Digital modulator with variations of phase and amplitude modulation
First Claim
1. A modulator, comprising:
- a source of digital information signal;
amplitude control signal generating means coupled to said source of digital information signal for generating a first digital amplitude control signal proportional to said digital information signal and for generating a second digital amplitude control signal equal in magnitude and opposite in polarity to said first digital amplitude control signal;
a digital sawtooth signal generator for generating a digital sawtooth signal having a recurrence rate equal to the desired carrier frequency;
first digital adding means coupled to said digital sawtooth signal generator and to said amplitude control signal generating means for adding together said digital sawtooth signal and said first digital amplitude control signal for generating a first phase-shifted digital sawtooth signal;
second digital adding means coupled to said digital sawtooth signal generator and to said amplitude control signal generating means for adding together said digital sawtooth signal and said second digital amplitude control signal for generating a second phase-shifted digital sawtooth signal;
first and second addressable memory means coupled to said first and second digital adding means, respectively, said first and second addressable memory means being addressed by said first and second phase-shifted digital sawtooth signal for generating first and second mutually phase-shifted sinusoidal analog signals; and
summing means coupled to said first and second addressable memory means for adding together said first and second mutually phase-shifted analog sinusoidal signals for generating a carrier signal at said recurrence rate amplitude-modulated by said digital information signal.
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Abstract
A phase modulator includes a digital frequency word generator, an adder and a register arranged to generate recurrent digital sawtooth signals at a carrier rate. A second digital adder is coupled to receive the sawtooth signals and also receives digital information signals. The adder produces recurrent digital sawtooth signals phase-modulated by the information signal. A pair of adders receive the digital sawtooth signals and mutually sign-reversed digital information signals to produce a pair of oppositely phase-modulated constant-amplitude signals in a pair of channels. A sine memory is addressed by the phase-modulated digital sawtooth signals to produce phase-modulated sinusoidal-representative digital signals. The digital signals are then converted to analog signals. Since the two channels contain signals which are phase-modulated but not amplitude-modulated, the signals may be amplified by nonlinear amplifiers. An adder is coupled to the outputs of the two channels to sum together the two phase-modulated signals to produce an amplitude-modulated signal. Combinations of amplitude and phase modulation may be generated by a combined structure.
110 Citations
9 Claims
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1. A modulator, comprising:
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a source of digital information signal; amplitude control signal generating means coupled to said source of digital information signal for generating a first digital amplitude control signal proportional to said digital information signal and for generating a second digital amplitude control signal equal in magnitude and opposite in polarity to said first digital amplitude control signal; a digital sawtooth signal generator for generating a digital sawtooth signal having a recurrence rate equal to the desired carrier frequency; first digital adding means coupled to said digital sawtooth signal generator and to said amplitude control signal generating means for adding together said digital sawtooth signal and said first digital amplitude control signal for generating a first phase-shifted digital sawtooth signal; second digital adding means coupled to said digital sawtooth signal generator and to said amplitude control signal generating means for adding together said digital sawtooth signal and said second digital amplitude control signal for generating a second phase-shifted digital sawtooth signal; first and second addressable memory means coupled to said first and second digital adding means, respectively, said first and second addressable memory means being addressed by said first and second phase-shifted digital sawtooth signal for generating first and second mutually phase-shifted sinusoidal analog signals; and summing means coupled to said first and second addressable memory means for adding together said first and second mutually phase-shifted analog sinusoidal signals for generating a carrier signal at said recurrence rate amplitude-modulated by said digital information signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification