A maximum of digitized fraction proportional - n frequency synthesizer and modulator with maximum suppression of the fractional spurs

摘要

A fractional-N frequency synthesizer is suggested. The synthesizer uses the Delta-Sigma frequency discriminator to convert the high frequency signal to digital format. The main feature of the invention is that the feedback error signal is generated by comparing the output bit stream from the discriminator with a bit stream digitally generated by performing Delta-Sigma modulation to the required fractional number. This makes the fractional spurious maximally reduced and be much predicable. Other synthesizer performance could also be very good as the result of low noise from a very simple high frequency circuit and the flexibility and precision from the maximally application of digital signal processing technique. Besides, the structure is especially suitable for adding the wideband modulation simultaneously.