Ground bounce

Ground bounce is usually seen on high density VLSI where insufficient precautions have been taken to supply a logic gate with a sufficiently low impedance connection to ground (or sufficiently high bypass capacitance).

In this phenomenon, when the base of an NPN transistor is turned on, enough current flows through the emitter-collector circuit that the silicon in the immediate vicinity of the emitter-ground connection is pulled partially high, sometimes by several volts, thus raising the local ground, as perceived at the gate, to a value significantly above true ground.

Relative to this local ground, the base voltage can go negative, thus shutting off the transistor.

As the excess local charge dissipates, the transistor turns back on, possibly causing a repeat of the phenomenon, sometimes up to a half-dozen bounces.

Ground bounce is one of the leading causes of "hung" or metastable gates in modern digital circuit design.