Amplifiers – Modulator-demodulator-type amplifier
Patent
1998-11-02
2000-09-26
Mottola, Steven J.
Amplifiers
Modulator-demodulator-type amplifier
330149, H03F 338
Patent
active
06124757&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an amplifier and to a method of reducing noise in an amplifier output. For example, the invention relates to audio amplifiers.
In a class D amplifier, a modulated input signal is switched to produce an output proportional to the input. Whilst such amplifiers are highly efficient, their output is inherently non-linear. Thus, any signal applied to the output stage via the power source will be modulated onto the output signal. For example, a 100 Hz power supply ripple would be modulated onto a 1 KHz audio tone. The non-linear output stage would then deliver the 1 KHz signal, intermodulation products at 900 Hz and 1100 Hz, and their harmonics.
The usual method of avoiding this problem is to provide a very well regulated power supply to thereby avoid or reduce power supply noise. However, such power supplies are relatively expensive.
The present invention seeks to provide an alternative solution to the problems identified.
According to the present invention there is provided an amplifier comprising an output stage to which an input signal is applied by way of input signal processing means, wherein the output stage comprises switching means for producing the output signal, and a power source coupled to said output stage, said amplifier further comprising noise reduction means arranged to apply signals from the power source to the input signal processing means such that an input signal applied to the output stage is modulated by any noise signals from the power source and is arranged to cancel said noise signals in the output stage.
Thus, in an amplifier of the invention, any noise from the power source which is applied to the output stage is also applied to the input stage and is utilised to modulate the signal input to the output stage in such a way that in the output stage the unwanted components cancel each other.
In an embodiment, the input signal processing means comprises a modulator for producing the input signal applied to the output stage. The said noise reduction means is arranged to apply said power signals to said modulator. Preferably, said noise reduction means is arranged to apply clock signals to said modulator, the clock signals being frequency modulated by signals from the power source.
In a preferred embodiment the modulator is a pulse-width modulator.
In an embodiment, a frequency modulator is arranged to apply the clock signals to the pulse-width modulator, the clock signals being frequency modulated by signals from the power source.
In an embodiment, the input signal processing means is coupled to said output stage, and the input signal is output by said input signal processing means and applied to said output stage. Of course, it is possible for intermediate stages to be provided between the input signal processing means and the output stage.
Similarly, the construction of the amplifier may be selected as required. Preferably, the amplifier is a class D amplifier, and, in a preferred embodiment, is a power amplifier.
It is also preferred that the amplifier is a digital amplifier, but the technique is equally applicable to analog circuits.
Preferably, the amplifier is an audio amplifier.
In one embodiment, the output stage incorporates a full bridge circuit. In an alternative embodiment, the output stage incorporates a half-bridge circuit.
Preferably, the output stage incorporates an H bridge power output switching circuit.
Additionally and/or alternatively to implementing the invention by hardware, it is possible to implement the required modulation function in software.
For example, in a digital amplifier, the input signal processing means may comprise a digital signal processor. Signals from the power source may be applied to the digital signal processor in conjunction with the amplifier input whereby the modulated input signal to be applied to the output stage is produced.
In one embodiment of a digital amplifier, the output of the digital signal processor is applied to the output stage by way of a pulse width modulation counter.
In an embodiment, an amp
REFERENCES:
patent: 4737731 (1988-04-01), Swanson
patent: 4952884 (1990-08-01), Tokumo et al.
patent: 5559467 (1996-09-01), Smedley
Patent Abstracts of Japan, vol. 003, No. 103, Aug. 31, 1979 & JP 54 080657, Jun. 27, 1979.
Harman International Industries Limited
Mottola Steven J.
LandOfFree
Amplifiers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Amplifiers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Amplifiers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2103352