Patent Publication Number: US-9838116-B2

Title: Detecting presence of active optical cables in peripheral component interconnect-express links

Description:
FIELD 
     Some embodiments described herein generally relate to detecting presence of an active optical cable (AOC) in a peripheral component interconnect-express (PCIe) link, and more generally to detecting presence of an apparatus with a specific input terminating impedance. 
     BACKGROUND 
     Unless otherwise indicated herein, the materials described herein are not prior art to the claims in the present application and are not admitted to be prior art by inclusion in this section. 
     A PCIe receiver in a PCIe link may include input stage terminals with resistors (e.g., 50-ohm resistors) referenced to a ground level. The input stage terminals with the resistors may be used for detecting presence of the PCIe receiver. When an AOC is applied in the PCIe link, an electrical-to-optical PCIe (OE-PCIe) transceiver of the AOC may not include an input stage terminal with a resistor referenced to the ground level for detection of the OE-PCIe transceiver. 
     The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. 
     BRIEF SUMMARY OF SOME EXAMPLE EMBODIMENTS 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Some example embodiments described herein generally relate to detecting presence of an AOC in a PCIe link and/or to detecting presence of an apparatus with a specific input terminating impedance. 
     In an example embodiment, a PCIe link may include an AOC that includes an electrical-to-optical PCIe (EO-PCIe) transceiver coupled to an electrical PCIe (E-PCIe) transmitter. The EO-PCIe transceiver may include a laser diode driver that includes a common mode voltage output terminal. The laser diode driver may include waveshapping, clock and data recovery (CDR), or other link circuits. The EO-PCIe transceiver may include a detection condition circuit that includes a decoupling capacitor. The decoupling capacitor may be referenced to a ground level and may connect to the common mode voltage output terminal of the laser diode driver. The detection condition circuit may create a receiver detection condition for a receiver detection circuit of the E-PCIe transmitter to detect presence of the AOC. 
     In another example embodiment, a PCIe link may include a first alternating current (AC) coupling capacitor that couples to a first output terminal of an E-PCIe transmitter. The PCIe link may include a second AC coupling capacitor that couples to a second output terminal of the E-PCIe transmitter. The PCIe link may include an AOC that includes an electrical-to-optical PCIe (EO-PCIe) transceiver that includes a laser diode driver. The laser diode driver may include a first input terminal that couples to the first output terminal of the E-PCIe transmitter via the first AC coupling capacitor. The laser diode driver may include a second input terminal that couples to the second output terminal of the E-PCIe transmitter via the second AC coupling capacitor. The EO-PCIe transceiver may include a detection condition circuit. The detection condition circuit may include a first direct current (DC) blocking capacitor that couples between the first AC coupling capacitor and the first input terminal of the laser diode driver. The detection condition circuit may also include a first inductive impedance that may be referenced to a ground level and may connect to a point in a first signal route between the first AC coupling capacitor and the first DC blocking capacitor. The detection condition circuit may also include a second DC blocking capacitor that couples between the second AC coupling capacitor and the second input terminal of the laser diode driver. The detection condition circuit may also include a second inductive impedance that may be referenced to the ground level and may connect to a point in a second signal route between the second AC coupling capacitor and the second DC blocking capacitor. A first combination of the first inductive impedance and the first DC blocking capacitor and a second combination of the second inductive impedance and the second DC blocking capacitor may each create a receiver detection condition for a receiver detection circuit of the E-PCIe transmitter to detect presence of the AOC. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a schematic diagram that illustrates an example PCIe link; 
         FIG. 2  is a schematic diagram that illustrates an example configuration of an AOC applied in a PCIe link; 
         FIG. 3  is a schematic diagram that illustrates an example implementation of an electrical-to-optical PCIe (EO-PCIe) transceiver in the AOC of  FIG. 2 ; 
         FIG. 4  is a schematic diagram that illustrates another example implementation of the EO-PCIe transceiver in the AOC of  FIG. 2 ; and 
         FIGS. 5A and 5B  are schematic diagrams that illustrate various example inductive impedances implemented in a detection condition circuit. 
     
