| 摘要 |
PROBLEM TO BE SOLVED: To reduce DC offset in a direct conversion receiver capable of receiving a plurality of bands. SOLUTION: LNAs 5a, 5b, quadrature mixers 6a, 6b, phase-shifters 7a, 7b, and VCOs 8a, 8b are made independent from one another for each frequency band and share LPFs 14a-14d, HPFs 16a-16d, baseband variable gain amplifiers 15a-15f, and a PLL circuit 10. The HPFs 16a-16d switch cut-off frequencies corresponding to the instruction of an HPF control part 29. The switching of circuits independently provided for each frequency band is executed together with the update of frequency data to the PLL circuit 10 when the switching of frequency bands occurs. On that occasion, the DC offset can be quickly converged by increasing the cut-off frequencies of the high-pass filters 16a-16d. COPYRIGHT: (C)2006,JPO&NCIPI
|
