Novel theory and architecture of a vector signal generator implemented with two PLLs

This paper presents a novel theory of a vector signal generator (VSG) consisting of two phase locked loop synthesizers. In classical PLL synthesizers the output signal is locked to phase and frequency of reference signal. However with the novel theory it is possible to obtain different output phases for the same output frequency of a PLL. Phase variation is achieved through the PLL divider control. Hence by adding the outputs of two PLLs at the same frequencies but different phases forms an amplitude modulated signal. The hardware of the VSG is realized and the novel measurements of amplitude modulation achieved with two PLLs are presented. Each PLL gives an output signal with highly stable amplitude and phase. Measurements of the VSG show that the addition of two PLLs results in a very stable amplitude level of the output signal.