Digital frequency modulator

An MSK modulator, comprising:

• 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.

A frequency modulator, comprising:

• 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.