Abstract:
An impedance matching broadband optical receiver circuit including an input terminal adapted to receive an input information bearing signal, extending over a broad input frequency band, and a plurality of output terminals operative to provide, in response to receipt of the input information bearing signal, respective outputs in generally non-overlapping frequency bands, plural ones of the outputs presenting different characteristic impedances to the input.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to broadband optical receivers generally and more particularly to impedance matching circuitry useful in broadband optical receivers.  
       BACKGROUND OF THE INVENTION  
       [0002]     The following U.S. patents are believed to represent the current state of the art:  
         [0003]     U.S. Pat. Nos. 5,179,461; 5,477,370; 5,347,388; 5,517,035; 5,013,903; 5,095,286 and 5,845,302.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention seeks to provide an improved impedance matching broadband optical receiver circuit.  
         [0005]     There is thus provided in accordance with a preferred embodiment of the present invention an impedance matching broadband optical receiver circuit including an input terminal adapted to receive an input information bearing signal, extending over a broad input frequency band, and a plurality of output terminals operative to provide, in response to receipt of the input information bearing signal, respective outputs in generally non-overlapping frequency bands, plural ones of the outputs presenting different characteristic impedances to the input.  
         [0006]     Preferably, the outputs in generally non-overlapping frequency bands are substantially non-overlapping at their peak input impedances.  
         [0007]     Preferably, the impedance matching broadband optical receiver circuit also includes a photodiode having an output which is coupled to the input terminal. Additionally or alternatively, the impedance matching broadband optical receiver circuit also includes a multiplexer combining the respective outputs.  
         [0008]     Preferably, the respective outputs include a CATV (50-862 MHz) output.  
         [0009]     Preferably, the impedance matching broadband optical receiver circuit also includes a high-pass network coupled to the input terminal. Preferably, the impedance matching broadband optical receiver circuit also includes at least one band-pass network coupled to the input terminal. Preferably, the impedance matching broadband optical receiver circuit also includes a low-pass network coupled to the input terminal.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0011]      FIG. 1  is a simplified block diagram illustration of an impedance matching broadband optical receiver circuit constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0012]      FIG. 2  is a simplified diagram illustrating the frequency distribution of each of a plurality of different impedances provided by the circuitry of  FIG. 1 ;  
         [0013]      FIGS. 3A and 3B  are simplified partially block diagram illustrations of two alternative embodiments of the circuitry of  FIG. 1 ; and  
         [0014]      FIG. 4  is a partially block diagram, partially schematic illustration of a preferred embodiment of the circuitry of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     Reference is now made to  FIGS. 1 and 2 , which show an impedance matching broadband optical receiver circuit constructed and operative in accordance with a preferred embodiment of the present invention and a preferred frequency distribution of each of a plurality of different impedances provided by the circuitry of  FIG. 1 . As seen in  FIG. 1 , a broadband input, preferably from a photodiode  100 , is received by the circuitry of the present invention, designated by reference numeral  102 , which provides a plurality of outputs O 1  . . . O N , each of which presents a different characteristic impedance to the input, the different impedances being designated as Z in1  . . . Z inN .  
         [0016]     In accordance with a preferred embodiment of the present invention, the plurality of outputs O 1  . . . O N  may be combined into a single output, preferably on a coaxial cable  104 , by a conventional multiplexer  106 .  
         [0017]      FIG. 2  illustrates a preferred frequency distribution of the outputs O 1  . . . O N , wherein it is seen that although the frequency curves partially overlap, the frequencies of the various outputs O 1  . . . O N  are distinct and non-overlapping at their respective peak input impedances.  
         [0018]     Reference is now made to  FIGS. 3A and 3B , which are simplified partially block diagram illustrations of two alternative embodiments of the circuitry  102  of  FIG. 1 . In the embodiment of  FIG. 3A , the output of a photodiode  300  is fed in parallel to a series combination of an inductor  302  and a low-pass filter  304 , providing a first output O 1 ; to at least one broadband transformer  306  including a capacitive filter  308 , providing at least one additional output O 2 ; and to a series combination of a capacitor  310  and a high-pass filter  312 , providing at least one additional output O 3 .  
         [0019]     In the embodiment of  FIG. 3B , the output of photodiode  300  is fed in parallel to a series combination of an inductor  322  and a low-pass filter  324 , providing a first output O 1 ; to at least one broadband transformer  326  including a capacitive filter  328 , providing at least one additional output O 2 ; preferably to a series combination of a capacitor  330  and a high-pass filter  332 , providing an additional output O N  and to at least one band-pass filter  334  providing at least one additional output O M . It is appreciated that by providing multiple band-pass filters defining different pass bands, in parallel to band-pass filter  334 , multiple outputs each having a different input impedance may be provided.  
         [0020]     Reference is now made to  FIG. 4 , which is a partially block diagram, partially schematic, illustration of a preferred embodiment of the circuitry of  FIG. 1 . As seen in  FIG. 4 , the output of photodiode  300  is coupled in parallel to a low-pass network  402 , a high-pass network  404  and a band-pass network  406 .  
         [0021]     The low-pass network  402  preferably is DC biased via a resistor  410  and outputs a signal of frequency preferably between 0.1 and 50 MHz preferably via a low-pass filter  412  connected at a junction of resistor  410  and an inductor  414 . The low-pass network  402  is operative to present a relatively high impedance, typically at least 2000 Ohms, to photodiode  300 .  
         [0022]     The high-pass network  404  preferably includes a capacitor and inductor network which presents a relatively low impedance, typically below 100 Ohms, to photodiode  300 .  
         [0023]     The band-pass network  406 , of which there may be multiple such networks having different pass bands, preferably includes a series inductor  420  connected to a broadband transformer  422 , including a capacitive filter  424 , and a band shaping grounded capacitor  426 . Band-pass network  406  presents an intermediate impedance, typically between 200 and 1000 Ohms, to photodiode  300 .  
         [0024]     The low-pass network  402  preferably outputs to a low frequency amplifier  430 , which provides an output in the 0.1-50 MHz frequency range.  
         [0025]     The high-pass network  404  preferably outputs to a DBS amplifier  432  which provides an output in the 950-2150 MHz range.  
         [0026]     The band-pass network  406  outputs via a DC blocking capacitor  434  to a CATV amplifier  436  which provides an output in the 50-860 MHz range.  
         [0027]     The outputs of the low-pass, high-pass and band-pass networks may be, but need not necessarily be, combined by a multiplexer  440  preferably including multiple capacitor and inductor networks.  
         [0028]     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove as well as modifications thereof which would occur to a person of ordinary skill in the art upon reading the foregoing description, and which are not in the prior art.