Patent ID: 7006936

Claim:
A pulse width measuring device comprising: an edge detecting circuit that outputs a detection signal by detecting a rise or fall of a signal to be measured; a control unit that outputs a count start/end signal, based on the detection signal; a counter circuit that counts a count clock signal, based on the count start/end signal; a count value storing unit that stores the count value of the counter circuit; and a selector circuit that selects a clock signal from a plurality of clock signals of different frequencies, based on a clock select signal, and outputs the selected clock signal as the count clock signal, the pulse width measuring device calculating the pulse width of the signal to be measured, based on the count value and the count clock signal, wherein: the counter circuit has a plurality of bits that are divided into an exponent and a significand; and the control unit comprises: an exponent storing unit that stores an exponent setting value that represents the number of bits of the exponent of the counter circuit; and a decoder unit that generates a count value setting signal for rewriting the count value of the counter circuit, based on the exponent setting value stored in the exponent storing unit, when the count value overflows in the counter circuit, the decoder unit then outputting the count value setting signal to the counter circuit.