Abstract: A new FM transmitter is reported.It adopts a fractional-N PLL synthesizer to realize the FM modulator.An extra offset current has also been applied to eliminate the effects of the mismatch in CP.The chip is fabricated with CSMC 0.5μm DPTM CMOS technology.Experiments show that it achieves THD≤0.08% and SNR≥82dB,and the maximum outband emission energy ≤-90dBc/Hz.Furthermore,it also uses an auto frequency adjusting method to avoid tuning up the external inductances.All these merits are very suitable for FM transmission.

Key words: FM, fraction N frequency synthesizer, in-band phase noise