power rf signal 16 is amplitude and phase modulated such as quadrature amplitude modulation qam the matching network 20 matches an output impedance of the rf generator 11 to the input impedance of the plasma chamber 18 fig8 shows a generic plasma generator system having a closed loop am fm mode rf signal generation system the rf generator 11 provides the am fm power rf signal 16 to the plasma chamber 18 through a matching network 20 and a reflected power meter 32 the reflected power meter 32 provides the measurement signal 34 indicative of the degree of rf coupling between the output of the matching network 20 and the input of the plasma chamber 18 the measurement signal 34 is applied to feedback blocks 36 and 37 the feedback block 36 controls the frequency of the vfo 24 as shown and described in fig4 the feedback block 37 generates the amplitude modulation signal 25 in accordance with a function a r and applies the amplitude modulation signal 25 to the variable gain rf amplifier 15 the rf generator 11 thereby provides the am fm power rf signal 16 in accordance with the modulating signal 24 and the amplitude modulating signal 25 the functions g r and a r can also be chosen such that the power rf signal 16 is amplitude and phase modulated such as qam fig9 and 10 show generic plasma generator systems that are similar except for the architecture of the rf generator 11 to the systems of fig7 and 8 respectively in fig9 and 10 the rf generator 11 has a vfo 13 with.