Digital quadrature demodulator with four phases mixing for digital radio receivers

A digital quadrature demodulator is proposed that gives the complex components of the received signal. The adoption of a modulated local oscillator (LO) with four periodic phase states synchronized with the sampling avoids the use of two mixing paths, simplifying the radio-frequency (RF) circuits and allowing an effective VLSI integration. This receiver minimizes the in-phase/quadrature (I/Q) mismatch and, with an adequate choice of the periodic modulating sequence, avoids the direct current (dc) offset of the direct conversion receivers. Index Terms--Digital quadrature demodulator, digital receiver, direct conversion receiver, low IF receivers, mismatch cancellation, VLSI integration.