:
P.AYYAPPA (11QNIAO401)
P.SHIREESHA(11QN1A0454)
M.MAHESH (11QN1A0405)
G.BHARATH (11QN1A0446)
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INTRODUCTIONFor complex arithmetic circuits,
Ground bounce noise is given an equal importance like leakage current, active power, delay and area.
Reduction of leakage power and ground bounce noise reduction using sleep transistor in 4 bit CMOS full adder implementation
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WHY ONLY MOSFET ?
BJT:In NPN current conduction occurs
by majority and minority charge carriers
Cannot withstand high temperature
Leakage current will be dissipated because of minority charge carriers
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CMOS LOGIC STYLE
CMOS=PMOS+NMOS
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COMBINATIONAL CIRCUIT FOR FULL ADDER
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FULL ADDER
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BOOLEN EXPRESSIONS FOR FULL ADDER
CARRY=AB+BC+ACSUM =A B C
REDUCED FORM:CARRY: AB+C(A+B) ________SUM:AB+C(A+B) (A+B+C)+ABC
++
+
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4-BIT FULL ADDERFor adding any bits of input we require
as many number of full adders
In this paper we are adding 4 bits of input
Four full adders can be taken in the form of “Ripple Carry Adder”
The generated carry is rippled to next full adder
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PROPOSED 4BIT RIPPLE CARRY ADDER
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POWER CONSUMPTION IN CMOS
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LEAKAGE POWERThe partial power dissipation at
sub threshold region where the voltage is less than vth(0<v<0.7)
P LEAKAGE = VDD ILEAKAGE
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POWER DISSIPATION IN CMOS
Ptotal (0→1) = CL VDD2 +tscVDD Ipeak
+VDDIleakage
%75 %5%20
CL
VDD VDD
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REASONS FOR LEAKAGE POWERPower loss at sub threshold
region
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REASONS FOR LEAKAGE POWER
Dissipation because of short circuit formed between V dd and ground
Gate tunneling current
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REASONS FOR LEAKAGE POWER
Formation of parasitic capacitors
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REDUCTION OF POWER CONSUMPTION IN CMOS
Power gating technique
Sleep transistor
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POWER GATING TECHNIQUEA flip-flop along with adder is used
Flip-flop is a sequential circuit and its o/p depends on present i/p and past o/p
The carry and sum circuits are divided into separate blocks and are cascaded
Size of the transistor can be reduced by changing the W/L ratio with appropriate values
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CONVENTIONAL CMOS FULL ADDER
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POWER GATING-MERITS Sub threshold current is directly
proportional to width/length ratio of transistor
This sizing reduces the standby leakage current(sub threshold current)
Reduces the area occupied by the circuit and silicon chip
Reduction in cost
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GROUND BOUNCE NOISEBecause of standby current
circuit ground is not connected properly to the actual ground
This produces noise at the transistors and is termed as ground bounce noise
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REDUCTION OF GROUND BOUNCE NOISE
For further modified design of the circuit the amount of noise at the ground will be more
We use sleep transistors to reduce the ground bounce noise
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FULL ADDER WITH SLEEP CIRCUIT
DESIGN:1 DESIGN:2
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COMPARISON Modified adder circuit of
Design 2 shown in Figure 3 W /L ratio of PMOS is 1.5
times that of W /L ratio of NMOS
each block has been treated as an equivalent inverter
Further compared to the Base case, Design 1 and Design 2, ground bounce noise produced
It is reduced by sleep transistor
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IMPROVED GROUND BOUNCE NOISE REDUCTION
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EXPLANATIONcontrol transistor is connected b/w gate
and source
When i/p is fed to the control transistor, a short circuit is formed
The sleep transistor acts as a diode
charge stored in the carry block is discharged through ST-1
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Same signals are applied to sum generation part also but with duration of half of the oscillation period.
Noise cancellation occurs once
the second sleep transistor (ST2) turns on due to phase shift between the noise induced by the second sleep transistor
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H-SPICE: