INTRODUCTION. Due to the growing market of portable devices (such as
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Due to the growing market of portable devices (such as
personal digital assistants, cellular phones, etc.), low power dissipation has become a very important issue in integrated circuit design. Among the many design techniques, the adiabatic approach is one method used in logic circuits to achieve low power design.
By applying the two ideas, one can achieve very low power dissipation in the circuit especially at low to moderate clock speed. The power saving of adiabatic circuit can reach up to more than 90 percent compared to conventional static CMOS circuit.
the output node is charged slowly compared to its time
constant and we ensure that the voltage drop across the
transistor is relatively small at the time when the switching
On the other hand,
instead of dumping the charge to ground on every clock
cycle, the charge can be designed to flow back to the power
Adiabatic: occurring without loss or gain of heat
Changing value of bit requires converting bit signal into heat
2 States: True, False
Speed is outstanding, but power dissipation is now a huge issue.
Returns value (energy) of the bit back to the source
3 States: True, False, Off
Very low power dissipation is achieved at expense of speed.
CMOS transistors dissipate power when they switch. The main part of this
dissipation is due to the need to charge and discharge the gate capacitance C
through a component that has some resistivity R. The energy dissipated when
charging of the gate is
E =RC/T· CV 2
Where T is the time it takes the gate to charge or discharge.
Power Dissipation in Adiabatic Charging
Better than CMOS by a factor of (2RC/T) “On resistance”Charging a load capacitance through a switch
to solve power disipation in switching , there are two fundamental rules
circuits must follow, the reasons for which are explained below.
The first is:
never to turn on a transistor when there is a voltage difference between the
drain and source.
The second says:
never to turn off a transistor that has current
flowing through it.
The second rule:
that adiabatic circuits must follow is never to turn off a
transistor when there is current flowing through it.
transistors are not perfect switches going from on to
off instantly. Instead, it gradually changes from on to off when the gate voltage
changes. Furthermore, the change is proportional to the speed atwhich the
gate voltage changes. A fact that when combined with the previous constraint,
implies that the transistor is in an “in between” state for a long period of time.
During this time, the voltage drop across the transistor greatly increases yet
the resistance is not high enough to bring power dissipation to zero.
Several designs of adiabatic CMOS circuits have been developed. Some of
themore interesting ones include Split-level Charge Recovery Logic (SCRL) .
SCRL (SplitlevelCharge Recovery Logic)
Difficulties and Remedies for Adiabatic Circuits
Challenges of Recovery Circuits
1. Circuit implementation of time-varying power
2. Computations should be implemented by low overhead circuit
structures that use standard MOSFET devices
Problems of Adiabatic Logic
There are two big challenges of energy recovering circuits:
It is very slow by today’s standards.
It requires 50% more area than conventional CMOS, and
simple circuit designs can be very complicated (consider
Adiabatic circuitry will always be behind conventional CMOS in speed, but
as conventional CMOS gets faster Adiabatic circuitry will get faster as well.
It may become practical in the near future. Source Coupled Adiabatic
Logic is the most promising technology at this time.
Single phase clocking is less complicated to implement, but multiple phase
clocking is faster. Which will win?
If Source Coupled Adiabatic Logic prevails, great attention must go into
sinusoidal clock generator circuits.
Article InformationSemi-custom design of adiabatic adder circuitsKanchana Bhaaskaran, V.S.; Salivahanan, S.; Emmanuel, D.S.VLSI Design, 2006. Held jointly with 5th International Conference on Embedded Systems and Design., 19th International Conference onVolume , Issue , 3-7 Jan. 2006 Page(s): 4 pp. - Digital Object Identifier 10.1109/VLSID.2006.144
Summary: The paper presents the design, evaluation and performance comparison of cell based, low power adiabatic adder circuits operated by two-phase sinusoidal power clock signals, as against the literatures providing the operation of various adiabatic circuits, focusing on inverter circuits and logic gates, powered by ramp, three phase and four phase clock signals. The cells are designed for the quasi-adiabatic families, namely, 2N2P, 2N2N2P, PFAL, ADSL and IPGL for configuring complex adder circuits. A family of adiabatic cell based designs for carry lookahead adders and tree adders were designed. The simulations prove that the cell based design of tree adder circuits can save energy ranging from 2 to 100 over a frequency range of operation of 2MHz to 200MHz against the static CMOS circuit implementation. The schematic edit and T-Spice of Tanner tools formed the simulation environment.
Making Adiabatic Circuits Attractive for Todays VLSI
Industry by Multi-Mode Operation
- Adiabatic Mode Circuits -
Stephan Henzler, Thomas Nirschl, Matthias Eireiner,
Ettore Amirante, Doris Schmitt-Landsiedel
Institute for Technical Electronics
Technical University of Munich
Full adiabatic as well as quasi adiabatic circuit styles have been
proven to reduce the dynamic power dissipation of integrated
logic circuits considerably . Even leakage power is reduced
due to clocking of the power supply. However, adiabatic circuits
have not been widely accepted from industry as they are deemed
to allow no ultra high speed signal processing.
Most signal processing circuits have strongly changing speed
requirements. For example a mobile phone has high speed modes
like data transmission mode, telephone mode or imageprocessing
and video mode where maximum speed is required.
there are also many modes where the system is snoozing or
waiting for interaction with the user, e.g. stand-by mode or PDAmode.
In these modes low power dissipation is the main challenge.
Speed is of minor interest, as it is not needed or limited
by other constraints like the handling of the user.
Hence a first
step to integrate adiabatic circuit styles into such applications
would require a circuit style that is capable of adiabatic lowpower operation but also of non adiabatic high-speed operation.