Modulation apparatus and method using zero-crossing detection

摘要

A spread spectrum apparatus for a code division multiple access communication system maintains orthogonality between transmission signals. In the spread spectrum apparatus, a spreader combines first and second input signals with corresponding pseudo noise sequences to generate first and second spread signals. A zero-crossing detector determines whether zero-crossing occurs between the first spread signal and the second spread signal to generate a zero-crossing detection signal. A first delay staggers the first spread signal in a first direction and a second delay staggers the second spread signal in a second direction. A first selector selects one of the first spread signal and a first staggered signal and a second selector selects one of the second spread signal and a second staggered signal in response to the zero-crossing detection signal. Accordingly, first and second staggered signals are selected when zero-crossing occurs, and first and second spread signals are selected when zero-crossing does not occur, thereby maintaining orthogonality of transmission signals.