    
    
     DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS 
     Embodiments described herein generally relate to detecting presence of an AOC applied in a PCIe link. 
     In some embodiments, an EO-PCIe transceiver of an AOC in a PCIe link may include a common mode voltage output terminal. A detection condition circuit, which may include a decoupling capacitor, may be referenced to a ground level and may connect to the common mode voltage output terminal of the EO-PCIe transceiver. The detection condition circuit may create a receiver detection condition for detecting presence of the AOC and/or the EO-PCIe transceiver of the AOC. The receiver detection condition may include a formation of an equivalent terminal referenced to the ground level with a single-end direct current (DC) impedance. For example, a laser diode driver of the EO-PCIe transceiver may include a differential input impedance of about 100 ohms, and the decoupling capacitor may enable a formation of an equivalent terminal referenced to the ground level with a single-end DC impedance of about 50 ohms. 
     Alternatively, the EO-PCIe transceiver of the AOC in the PCIe link may not include a common mode voltage output terminal. A detection condition circuit, which may include DC blocking capacitors and inductive impedances, may create a receiver detection condition for detecting presence of the AOC and/or the EO-PCIe transceiver of the AOC. The receiver detection condition may include a formation of an equivalent terminal referenced to the ground level with a single-end DC impedance. In some embodiments, each inductive impedance may include a series connection of an inductor and a resistor. Alternatively, each inductive impedance may include a first resistor, a second resistor, and an inductor, where the first resistor and the inductor may be coupled using a parallel connection, and the second resistor may be coupled to the parallel connection of the first resistor and the inductor using a series connection. 
     In some embodiments, the AOC may be configured for a form factor including, but not limited to, small form-factor pluggable (SFP), quad small form-factor pluggable (QSFP), 12× small form-factor pluggable (CXP), and/or another suitable form factor. 
     Reference will now be made to the drawings to describe various aspects of some example embodiments of the invention. The drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale. 
       FIG. 1  is a schematic diagram that illustrates an example PCIe link  100 , arranged in accordance with at least some embodiments described herein. The PCIe link  100  may include an electrical PCIe (E-PCIe) transmitter  102 , an E-PCIe receiver  104 , alternating current (AC) capacitors  114  and  116 , PCIe link media  118  and  120 , and other suitable components. In some embodiments, each of the E-PCIe receiver  102  and the E-PCIe transmitter  104  may include an E-PCIe transceiver. 
     The E-PCIe transmitter  102  may include a receiver detection circuit  106 , an amplifier  108 , resistors  110  and  112 , input terminals  101  and  103 , output terminals  105  and  107 , and/or other suitable components. Signals may be inputted to the amplifier  108  through the input terminals  101  and  103 . The amplifier  108  may output signals to the AC coupling capacitors  114  and  116  through the output terminals  105  and  107 . 
     The E-PCIe receiver  104  may include single-end direct current (DC) impedances  124  and  126  referenced to a ground level, an amplifier  122 , and other suitable components. In some embodiments, the DC impedances  124  and  126  may include resistors each with a value of 50 ohms or another suitable value. The E-PCIe receiver  104  may establish a receiver presence detection condition for the receiver detection circuit  106  by including the DC impedances  124  and  126  referenced to the ground level, so that the receiver detection circuit  106  may detect presence of the E-PCIe receiver  104 . 
     For example, the receiver detection circuit  106  may detect presence of the E-PCIe receiver  104  by measuring at the output terminal  105  a voltage changing rate of a resistor-capacitor (RC) circuit, where the RC circuit may be formed by the AC coupling capacitor  114  and the DC impedance  124 . The voltage changing rate at the output terminal  105  may be illustrated by: 
                         d   ⁢           ⁢     V   105         d   ⁢           ⁢   t       =       -       V   0         R   124     ⁢     C   114           ⁢     e     -     t       R   124     ⁢     C   114                 ,           (   1   )               
where V 105  may represent a voltage at the output terminal  105 , V 0  may represent a pulse voltage amplitude of the receiver detection circuit  106 , R 124  may represent a resistance value of the DC impedance  124 , and C 114  may represent a capacitance value of the AC coupling capacitor  114 .
 
     Alternatively or additionally, the receiver detection circuit  106  may detect presence of the E-PCIe receiver  104  by measuring at the output terminal  107  a voltage changing rate of a RC circuit, where the RC circuit may be formed by the AC coupling capacitor  116  and the DC impedance  126 . The voltage changing rate at the output terminal  107  may be illustrated by: 
                         d   ⁢           ⁢     V   107         d   ⁢           ⁢   t       =       -       V   0         R   126     ⁢     C   116           ⁢     e     -     t       R   126     ⁢     C   116                 ,           (   2   )               
where V 107  may represent a voltage at the output terminal  107 , R 126  may represent a resistance value of the DC impedance  126 , and C 116  may represent a capacitance value of the AC coupling capacitor  116 .
 
