2. Power dissipation is defined as the measure
of rate at which the energy is dissipated or
lost from an electrical system. When an
electric current works on a conductor , the
internal energy of that conductor increases
causing its temperature to rise above the
surrounding temperature. This causes
energy to dissipate away from the
conductor into the surrounding through the
process of heat transfer.
3. The below factors should be considered
for estimating power dissipation
4. The various types of power dissipations are:
Dynamic power dissipation
Short circuit power dissipation
7. In this we have sandwiched a layer of thickness d of
insulating material between a metal plate and the semi-
conductor. Here we have assumed the semiconductor
to be of P-type
8. In an ideal MIS diode, the insulator has
an infinite resistance and does not have
either the mobile charge carriers or
The Fermi levels in the metal line up with
the Fermi level in the semiconductor.
The level in the metal itself is same
This is called the Flat-Band condition
10. When the voltage V is negative, the
holes in the P-Type semiconductor are
attracted to and accumulate at the
semi-conductor surface in contact with
This is called as Accumulation.
In the absence of the current flow, the
carriers in the semi-conductor are in the
state of equilibrium and the Fermi level
appears as a straight line.
11. The intrinsic Fermi level has a higher
value at the surface than at a point
deep in the substrate and the energy
levels Ec , Ev and Ei bend upward near
The Fermi Level Ef in the semiconductor is
now -qV below the Fermi level in the
13. When the applied voltage V is positive
but small, the holes in the P-Type
semiconductor are repelled away from
the surface and leave negatively
charged acceptor ions behind.
A depletion region, extending from the
surface into the semiconductor is
This is the depletion condition.
Besides repelling the holes, the positive
voltage on the gate attracts electrons in
the semiconductor to the surface.
14. The surface is said to have begun to get
inverted form original P-Type to N-Type.
While V is small , the concentration of
holes is still larger than the concentration
This is the weak inversion condition.
The bands at this stage bend downward
near the suface.
16. If the applied voltage is increased
sufficiently, the bands bend far enough
that level Ei at the surface crosses over to
the other side of level Ef.
It is brought about by the tendency of
carriers to occupy states with the lowest
The kinetic energy of the electrons is zero
when they occupy a state at the bottom
edge of the conduction band.
In the present condition of inversion level
Ei bends to be closer to level Ec.
17. The electron density at the surface is still
smaller than the hole density deep inside
When V is increased to the extent that
the electron density at the surface ‘ns’
becomes greater than the hole density
in the bulk, onset of strong inversion is
said to take place.
18. Minimizing the power consumption of circuits is
important for a wide variety of applications
because of the increasing levels of integration
and the desire for portability. Since
performance is often limited by the arithmetic
components speed, it is also important to
maximize the speed.
The compromise between these two
conflicting demands of low power dissipation
and high speed can be accomplished by
selecting the optimum circuit architecture.
19. An important attribute of arithmetic
circuits for most applications is
maximizing speed (for general purpose
applications) or throughput (for signal
For a growing number of applications,
minimizing the power consumption is also
of great importance.
The most direct way to reduce the
power is to use CMOS circuits, which
generally dissipate less power.
20. For CMOS, the use of adders with
minimum power consumption is
attractive to increase battery life to
avoid local areas of high power
There are four factors which influence
the power dissipation of CMOS circuits:
Circuit design style
21. There are a number of CMOS circuit
design styles, both static and dynamic in
The full Adder is the basis for almost
every arithmetic unit, therefore any
investigation into the suitability of circuit
design style for use in arithmetic units
must focus on the design of full adder.
22. Static CMOS Full Adder
The above figure shows a full adder
designed using static complementary
MOS logic employing both P and N type
23. The P- Logic tree(upper half of the
circuit) allows the output to be charged
high, while the N-tree (lower half of the
circuit) allows the output to be
discharged to ground.
Both the complemented and un-
complemented inputs are required and
both the ‘sum’ and ‘carry’ and the
‘complemented sum and carry’ are
The sum and carry functions are
computed independently of each other.
24. Full Adders constructed using NO RAce
dynamic CMOS logic(NORA) employ
alternating stages of P and N type logic
to form carry and sum outputs.
NO Race dynamic CMOS logic (NORA) Full Adder
NO Race dynamic CMOS logic (NORA)
25. The P-Type stage that forms the carry
output is dynamically pre-charged high
while the N-Type transistor that computes
the sum output is dynamically pre-
This pre-charging and pre-discharging
process requires a two-phase
NORA logic is unique because it doesn’t
require complemented inputs and
doesn’t compute both complemented
and un-complemented outputs.
27. Cascode Voltage Switch Logic (CVSL) is
a dynamic logic family. It requires a two-
The complement of the clock signal is
not necessary unlike NORA.
In CVSL Full Adder circuit , the outputs
and their complements are all pre-
charged high while the clock is low.
The complementary cascoded
differential N-Type transistor trees pull
either the output or its complement low.
The sum and carry are computed
independently of each other.
29. The DCVSL is formed by replacing the P-
type transistor in CVSL with a cross
coupled pair of P transistor yields a static
version of that logic.
When the output at one side gets pulled
low, then the opposite P transistor will be
turned on and the output on that side
will be pulled high.
31. CMOS non threshold logic employs the
same binary decision trees and cross
coupled P transistors as DCVS but an
extra N-Type transistors are added.
Two N-Type transistors are placed in
between the cross coupled P transistors
and the output in order to lower the
voltage level of the high output .
Another two N transistors are placed
between the N Transistors trees and
ground in order to raise the voltage level
of the low output.
33. ECDL is an extension to the DCVS Full
ECDL uses a completion signal, DONE, to
pre-discharge the outputs of each
The DONE input signal goes low when
the previous stage has finished its
Enhancement source Coupled Logic is
another variation on the DCVS full adder.