Period and frequency measuring instrument

An instrument for determining the period and frequency of an input signal, comprising clock means for providing first and second clock signals,

• first divider means for dividing said input signal by a predetermined division factor to output a divided signal having a minimum period, wherein a first fractional time is defined between a first output of said first divider means and the first clock pulse of said first clock signal thereafter, and a second fractional time is defined between the following output of said first divider means and the first clock pulse of said first clock means thereafter,
• gate signal generating means for generating a gate signal synchronized with said first clock signal,
• counter means for counting the clock pulses of said first clock signal during said gate signal,
• expansion means for expanding each said fractional time, at least the expanded first fractional time being shorter than the minimum period of said divided signal,
• up-down counter means for providing a count of the clock pulses of said second clock signal corresponding to the difference between the first and second expanded fractional times, and
• calculator means for calculating the period and frequency of said input signal by adding the count from said counter means to a value corresponding to the count from the up-down counter means.