SIGNAL DEMODULATOR OF ZERO IF RECEIVER USING SAMPLING TECHNIQUE

摘要

Apparatus is depicted which enables the sampling of the phase angle of a modulated signal and manipulates the sample signals to demodulate the same. The apparatus is particularly adaptable for use in demodulating the I and Q channel signals of a zero IF receiver. The system contains an angle sensing circuit which combines the I and Q channel signals in differential form to produce a series of output signals of an angular range indicative of the present value of the instanteous phase. The signals from the angle detector are coupled to an octant decoder which operates to determine the particular octant that the angle is to be included in. In the present system eight octants are used, each comprising 45°. The octant decoder determines which octant the angle belongs in and assigns a predetermined angle value to that angle. In one embodiment, the assigned angle values are 0°, 45°, 90°, 135°, 180°, 225°, 270° or 315. degree.. The value of the assigned angles are then sampled by means of a clock at a high frequency rate whereby the resultant pulses indicative of the angles are then processed as differentiated to produce an output signal indicative of the information content on the original signal.