Signal transmission circuit with improved digital signal recovery

Claim 2

A digital signal transmission circuit capable of restoring high frequency signals degraded during transmission comprising: signal transmitting means whose response to high frequency signals is characterized by a transfer function KH(t), and a -3 db corner frequency of 1/(2πRC); input means for supplying a digital input signal to said signal transmitting means; a digitizing circuit adapted to receive an input signal of variable amplitude, and to produce a digital output signal having first and second values in response to input signal values respectively less than and greater than a digitizing threshold; summing means connecting said signal transmitting means and said digitizing circuit, said summing means being operable to combine a signal supplied by said signal transmitting means and a feedback signal; a feedback circuit having a transfer function kH(t) proportional to transfer function KH(t), said feedback circuit comprising a resistor and a first capacitor connected in series between the output of said digitizing circuit and ground; and coupling means comprising a voltage divider having a first terminal connected to the junction between the resistor and the first capacitor in said summing means, a second terminal connected to ground and a variable voltage terminal connected to said summing means through a second capacitor.

Claim 3

The digital signal transmission circuit of claim 1 wherein said signal transmitting means comprises: a fiber-optic element; a light emitting diode for supplying an optical signal corresponding to the digital input signal to said fiber-optic element; and means for receiving the optical signal from said fiber-optic element and producing a corresponding electrical signal.

Claim 4

In a digital signal transmission circuit including signal transmitting means having a limited high frequency response characterized by a -3 db corner frequency of 1/(2πRC), as a result of which high frequency signals are degraded during transmission, and further including digitizing means for producing a digital output signal having first and second values in response to input signal amplitudes respectively less than and greater than a digitizing threshold, improved signal restoring means comprising: a feedback circuit having a high frequency response substantially identical to the high frequency response of said signal transmitting means, said feedback circuit comprising a resistor of resistance R and a first capacitor of capacitance C connected in series between the output signal terminal of said digitizing means and ground, a voltage divider connected to the junction between said resistor and said first capacitor, and a second capacitor connected between a variable voltage terminal on said voltage divider and said summing means means for supplying the digital output signal to said feedback means so that said feedback means produces a feedback signal in the form of an inverted replica of the degraded signal transmitted by said signal transmitting means; summing means for combining the feedback and degraded signals to form a difference signal; and means for supplying the difference signal as the input signal to said digitizing means.

Claim 5

In a digital signal transmission circuit including signal transmitting means having a limited high frequency response characterized by a -3 db corner frequency of 1/(2πRC), as a result of which high frequency signals are degraded during transmission, and further including digitizing means for producing a digital output signal having first and second values in response to input signal amplitudes respectively less than and greater than a digitizing threshold, improved signal restoring means comprising: a feedback circuit having a high frequency response substantially identical to the high frequency response of said signal transmitting means, said feedback circuit comprising a resistor of resistance R and a first capacitor of capacitance C connected in series between the output signal terminal of said digitizing means and ground, a voltage divider connected to the junction between said resistor and said first capacitor, and a second capacitor connected between a variable voltage terminal on said voltage divider and said summing means means for supplying the digital output signal to said feedback means so that said feedback means produces a feedback signal in the form of an inverted replica of the degraded signal transmitted by said signal transmitting means; summing means for combining the feedback and degraded signals to form a difference signal; and means for supplying the difference signal as the input signal to said digitizing means.

Claim 6

A digital signal transmission circuit with feedback means for achieving enhanced high frequency performance comprising: input means for supplying a digital input signal; signal transmission means connected to receive the digital input signal, said signal transmission means comprising a fiber-optic element, a light emitting diode for supplying an optical signal corresponding to the digital input signal to said fiber-optic element, and a photodetector device for receiving the optical signal from said fiber-optic element and producing a corresponding electrical output signal, the frequency response characteristics of said signal transmission means being such that the output signal is a degenerate form of the digital input signal; digitizing means responsive to a variable amplitude input signal for producing a digital output signal having first or second values if the amplitude of the input signal is respectively less than or greater than a digitizing threshold; summing means connecting said signal transmission means to said digitizing means; feedback means having frequency response characteristics substantially identical to the frequency response characteristics of said signal transmission means; means for supplying the digital output signal to said feedback means, whereby said feedback means produces a feedback signal which is a delayed inverted replica of the output signal of said signal transmission means; and means for connecting said feedback means to said summing means so that said summing means supplies a signal to said digitizing means representative of the combined feedback signal and the output signal of said signal transmission means.

Claim 7

A digital signal transmission circuit with feedback means for achieving enhanced high frequency performance comprising: input means for supplying a digital input signal; signal transmission means connected to receive the digital input signal, said signal transmission means comprising a fiber-optic element, a light emitting diode for supplying an optical signal corresponding to the digital input signal to said fiber-optic element, and a photodetector device for receiving the optical signal from said fiber-optic element and producing a corresponding electrical output signal, the frequency response characteristics of said signal transmission means being such that the output signal is a degenerate form of the digital input signal; digitizing means responsive to a variable amplitude input signal for producing a digital output signal having first or second values if the amplitude of the input signal is respectively less than or greater than a digitizing threshold; summing means connecting said signal transmission means to said digitizing means; feedback means having frequency response characteristics substantially identical to the frequency response characteristics of said signal transmission means; means for supplying the digital output signal to said feedback means, whereby said feedback means produces a feedback signal which is a delayed inverted replica of the output signal of said signal transmission means; and means for connecting said feedback means to said summing means so that said summing means supplies a signal to said digitizing means representative of the combined feedback signal and the output signal of said signal transmission means.