In the field of data communications there often exists the need to recover the timing of a critically-timed transported signal. A trigger must be derived from the data itself when an external trigger is unavailable. This is particularly true within test, measurement, design, troubleshooting, diagnostic, and calibration applications requiring, or benefiting from, the use of multi-rate, high-sensitivity clock and data recovery.
Although there are many clock and data recovery (CDR) circuits and related devices, systems, and methods known in the art, many deficiencies also exist. For example, known CDR devices are often plug-in modules that do not provide the ability to use the device in a stand-alone manner. Known devices require that the user purchase a more expensive CDR plug-in module manufactured by the digital communications analyzer (DCA) manufacturer. This further assumes that unused channel or plug-in space is even available in the DCA mainframe. Additionally, known devices in the art often limit the user to a particular DCA manufacturer. Known devices are not compact such that they can be used easily and conveniently in a test station configuration with minimal space requirements. Known CDR devices are expensive to manufacture and use, relative to the system and method of the present invention. Additionally, known CDR devices provide a direct input level sensitivity that is unable to recover at lower level inputs. For example, measurement accuracy in known systems often degrades below approximately −8 dBm. Known CDR systems are unable to provide adequate trigger rates that are needed for optical/electrical testing. Furthermore, known CDR devices do not provide optical-to-electrical conversion as a component of the same system. Known CDR devices do not provide the multiple electrical clock outputs of both OC-192 and OC-48. Finally, many CDR devices known in the art require an optical input for RF electrical measurement and evaluation, and are unable to allow the system to trigger directly from an RF electrical input in substitution of an optical input. One that is known is a plug-in device and not a stand alone module.
Thus, what is needed is a stand-alone and cost-efficient system for OC-192 multi-rate, high-sensitivity clock and data recovery that includes a variable/adjustable decision threshold, RF input clock recovery, and an optical-to-electrical conversion feature. Additionally, what is needed is a CDR system that does not require an optical input for RF electrical measurement and evaluation. Additionally, what is needed is a CDR system that provides multiple electrical clock outputs. Furthermore, what is needed is a CDR system that also optionally is capable of converting an optical signal to an electrical signal, bypassing the clock and data recovery circuit. A CDR system is needed that does not limit its user to a particular DCA manufacturer. Finally, what is needed is a CDR system that provides all of the above in a single, stand-alone hardware unit. The present invention provides such a system.