| 摘要 |
<p>A differentially encoded quadrature modulation method comprises the steps of setting an index corresponding to a phase variation value constituted of input data, forming a phase value to obtain a phase-modulated output phase value from a given table and forming a channel signal to obtain in-phase (I) and quadrature (Q) channel signals from a given table using the phase value. The apparatus for performing the above comprises a signal converter for converting serially input data into two binary signal trains, a signal forming portion for obtaining channel signals, a digital-to-analog converter for converting the respective signals into two analog signals, a baseband filter for baseband-pass-filtering the signals, a phase shifter for shifting a carrier by 90 DEG , first and second multipliers for multiplying the filtered signals with the carrier and phase-shifted carrier, respectively, and a mixer for mixing the respectively obtained signals and outputting a combined signal. Accordingly, the phase difference according to symbol is implemented alter being assigned to the corresponding index value stored in a look-up table. The final modulation output phase together with the previous phase value is directly obtained by using the look-up table. Accordingly, the construction of the circuit is simplified and the size of the chip is reduced for lower power consumption. Also, modulation speed is improved and a reliable modulation signal can be formed.</p> |
