Abstract: The present invention is directed to a system and method which allows for power amplification of an input signal using power amplification combined by changing the center frequency with an up-converter to shift a baseband signal to a signal at a carrier frequency in the same process. This then provides a digital implementation that is power efficient and has little or no linearity issue-technology suitable for a silicon chip and broadband operation. In one embodiment, each input sample is replaced with a number of sub-samples within the same sample interval, the total weight of the sub-samples being equal to the replaced sample. This sample to sub-samples process alters the frequency response of the sampled signal and reduces the amplitude dynamic range of the load driver, thereby simplifying the filter requirements for digital to analog conversion while reducing linearity requirement of the load driver. This process can be implemented by digital circuits which results in broadband operation.

Abstract: An ADPCM encoder and decoder includes an adaptive quantizer and an adaptive predictor. A quantizing-step-size adaptation circuit determines a quantizing-step-size for the adaptive quantizer in dependence upon the ADPCM signal. When the quantizing-step-size is small, updating of predictor coefficients, produced in the adaptive predictor, in dependence upon a reconstructed signal and a reconstructed error signal derived from the ADPCM signal, is inhibited, the predictor coefficients being updated only in dependence upon a leakage function. This enables improved tracking to be achieved by the ADPCM arrangement.