Enhance GMSK performance with two-point modulation

DATA-COMMUNICATIONS systems that employ modulation techniques requiring goo d low-frequency response place unique demands on system signal sources, usu ally a phase-locked-loop (PLL) frequency synthesizer. For example, Gaussian minimum-shift-keying (GMSK) and four-level frequency-shift-keying (FSK) mo dulation schemes require modulation response extending to DC, an attribute that is not easily accommodated by many modulators. This article will discu ss the problems encountered when designing GMSK modulators with respect to the characteristics of PLL frequency synthesizers, and show how two-point m odulation can be used to salve these problems.