Zero IF receiver AM/FM/PM demodulator using sampling techniques

Apparatus for demodulating the information content contained in the I and Q channel signals of a zero IF receiving apparatus comprising:

• first and second amplifying means with said first amplifier responsive to said signal in said I channel for providing at an output an amplified version of said I channel signal, and with said second amplifier responsive to said signal in said Q channel for providing at an output an amplified version of said Q channel signal,
• angle sensing means responsive to said amplified I and Q channel signals to provide at an output angle signals indicative of a phase angle associated with said I and Q channel signals being within specified ranges of angles,
• octant sensing means responsive to said angle signals to determine which one of a plurality of octants said phase angle is in to specify said phase angle by a predetermined value according to said octant whereby said angle is specified as 360/n, where n is a positive number according to said phase angle as located within one of said octants, and
• means for processing said predetermined values to demodulate the information content in said I and Q channels.

Apparatus for use in demodulating the information content in the I and Q channel signals of a zero IF receiving apparatus of the type further employing a voltage controlled oscillator having an output coupled to inputs of first and second mixers, with other inputs of said mixers coupled to the quadrature signals derived from a local oscillator to provide at the outputs of said mixers a I' and Q' channel signal, comprising,

• angle sensing means responsive to said I' and Q' channel signals to provide at an output angle signals indicative of phase angles associated with said I' and Q' signals being within specified ranges of angles,
• octant decoder means responsive to said angle signals to provide at outputs thereof an indication of which one of a plurality of octants each of said phase angles is in to specify said phase angle as one between 0.degree. to 360.degree. for assigning one of a plurality of predetermined angular values to said phase angles
• first multiplying means having first and second inputs adapted to receive said I and Q channel signals and further inputs coupled to said outputs of said octant decoder means to provide at an output product signals indicative of the I and Q signals as modified by the I' and Q' signals,
• differentiation means coupled to the output of said multiplying means to provide a control signal for said voltage controlled oscillator with said control signal indicative of one type of information content in said I and Q channels.

A method for demodulating the phase information content in a modulated signal having the form of V+A sin .delta. in one channel indicative of a first signal and of V+A cos .delta. indicative of a second signal in another channel, comprising the steps of:

• (a) forming a differential signal from each of said channel signals to provide a third signal of the form V-A sin .delta. and a fourth signal of the form of V-A cos .delta..
• where
• V is a constant
• A is a constant
• and
• .delta. is a time varying phase function:
• (b) combining said first and second signals and said third and fourth signals to provide a series of composite signals each indicative of a given range of angular values indicative of the phase angle of said modulated signals,
• (c) sampling said series of signals to determine which one of a plurality of octants each of said signals are in,
• (d) assigning a predetermined value to each of said sampled signals according to said octant determination,
• (e) processing said assigned values to demodulate said information content.