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EMC current drive to control the IC core supply voltage Disclosure Number: IPCOM000029455D
Publication Date: 2004-Jun-29
Document File: 2 page(s) / 25K

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EMC current drive to control the IC core supply voltage

A way to provide supply voltage to an IC by means of a current source is derived from the fact that in order to ensure that on-chip switching current remains on-chip, no (low) impedance may appear off-chip in parallel to the power pins. Under this condition, the noise sources due to switching of the IC will be enforced to close its current path solely through the on-chip decoupling capacitances (as drawn in the IC).

This approach assumes that:

Sufficient on-chip decoupling is present to sustain operation during over successive clock periods. As such, (only) the average (re-charge) current required by the IC will be considered constant when integrated over a full clock period.

A power management block will be added on or in parallel to the IC to control the current source. The power transistor shall be off-chip to reduce power dissipation of the IC (this transistor can be incorporated when the currents are small).

The power control block switching frequency is assumed to be in the lower MHz region whereas the clock frequency of the IC may be hundred of MHz or even above 1 GHz. This also requires that no intermediate changes of the supply current may appear which are e.g. highly data dependent related. On-chip decoupling and balanced coded busses between the blocks of the SoC in the IC may avoid these problems.

The idea behind this approach split in two parts:

Over-voltage protection and current sensing

A control block for the switching transistor

Required sequence of the power management block:

T1: The output voltage needs to be zero and the required supply current has to be achieved through the bypass transistor (this part is identical to an existing IBM patent)

T2: The current though the inductance is increase by the power control block up until the required current has been reached. The output voltage is still zero (voltage reference is short-circuited)

T3: The short-circuit across the voltage reference is removed and the supply voltage will increase up until the voltage required by the IC and set by the voltage reference ratio. The current that was running through the bypass transistor will diminish and the supply current through the IC will reach its nominal value.

T3a: When the voltage across the IC is too high, the bypass transistor will react and clamp the voltage to the required level. Thereafter, the current control block will adjust the timing such that the current through the bypass transistor will diminish.

T3b: When the voltage across the IC is s...