It is well known that an inductor typically resists a change in the current flowing through it by generating a counteracting voltage drop. This phenomenon can be troublesome for electronic circuits that accommodate fast-switching operations. Rapidly changing currents can induce voltage fluctuations (i.e., inductive noise) in parasitic inductors that are inherent in most circuits. For example, a memory array employing a differential bi-directional bus may have inductive noise problems. During a bus-turnaround between READ and WRITE operations, current ramp profiles on the memory array's power supply rails can induce large voltage fluctuations as well as ground bounce. Such inductive noise problems can be exacerbated when a memory chip is packaged with inexpensive materials with large associated parasitic inductances. Typically, in a dynamic random access memory (DRAM), the input/output (I/O) subsystem contributes the most to the current ramp profile on the power rails.
In FIG. 1, there are shown two sets of current profiles and voltage fluctuation waveforms in an output subsystem of a DRAM. As can be seen, a relatively slow current ramp (102) causes a moderate voltage fluctuation (104) on the power rail. If the current ramps up faster (106), larger voltage spikes (108) can be induced on the power rail, which may impact the behavior of the internal circuits.
Most existing solutions to inductive noise problems focus on design, layout or packaging techniques of the affected integrated circuits. One common approach is to separate the power pins for a chip's core circuits and its I/O drivers. Another approach involves restricting the number of I/O drivers connected to a single supply pin. Selection of the position of power and ground pins on the package can also affect inductive noise. However, these solutions are typically useful only to the specific circuits for which they are designed. A slightly different circuit may require a complete different solution. There has not been a system-level solution that can reduce the effect of inductive noise regardless of the underlying physical circuits.
In view of the foregoing, it would be desirable to provide a solution for reducing inductive noise which overcomes the above-described inadequacies and shortcomings.