Detection circuit, electronic circuit and detection method

A detection circuit for detecting a clock signal includes a multiplexer, a digital-to-analog converter, a comparator, and a counter. The multiplexer outputs either a first signal or a second signal as a selection signal. The digital-to-analog converter outputs a reference voltage according to the selection signal. The comparator compares the clock signal with the reference voltage to generate a comparison signal. The counter counts a reference clock signal to generate an overflow signal, and resets the overflow signal according to the comparison signal. The overflow signal indicates amplitude of the clock signal.