PLL frequency synthesizer

Abstract

It is an object of the present invention to reduce the amount of spurious noise generated by an emission line spectrum of a signal propagating around the PLL of a PLL frequency synthesizer carrying out digital-signal processing. In order to achieve the object described above, the present invention provides a PLL frequency synthesizer with the following configuration. In a PLL frequency synthesizer having a charge-pump circuit, a waveform converter is provided at a stage behind the charge-pump circuit. The waveform converter converts the voltage waveform on a time axis of a rectangular wave output by the charge-pump circuit into a waveform which: is symmetrical with respect to a predetermined point of time; oscillates so as to have no direct-current component; and has a maximum value of the absolute values of maximums of wave heights thereof located at the center wherein the absolute value decreases uniformly as the wave height is separated farther away from the center. As a result, the amplitudes of a limited number of emission line spectra forming a spurious signal superposed on a signal propagating around the PLL can be made uniform and a maximum thereof can be held at a low value, allowing the direct-current component to be eliminated from the signal propagating around the PLL.

Dependencies are inferred from the claim text.