Glitch removal is the elimination of

glitches A glitch is a short-lived fault in a system, such as a transient fault that corrects itself, making it difficult to troubleshoot. The term is particularly common in the computing and electronics industries, in circuit bending, as well as amo ...

unnecessary signal transitions without functionalityfrom electronic circuits.

Power dissipation In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to ...

of a gate occurs in two ways: static power dissipation and dynamic power dissipation. Glitch power comes under dynamic dissipation in the circuit and is directly proportional to switching activity. Glitch power dissipation is 20%–70% of total power dissipation and hence glitching should be eliminated for low power design. Switching activity occurs due to signal transitions which are of two types: functional transition and a

glitch A glitch is a short-lived fault in a system, such as a transient fault that corrects itself, making it difficult to troubleshoot. The term is particularly common in the computing and electronics industries, in circuit bending, as well as among ...

. Switching power dissipation is directly proportional to the switching activity (α), load

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized ar ...

(C), Supply voltage (V), and

clock frequency In computing, the clock rate or clock speed typically refers to the frequency at which the clock generator of a processor can generate pulses, which are used to synchronize the operations of its components, and is used as an indicator of the pr ...

(''f'') as: : P = α·C·V²·''f'' Switching activity means transition to different levels. Glitches are dependent on signal transitions and more glitches results in higher power dissipation. As per above equation switching power dissipation can be controlled by controlling switching activity (α),

voltage scaling Dynamic voltage scaling is a power management technique in computer architecture, where the voltage used in a component is increased or decreased, depending upon circumstances. Dynamic voltage scaling to increase voltage is known as overvolting; d ...

etc.

Glitch reduction techniques

Reducing switching activity

As discussed, more transition results in more glitches and hence more power dissipation. To minimize glitch occurrence, switching activity should be minimized. For example, Gray code could be used in counters instead of binary code, since every increment in Gray code only flips one bit.

Gate freezing

Gate freezing minimizes power dissipation by eliminating glitching. It relies on the availability of modified standard library cells such as the so-called F-Gate. This method consists of transforming high glitch gates into modified devices which filter out the glitches when a control signal is applied. When the control signal is high, the F-Gate operates as normal but when the control signal is low, the gate output is disconnected from the ground. As a result it can never be discharged to logic 0 and glitches are prevented.

Hazard filtering and balanced path delay

Hazards in digital circuits are unnecessary transitions due to varying path delays in the circuit. Balanced path delay techniques can be used for resolving differing path delays. To make path delays equal, buffer insertion is done on the faster paths. Balanced path delay will avoid glitches in the output. Hazard filtering is another way to remove glitching. In hazard filtering gate propagation delays are adjusted. This results in balancing all path delays at the output. Hazard filtering is preferred over path balancing as path balancing consumes more power due to the insertion of additional buffers.

Gate sizing

Gate upsizing and gate downsizing techniques are used for path balancing. A gate is replaced by a logically equivalent but differently-sized cell so that delay of the gate is changed. Because increasing the gate size also increases power dissipation, gate-upsizing is only used when power saved by glitch removal is more than the power dissipation due to the increase in size. Gate sizing affects glitching transitions but does not affect the functional transition.

Multiple threshold transistor

The delay of a gate is a function of its

threshold voltage The threshold voltage, commonly abbreviated as Vth or VGS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (VGS) that is needed to create a conducting path between the source and drain terminals. It is an important s ...

. Non-critical paths are selected and threshold voltage of the gates in these paths is increased. This results in balanced propagation delay along different paths converging at the receiving gate. Performance is maintained since it is determined by the time required by the critical path. A higher threshold voltage also reduces the

leakage current In electronics, leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow of cu ...

of a path.

References

External links

* Patent US6356101 B1: Glitch Removal Circuitary, 2002-03-12, http://www.google.co.in/patents/US6356101. * https://learn.digilentinc.com/Documents/277 Digital electronics Electronics optimization Software bugs Computer errors Energy conservation