Spectrum analyzer circuit for pulsed input signals

摘要

A spectrum analyzer for measuring the frequency spectrum of a pulsed input signal includes a synthesized local oscillator for providing an oscillator signal. The local oscillator is responsive to a digital control input signal to sweep the frequency of the oscillator signal from a start frequency to a stop frequency wherein the values of the start and stop frequencies are determined by the control signal. The oscillator is further responsive to the control signal to stop sweeping the oscillator signal. The oscillator signal is mixed with the pulsed input signal and filtered to determine the peak voltage of a predetermined frequency component of the mixed input signal. A data processor is provided for providing the control signal to the local oscillator. The data processor is adapted to adjust the control signal so that the start frequency of the oscillator is equal to its previous stop frequency minus a predetermined frequency difference. The frequency difference is determined to compensate for the circuit delay of the spectrum analyzer and the sweep start-up transients of the local oscillator. The local oscillator is started at a time prior to the measurement interval so that at the beginning of the measurement interval the frequency of the local oscillator is equal to the stop frequency of the previous measurement interval.