| 摘要 |
PROBLEM TO BE SOLVED: To allow an orthogonal modulator to cope with dispersion in components and a change over aging and to ensure high modulation accuracy by detecting an error caused in an analog circuit and adding a signal having an inverse characteristics to that of the error to the data before D/A conversion so as to relax circuit design requirements. SOLUTION: A digital quadrature demodulator 12 converts a received signal into a base band signal consisting of an I component (I') and a Q component (Q') and gives the converted signal to an error detection/compensation circuit 1. The error detection/compensation circuit 1 compensates a modulation error by using original signals I, Q and feedback signals I', Q'. that is, the error detection/compensation circuit 1 detects a DC offset and a phase error, and conducts processing to obtain an in-phase component (I') and a quadrature component (Q') resulting from adding a signal having an inverse characteristics to that of the errors to the in-phase component (I) and a quadrature component (Q). Thus, the in-phase component (I') and the quadrature component (Q') to which the signal with the inverse characteristics is added are D/A- converted and subject to quadrature modulation so as to cancel a DC offset component of a D/A converter and a phase error component of an LO signal. As a result, only a signal component remains in a modulation wave. |
