All-digital RF frequency modulation

The past several years have successfully brought all-digital techniques to the RF frequency synthesis, which is used for frequency translation between the baseband and RF frequencies in wireless transmitters and receivers. Reference [1] has described the recent journey of digitizing RF frequency synthesizers, such that now they are amenable to nanoscale CMOS technology with area, power and performance metrics well exceeding those of the traditional charge-pump PLL´s. This paper examines an important aspect of the all-digital frequency synthesizers, which takes on some of the transmitter functionality by allowing to directly perform the carrier frequency modulation. This is useful in today´s wireless system, which either completely rely on the frequency modulation to convey the information or use it as part of a polar vector modulation. A novel multi-rate polar transmitter is proposed in which the modulating data rate is independent from the reference frequency.