Patent Application
20070164754
1. Field of the Invention
The invention relates to non-invasive, on-chip detection of power supply noise that is beyond the control of off-chip power supply feedback. The noise is of the type characterized as over shoot, and is constrained by a maximum allowed level and a minimum allowed level, and is controllable, e.g., by limiting, clipping, or clamping to lessen or eliminate intermittent spuriously generated components from a signal.
2. Background Art
Integrated circuits are highly susceptible to upsets arising from excursions in the output of on-chip power supplies. One problem area is managing high frequency power supply noise that is beyond the control of off-chip power supply feedback.
The system described herein manages high frequency power supply noise that is beyond the control of off-chip power supply feedback. The on-chip power supply noise sensor detects high frequency overshoots and undershoots of the power supply voltage.
The sensor has two resistor chains that span the full power rail, with a reactive element to form a low pass filter or time constant circuit, as part of one of the resistor chains. By this expedient the high frequency transient behavior differs between the two chains, while the low frequency behavior is equivalent. This allows a voltage comparison to be made, for example with comparators. The comparator output can be latched or transmitted as a sampling signal.
Various aspects of our invention are illustrated in the Figures appended hereto.
The system of our invention manages high frequency power supply noise that is beyond the control of off-chip power supply feedback. The lower power on-chip power supply noise sensor detects high frequency overshoots and undershoots of the power supply voltage. The sensor has two resistor chains. These chains span the full power rail from input to ground. One resistor chain has a reactive element to thereby form a low pass filter, as part of one of the resistor chains. By this expedient the high frequency transient behavior differs between the two chains, while the low frequency behavior is equivalent between the chains. This allows a voltage comparison to be made, for example with comparators. The comparator output can be latched or transmitted as a sampling signal, for example to trigger a reset.
The on-chip noise sensor has a pair of comparators, where one of the comparators has a plus input 21′ from a tap 21 on the resistor chain 1,2 and a minus input 23′ from the tap 23 on the capacitor 7. The other capacitor has a plus input 25′ from the low pass filter tap 25 between the capacitor 7 and ground, and a minus input 21′ from a tap 21 on the resistor chain 2, 1.
By comparing the voltage on node 21 with the voltages on nodes 23, and 25 it is possible to generate a digital signal. This digital signal can be used to set a latch or as a sampling signal to inform other circuitry that there was a large magnitude noise event in the system.
This allows testing multiple thresholds by tapping off of different points on the second resistor chain, that is between Node 23 and ground. For example, in
If a noise event occurred, e.g., where the power supply increased to 1.4 volt, then dropped back to a nominal value of 1.0 Volt, Node 21 would jump to 0.7 Volt while Node 23 would stay at 0.67 Volt. This would cause 31 OUT1 to go high, indicating an excursion event.
The analogous output would occur at 33 OUT2 is the power supply voltage drops low.
The detector has a sensitivity advantage in that the voltage is determined from a ratio of resistances, the variation in Node 21 can be set to be very close to the power supply noise variation itself.
While the invention has been described with respect to certain preferred embodiments and exemplifications, it is not intended to limit the scope of the invention thereby, but solely by the claims appended hereto.
