A time-to-digital converter includes a phase-difference enhancement section configured to receive first and second input signals having a reference phase difference Δt, and to output first and second output signals having an enhanced phase difference; and a comparison section configured to receive the first and second output signals, to compare a phase difference between the first and second output signals with a reference delay time τ, and to output a comparison signal. The time-to-digital converter has a high resolution. That is to say, the time-to-digital converter has a resolution less than the minimum phase delay time of a delay element, which is obtainable in a corresponding semiconductor process.