Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Generating rectangular
Reexamination Certificate
2001-09-11
2003-07-15
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Generating rectangular
C327S105000, C708S252000, C708S250000, C331S078000
Reexamination Certificate
active
06593788
ABSTRACT:
BACKGROUND
The invention concerns a method to generate a random signal and a random signal generator.
From the ‘Alpha-particle random number generator’ IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 30, No.9, February 1988 (1988-02), pages 337-339, XP002140868 IBM CORP. NEW YORK, US ISSN: 0018-8689, a random signal generator is known, that has four non-deterministic random sequence generators, each of them having a feed-back shift register. The shift registers are subjected to alpha radiation of a radioactive material, what generates, when penetrating in the semiconductor chip of the shift register, electron hole pairs, which can randomly change the memory content of the shift register. The outputs of two of the four random sequence generators are connected to the inputs of an exclusive-or gate. The outputs of this exclusive-or gate are connected to an input of a further exclusive-or gate, the output of which is connected to the random signal output. Therefore the random signal fed to the random signal output is generated by means of the exclusive-or gate by mixing the output signals of the individual random sequence generators, resulting in the random signal fed to the random signal output having a stronger random nature than the output signals of the individual random sequence generators. Nevertheless, by these measures the statistical independence of the signal levels or the random values of the random signal appearing at the output of the random signal generator is improved only to a limited extent. Although the quality of the random signal could be improved by that the number of the random sequence generators, the output signals of which are exclusive-or connected with one another, is correspondingly increased, the construction of the random signal generator, however, becomes more complicated and expensive. In addition, the random signal generator has the disadvantage that the alpha-radiation requires an expensive shielding to prevent damages to health and/or interference with other electrical circuits.
From WO 97/43709 a random signal generator is already known that has a non-deterministic random signal generator that has a voltage-controlled oscillator, the frequency control input of which is connected to a noise voltage source. On its output the oscillator has an oscillator signal, the frequency of which randomly fluctuates about a centre frequency corresponding to a stochastically changing noise voltage applied to the frequency control input. The random sequence generator has a plurality dynamic flip-flops, which with their data input are connected to a ring oscillator allocated to them. At the same time each flip-flop has its own ring oscillator, while the frequencies of these ring oscillators slightly deviate from one another and are greater in each case than the frequency of the voltage-controlled oscillator of the random signal generator. Each clock input of the flip-flops is connected to the output of the random signal generator, so that in the case of a clock slope of the oscillation signal of the voltage-controlled oscillator with randomly changing frequency one signal value of the individual oscillation signal of the ring oscillators is scanned and read into the flip-flop allocated to the respective ring oscillator. The signal values intermediately stored in the individual flip-flops are then emitted to a respective output of the flip-flop and form the random signal to be generated. On this occasion each signal fed to the outputs of the flip-flops represents a binary number of a random number to be generated with several digits. According to the patent, the binary values of the digital signals fed to the output of the flip-flops are to be evenly distributed, i.e. on average the outputs of the flip-flop should have an approximately equal number of logical “ones” and “zeros”.
The prior known random number generator has, however, the disadvantage that the individual number signals or the binary positions of the random number allocated to them depend, to a certain degree, from one another. It may also result in a correlation of two random numbers which are read out immediately in succession from the random signal generator. Therefore, after a sufficiently long observation of the random numbers emitted by the random number generator, an observer can make conclusions regarding the properties of the random signal generator or random number generator, in particular regarding the properties of the ring oscillators contained therein. An additional disadvantageous fact is that a defect in the noise voltage source and/or in the voltage-controlled oscillator of the random signal generator may result in an oscillation of the voltage-controlled oscillator with a constant frequency, so that the correlation of the random numbers will strongly increase, i.e. the random nature of the random signals or the random numbers represented by this signal will decrease without the user of the random number generator noticing this. For certain applications, for example, when encoding messages or identifying a sender of a message by means of a “digital” signature, it is, however, necessary that the random nature of the generated signal or of the random numbers be as great as possible so that the random numbers could not be predicted.
From EP 0 782 069 A1 a pseudo-random number generator is known, that has several deterministic random sequence generators, each of them having an output for a pseudo-random signal. These outputs are connected to an input each of a combination device, that has an output for a combination signal formed by non-linear combination of the pseudo-random signals. The combination signal output is connected to the data input of a shift register having a plurality of memory elements, into which the data read out from the combination signal output can be sequentially read. The data outputs of the memory elements of the shift register are connected to an input each of a non-linear connecting device. This has an output for a signal that is formed by the non-linear combination of the data signals applied to the data outputs of the memory elements of the shift register. The individual positions of the random number to be generated are emitted on this output in succession synchronously with a clock signal. The prior known pseudo-random number generator has the disadvantage that the signal appearing on the output of the connecting device can be described by a mathematical function despite the relatively elaborate combination of several pseudo-random signals into a random number signal. Therefore the random numbers, generated with the random number generator, can be predicted with the knowledge of this mathematical function and the state of the random signal generator. An additional disadvantage is that the random signal generator has a relatively complicated construction.
A random signal generator is also known, wherein an analog noise signal of a noise source is amplified with a high-frequency amplifier and subsequently the signal level of this amplifier is digitalised. The random number to be generated is then sequentially read out on the output of the high-frequency amplifier, whereby both signal levels, defined by digitalising the amplifier output signal, are interpreted as binary values of a binary number. This random signal generator is, however, also relatively expensive, because for the purpose of avoiding correlations between the digital output signal of the random number generator and the analog noise signal an elaborate shielding of the high-frequency amplifier is required. In addition, the noise source has to be shielded against external electro-magnetic interferences.
SUMMARY
Therefore the task is to specify a method, with which a random signal, that has signal levels or random values which are, as far as possible, statistically independent from one another and uniformly distributed, can be generated. There is also the additional task to provide a random signal generator which, though having a simple construction, can generate as far as possible, statistically independen
Le Dinh T.
Volpe and Koenig P.C.
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