Method and apparatus for error reduction in digital information transmission systems

A system for transmitting information from a first location to a second location in digital form with reduced errors due to idle channel, cross talk and quantizing error noise, said system comprising:

• input terminal means adapted to be coupled to a source of analog information signals at said first location, said analog information input signals having a spectral content lying within a predetermined operating frequency band;
• means for generating a controlled noise signal train having a spectral content devoid of frequency components within the limits of said operating frequency band and narrowly centered about a predetermined frequency lying substantially outside said operating frequency band;
• means coupled to said input terminal means and said generating means for combining said analog information signals with said controlled noise signal train to produce a composite signal;
• means for converting said composite signal to equivalent digital form by quantizing said composite signal with a predetermined number of quantizing levels each having a predetermined magnitude with a predetermined sampling frequency;
• said generating means including means for limiting the amplitude of said controlled noise signal train to a range from about 1/4 to about 1/2 the magnitude of said quantizing levels;
• transmission means having an input coupled to the output of said converting means for transmitting said digital signals to said second location;
• means at said second location for reconverting said digital signals to equivalent analog form;
• and,
• means for filtering said reconverted analog signals to remove substantially all frequency components lying outside said predetermined operating frequency band.

A system for converting analog signals to equivalent digital signals for subsequent processing, said system comprising:

• input terminal means adapted to be coupled to a source of analog information signals having a spectral content lying within a predetermined frequency band;
• means for generating a controlled noise signal train having a spectral content devoid of components within the limits of said operating frequency band and narrowly centered about a predetermined frequency lying substantially outside said operating frequency band;
• means coupled to said input terminal means and said generating means for combining said analog information signals with said controlled noise signal train to produce a composite signal;
• and,
• means coupled to said combining means for converting said composite signal to equivalent digital form by quantizing said composite signal with a predetermined number of quantizing levels each having a predetermined magnitude with a predetermined sampling frequency, said converting means including an output terminal means for manifesting said equivalent digital signals;
• said generating means including means for limiting the amplitude of said controlled noise signal train to a range from about 1/4 to about 1/2 the magnitude of said quantizing levels.