Frequency stabilized direct GMSK modulator

A phase locked loop based architecture is proposed for generation and frequency stabilization of direct Gaussian minimum shift keying (GMSK) at microwave and millimeterwave frequencies. A continuous phase frequency shift keyed (CPFSK) signal with a modulation index of 0.5 is produced at the desired output frequency using a full 360 degree linear continuous phase modulator that is controlled by the integrated baseband information signal. This modulated signal is used as the reference signal for a phase locked high power voltage controlled oscillator. The phase locked loop facilitates reference signal frequency tracking and provides Gaussian spectral shaping to the modulated output signal. Phase locked loop imperfections and their effect on the modulated output signal are considered and simulation results are presented.