Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
1997-12-18
2001-08-28
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
Reexamination Certificate
active
06281723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an integrated circuit power-on/power-off checking device, namely a device to check power-on and power-off operations in an integrated circuit.
2. Description of the Related Art
A power-on/power-off checking device monitors the level of the supply voltage to enable, if necessary, the resetting of certain electronic elements such as sequential circuits and prevent access to certain electronic functions. The checking device therefore fulfills a detection function that is very important for the operating security of the integrated circuit, enabling the activated integrated circuit to be in a clearly determined state (a resetting state) and making it possible, when there are conditions of supply that do not comply with specifications, to prevent access to certain functions in order to preserve the integrity of the integrated circuit.
To obtain a high level of security, the common practice is to use a checking circuit with a voltage reference circuit enabling the detection of the level of the supply voltage with respect to a threshold voltage Vs established by the voltage reference circuit. A checking device of this type is described, for example, in the French patent application No. 96 01378.
A device of this kind includes a circuit for current biasing the voltage reference circuit, enabling the permanent detection of the level of the supply voltage. The point of connection between the voltage reference circuit and the bias circuit gives a detection signal capable of causing the switch-over of the inverters of an output stage. This output state delivers a neutralization or power-on reset signal POR that is applied to a resetting and inhibition circuitry of the integrated circuit.
As shown schematically in
FIG. 1
, this neutralization signal POR follows the level of the supply voltage Vdd so long as this level is below the detection threshold Vs. When the level is greater than the detection threshold Vs, the signal POR is drawn to zero volts.
When the signal POR follows the supply voltage Vdd, it is perceived as a “1” by the resetting and inhibition circuitry which is then activated. It will be noted however that this can be done only when the supply voltage Vdd has a sufficient level, at least equal to a level Vf, at which the circuitry can function. The detection threshold Vs is necessarily greater than this minimum level Vf. It is in the period of time when the voltage Vdd is between Vs and Vf that the resetting is done and that the locking of certain access paths is done through the pulse of the signal POR. As soon as the supply voltage Vdd is greater than the detection threshold Vs, the resetting and inhibition circuitry is deactivated and the integrated circuit is operational, reset and has all its electronic functions valid.
The constant current bias of the voltage reference circuit leads to permanent power consumption in the integrated circuit, even in standby mode, when the integrated circuit is not selected. In this standby mode, this consumption is highly inconvenient because it is greater than the consumption in standby mode of the rest of the integrated circuit. As an order of magnitude, the consumption is, for example, in the range of 10 micro-amperes for the control device alone, and some nano-amperes for the rest of the integrated circuit. When the integrated circuit is selected, this consumption of the control device becomes negligible with respect to the consumption of the other electronic functions of the circuit.
SUMMARY OF THE INVENTION
It is an object of the invention to reduce consumption in standby mode of the control device while at the same time enabling the device to fullfill its detection functions which are vital for the operating security of the integrated circuit.
One solution to this technical problem is achieved in an embodiment the invention by making provision, in the checking device, for a control circuit capable of activating or deactivating the bias circuit as a function of the prevailing mode of operation of the integrated circuit. In order to activate this bias circuit only for “risky modes” of operation, a capacitor may be provided in parallel with the bias circuit.
In this way, in standby mode and in the other possible modes of operation considered to be what are referred to as “no-risk” modes, the consumption of the control device is zero unless a power-on or power-off operation is detected through the capacitor, then leading to a transient consumption due to the charging or discharging of the capacitor.
The determination of the risky modes of operation depends on the integrated circuit considered (for example a circuit with or without a non-volatile memory, with series or parallel access) and on the application for which it is intended. For example, in certain cases, the mere selection of the integrated circuit makes it transition from a no-risk standby mode to a risky operating mode. In other cases, it is the selection of a special electronic function that has this effect. For example, it might be a writing operation in a non-volatile memory of the integrated circuit. A checking device of this kind however has the drawback of having a particularly slow response time in the event of a drop in voltage due to the discharge time of the capacitor. If the drop in voltage is swift, there is a risk that the detection will be delayed and will no longer enable either resetting or locking, the level of supply voltage being then already below the minimum threshold Vf of operation.
Thus, in one embodiment of the invention, the checking device also includes a transistor for discharging of the capacitor. This discharging transistor is controlled by a dynamic detection circuit to detect the negative transition of the supply voltage.
When this circuit detects a negative transition, the discharging transistor comes on, swiftly discharging the capacitor and thus preparing the device for the detection of a new build-up of voltage.
However, a dynamic circuit of this kind for the detection of negative transition may lead to untimely detection, for example, if the supply voltage oscillates because of non-stabilized supply. Thus, in one embodiment, the invention proposes a particular structure of the dynamic detection circuit comprising a filtering stage.
In this embodiment, it is possible to use the output of the dynamic detection circuit for the direct generation of the neutralization signal POR, without using the circuitry of the control device while at the same time preparing the checking device for the detection of a build-up of voltage.
In another variant of the checking device according to an embodiment of the invention, the material configuration enabling the selection of at least one of two possible threshold values. This variant may be very useful in practice. Indeed, we have seen that the detection threshold Vs has been typically fixed by the technology of the integrated circuit.
In certain cases however, it will also depend on the environment of applications for which the integrated circuit is intended. In some applications, an integrated circuit may be associated with other integrated circuits. It may be that the range of voltage within which each of these circuits can work is not the same for the others. For example, it is possible in one and the same application to have a microprocessor circuit working between 3 and 6 volts and a memory circuit working between 2 and 6 volts. Between 2 and 3 volts, the microprocessor circuit may send out incomprehensible commands that could prompt operations within the perfectly operational memory circuit. For this application, it is therefore not desirable to allow the memory circuit to work between 2 and 3 volts. A detection threshold of about 3.5 volts will be chosen for the control device of this memory circuit.
This variant of the invention therefore enables the serial production of integrated circuits with configurable detection thresholds enabling the programming of each circuit in the last layers produced in the manufacturing p
Galanthay Theodore E.
Morris James H.
SGS-Thomson Microelectronics S.A.
Wolf Greenfield & Sacks P.C.
Zweizig Jeffrey
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