Facsimile system with selective contrast control

Claim 2

In a facsimile transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from said document, an improved transmitter comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a nonlinear feedback circuit coupled therebetween; c. means coupling said input circuit of said Schmitt trigger to said input terminals; d. at least one varistor coupled to said feedback circuit to improve the character of said electrical signals; e. and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission.

Claim 3

The improved transmitter of claim 1, and further comprising a resistor coupled in series between said Schmitt trigger input circuit and said input terminals, and a selectively operable switch for short-circuiting said resistor.

Claim 4

The improved transmitter of claim 1, and further comprising clamping circuit means coupled to said output circuit of said Schmitt trigger circuit for limiting the direct-current voltage variation of said Schmitt trigger output.

Claim 5

The improved transmitter of claim 1, and further comprising a clamping circuit coupled to said output circuit of said Schmitt trigger for limiting the direct-current voltage variation thereof, and a serially connected resistor and diode rectifier coupled between said input circuit of said Schmitt trigger and a point of reference potential.

Claim 6

The transmitter of claim 1 further comprising means for selectively increasing the gain of said Schmitt triggeR circuit as the input increases.

Claim 7

The transmitter of claim 5 wherein the means for increasing comprises a parallel resistor varistor combination connected between the emitters of said first and second electron current devices.

Claim 8

The transmitter of claim 1 further comprising means for selectively decreasing the gain of said Schmitt trigger circuit as the input level increases.

Claim 9

The transmitter of claim 7 wherein the means for decreasing comprises a resistor and series varistor coupled between the input of said first electron current device and a point of reference potential.

Claim 10

The improved transmitter of claim 8, and further comprising a resistor coupled between said input of said Schmitt trigger and said input terminals, and a selectively operable switch connected in parallel with said resistor for selectively short-circuiting said resistor.

Claim 11

In a facsimile transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from said document, an improved transmitter comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a feedback circuit coupled therebetween; c. means coupling said input circuit of said Schmitt trigger to said input terminals comprising a resistor and a selectively operable switch in parallel with said resistor for selectively short-circuiting said resistor; d. and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission.

Claim 12

In a facsimile transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from said document, an improved transmitter comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a feedback circuit coupled therebetween; c. means coupling said input circuit of said Schmitt trigger to said input terminals comprising a resistor and a selectively operable switch in parallel with said resistor for selectively short-circuiting said resistor; d. and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission.

Claim 13

In a facsimile receiver having means for receiving electrical signals and producing an output on a document indicative of the information scanned from a document at a remote location, an improved receiver comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. an amplifier circuit having an input coupled to said input terminals and having an output adapted to be coupled to a transducer that converts electrical signals into information on a document; c. and a feedback circuit comprising a series resistor and varistor coupled to increase the gain of the amplifier as the input level increases.

Claim 14

In a facsimile receiver having means for receiving electrical signals and producing an output on a document indicative of the information scanned from a document at a remote location, an improved receiver comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. an amplifier circuit having an input coupled to said input terminals and having an output adapted to be coupled to a transducer that converts electrical signals into information on a document; c. and a feedback circuit comprising a series resistor and varistor coupled to increase the gain of the amplifier as the input level increases.

Claim 15

The improved resistor of claim 11, and further comprising a threshold circuit having current limiting devices and a varistor coupled to said feedback circuit.

Claim 16

The improved receiver of claim 11, and further comprising a voltage divider potentiometer connected to one current control device of said amplifier.

Claim 17

The improved receiver of claim 11, and further comprising an adjustable resistor connected in series between the output and input of two adjacent current control devices of said amplifier.

Claim 18

The improved receiver of claim 11, and further comprising current limiting devices and a varistor coupled to said feedback circuit to provide threshold control, and a voltage divider potentiometer coupled to one electron current control device of said amplifier to provide background control.

Claim 19

The improved receiver of claim 11, and further comprising current limiting devices and a varistor coupled to said feedback circuit to provide threshold control, and an adjustable resistor coupled in series between the output and input of two adjacent current control devices of said amplifier to provide saturation control.

Claim 20

The improved receiver of claim 11, and further comprising a voltage divider potentiometer coupled to one electron current control device of said amplifier to provide background control, and an adjustable resistor coupled in series between the output and input of two adjacent current control devices of said amplifier to provide saturation control.