       FIG. 2  is a schematic diagram that illustrates an example AOC  202  applied in a PCIe link  200 , arranged in accordance with at least some embodiments described herein. The PCIe link  200  may include components similar or identical to those of the PCIe link  100  of  FIG. 1 . Description for the similar or identical components will not be repeated here. 
     The AOC  202  may be coupled to the E-PCIe transmitter  102  via the AC coupling capacitors  114  and  116 . The AOC  202  may also be coupled to the E-PCIe receiver  104 . The AOC  202  may include an electrical-to-optical PCIe (EO-PCIe) transceiver  204 , an optical-to-electrical (OE-PCIe) transceiver  208 , and an optical cable  206 . The optical cable  206  may couple between the EO-PCIe transceiver  204  and the OE-PCIe transceiver  208 . In some embodiments, the optical cable  206  may include a single optical fiber or a ribbon optical fiber cable. The EO-PCIe transceiver  204  may be coupled to the E-PCIe transmitter  102  through the AC coupling capacitors  114  and  116  and may be considered a PCIe receiver with respect to the E-PCIe transmitter  102 . The OE-PCIe transceiver  208  may be coupled to the E-PCIe receiver  104  and may be considered a PCIe transmitter with respect to the E-PCIe receiver  104 . 
       FIG. 3  is a schematic diagram that illustrates an example implementation  300  of the EO-PCIe transceiver  204  of  FIG. 2 , arranged in accordance with at least some embodiments described herein. The EO-PCIe transceiver  204  may include a laser diode driver  302 , a laser diode  328 , a detection condition circuit that includes a decoupling capacitor  310 , and/or other suitable components. 
     The laser diode driver  302  may include input terminals  306  and  308 ; a common mode voltage output terminal  304 ; resistors  312 ,  314 , and  318 ; a common mode voltage  316 ; amplifiers  320  and  324 ; a feedback control circuit  322 ; a communication circuit  326 ; and/or other suitable components. The input terminal  306  of the laser diode driver  302  may be coupled to the output terminal  105  of the E-PCIe transmitter  102  through the AC coupling capacitor  114 . The input terminal  308  of the laser diode driver  302  may be coupled to the output terminal  107  of the E-PCIe transmitter  102  through the AC coupling capacitor  116 . The resistors  312  and  314  may each have a resistance value of 50 ohms or another suitable value. The laser diode driver  302  may include a differential input impedance of about 100 ohms or another suitable value. 
     The decoupling capacitor  310  may be connected to the common mode voltage output terminal  304  and referenced to a ground level. Even though the EO-PCIe transceiver  204  does not actually include a single-end DC impedance of 50 ohms referenced to the ground level, the EO-PCIe transceiver  204  includes the decoupling capacitor  310  connected to the common mode voltage output terminal  304 . Thus, a receiver detection condition may be created for the receiver detection circuit  106  of the E-PCIe transmitter  102  to detect presence of the EO-PCIe transceiver  204 . 
     For example, with reference to  FIG. 3 , a voltage changing rate at the output terminal  105  may be illustrated by: 
                         d   ⁢           ⁢     V   105         d   ⁢           ⁢   t       =       -       V   0         R   312     ⁢     C   ^           ⁢     e     -     t       R   312     ⁢     C   ^                 ,           (   3   )                   C   ^     =       C   114       1   +       C   114       0.5   ⁢     C   310               ,           (   4   )               
where R 312  may represent a resistance value of the resistor  312 , and C 310  may represent a capacitance value of the decoupling capacitor  310 . If 0.5C 310 &gt;&gt;C 114  and R 312 =R 124 , then Ĉ≈C 114  and equation (3) may be similar or identical to equation (1). Thus, an equivalent RC circuit similar to that formed by the DC impedance  124  and the AC coupling capacitor  114  of  FIG. 1  may be formed in the example of  FIG. 3 . The receiver detection circuit  106  of the E-PCIe transmitter  102  may detect presence of the EO-PCIe transceiver  204  by measuring the voltage changing rate at the output terminal  105 .
 
     Alternatively or additionally, a voltage changing rate at the output terminal  107  may be illustrated by: 
                         d   ⁢           ⁢     V   107         d   ⁢           ⁢   t       =       -       V   0         R   314     ⁢     C   ^           ⁢     e     -     t       R   314     ⁢     C   ^                 ,           (   5   )                   C   ^     =       C   116       1   +       C   116       0.5   ⁢     C   310               ,           (   6   )               
where R 314  may represent a resistance value of the resistor  314 . If 0.5C 310 &gt;&gt;C 116  and R 314 =R 126 , then Ĉ≈C 116  and equation (5) may be similar or identical to equation (2). Thus, an equivalent RC circuit similar to that formed by the DC impedance  126  and the AC coupling capacitor  116  of  FIG. 1  may be formed in the example of  FIG. 3 . The receiver detection circuit  106  of the E-PCIe transmitter  102  may detect presence of the EO-PCIe transceiver  204  by measuring the voltage changing rate at the output terminal  107 .
 
