Phase angle detector and frequency discriminator employing the same

According to the present invention, in accordance with the first to fourth quadrants on the phase plane for signal points, a phase angle detector converts an I channel signal or a Q channel signal obtained by a demodulator, by using individually set operating expressions, so as to correlate the angle (phase angle) for a signal point on the plane phase with a predetermined one-dimensional coordinate. More specifically, the phase angle that extends from a border point in an arbitrary quadrant on the phase plane to a border position shifted 360° is allocated for a specific one-dimensional coordinate. The coordinate value on the one-dimensional coordinate is calculated by using the operating expression which is set in accordance with the first to the fourth quadrant of the signal point which is detected using the I channel signal and the Q channel signal. This can be an arbitrary expression; however, as simple an operating expression as possible is selected so that the calculation can be performed by as simple a circuit as possible.