| 摘要 |
PURPOSE:To attain the measurement of a pseudo lock range of a PLL circuit and to facilitate the measurement of a lock range by using a phase comparator with the high sensitivity for measuring a phase difference of different frequencies and differentiating an output voltage of a low pass filter with respect to a reference frequency. CONSTITUTION:This measuring instrument is provided with a phase comparison means 20, which measures a time interval between a point of time of the rise of a waveform of a low frequency input of 2-frequency inputs and a point of time of the fall of a waveform of a high frequency input generated at first from the rising point of time of the waveform to measure the phase difference of two frequency inputs. When a frequency shift is given to a reference frequency input and a low pass filter 22 is connected to the phase comparison means 20, a reference frequency at which an output of the phase comparison means 20 is changed suddenly is obtained to decide the boundary between a lock range and a pseudo lock range. Thus, a phase error due to frequency division is avoided and a phase difference is measured with sufficient accuracy and the frequency of the pseudo lock range and the lock range is easily measured from a suddenly changed output. |
