The present invention is directed to electrical amplifier apparatuses, and especially to electrical amplifier apparatuses adaptively controlling output to accommodate signal clipping to improve recovery from signal clipping.
The present invention is generally useful in electrical signal amplifiers. The present invention is particularly advantageously employed in audio signal amplifying apparatuses. Amplification of electrical signals, and especially audio signals, is a challenging area of analog circuit design. Unlike some other linear circuits, audio systems are required to function with high fidelity over a broad dynamic range. While the average power required for most music listening (an example of use of an audio amplifying apparatus) is quite low, there can be peak output levels which are larger than the supply rail—the signal provided for operating the amplifier. When the output signal levels exceed the supply rail, clipping occurs at the outputs of the amplifier. Ideally the amplifier output signal will exactly match the shape of the input signal with a perfect cutoff for levels above the supply voltage. Class-AB power amplifiers typically will have no trouble achieving this kind of performance provided that good design techniques are employed. Class-D amplifiers however, which are rapidly increasing in popularity for audio amplifying applications, present challenging design issues in order to approach such ideal clipping performance.
A problem that may be experienced during a clipping condition in an amplifier is that, while clipping (i.e., while the output signal levels of the amplifier exceed the supply rail), may be illustrated by way of example and not by way of limitation, in the contest of an exemplary Class D amplifier. The exemplary amplifier receives input signals at an integrator unit. The integrator unit integrates the input signals (using integrating capacitors in a feedback arrangement, which will be described in greater detail hereinafter in connection with FIGS. 1–4. When a clipping condition exists, the amplifier output can no longer maintain proportionality with the input signals received by the amplifier. During this clipping condition, integrating capacitors continue to be charged, so that the output of an integrating unit becomes larger than the reference signal. When the input signal returns to a lower level at which clipping does not occur, the amplifier takes a finite time to reduce the excess charge that has been accumulated in the integrating capacitors during clipping conditions. After the excess charge is reduced, the amplifier can return to normal operations. The delay in reducing excess charge in the integrating capacitors causes distortion during clipping recovery. A user of an audio amplifier system can notice noise occasioned by the distortion that occurs during clipping recovery operation.
There is a need for an amplifier apparatus that can reduce time required for clipping recovery operations.