Non-synchronous duobinary encoding

Claim 2

An encoder for encoding data signals of the type that make successive excursions from a predetermined level as a function of time; said encoder comprising the combination of bipolar means selectively operable in inverting, non-inverting, and quiescent modes; and control means coupled to said bipolar means for controlling the operating mode thereof in response to said data signal; said control means including first means for holding said bipolar means in said quiescent mode whenever said data signal is at said predetermined level, and second means for selectively operating said bipolar means in said inverting and non-inverting modes during said excursions, said second means selecting the operating mode for each of said excursions as a function of the operating mode selected for any immediately preceding excursion and the amount of time elapsed since said preceeding excursion.

Claim 3

The encoder of claim 1 wherein said bipolar means comprises an operational amplifier having inverting and non-inverting inputs; said control means comprising first and second gates having outputs coupled to the inverting and non-inverting inputs, respectively, of said operational amplifier; said first means applies a disabling signal to one input of each of said gates whenever said data signal is at said predetermined level; and said second means has first and second complementary outputs coupled to further inputs of said first and second gates, respectively, whereby one of said gates is enabled and other is disabled during each excursion of said data signal from its reference level.

Claim 4

The encoder of claim 2 wherein said second means comprises a bistable device to provide said complementary outputs, and means for applying clock pulses at a predetermined repetition rate to said bistable device whenever said data signal is at said predetermined level to thereby cyclically switch said bistable device between one operating state and another while said data signal is at said level.

Claim 5

The encoder of claim 3 wherein said second means further includes an astable multivibrator for supplying said pulses, starting substantially coincidentally with said data signal going to said predetermined level and continuing thereafter at said predetermined rate until said data signal departs from said level.

Claim 6

In a limited bandwidth facsimile system including means for supplying a non-synchronous baseband signal having runs of unknown length at first and second levels to represent black and white picture elements, respectively, a two-to-three level encoder comprising the combination of bipolar means selectively operable in inverting, non-inverting and quiescent modes for generating an encoded version of said baseband signal; and control means coupled to said bipolar means for controlling the operating mode thereof in response to said baseband signal; said control means including first means for holding said bipolar means in said quiescent mode whenever said baseband signal is at one of said levels, and second means for selectively operating said bipolar means in one or the other of said modes whenever said baseband signal is at the other of said levels, said second means selecting the operating mode of said bipolar means for each run of said baseband signal at said other level as a function of the operating mode selected for any immediateLy preceeding run at said other level and the length of any intervening run at said one level.

Claim 7

In a limited bandwidth facsimile system including means for supplying a non-synchronous baseband signal having runs of unknown length at first and second levels to represent black and white picture elements, respectively, a two-to-three level encoder comprising the combination of bipolar means selectively operable in inverting, non-inverting and quiescent modes for generating an encoded version of said baseband signal; and control means coupled to said bipolar means for controlling the operating mode thereof in response to said baseband signal; said control means including first means for holding said bipolar means in said quiescent mode whenever said baseband signal is at one of said levels, and second means for selectively operating said bipolar means in one or the other of said modes whenever said baseband signal is at the other of said levels, said second means selecting the operating mode of said bipolar means for each run of said baseband signal at said other level as a function of the operating mode selected for any immediateLy preceeding run at said other level and the length of any intervening run at said one level.

Claim 8

An encoder according to claim 5 wherein said control means comprises first and second gates which are simultaneously disabled by said first means when said baseband signal is at said one level and selectively enabled and disabled by said second means when said baseband signal is at said other level.

Claim 9

An encoder according to claim 6 wherein each of said gates has a first input and a second input, said first means applies a disabling signal to the first input of each of said gates whenever said baseband signal is at said one level; and said second means includes a clock controlled bistable device having complementary outputs coupled to the second inputs of said first and second gates, respectively, for alternately and cyclically applying an inhibiting signal to one and then the other of said gates whenever said baseband signal is at said one level, whereby one of said gates is enabled and the other is disabled when said baseband signal goes to said other level.

Claim 10

An encoder according to claim 7 wherein each of said picture elements is allotted a predetermined amount of time; and said bistable device cycles with a period selected to equal twice the amount of time allotted to each picture element, starting substantially coincidentally with said baseband signal going to said one level and continuing thereafter until said baseband signal goes to said other level.

Claim 11

An encoder according to claim 8 wherein said one and said other levels represent black and white picture elements, respectively, whereby white picture elements straddling any single, isolated, black picture element are encoded with opposite polarities, thereby virtually forcing the system to respond to isolated black picture elements.

Claim 12

An encoder according to claim 6 wherein said bipolar means comprises a unity gain operational amplifier having an inverting input coupled to an output of said first gate and a non-inverting input coupled to an output of said second gate.

Claim 13

An encoder according to claim 10 wherein each of said gates has a first input and a second input; said first means applies a disabling signal to the first input of each of said gates whenever said baseband signal is at said one level; and said second means includes a clock controlled bistable device having complementary outputs coupled to the second inputs of said first and second gates, respectively, for alternately and cyclically applying an inhibiting signal to one and then the other of said gates whenever said baseband signal is at said one level, whereby one of said gates is enabled and the other is disabled when said baseband signal goes to said other level.

Claim 14

An encoder according to claim 11 wherein each of said picture elements is allotted a predetermined amount of time; and said bistable device cycles with a period selected to equal twice the amount of time allotted to each picture element, starting substantially coincidentally with said baseband signal going to said one level and continuing thereafter until said baseband signal goes to said other level.

Claim 15

An encoder according to claim 12 wherein said one and said other levels represent black and white picture elements, respectively, whereby white picture elements straddling any single, isolated, black picture element are encoded with opposite polarities, thereby virtually forcing the system to respond to isolated black picture elements.

Claim 18

The method of claim 14 wherein a first count is accumulated substantially simultaneously with said data signal going to said second level, and said encoded signal is readjusted to said one level if the accumulated count is even when said data signal goes to said first level and to said other level if the accumulated count is odd.

Claim 19

The method of claim 15 wherein said data signal is a facsimile baseband signal having white picture elements represented by said first level and black picture elements represented by said second level, with each of said picture elements being allotted a predetermined amount of time; and said counts are accumulated, starting at the outset of each run at said second level and continuing thereafter, with a period selected to equal twice the amount of time allotted to each picture element, until said baseband signal goes to said first level; whereby white picture elements straddling any single, isolated, black picture elements are encoded at different ones of said upper and lower levels.