FREQUENCY MEASURING DEVICE

PURPOSE:To highten a frequency measuring accuracy by measuring a wavelength of an input signal based on a cumulative value of a count value of a wavenumber of burst signal and a sum of each unit time of a measurement period. CONSTITUTION:A trigger generating circuit 4 sends a trigger signal to a reference signal generating circuit 5 when a signal which exceeds a specified level from an input terminal 1 is detected 3 and the circuit 5 supplies a gate signal with a unit time TG to a gate circuit 8. On the other hand, an input signal at the terminal 1 is subjected to waveform-shaping 2 and 1/N frequency-division and then is supplied to a circuit 8. The circuit 8 is opened by the gate signal and counts a wavenumber 10 of a signal which is divided by N. This output is cumulated by an addition circuit 12 and an accumulator 13 and is fed to a frequency operation circuit 14. Also, the unit time TG is multiplied by m which indicate the number of times where the circuit 8 is opened within a measurement period and is supplied to the circuit 14. A frequency is calculated by the circuit 14 from an accumulated output of the counter 10, a sum (mXTG) of a gate time, and the frequency-division ratio N from a terminal 9.