Claim 21

The improved receiver of claim 11, and furthEr comprising current limiting devices and a varistor coupled to said feedback circuit to provide threshold control, a voltage divider potentiometer coupled to one electron current control device of said amplifier to provide background control, and an adjustable resistor coupled in series between the output and input of two adjacent electron current control devices of said amplifier to provide saturation control.

Claim 22

A facsimile transmission system comprising: a transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned, said transmitter comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a nonlinear feedback circuit coupled therebetween; c. means coupling said input circuit of said Schmitt trigger to said input terminals; d. at least one rectifier device coupled to said feedback circuit to improve the character of said electrical signals; e. and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission; f. and a receiver having means for receiving electrical signals and producing an output on a document indicative of the information scanned by the transmitter, said receiver comprising; g. input terminals for receiving electrical signals indicative of the information scanned from a document; h. an amplifier circuit having an input coupled to said input terminals and having an output adapted to be coupled to a transducer that converts electrical signals into information on a document; i. and a feedback circuit comprising a series resistor and rectifier device coupled to increase the gain of the amplifier as the input level increases.

Claim 23

A facsimile transmission system comprising: a transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned, said transmitter comprising: a. input terminals for receiving electrical signals indicative of the information scanned from a document; b. a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a nonlinear feedback circuit coupled therebetween; c. means coupling said input circuit of said Schmitt trigger to said input terminals; d. at least one rectifier device coupled to said feedback circuit to improve the character of said electrical signals; e. and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission; f. and a receiver having means for receiving electrical signals and producing an output on a document indicative of the information scanned by the transmitter, said receiver comprising; g. input terminals for receiving electrical signals indicative of the information scanned from a document; h. an amplifier circuit having an input coupled to said input terminals and having an output adapted to be coupled to a transducer that converts electrical signals into information on a document; i. and a feedback circuit comprising a series resistor and rectifier device coupled to increase the gain of the amplifier as the input level increases.

Claim 26

A facsimile transmitter comprising: a. scanning means for optically scanning an information bearing document; b. first transducer means for converting light energy into electrical signals representative of said information; c. analog signal processing means responsive to said electrical signals and operable in a first mode to nonlinearly amplify said electrical signals in a first manner and operable in a second mode to nonlinearly amplify said electrical signals in a second manner whereby said first and second manners yield output signals which are identical for both maximum and minimum values of said electrical signals and nonidentical output signals for all values intermediate said maximum and said minimum values; and d. second transducer means responsive to said amplified electrical signals to produce energy signals representative of said information.

Claim 27

A facsimile transmitter comprising: a. scanning means for optically scanning an information bearing document; b. first transducer means for converting light energy into electrical signals representative of said information; c. analog signal processing means responsive to said electrical signals and operable in a first mode to nonlinearly amplify said electrical signals in a first manner and operable in a second mode to nonlinearly amplify said electrical signals in a second manner whereby said first and second manners yield output signals which are identical for both maximum and minimum values of said electrical signals and nonidentical output signals for all values intermediate said maximum and said minimum values; and d. second transducer means responsive to said amplified electrical signals to produce energy signals representative of said information.

Claim 28

The facsimile transmitter of claim 21 further comprising clamping means for limiting the magnitude of said amplified signals.

Claim 29

In a facsimile transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from said document an improved transmitter comprising: input terminals for receiving electrical signals indicative of the informatiOn scanned from a document; a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a nonlinear feedback circuit coupled therebetween to provide analog output signals in response to analog input signals; means coupling said input circuit of said Schmitt trigger circuit to said input terminals; and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission.

Claim 30

In a facsimile transmitter having means for scanning a document to be transmitted and producing electrical signals indicative of the information scanned from said document an improved transmitter comprising: input terminals for receiving electrical signals indicative of the informatiOn scanned from a document; a Schmitt triggerlike circuit having first and second electron current devices coupled together between an input circuit and an output circuit, said devices having a nonlinear feedback circuit coupled therebetween to provide analog output signals in response to analog input signals; means coupling said input circuit of said Schmitt trigger circuit to said input terminals; and means coupled to said output circuit and adapted to be coupled to a voltage controlled oscillator for applying said signals thereto for transmission.

Claim 31

The transmitter of claim 23 further comprising means to alter the sensitivity of said Schmitt triggerlike circuit.