Mixer-free all digital quadrature demodulation

All digital quadrature demodulation methods based on direct IF (intermediate frequency) sampling have advantages over conventional analog quadrature demodulation methods in matching accuracy between the inphase and quadrature channels. If we delicately select the sampling frequency and the sampling phase, the NCO (numerical-controlled oscillator) and mixers can be replaced by simple logic circuits. Because the ordinary NCO and mixers are eliminated, these types of demodulators are termed 'mixer-free demodulators'. Various mixer-free all digital quadrature demodulation methods based on first-order sampling and second-order sampling are introduced and compared in this paper.