Detector for AM-FM signals

An AM-FM detector comprising:

• a. a source selectively providing either frequency modulated signals of a first predetermined center frequency or amplitude modulated signals of a second predetermined center frequency,
• b. phase shift means which for frequency modulated signals produces a substantially linear change of phase with frequency through a range lying to either side of an odd multiple of 90.degree. and which for amplitude modulated signals produces a phase inversion,
• c. a differentially connected emitter follower pair comprising a pair of transistors, the collectors of both transistors being jointly coupled to a bias source;
• the emitters of both transistors being jointly coupled to ground through a load impedance, and the base of one transistor being coupled to said source without phase shift and the base of the other transistor being coupled to said source through said phase shift means to produce at the joined emitters an output waveform representing the greater of the two input waveforms and having zero crossing widths proportional to the phase separation of the input wave;
• whereby for FM operation an output wave-form is provided having a portion of one polarity which is broad and double peaked while having a portion of the other polarity which is narrow and single peaked, and whereby for AM operation full wave rectification is achieved;
• and
• d. integrating means coupled to said load impedance which for FM operation converts said variable width portions of said other polarity to a time averaged waveform whose amplitude is proportional to said frequency deviation to obtain the original signal modulation and which for AM operation derives the average amplitude of said full wave rectified signal to obtain the original signal modulation.

A frequency modulation detector responsive to frequency modulated signals of predetermined center frequency, comprising:

• a. a pair of transistors each having an emitter, base and collector electrode, the collector electrodes being connected to a bias source and the emitter electrodes being joined together and connected to a load impedance,
• b. first input means for applying said frequency modulated signals to the base electrode of one of said transistors, said frequency modulated signals being in the form of a first input waveform,
• c. second input means for applying said frequency modulated signals that have been shifted in phase so as to exhibit a substantially linear change of phase as a function of frequency through a range lying to either side of an odd multiple of 90.degree. to the base electrode of the other of said transistors, the phase shifted frequency modulated signals being in the form of a second input waveform, said first and second transistors conducting in accordance with the predominant one of said first and second input waveforms so as to generate an output waveform at said load impedance which represents the predominant one of the two input waveforms and which intersects an established reference level with reference level crossing widths that are a function of the relative phase of said two input waveforms,
• d. integrating means coupled to said load impedance for converting the output waveform to a time averaged waveform whose amplitude is proportionl to said relative phase and therefore the frequency deviation of said signals, and
• e. limiting means coupled between said load impedance and said integrating means for removing amplitude variations in said output waveform.