Abstract:
Configurable communications modules and methods of making the same are described. In one aspect, a communications module includes a data channel and a termination impedance controller. The data channel is operable to translate data signals in at least one direction between a transmission cable interface and a host device interface. The data channel has a variably configurable termination impedance at a host device node that is connectable to a host device. The termination impedance controller is operable to set the variably configurable termination impedance of the data channel to match the termination impedance to the host system.

Description:
TECHNICAL FIELD 
     This invention relates to configurable communications modules and methods of making the same. 
     BACKGROUND 
     Transmission cables may be used to transmit data between workstations, mainframes and other computers, as well as provide data connections to mass storage devices and other peripheral devices. Data may be transferred using a variety of transmission cable technologies, including multimode optical fiber cables, single mode optical fiber cables, and copper cables (e.g., twinax and coax copper cables). Standard communications modules have been developed to transition between different transfer media and the electronic components inside a computer or peripheral device. Among the common communication modules are transmitter modules, receiver modules, and transceiver modules. 
     A communications module produces a standardized output to the host system in accordance with prescribed protocols, regardless of the medium (e.g., optical fiber or copper) through which the data is transmitted or received. For example, an optoelectronics transceiver module enables bidirectional data transmission between an electrical interface and an optical data link. A copper transceiver module, on the other hand, enables bidirectional data transmission between two electrical devices. 
     A communications module typically plugs into a cage that extends out of the rear panel of a host device (e.g., a computer or a peripheral device). The cage connects the transceiver module to a motherboard or circuit card in the computer or peripheral device. 
     SUMMARY 
     The invention features configurable communications modules and methods of making the same. 
     In one aspect of the invention, a communications module includes a data channel and a termination impedance controller. The data channel is operable to translate data signals in at least one direction between a transmission cable interface and a host device interface. The data channel has a variably configurable termination impedance at a host device node that is connectable to a host device. The termination impedance controller is operable to set the variably configurable termination impedance of the data channel. 
     In one aspect of the invention, a communications module includes a receiver data channel, a transmitter data channel, a termination impedance controller, and a housing. The receiver data channel is operable to translate data signals from a transmission cable interface to a host device interface. The transmitter data channel is operable to translate data signals from the host device interface to the transmission cable interface. Each of the receiver data channel and the transmitter data channel has a respective variably configurable termination impedance at a respective host device node connectable to the host device. The termination impedance controller is operable to set the respective variably configurable termination impedance of each of the receiver data channel and the transmitter data channel. The housing contains the receiver data channel, the transmitter data channel, and the termination impedance controller. The housing has a transmission cable interface end that is connectable to a transmission cable and a host device interface end that is connectable to a host device. 
     In another aspect, the invention features a method of making a communications module. In accordance with this inventive method, a data channel is obtained. The data channel is operable to translate data signals in at least one direction between a transmission cable interface and a host device interface. The data channel has a variably configurable termination impedance at a host device node that is connectable to a host device. The data channel is mounted in a housing having a first end that is connectable to a transmission cable and a second end that is connectable to a host device. The variably configurable termination impedance of the data channel is set to a termination impedance value substantially matching a target host device termination impedance value. 
     Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of a communications module. 
         FIG. 2  is a circuit diagram of an embodiment of an output stage of the data channel in the communications module embodiment of  FIG. 1  that includes a variable resistance circuit. 
         FIG. 3A  is a circuit diagram of an implementation of the variable resistance circuit of  FIG. 2 . 
         FIG. 3B  is a circuit diagram of an implementation of the variable resistance circuit of  FIG. 2 . 
         FIG. 4  is a block diagram of an optical transceiver implementation of the communications module of  FIG. 1 . 
         FIG. 5  is a flow diagram of an embodiment of a method of making a communications module. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
       FIG. 1  shows an embodiment of a communications module  10  that includes a module housing  12  that contains a data channel  14  and a termination impedance controller  16 . In a typical implementation, data channel  14  and termination impedance controller  16  are mounted on a common substrate (e.g., a printed circuit board). 
