To provide an FM transmitting circuit configured to suppress generation of harmonics due to nonlinear amplitude control processing for determining a maximum frequency shift when an audio signal is processed and also to significantly reduce a circuit scale and reduce power consumption as compared with a prior art.
The FM transmitting circuit includes a nonlinear amplitude control circuit 5 which performs amplitude adjustment for limiting the degree of modulation of a signal output from a pre-emphasis circuit 3, and an LPF 7 and an FM modulator 10 provided at a stage subsequent to the nonlinear amplitude control circuit 5. The DM transmitting circuit includes also a CIC up-sampler 4 provided between the nonlinear amplitude control circuit 5 and pre-emphasis circuit 3 and performing up-sampling at a predetermined up-sampling ratio using a predetermined number of stages of CIC filters, and a CIC down-sampler 6 provided between the nonlinear amplitude control circuit 5 and LPF 7 and performing down-sampling at a predetermined down-sampling rate using the CIC filters.
COPYRIGHT: (C)2010,JPO&INPIT
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Kyousei Tamura
Masahiro Ishino