Transmitter PLL with Bandwidth on Demand

An embodiment of the present invention provides transmitter having a phase locked loop that has a dynamically controllable loop bandwidth. A transmit modulator is coupled to the PLL for performing vector modulation in response to transmission symbols. Each transmission symbol comprises an amplitude signal and a phase signal. A controller is coupled to the PLL and to the transmit modulator and is operable to detect when a criteria of the transmission symbols crosses a threshold and to adjust loop bandwidth in response to crossing the threshold. The criteria of the transmission symbols may be a function of the amplitude signal or a function of the phase signal, and may be the amplitude signal, a first derivative of the amplitude signal, a second derivative of the amplitude signal, a square of the amplitude signal, a derivative of the amplitude signal squared, the phase signal, or a derivative of the phase signal.