Linear amplification by time-multiplexed spectrum

A new waveform processing technique for reducing intermodulation distortion (IMD) generated by an amplitude-modulated signal is presented. The technique eliminates amplifier-generated IMD by time-multiplexing portions of the signal spectrum prior to amplification. The input signal is described as a sum of sinusoidal signals. The peak-to-average ratio of the time-multiplexed amplifier input is lower than that of its non-multiplexed counterpart, but it contains spectral aliases at multiples of the switching frequency. Thus, the reduction in distortion of the desired amplified signal is achieved at the expense of momentarily widening the signal bandwidth. Following amplification, the desired signal is recovered using a bandpass filter which spreads the signal in time and narrows its bandwidth. An analytical expression for distortion reduction when amplifying two multiplexed carriers is developed along with measurements verifying the theory. Distortion reduction is demonstrated experimentally at 3.6 GHz for 2 20 multiplexed carriers, and linear recovery is demonstrated for four multiplexed carriers. The technique reduces third-order IMD by 8 22 dB in experimental measurements of three different amplifiers. The presented technique has the unique property of improving linearity without requiring feedback, feedforward cancellation or calibration.