Apparatus and method for reducing low-frequency distortion in frequency converted signals

Abstract

An apparatus for reducing undesirable low-frequency distortion in a direct conversion communication receiver includes a signal generator to produce a first periodic signal and a second periodic signal. A merge circuit combines an input signal and the first periodic signal to produce a modulated signal with a polarity switched component. A frequency translation circuit converts the modulated signal into a baseband signal with a spectrum substantially equal to the modulated signal, but centered around a carrier frequency of approximately zero and including a low-frequency error component. An output modulator circuit combines the baseband signal with the second periodic signal to produce a modified baseband signal wherein the low-frequency error component is shifted to a high frequency spectrum position and the polarity switched component is eliminated. A low-pass filter subsequently removes the low-frequency error component from the modified baseband signal, resulting in a baseband output signal with reduced low-frequency distortion.

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