DATA MODULATOR EMPLOYING SINUSOIDAL SYNTHESIS

• US 3,623,160 A
• Filed: 09/17/1969
• Issued: 11/23/1971
• Est. Priority Date: 09/17/1969
• Status: Expired due to Term

• Current Assignee: Donald G. Shuda, George R. Giles, Kenneth R. Macdavid
• Original Assignee: Donald G. Shuda, George R. Giles, Kenneth R. Macdavid
• Inventors: Giles, George R., Shuda, Donald G., MacDavid, Kenneth R.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Glassman, Jeremiah
• Application Number:
  US04/858,721
• Time in Patent Office: 797 Days
• Field of Search: 340/347 325/38A,38,163,153 179/15
• US Class Current: 341/147
• CPC Class Codes: H04L 25/49 using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems spectral shaping H04L25/03828
• CPC Class Codes: H04L 27/26 Systems using multi-frequency codes H04L27/32 takes precedence

Abstract

Multitone data-transmitting apparatus employing sinusoidal synthesis with harmonic cancellation. A multitone data transmitter employs relative phase displacements between plural digital waveforms all of which are representative of a tone to be transmitted and a weighted summing network for summing the plural waveforms so as to cancel undesirable harmonics of the frequency tone to be transmitted. In the illustrated FSK modulator, four square waves having relative phase shifts of pi /4 radians are given suitable summing weights so as to cancel the third and fifth harmonic of any selected one of the FSK tones.

Claims

1. A digital data modulator responsive to a bivalued digital data signal to produce a modulated signal, said modulator comprising:

modulation-encoding means responsive to said bivalued digital data signal to produce an encoded pulse train, one characteristic of which is varied according to the selected type of modulation;

a square wave generator responsive to said encoded pulse train to produce n square waves, all of which have the same variable characteristic as said one characteristic of the pulse train, and all of which are phase displaced from one another;

a summation network for summing said n square waves with weightings to produce an approximate sinusoidal wave, a like characteristic of which varies according to the variations of the characteristics of said square waves and pulse train, the relative square wave displacements and summation network weightings being such as to eliminate a selected set of harmonics of the fundamental frequency of the approximate sinusoidal wave; and

means for filtering said approximate sinusoidal wave to produce said modulated signal.

2. The invention according to claim 1 wherein said n square waves have relative phase displacements of pi /n or multiples thereof from one another;

and wherein said summing means includes a summing node commonly coupled to plural summing branches each receiving a different one of said square waves.

3. The invention according to claim 2 wherein said square wave generator includes a digital counter having n stages, with each stage producing one of said n waves.

4. The invention according to claim 3 wherein said filter means presents an effective zero AC impedance to said summing node;

and wherein said filtered wave is adapted to be coupled to a communication channel.

5. The invention according to claim 4 wherein said cancelled harmonics include the even harmonics and every other odd pair of odd harmonics beginning with the third and fifth harmonics.

6. The invention according to claim 5 wherein said modulation type is frequency modulation such that the variable signal characteristic is frequency.

7. A frequency shift keying modulator comprising frequency tone encoding means responsive to a multilevel digital signal to provide a tone-encoded wave, square wave producing means responsive to said tone-encoded wave for producing n square waves, all of which are functionS of said tone-encoded wave and which are phase displaced from one another;

summation means for summing said n square waves with weightings to produce an approximate sinusoidal wave of fundamental frequency fo with certain ones of the harmonics of fo being cancelled in the summation; and

means for filtering said sinusoidal wave.

8. The invention according to claim 7 wherein said multilevel digital signal has first and second levels indicative of first and second binary values, respectively;

and wherein said cancelled harmonics include the even harmonics and the third and fifth odd harmonics of fo.

9. The invention according to claim 8 wherein said n digital waves are phase displaced from one another by pi /n radians or multiples thereof.

10. The invention according to claim 9 wherein said summation means includes a summing node commonly coupled to n summing branches having relative summing weights and receiving separate ones of the digital waves;

and wherein said said wave-producing means includes an n-stage digital counter responsive to said tone-encoded wave to provide from each of its stages one of said n square waves.

11. The invention according to claim 10 wherein said filter means presents an effective zero AC impedance to said summing node.