Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-02-09
2001-01-09
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S282000
Reexamination Certificate
active
06172494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a circuit arrangement for delivering a supply current.
2. Description of the Related Art
The term “Differential Power Analysis”, abbreviated hereinafter as DPA, is used to denote a method whereby, via measurement of the supply current of an electronic circuit or by measurement of voltage dips in the supply voltage whereby the supply current is applied to the electronic circuit, in addition to measurement of input and output signals of the electronic circuit, to extract knowledge concerning the operations taking place in the electronic circuit. DPA has notably become known as an analysis method for the discovery of encrypted instructions or data in programmable integrated electronic circuits for identification devices. This could affect the security of credit cards, access control and the like.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a circuit arrangement for delivering a supply current for an electronic circuit which precludes the extraction of information as regards the internal operations of the electronic circuit by measurement of the supply current or the supply voltage, thus preventing undesirable discovery of details of the electronic circuit by way of DPA means.
This object according to the invention is achieved by means of a circuit arrangement for delivering a supply current for an electronic circuit from a supply voltage source, which arrangement includes a controllable current source arrangement which can be switched over so as to deliver a first and a second predetermined constant current, the second constant current being larger than the first constant current, and whose input is connected to the supply voltage source while its output is connected to an energy storage element and the electronic circuit, and also includes a first reference voltage source for preparing a first and a second reference voltage, being higher than the first reference voltage, as well as a comparison arrangement for comparing a supply voltage, produced in the electronic circuit and the energy storage element by the supply of the supply current, with the first and the second reference voltage and for switching over the current source arrangement to the first constant current when the supply voltage exceeds the second reference voltage and to the second constant current when the supply voltage is lower than the first reference voltage.
The steps proposed by the invention render the supply current and the supply voltage for the electronic circuit independent of the processes taking place inside the electronic circuit so that the supply current and the supply voltage become useless as measured quantities that can be extracted by means of DPA. This effectively counters attacks on the electronic circuit by DPA. Moreover, the invention offers the advantage that the supply current can be adapted, within given limits, to the actual power requirements of the electronic circuit. According to the invention, the supply current is not constant during the entire operation of the electronic circuit, but is adapted to the actual power requirements of the electronic circuit, however, without surrendering information concerning the internal processes of the electronic circuit to the environment. On the other hand, however, the supply current can be reduced in the case of a lower power consumption of the electronic circuit and it need not always assume a value corresponding to the highest possible power requirements of the electronic circuit, i.e. the power requirements for that function of the electronic circuit for which the electronic circuit has the highest power consumption. As a result, the supplied power is more effectively used for the electronic circuit, however, without degrading the protection against attacks by the DPA in order to achieve such higher efficiency and improved economy.
The power requirements in an electronic circuit differ as a function of its construction, mode of operation or operating state. In electronic circuits constructed by means of CMOS components, operating in synchronism on the basis of a clock signal, the highest power requirements exist at an instant in time which is situated a short distance in time from the edges of the clock signal. Should, in relation to the other time intervals, a very strong rise of the power requirements occur at this instant, such power requirements can be met by the energy storage element. The supply of energy to the electronic circuit from the energy storage element bridges the time interval possibly required to switch over the current source arrangement should such switching-over be necessary in order to sustain an adequate supply of energy. This is notably the case when the increased power requirements persist in time. The comparison arrangement ensures that the values of the supply voltage applied to the electronic circuit always lie in the permissible voltage range between the first and the second reference voltage.
An attractive embodiment of the circuit arrangement according to the invention is characterized in that it includes a second reference voltage source for presenting a third reference voltage which is lower than the first reference voltage and represents a minimum value of the supply voltage for the specified operation of the electronic circuit, as well as a reset arrangement which is supplied with the third reference voltage and the supply voltage for the purpose of comparison and resets the electronic circuit to a basic state when the supply voltage is less than the third reference voltage.
Thus, in case the supply of the second constant current cannot adequately meet the power requirements of the electronic circuit, the reset arrangement resets the electronic circuit to its basic state in order to avoid incorrect operation.
A further embodiment of the circuit arrangement according to the invention includes a switch-over lead via which the current source arrangement is switched over directly by the electronic circuit. Notably in the case of executions of functions which are strictly specified in time in the electronic circuit a predictable increase of the power requirements can thus be provided by the comparison arrangement even before the switching over is initiated. This creates additional flexibility in the supply of power to the electronic circuit. It is thus notably possible to set the energy storage element timely to the best possible operating state before a function step takes place in the electronic circuit which involves a particularly high power consumption.
Predetermination of the direct switching over of the current source arrangement by a selectable function execution in the electronic circuit is particularly simple and effective when the electronic circuit is constructed as a programmable arrangement for electronic data processing involving switching-over instructions for the current source arrangement.
The circuit arrangement according to the invention can be used preferably for security and identification systems, particularly for systems involving chip cards or electronic labels. The circuit arrangement according to the invention is then particularly suitable for use in portable data carriers of such systems, i.e. in the chip cards or labels themselves.
REFERENCES:
patent: 5315219 (1994-05-01), Kishi
patent: 5783933 (1998-07-01), Bailly
patent: 5828208 (1998-10-01), Oku
patent: 5969513 (1999-10-01), Clark
Nguyen Matthew
U.S. Philips Corporation
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