Method for finely tuning the frequency of a radio signal

摘要

The invention relates to a method for converting a digital baseband signal into an a-nalogue RF signal or vice versa. If a digital baseband signal is converted into an analogue RF signal the phase noise and spurious emissions are limiting factors as far as the signal quality is concerned. It is an object to achieve a signal with low phase noise and no spurious emissions. It is suggested to convert the signal in the digital domain by a complex modulator and in the analogue domain by an I/Q modulator. As an example, the frequency step size of an NCO driving the complex modulator may be chosen to be smaller than the frequency step size of an LO driving the I/Q modulator.