Nonintegrating lightwave receiver
First Claim
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1. Apparatus (FIGS. 9, 12, 33/40) for amplifying a NRZ digital optical signal having a bit rate B and bandwidth Δ
- f comprising;
a nonintegrating receiver having an input capacitance CT and including;
a photodiode for receiving said signal and converting it to an electrical current is,an input terminal to which said electrical current is applied and an output terminal at which an amplified output voltage vo appears,a voltage amplifier connected between said terminals, said amplifier having a forward voltage gain (-A) with poles therein at a frequencies fai outside Δ
f, anda negative feedback circuit, connected between said terminals, including a current source for generating a feedback current if which is proportional to vo, said current source having a transconductance gf which is of opposite sign to A and comprisinga voltage integrator having its input connected to said output terminal and having a pole in its transfer function at a frequency fi, anda parallel combination of a feedback resistor RF and a feedback capacitance CF connected between said input terminal and the output of said integrator, said combination having a zero in its transfer function at fi so that said transconductance gf is essentially constant with frequency within Δ
f,the output voltage vf of said integrator being related to vo, in the frequency domain, by the relationship vf =avo /(s+2π
fi), the equivalent input conductance ge of said amplifier being given by ge =1/Agf, and for said receiver to be nonintegrating Aa>
2π
CT 0.56B/CF,said feedback circuit in combination with CT producing a feedback voltage gain β
with a feedback pole therein at a frequency ff within Δ
f, and said amplifier and said feedback circuit forming a loop circuit having a loop gain Aβ
, and for stability said feedback circuit pole being the dominant pole in Aβ
versus frequency, anda range extender for preventing the saturation of said receiver at high amplitudes of is includinga variable resistor Rs having one end connected to said input terminal, andan automatic gain control (AGC) circuit responsive to said optical signal for decreasing Rs when is reaches said high amplitudes,said AGC circuit having a threshold below which the output voltage of said amplifier increases with increasing current and above which said output voltage is essentially constant, andsaid variable resistor has a high resistance Rs2 below said threshold and a lower variable resistance Rs1 above said threshold.
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Abstract
A nonintegrating, high sensitivity, wide dynamic range receiver is described. A voltage dependent current source is connected in negative feedback with a forward voltage amplifier. The transconductance of the current source is essentially independent of frequency within the signal bandwidth frequency, and the feedback pole is the dominant pole in the loop gain. To prevent saturation by high intensity input signals the receiver is combined with a range extender circuit.
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Citations
4 Claims
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1. Apparatus (FIGS. 9, 12, 33/40) for amplifying a NRZ digital optical signal having a bit rate B and bandwidth Δ
- f comprising;
a nonintegrating receiver having an input capacitance CT and including; a photodiode for receiving said signal and converting it to an electrical current is, an input terminal to which said electrical current is applied and an output terminal at which an amplified output voltage vo appears, a voltage amplifier connected between said terminals, said amplifier having a forward voltage gain (-A) with poles therein at a frequencies fai outside Δ
f, anda negative feedback circuit, connected between said terminals, including a current source for generating a feedback current if which is proportional to vo, said current source having a transconductance gf which is of opposite sign to A and comprising a voltage integrator having its input connected to said output terminal and having a pole in its transfer function at a frequency fi, and a parallel combination of a feedback resistor RF and a feedback capacitance CF connected between said input terminal and the output of said integrator, said combination having a zero in its transfer function at fi so that said transconductance gf is essentially constant with frequency within Δ
f,the output voltage vf of said integrator being related to vo, in the frequency domain, by the relationship vf =avo /(s+2π
fi), the equivalent input conductance ge of said amplifier being given by ge =1/Agf, and for said receiver to be nonintegrating Aa>
2π
CT 0.56B/CF,said feedback circuit in combination with CT producing a feedback voltage gain β
with a feedback pole therein at a frequency ff within Δ
f, and said amplifier and said feedback circuit forming a loop circuit having a loop gain Aβ
, and for stability said feedback circuit pole being the dominant pole in Aβ
versus frequency, anda range extender for preventing the saturation of said receiver at high amplitudes of is including a variable resistor Rs having one end connected to said input terminal, and an automatic gain control (AGC) circuit responsive to said optical signal for decreasing Rs when is reaches said high amplitudes, said AGC circuit having a threshold below which the output voltage of said amplifier increases with increasing current and above which said output voltage is essentially constant, and said variable resistor has a high resistance Rs2 below said threshold and a lower variable resistance Rs1 above said threshold. - View Dependent Claims (2)
- f comprising;
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3. Apparatus (FIGS. 9, 16, 33-40) for amplifying a NRZ digital optical signal having a bit rate B and bandwidth Δ
- f comprising;
a nonintegrating receiver having an input capacitance CT including a photodiode for receiving said signal and converting it to an electrical current is, an input terminal to which said electrical current is applied and an output terminal at which an amplified output voltage vo appears, a voltage amplifier connected between said terminals, said amplifier having a forward voltage gain (-A) with poles therein at a frequencies fp outside Δ
f, anda negative feedback circuit, connected between said terminals, including a current source for generating a feedback current if which is proportional to vo and which is subtracted from is at said input terminal, the transconductance gf of said current source being essentially independent of frequency within Δ
f and of opposite sign to A,said current source comprising a field effect transistor QF having a source and drain, a channel coupling said source to said drain, and a gate for controlling the flow of current from said source to said drain through said channel, said source and drain being connected between said input and output terminals, and including means for biasing QF into the linear region of its current-voltage characteristic, said transistor having a source-to-drain conductance gsd and capacitance Csd where, for said receiver to be nonintegrating,
space="preserve" listing-type="equation">A≧
2π
C.sub.T 0.56B/g.sub.sdand
space="preserve" listing-type="equation">C.sub.sd ≦
g.sub.sd /2π
Bsaid feedback circuit in combination with CT producing a feedback voltage gain β
with a feedback pole therein a frequency ff within Δ
f, and said amplifier and said feedback circuit forming a loop circuit having a loop gain Aβ
, and for stability said feedback circuit pole being the dominant pole in Aβ
versus frequency,a range extender for preventing the saturation of said receiver at high amplitudes of is including a variable resistor Rs having one end connected to said input terminal, and an automatic gain control (AGC) circuit responsive to said optical signal for decreasing Rs when is reaches said high amplitudes, said amplifier having an equivalent input resistance Re =1/ge, said AGC circuit having a threshold below which the output voltage of said amplifier increases with increasing current and above which said output voltage is essentially constant, and said variable resistor has a high resistance Rs2 below said threshold and a lower variable resistance Rs1 above said threshold. - View Dependent Claims (4)
- f comprising;
Specification
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Current AssigneeAT&T, Inc.
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Original AssigneeAT&T, Inc.
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InventorsWilliams, Gareth F.
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Primary Examiner(s)NOT, DEFINED
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Assistant Examiner(s)Wan, G.
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Application NumberUS06/718,712Time in Patent Office337 DaysField of Search330/59, 330/278, 330/279, 330/282, 330/284, 455/619, 250/214 AGUS Class Current330/59CPC Class CodesH03F 1/083 in transistor amplifiers H0...H03F 3/087 with IC amplifier blocks H0...H04B 10/6931 Automatic gain control of t...
