Digital FM Transmitter with Variable Frequency Complex Digital IF

This patent portfolio discloses an integrated circuit for digitally synthesizing a signal for FM transmission through direct digital frequency synthesis (DDFS), using a method that is extensible to simultaneous OFDM (HD radio) transmission. DDFS systems have advantages over conventional techniques, including precise frequency control, wide tuning range and arbitrarily low noise. However, normal DDFS systems require high sampling rates and therefore higher power than is practical for consumer uses.

 

By use of the disclosed IP, all processing is done at baseband or as a heterodyne around a fixed frequency in the center of the desired band, allowing sampling rates driven only be the width of the band rather than the carrier frequency. Lower sampling rates imply lower power. The method is particularly useful for implementing simultaneous high-quality low-cost FM and (OFDM) HD radio transmitters. Additionally, since the complex digital IF is completely variable, channel spacing and frequency ranges are easily accommodated.