Direct GMSK modulation with a phase-locked power oscillator

A phase-locked-loop (PLL)-based architecture is proposed for direct generation of frequency stable, high-power Gaussian minimum shift keying (GMSK) and other continuous phase modulations at microwave and millimeter-wave frequencies. A continuous phase frequency shift-keyed (CPPSK) signal with a modulation index of 0.5 is produced at the desired output frequency using a full 360° 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 PLL facilitates reference signal frequency tracking and provides Gaussian spectral shaping to the modulated output signal, PLL imperfections and their effect on the modulated output signal are considered, and simulation results are presented