Impact of Gate Leakage on Efficiency of Circuit Block Switch-Off Schemes

Two different schemes to switch-off unused circuit blocks (ZigZag-cut-off scheme' and n-/p-block MTCMOS cut-off schemê '̂ ''̂ '̂ '̂ are examined in deep-submicron technologies by analytical investigation and simulation. The theoretical basis of the ZigZag-scheme is given and particular design constraints are discussed. It is shown that the power-saving benefits of the ZigZag-scheme are critically dependent on the gate-leakage, whereas nor pblock switching keep their effectiveness. Finally it is derived that n-block switching tends to cause severe glitch activity during power-up process degrading both power-up-time and energy loss. The ZigZag-scheme however does not suffer from this effect. The advantages and drawbacks of the two schemes are compared depending on the available technology generation. Finally recent extensions to ZigZag are discussed.