Patent ID: 8509296
Filing Date: 2013-08-13
Classification: G01R

Abstract:
1. A spectrum analyzer comprising: a frequency conversion section that mixes a local signal subjected to a frequency sweep with an input signal of an analysis target so as to extract a signal component of a predetermined intermediate frequency band from the mixing result; a local signal generation section that includes a fractional-N PLL synthesizer, wherein the PLL synthesizer includes: a VCO; a fractional frequency divider divides a frequency of an output signal of the VCO; a reference signal generator outputs a reference signal; a phase frequency comparator receives an output of the frequency divider and the reference signal, and outputs a phase error signal; and, a loop filter receives the phase error signal and outputs a control signal; wherein the PLL synthesizer locks the frequency of the output signal of the VCO to a product between a frequency of the reference signal and a frequency division ratio of the frequency divider in response to a control signal; and wherein the local signal generation section provides the output of the PLL synthesizer or a multiplication output thereof as the local signal to the frequency conversion section, and updates the frequency division ratio of the frequency divider sequentially so as to chronologically output the signal component of the input signal within a designated analysis target frequency range from the frequency conversion section in order of the frequency thereof, thereby sweeping a frequency of the local signal, a signal processing section that performs a band limiting process of a designated resolution bandwidth and an amplitude detection process on the signal output from the frequency conversion section during the frequency sweep of the local signal so as to obtain a spectrum waveform within the analysis target frequency range; a display section that displays the spectrum waveform which can be obtained by the signal processing section; and an operation section that arbitrarily designates the analysis target frequency range and the resolution bandwidth, wherein a band of the loop filter of the fractional-N PLL synthesizer of the local signal generation section and the frequency of the reference signal are set to be changeable, wherein the spectrum analyzer is provided with wherein the setting section performs a setting process including, thereby sweeping the local signal of the local signal generation section under the set conditions.