| 摘要 |
PURPOSE: A digital modulator in a base station transmitter is provided to enhance speech quality by minimizing the noise signal inflow in an analog signal processing path. CONSTITUTION: A CDMA base station modem(211) modulates a voice-coded digital signal according to the CDMA standard. A digital combiner(212) separates band-spreaded digital signals into I0,I1 channels and Q0,Q1 channels. A plurality of multiplexers(237-1,237-2) sum the I0,I1 and Q0,Q1 channels transmitted as TTL signals to transmit 12 bit serial signals to a plurality of digital FIR low-pass filters. A plurality of digital mixers(234-1,234-2) modulate digital band signals from the digital FIR low-pass filters(233-1,233-2) into an intermediate-frequency band. A digital adder(235) sums CDMA analog signals from the digital mixers(234-1,234-2) for QPSK modulation. A D/A converter(232) converts a CDMA digital signal from the digital adder(235) into an analog signal. A band filter(236) cancels spurious components of a QPSK modulated signal from the D/A converter(232).
|
