A number of recent papers have suggested that a combination of positive and negative feedback loops can result in an amplifier in which total distortion cancellation occurs, so that the amplifier in principle produces zero distortion. Such a property is known to be achievable through the use of error feedforward, but can feedback also achieve the same end? We analyze the configuration in question and show that the apparent distortion cancellation is the result of ignoring the requirements for the physical realizability of the gain blocks and summers used. When these are properly accounted for, we find that stable feedback can only produce finite distortion reduction, as expected, except possibly at discrete frequencies.
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