Digital frequency modulator
First Claim
1. A frequency modulator, comprising:
- a source of digital sawtooth signal having a recurrence rate equal to the rest recurrence rate of the carrier to be frequency-modulated;
a source of digital information signal;
digital ramp signal generating means coupled to said source of digital information signal for generating a digital ramp signal having slope and polarity, at least said polarity being controlled in response to said digital information signal;
adding means coupled to said source of digital sawtooth signal and to said digital ramp signal generating means for adding together said digital sawtooth signal and said digital ramp signal for generating a frequency-modulated digital sawtooth signal; and
memory means including addressable memory locations, said memory means being coupled to said adding means for being addressed by said frequency-modulated digital sawtooth signal, each of said memory locations which is accessed being preprogrammed with a portion of a sinusoidal signal, whereby said memory means produces a frequency-modulated sinusoidal signal.
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Accused Products
Abstract
An MSK modulator includes a source of digital sawtooth signals having a recurrence rate equal to the desired recurrence rate of the unmodulated carrier. The digital sawtooth signal is applied to an adder together with a phase control digital signal. The phase control digital signal phase-shifts the digital sawtooth signal. The phase-shifted digital sawtooth signal is applied to a sine ROM to produce a digital sinusoid with an unmodulated recurrence rate equal to the recurrent rate of the digital sawtooth signal. When the phase control signal is an accumulated signal, the digital sinusoid is frequency-modulated. The phase control signal for MSK modulation is a ramp signal generated by a controlled accumulator. The accumulator includes a controllable clocked adder/subtractor, the output of which is coupled by way of a register back to an input. The other input of the adder/subtractor is coupled to receive a fixed ramp rate controlling word. At each clock cycle, the accumulator adds (subtracts) the ramp rate word from the sum under the control of the MARK (SPACE) information content of the information signal to form a two-frequency MSK modulation. More general frequency modulation is accomplished by an accumulator with an input word which responds to the instantaneous amplitude of the information signal. A clocked delay and a subtractor indicate the direction of frequency deviation.
84 Citations
15 Claims
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1. A frequency modulator, comprising:
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a source of digital sawtooth signal having a recurrence rate equal to the rest recurrence rate of the carrier to be frequency-modulated; a source of digital information signal; digital ramp signal generating means coupled to said source of digital information signal for generating a digital ramp signal having slope and polarity, at least said polarity being controlled in response to said digital information signal; adding means coupled to said source of digital sawtooth signal and to said digital ramp signal generating means for adding together said digital sawtooth signal and said digital ramp signal for generating a frequency-modulated digital sawtooth signal; and memory means including addressable memory locations, said memory means being coupled to said adding means for being addressed by said frequency-modulated digital sawtooth signal, each of said memory locations which is accessed being preprogrammed with a portion of a sinusoidal signal, whereby said memory means produces a frequency-modulated sinusoidal signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An MSK modulator, comprising:
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a source of MARK and SPACE data signal, each said data bit having a predetermined duration; a ramp signal generator coupled to said source of MARK and SPACE data signal for generating a ramp signal having a predetermined slope and a polarity which is positive in response to one of said MARK and SPACE and which is negative in response to other of said MARK and SPACE; a sawtooth generator for generating sawtooth signals having a recurrence rate equal to the MSK carrier recurrence rate; summing means coupled to said ramp signal generator and to said sawtooth generator for controlling the phase of said sawtooth signals in response to said ramp signal to generate a phase-controlled sawtooth signal, whereby said phase is progressively advanced when said ramp signal has a positive polarity and is progressively retarded when said ramp signal has a negative polarity; memory means coupled to said summing means for being addressed by said phase-controlled sawtooth signal, said memory means being preprogrammed at each accessible memory location with a portion of a sinusoid whereby an MSK-modulated signal is generated in which the phase is controlled for linear increment or decrement corresponding to a recurrence rate which is greater or less, respectively, than said MSK carrier recurrence rate. - View Dependent Claims (11, 12, 15)
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13. A frequency modulator, comprising:
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a source of digital information; a source of increment word; a clock; accumulating means coupled to said source of digital information, to said source of increment word and to said clock for accumulating at each clock cycle positive and negative values of said increment word under control of said digital information to form an accumulated signal; a source of digital sawtooth signals having a recurrence rate; adding means coupled to said accumulating means and to said source of digital sawtooth signals for adding together said digital sawtooth signals and said accumulated signal to form frequency-modulated sawtooth signals; and memory means coupled to said adding means for receiving said frequency-modulated sawtooth signals therefrom, for addressing memory locations preprogrammed with sinusoid amplitude information for generating a frequency-modulated sinusoidal signal in response to said frequency-modulated sawtooth signal. - View Dependent Claims (14)
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Specification