     Module housing  12  is configured to connect physically with transmission cable  18  and a host device  20 . In general, transmission cable  18  may be any kind of optical or electrical communication cable and host device  20  maybe any kind of device (e.g., a computer or peripheral electronic device). In some implementations, transmission cable  18  includes a connector that is pluggable into a media connector of module housing  12 . The media connector of module housing  12  may support any high-performance optical or electrical serial transmission medium technology. In the case of electrical transmission media, the media connector may be, for example, a DB-9 electrical connector, an RJ45 receptacle, or a HSSDC electrical connector. In the case of optical transmission media, the media connector may be, for example, a single connector (SC) duplex media connector, and LC connector, or an MTP/MPO connector. In some embodiments, module housing  12  is pluggable into a mating receptacle of host device  20 . The module housing in these embodiments may be implemented in accordance with any pluggable communications module standard, including the Giga-Bit Interface Converter (GBIC) standard, the small form pluggable (SFP) standard, and the small form factor (SFF) standard. 
     Data channel  14  translates data signals in at least one direction between an interface  22  of a transmission cable  18  and an interface  24  of a host device  20 . In general, data channel  14  is configured to connect and/or translate (or convert) data signals from a first serial transmission medium to a second serial transmission medium. In  FIG. 1  data channel  14  is shown as having only a single (receiver) interface translation channel. Depending on the particular implementation, however, data channel  14  may provide bidirectional or unidirectional, single channel or multi-channel transmission of data between the first and second transmission media. For example, in a bidirectional optical transceiver implementation, data channel  14  provides bidirectional data transmission between an electrical interface in host device  20  and an optical data link in transmission cable  18 . The interface translation channel may be a differential data translation channel, as shown in  FIG. 1 , or a single-ended data translation channel. 
     Transmission cable interface  22  is characterized by a characteristic impedance  26  and host device interface  24  is characterized by a characteristic impedance  28 . Similarly, data channel  14  has a termination impedance  30  at a cable node  32  and a termination impedance  34  and a host device node  36 . For high-speed data transmission applications, the cable and data channel termination impedances  26 ,  30  at node  32  preferably are matched to reduce reflections and other losses. Similarly, the host device and data channel termination impedances  28 ,  34  at node  36  preferably are matched to reduce reflections and other losses. In  FIG. 1 , each of the termination impedances  26 ,  28 ,  30 ,  34  is represented by a single resistive element. In general, each of the data channel  14 , transmission cable interface  22 , and host device interface  24  may include one or more elements having an equivalent impedance value corresponding to the values of termination impedances  26 ,  28 ,  30 ,  34 . 
     In order to accommodate host devices that have host device interfaces  24  with different respective termination impedances  28 , termination impedance  34  of data channel  14  is variably configurable. For example, a legacy GBIC host interface has a 75 ohm (150 ohm differential) termination impedance, whereas a small form pluggable host interface has a 50 ohm (100 ohm differential) termination impedance. As explained in detail below, termination impedance controller  16  is operable to set the variably configurable termination impedance  34  of data channel  14  to an impedance value substantially matching a target termination impedance value of a target host device interface. 
     Referring to  FIG. 2 , in some embodiments, data channel  14  includes a differential amplifier  40  connected to host device node  36 . Differential amplifier  40  includes a pair of input transistors  42 ,  44  with gates connected respectively to V IN + and V IN − signals and sources connected to a common biasing current source  46 . The drains of transistors  42 ,  44  are connected to a drain voltage rail V DD  through respective variable resistance circuits  48 ,  50 . The differential output signals V OUT + and V OUT − produced at the drains of transistors  42 ,  44  are delivered to the host device node  36 . The impedance values of resistance circuits  48 ,  50  determine the termination impedance of data channel  14  at node  36 . These impedances are set by termination impedance controller  16 . In most applications, the impedance values of resistance circuits  48 ,  50  are set to be substantially equal. In some applications, however, resistance circuits  48 ,  50  may be set to have different impedance values. 
