in this study, the measurable phase difference was extended
by dividing the received signals by the frequency
to increase the measurement range while using the stable
40 kHz general purpose sensors. As shown in Fig. 2, when
the signal passes through a 1/2-frequency divider, the
frequency is reduced by half. 40 kHz signal through the
1/2-frequency divider two times, the frequency of output
signal becomes 10 kHz. Measurable phase difference is
expanded four times until 50 ls.
It is widely known that the frequency divider is implemented
using flip-flops [11,12]. In this study, the frequency