Time dependent two-to-three level alternate encoding

Claim 2

An encoder for encoding a data signal of the type that makes successive excursions from a predetermined level, 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 means for holding said bipolar means in said quiescent state whenever said data signal is at said predetermined level; and timing means triggered when said data signal goes to said predetermined level for operating said bipolar means in different ones of said inverting and non-inverting modes during adjacent excursions of said data signal from said predetermined level only if the adjacent excursions occur within a predetermined period of time.

Claim 3

The encoder of claim 1 wherein said control means comprises a pair of gates, each having first and second inputs and an output; said bipolar means comprises an operational amplifier having an inverting input coupled to the output of one of said gates and a non-inverting input coupled to the output of the other of said gates; said means for holding said bipolar means in said quiescent state comprises means for applying a disabling signal to the first input of each of said gates when said data signal is at said predetermined level; and said timing means comprises a bistable device having one output coupled to the second input of one of said gates and a complementary output coupled to the second input of the other of said gates, whereby one of said gates is enabled and the other is disabled whenever said data signal departs from said predetermined level.

Claim 4

The encoder of claim 2 wherein said operational amplifier is unity gain device.

Claim 5

The encoder of claim 2 wherein said timing means further includes means for switching said bistable device from one stable state to another whenever said data signal goes to said predetermined level and again whenever said data signal remains at said predetermined level for said predetermined period of time.

Claim 6

The encoder of claim 4 wherein said means for switching said bistable means comprises a pair of serially connected one-shot multivibrators having a combined on-time selected to equal said predetermined period of time.

Claim 7

The encoder of claim 1 wherein said timing means comprises a bistable device for switching said bipolar means between said inverting and non-inverting modes; and means for switching said bistable device from one stable state to another, once when said data signal goes to said predetermined level and again if said data signal remains at said predetermined level for said predetermined period of time.

Claim 8

The encoder of claim 6 wherein said means for switching said bistable means comprises serially connected one-shot multivibrator means having an overall on-time selected to equal said predetermined period of time, and a gate having one input coupled to an output of said multivibrator means and another input coupled to receive a version of said data signal, whereby said gate supplies a pulse for reversing the state of said bistable device each time said data signal goes to said predetermined level and whenever said data signal remains at said predetermined level for said predetermined period of time.

Claim 9

In a limited bandwidth facsimile system including means for supplying a non-synchronous baseband signal having runs of unknown duration 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 means for holding said quiescent mode whenever said baseband signal is at one of said levels, and timing means triggered when said baseband signal goes to said one level for operating said bipolar means, during adjacent runs of said baseband signal at the other of said levels, in different ones of said inverting and non-inverting modes only if said runs occur within a predetermined period of time and otherwise in a selected one of said inverting and non-inverting modes.

Claim 10

In a limited bandwidth facsimile system including means for supplying a non-synchronous baseband signal having runs of unknown duration 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 means for holding said quiescent mode whenever said baseband signal is at one of said levels, and timing means triggered when said baseband signal goes to said one level for operating said bipolar means, during adjacent runs of said baseband signal at the other of said levels, in different ones of said inverting and non-inverting modes only if said runs occur within a predetermined period of time and otherwise in a selected one of said inverting and non-inverting modes.

Claim 11

The limited bandwidth facsimile system with the encoder according to claim 8 wherein said one and said other levels represent black and white picture elements, respectively, whereby runs of white picture elements are encoded with opposite polarities if separated by a run of black picture elements which is completed with said predetermined period of time and otherwise with the same polarity.

Claim 12

The limited bandwidth facsimile system with the encoder according to claim 9 wherein each of said picture elements is allotted a predetermined amount of time, and said predetermined period of time is selected to equal twice said amount of time, whereby adjacent runs of white picture elements straddling any single, isolated, black picture element are encoded with opposite polarities and other adjacent runs of white picture elements are encoded with the same polarity.

