Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Generating rectangular
Patent
1994-09-08
1996-06-25
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Generating rectangular
327175, 364717, 331 78, 380 49, 375356, H03K 384, H04L 906
Patent
active
055303900
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to methods of controlling electrical systems, and to electrical systems using such methods.
Many electrical systems, particularly those incorporating processor means or other logic circuits, utilise clock signals. However, clock signals contain high frequency harmonics and these cause interference effects. In audio systems, the harmonics may be within the audio band, and this is directly audible. In other environments intermodulation can generate unwanted spikes and tones. These interference effects can make it difficult, for example, to design digital circuits which meet EC regulations controlling electromagnetic radiation.
In some cases it is possible to avoid the worst interference effects by shielding such that there is no coupling between circuits, but this is an expensive solution which is never totally successful. Furthermore, a single spike in a frequency spectrum is difficult to cope with even if the spike has a relatively low level as compared to background noise.
According to the present invention there is provided a method of controlling an electrical system comprising at least one system component arranged to be controlled by the application of a clock signal, the method comprising the step of utilizing at least one randomised clock signal, said randomised clock signal comprising a series of pulses arranged to have a random mark-space ratio.
Because the clock signals are randomised they are no longer cyclic or repetitive, and individual spikes no longer appear in the frequency spectrum. The resulting frequency spectrum is relatively flat, with a raised noise floor, and this makes it easier, for example, to control electromagnetic emissions.
In an embodiment, the method further comprises the steps of providing a regular clock signal for the system, and then randomising said regular clock signal to provide one or more randomised clock signals for controlling system components.
Preferably, the method further comprises the step of applying a respective randomised clock signal to each system component which is controlled by the application of a clock signal, the step of generating the or each randomised clock signal by dividing a regular clock signal.
In an embodiment, the or each randomised clock signal may be generated by way of a random number generator to which a regular clock signal is applied.
Preferably, said electrical system utilises digital control means arranged to generate and apply said randomised clock signal to logic means of said system, said logic means being arranged to be controlled by the arriving clock pulses of said randomised clock signal. For example, said logic means may be clocked by edges of the randomised clock signal.
In one embodiment, one selected edge of each said randomised clock signal occurs substantially concurrently with a selected edge of said regular clock signal. Preferably, said selected edges are rising edges.
In a preferred embodiment, said randomised clock signal is generated by way of a random number generator arranged to apply a random sequence to one input of a bistable circuit, and further comprising applying the regular clock signal to the clock input of said bistable circuit so that rising edges of the randomised output signal coincide with rising edges of the regular clock signal.
In a preferred embodiment, where said electrical system utilises digital control means, the method further comprises the steps of coding digital signals, transmitting the coded digital signals to at least one system component, and at the or each said system component receiving and decoding the coded digital signals, wherein the step of coding the digital signals comprises randomising or scrambling said digital signals such that they are not cyclic or repetitive.
In a preferred embodiment, the electrical system comprises a number of system components connected serially to form a serial loop, and said method comprises the step of transmitting coded digital signals undirectionally around the serial loop.
Preferably, one said system component is
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Callahan Timothy P.
Englund Terry L.
Soundcraft Electronics Limited
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