     Referring to  FIGS. 3A and 3B , in general, resistance circuits  48 ,  50  may be implemented by one or more circuit elements that cooperatively provide a variably configurable termination impedance that may be set to any one of multiple different target impedance values by termination impedance controller  16 .  FIG. 3A  shows an embodiment in which each of the resistance circuits  48 ,  50  is implemented by a field effect transistor  52 , which has a voltage-controlled resistance value. For small drain-source voltages of either polarity, the resistance value of transistor  52  decreases with increasing applied gate-source bias (V CNTL ).  FIG. 3A  shows an embodiment in which each of the resistance circuits  48 ,  50  is implemented by a resistor  54  that is connected in parallel with a switch  56  and a resistor  58 , which are connected in series. In some embodiments, switch  56  is implemented by a transistor, in which case termination impedance controller  16  opens and closes the switch with the electrical control signal V CNTL . In other embodiments, switch  56  is implemented by a mechanical switch, in which case the termination impedance controller  16  includes an actuatable element that enables manual control of the mechanical switch. When switch  56  is open, the effective resistance of each resistance circuit  48 ,  50  corresponds to the resistance of resistor  54 . When switch  56  is closed, the effective resistance of each resistance circuit  48 ,  50  corresponds to the effective resistance of resistor  54  in parallel with the combined resistance of transistor  56  and resistor  58 . In other embodiments, resistance circuits  48 ,  50  may be implemented in different ways. 
       FIG. 4  shows an exemplary embodiment of communications module  10  that is implemented in the form of a GBIC optical transceiver module  60 . Transceiver module  60  includes an electrical connector  62  for connecting the module  60  to host device interface  24  and an optical connector  64  for connecting the module  60  to transmission cable interface  22 . An optical receiver  66  is coupled to an amplifier and loss-of-signal (LOS) detector circuit  68 . An optical transmitter  70  is coupled to a laser driver and power control circuit  72 . A receiver termination circuit  74  converts the signals output from the amplifier and LOS detector circuit  68  into receive data and receive LOS signals  76  and a drive circuit  78  transmits transmit data and other signals to the laser driver and power control circuit  72 . A power management and surge control circuit  82  provides power to the circuits of transceiver module  60  and protects against power surges. A module definition (MOD_DEF) and termination impedance controller  84  generates a set of standard module definition signals  86  and generates control signals (V CNTL ) for setting the variably configurable termination impedances of the transmitter and receiver data channels. 
     In general, the module definition and termination impedance controller  84  is not limited to any particular hardware or software configuration, but rather may be implemented in any computing or processing environment, including in digital electronic circuitry or in computer hardware, firmware, or software. In one exemplary implementation, the module definition and termination impedance controller  84  is implemented in firmware by a programmable EEPROM controller module. 
     Referring to  FIG. 5 , in some embodiments, communications module  10  may be manufactured as follows. A communications circuit is obtained (step  90 ). The communications circuit incorporates a unidirectional or bidirectional data channel that includes a variably configurable termination impedance. The communications circuit also incorporates a termination impedance controller. In some implementations, the data channel and the termination impedance controller are mounted on a common printed circuit board substrate. A communications module is formed by mounting the communications circuit in a housing having a first end connectable to a transmission cable and a second end connectable to a host device (step  92 ). If a target termination impedance value corresponding to a target host device is known (step  94 ), the variably configurable termination impedance value of the data channel is set to a termination impedance value substantially matching the target host device termination impedance value (step  96 ). 
     The variably configurable termination impedance value is set by appropriate configuration of the termination impedance controller. For example, in some implementations, the termination impedance controller may be programmed to generate control signals V CNTL  that produce the target termination impedance at the host device node  36 . In other implementations, termination impedance controller may be configured manually to open or close a mechanical switch that produces the target termination impedance at the host device node  36 . 
     If the target termination impedance is not known (step  94 ), the communications module is stored (step  98 ). After the target termination impedance value has been determined (step  94 ), the variably configurable termination impedance value of the data channel is set to a termination impedance value substantially matching the target host device termination impedance value (step  96 ). 
     Other embodiments are within the scope of the claims. 
     For example, in some embodiments, termination impedance  30  of data channel  14  is variably configurable to accommodate transmission cables  18  having interfaces  22  with different respective termination impedances. In these implementations, termination impedance controller is configured to set the termination impedance  30  to a target impedance value substantially matching the characteristic impedance  26  of transmission cable interface  22 .