       FIG. 4  is a schematic diagram that illustrates another example implementation  400  of the EO-PCIe transceiver  204  of  FIG. 2 , arranged in accordance with at least some embodiments described herein. The EO-PCIe transceiver  204  may include a laser diode driver  402 , the laser diode  328 , and/or other suitable components. 
     The laser diode driver  402  may include the input terminals  306  and  308 ; the resistors  312 ,  314 , and  318 ; the common mode voltage  316 ; the amplifiers  320  and  324 ; the feedback control circuit  322 ; the communication circuit  326 ; and/or other suitable components. The laser diode driver  402  may include components identical or similar to those of the laser diode driver  302  of  FIG. 3 , and similar description will not be repeated here. Unlike the laser diode driver  302  of  FIG. 3 , the laser diode driver  402  does not include a common mode voltage output terminal. 
     A detection condition circuit may be inserted in the PCIe link to facilitate the receiver detection circuit  106  of the E-PCIe transmitter  102  to detect presence of the EO-PCIe transceiver  204 . The detection condition circuit may include DC blocking capacitors  406  and  408  and inductive impedances  402  and  404 . The DC blocking capacitor  406  may couple between the AC coupling capacitor  114  and the input terminal  306  of the laser diode driver  402 . The inductive impedance  402  may be referenced to the ground level and may connect to a point in a first signal route between the AC coupling capacitor  114  and the DC blocking capacitor  406 . The DC blocking capacitor  408  may couple between the AC coupling capacitor  116  and the input terminal  308  of the laser diode driver  402 . The inductive impedance  404  may be referenced to the ground level and may connect to a point in a second signal route between the AC coupling capacitor  116  and the DC blocking capacitor  408 . 
     The inductive impedances  402  and  404  may include an impedance value of about 0.50 ohms at low frequencies (e.g., at a frequency close to DC) and may include a higher impedance value at high frequencies. Example implementations of the inductive impedances  402  and  404  are provided with reference to  FIGS. 5A and 5B . 
     Turning to  FIG. 5A , an example inductive impedance  500  is illustrated. The inductive impedances  402  and  404  of  FIG. 4  may each include a structure similar or identical to the inductive impedance  500  of  FIG. 5A . The inductive impedance  500  may include an inductor  502  and a resistor  504  coupled in a series connection. The resistor  504  may have a value of 50 ohms or another suitable value. Turning to  FIG. 5B , another example inductive impedance  550  is illustrated. The inductive impedances  402  and  404  of  FIG. 4  may each include a structure similar or identical to the inductive impedance  550  of  FIG. 5B . The inductive impedance  550  may include an inductor  552 , a resistor  554 , and a resistor  556 . The inductor  552  and the resistor  556  may be coupled in a parallel connection. The parallel connection of the inductor  552  and the resistor  556  may then be connected to the resistor  554  in a series connection. The resistor  554  may have a value of about 50 ohms or another suitable value. The resistor  556  may have a value of about 500 ohms or another suitable value. The inductor  502 / 552  may have an inductance value of about 82 nanoHenry (nH) or another suitable value. 
     With combined reference to  FIGS. 4 and 5A , the receiver detection circuit  106  of the E-PCIe transmitter  102  may charge a voltage from V 1  to V 2 . A voltage at the output terminal  105  may be illustrated by: 
                       V   105     =       V   2     -           (       V   2     -     V   1       )     ⁢   R       4   ⁢     ω   0     ⁢     L   502     ⁢         ξ   2     -   1           ⁢     (       e       -       ω   0     ⁡     (     ξ   +         ξ   2     -   1         )         ⁢   t       -     e       -       ω   0     ⁡     (     ξ   -         ξ   2     -   1         )         ⁢   t         )           ,           (   7   )               
where
 
                 ω   0     =     1         L   502     ⁢     C   114             ,     ξ   =         R   2     ⁢         C   114       L   502           ≥   870       ,     V   =       V   2     -     V   1         ,         
R may represent a sum of a resistance value of the resistor  504  and an internal impedance of the receiver detection circuit  106  of the E-PCIe transmitter  102 , and L 502  may represent an inductance value of the inductor  502 . If R 504 &lt;&lt;R 312 +0.5R 318 , where R 504  may represent a resistance value of the resistor  504  and R 318  may represent a resistance value of the resistor  318 , then R≈R 504 . Combining equations (1) and (7), and assuming the components have the specific values mentioned V 105  from equation (7) may have a voltage changing rate approximate to that of equation (1) when t&gt;5 nanoseconds (ns), with a voltage difference less than 5%. If t≦5 ns may be ignored while the receiver detection circuit  106  may have voltage transition, a voltage changing rate at the output terminal  105  may be detected with tolerance to determine presence of the EO-PCIe transceiver  204  and/or presence of the AOC  202  in the PCIe link. Similarly, a voltage changing rate may be determined for the output terminal  107  to detect presence of the EO-PCIe transceiver  204  and/or presence of the AOC  202  in the PCIe link.
 
     The present disclosure is not to be limited in terms of the particular embodiments described herein, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that the present disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.