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Nonintegrating lightwave receiver

  • US 4,574,249 A
  • Filed: 04/01/1985
  • Issued: 03/04/1986
  • Est. Priority Date: 09/08/1981
  • Status: Expired due to Fees
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>



    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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