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US 3,943,296 AGranted
Method and apparatus for reducing noise in pam time division networks
AssigneeBell Telephone Laboratories, Incorporated
InventorJohn Francis O'Neill
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AssigneeBell Telephone Laboratories, Incorporated
InventorJohn Francis O'Neill
Estimating the term…
In pulse amplitude modulated time division switching systems, noise and crosstalk often result because the time division switches used to connect individual channels to a common bus are not perfect open circuits when they are in the off-state. The switches in the off-state possess a small parasitic capacitance which couples energy on the common bus to the channel resulting in a noise signal during time slots which are not associated with the channel. A method is disclosed for substantially reducing crosstalk and noise induced by stray capacitances without increasing the complexity of the time division switch. Each pulse on the common bus is converted into a bipolar pulse in which positive and negative portions have equal average values. In addition, the timing of each of the time division switches is modified to extract the desired signal by sampling the first portion of the bipolar pulse in the appropriate time slot for that channel, and rejecting the second portion of the bipolar pulse. The noise energy which is coupled from the common bus to the channel by stray switch capacitance during other time slots remains essentially bipolar in form and tends to cancel itself. The noise power at low frequencies is therefore substantially reduced. Apparatus is also disclosed for converting pulses on the common bus into the bipolar format required by the invention.
A pulse amplitude modulated time division switching system comprising a plurality of sources of low frequency information, a sampling bus, means for applying pulses modulated by said information sources to said bus in a repetitive multiplexed sequence, said applying means including means for generating for each information modulated pulse a pair of pulses, each pulse of said pulse pair having an equal average value but being opposite in polarity, a plurality of outputs, means for repetitively connecting said outputs to said sampling bus so that each of said outputs receives pulses from one of said information sources, said connecting means including means for connecting said outputs to receive the first pulse of said pulse pair, but to block the second pulse of said pulse pair, and means for integrating the received pulses to recover said low frequency information.
A method for increasing the signal to noise ratio in a time division switching network having a plurality of sources of low frequency information, a sampling bus having pulses modulated by said information sources impressed thereon in a repetitive multiplexed sequence, a plurality of outputs, means for repetitively connecting said outputs to said sampling bus so that each of said outputs receives pulses from one of said information sources, and means for integrating the received pulses to recover said low frequency information, said method comprising the steps of,
An arrangement for increasing the signal to noise ratio in a time division switching network having a plurality of sources of low frequency information, a sampling bus having pulses modulated by said information sources impressed thereon in a repetitive multiplexed sequence, a plurality of outputs, means for repetitively connecting said outputs to said sampling bus so that each of said outputs receives pulses from one of said information sources and means for integrating the received pulses to recover said low frequency information, said arrangement comprising,
In a switching system having a plurality of communications stations each having means for generating amplitude modulated pulses, a common communications bus having an input and an output, means for connecting said stations in pairs in a time slot associated with said pair to said input and said output of said bus for allowing said amplitude modulated pulses to pass between said stations, an improvement for reducing noise and crosstalk comprising
A method for reducing crosstalk and noise in a switching system wherein pairs of stations are sequentially connected in pairs of a common bus in an associated time slot to transfer information by means of amplitude modulated pulses, said method comprising the steps of
An arrangement for reducing crosstalk and noise in a pulse amplitude modulated switching system having a common bus with an input and an output, a plurality of communicating stations producing modulated information pulses, each of said stations being connectable to said common bus by a time division switch and timing means for controlling said time division switches to connect said communicating stations in pairs to said input and said output of said common bus during a respective time slot, said arrangement comprising,
A method for reducing crosstalk and noise in a switching system having a plurality of stations sequentially connectable to a common bus in an associated time slot to transfer information therebetween,
Dependencies are inferred from the claim text.