Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Generating sinusoidal output
Reexamination Certificate
2001-02-15
2003-06-03
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Generating sinusoidal output
C327S299000, C327S361000
Reexamination Certificate
active
06573766
ABSTRACT:
The present invention relates to a method and apparatus for synthesising approximations to sine waves over a range of frequencies.
As shown in
FIG. 6
, an approximation to a sine wave
105
may be generated from a conveniently compact device by combining a number of pulse width modulated signals
102
,
103
,
104
generated by a microprocessor from its own clock signal
101
. In order to produce a sine wave
105
having a different frequency, the frequency of the clock signal
101
is divided by a number such as
1
,
2
,
3
,
4
. . . etc. However, this produces discrete coarse steps in the resultant range of sine wave frequencies produced. For example if the clock signal in
FIG. 6
has a frequency of 16 MHz, as may be used with a microprocessor, the highest sine wave frequency that can be synthesised in this example is 1 MHz, as sixteen clock cycles are needed to synthesise each sine wave cycle. The next highest sine wave frequency available is achieved by halving the clock frequency to 8 MHz producing a sine wave of 500 kHz. The next highest sine wave frequency is achieved by dividing the clock frequency by three to give a frequency of 5.3 MHz producing a resultant sine wave frequency of 330 kHz and so on.
As can be seen, large discrete steps or poor frequency resolution is produced in the resultant range of sine wave frequencies available.
According to a first aspect of the present invention an apparatus for synthesising an approximation to a sine wave comprises:
means for generating a number of pulse width modulated signals from a clock signal; and
means for combining the generated pulse width modulated signals to produce an approximation to a sine wave;
wherein the clock signal is provided by an oscillator arranged to produce clock signals over a continuous range of frequencies.
According to a further aspect of the present invention a method of synthesising an approximation to a sine wave comprises:
generating a number of pulse width modulated signals from a clock signal; and
combining the generated pulse width modulated signals to produce an approximation to a sine wave;
wherein the clock signal is provided by an oscillator arranged to produce clock signals over a continuous range of frequencies.
The use of the oscillator to produce clock signals over a continuous range of frequencies enables the production of resultant sine waves with a continuous range of frequencies rather than the discrete range discussed above.
The oscillator preferably produces a variation in its output clock signal frequency as a result of a variation in an input controlling electrical signal. The input controlling electrical signal that is varied is preferably a voltage making the oscillator a voltage controlled oscillator.
The output frequency of the oscillator and also of the approximation to a sine wave can thus be controlled by simply varying an input signal to the oscillator.
The approximation to a sine wave may be “smoothed” to remove at least some of the high frequency components by passing the signal through a low pass filter.
The sine wave produced may be used in a number of applications such as to match the frequency of the produced sine wave with the frequency of another detected signal or to provide stimulation which produces a particular effect at a particular unknown frequency which is then detected. In such applications it would be desirable to be able to determine the particular frequency which, in the above examples matches the detected frequency or produces the particular effect. The frequency need not necessarily be consistently related to the controlling input signal applied to the oscillator but may be variable due to, for example temperature changes.
To accurately determine a particular frequency of a synthesised approximation to a sine wave, the number of cycles of one of the pulse width modulated signals or the clock signal produced over a given period of time such as one second may be counted and/or the time taken to produce a fixed number of cycles may be measured and from this the frequency determined.
The means for generating pulse width modulated signals from a clock signal is preferably a processing means.
REFERENCES:
patent: 3801807 (1974-04-01), Condon
patent: 3995222 (1976-11-01), Mitarai
patent: 4481489 (1984-11-01), Kurby
patent: 5389897 (1995-02-01), Gebara
patent: 5521556 (1996-05-01), O'Shaughnessy et al.
patent: 6323739 (2001-11-01), Andrews
patent: 2062990 (1981-05-01), None
Byrne David
Humphrey Francis Alan
Price Barry Leonard
Callahan Timothy P.
Holt William H.
Lattice Intellectual Property Ltd.
Luu An T.
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