Claim 13

The limited bandwidth facsimile system with the encoder according to claim 8 wherein said timing means comprises a bistable device for selectively conditioning said bipolar means for operation in said inverting and non-inverting modes; and means coupled to said bistable device for switching said device from one stable state to another each time said baseband signal goes to said one level and again whenever said baseband signal remains at said one level for said predetermined period of time.

Claim 14

The limited bandwidth facsimile system with the encoder according to claim 11 wherein each of said picture elements is allotted a predetermined amount of time, said one and said other levels represent said black and white picture elements, respectively, and said time period is selected to equal twice the amount of time allotted to each picture element, whereby said bipolar means is operated in different ones of said inverting and non-inverting modes for encoding adjacent runs of white picture elements straddling any single, isolated, black picture element.

Claim 15

The limited bandwidth facsimile system with the encoder according to claim 8 wherein said bipolar means comprises an operational amplifier having inverting and non-inverting inputs, said timing means comprises a bistable device having a pair of complementary inputs, and said control means includes first and second coincidence gates having first inputs coupled to different ones of the outputs of said bistable device, and outputs coupled to the inverting and non-inverting inputs, respectively, of said operational amplifier, whereby one of said gates is enabled and the other is disabled whenever said baseband signal goes to said other level, thereby operating said operational amplifier in a selected one of said inverting and non-inverting modes when said baseband signal is at said other level.

Claim 16

The limited bandwidth facsimile system with the encoder according to claim 13 wherein said timing means further includes means for switching said bistable device from one stable state to another, once when said baseband signal goes to said one level and again if said baseband signal remains at said level for said predetermined period of time.

Claim 17

The limited bandwidth facsimile system with the encoder according to claim 14 wherein said one and said other levels represent black And white picture elements, respectively, whereby said operational amplifier operates in different ones of said inverting and non-inverting modes for encoding adjacent runs of white picture elements occurring within said predetermined period of time and in a selected one of said inverting and non-inverting modes for encoding other adjacent runs of white picture elements.

Claim 18

The limited bandwidth facsimile system with the encoder according to claim 14 wherein said means for switching said bistable device includes one-shot multivibrator means for supplying a switching pulse for said bistable device whenever said baseband signal remains at said one level for said predetermined time period.

Claim 19

The limited bandwidth facsimile system with the encoder according to claim 16 wherein each of said picture elements is allotted a predetermined amount of time, said one and said other levels represent white and black picture elements, respectively, and said period of time is selected to equal twice the amount of time allotted to each of the picture elements, whereby said operational amplifier operates in a selected one of said inverting and non-inverting modes for encoding any adjacent runs of white picture elements separated by plural black picture elements and in different ones of said inverting and non-inverting modes for encoding any adjacent runs of white picture elements separated by a single black picture element.

Claim 20

The limited bandwidth facsimile system with the encoder according to claim 17 wherein said multivibrator means comprises a plurality of serially connected one-shot multivibrators having an overall on-time equal to twice the amount of time allotted to each of said picture elements; and further including gate means having one input coupled to receive a version of said baseband signal, another input coupled to receive said switching pulse and an output coupled to said bistable device, whereby the state of said bistable device is reversed each time said baseband signal goes to said one level and whenever said baseband signal remains at said one level for a period equal to twice the amount of time allotted to each picture element.

Claim 23

The method of claim 19 wherein said data signal is a facsimile baseband signal having black and white picture elements represented by said first and second levels, respectively, whereby said encoded signal passes through said mid-level while encoding adjacent runs of black picture elements to thereby aid in recovering any short runs of black picture elements.

Claim 24

The method of claim 20 wherein each of said picture elements is allotted a predetermined period of time, and said predetermined time period is selected to equal twice the amount of time allotted to each picture element, whereby any change of said encoded signal from one of said upper and lower levels to the other uniquely and positively identifies a single, isolated, black picture element.