Analog or serial digital video input with automatic video switch

#The present invention relates to video test and measurement instruments, and more particularly to a video test and measurement instrument having a single input for receiving either an analog or a serial digital video signal with the ability to automatically switch internal processing accordingly.

#In the current transitional stage from analog to digital video environments, many video studios operate in a mixed environment—having both analog and serial digital video sources available. In order to observe the quality of the video signal from these sources, a user has to know which type of source is being tested/measured in order to use an appropriate instrument. This in the past has required the user to have at least two instruments with him—one for analog video and one for digital video. Alternatively the user has a single instrument with a converter to convert from the type of signal of the source to the type of signal acceptable by the instrument. Currently there are waveform monitors available for both analog and digital video signals. But these instruments have separate analog and digital video input ports. Even with these instruments the user has to know what type of source he is measuring in order to connect it to the proper video input port. For a handheld instrument with limited real estate, having two different video input ports is not practical.

#What is desired is the ability to have a single video input port for an instrument that accepts either analog or serial digital video signals with an automatic video switch between analog and digital video input paths within the instrument.

#FIG. 1 is a block diagram view of an input section of a video test and measurement instrument according to the present invention.

#Referring now to FIG. 1 a video signal, either analog or serial digital format, is received at a video input port 11 of a video test and measurement instrument 10 and routed to both analog and digital video input paths 13, 15. The analog video input path 13 may include an analog video buffer 12 that receives the video signal and routes it as an analog video signal to a video switch 14. The digital video input path 15 has a conventional digital video receiver that may include an automatic equalizer 16, a clock recovery and data slicing module 18, a serial to parallel converter 20 and a composite encoder 22 in series to process the input video signal, the output of which is a digital video signal for input to the video switch 14. The output of the digital receiver may be converted to analog by a digital to analog converter as part of the encoder 22 prior to input to the video switch 14, or alternatively the output of the analog video buffer 12 may be converted to digital by an analog to digital converter prior to input to the video switch so that both inputs to the video switch are in the same video format. Which video input path 13, 15 is converted to the other video format is a function of the processing hardware in the instrument at the output of the video switch 14.

#A decision module 24 may receive a carrier detect signal from the equalizer 16, a clock recovery lock signal from the clock recovery module 18 and/or a video standard signal from the converter 20. From these information signals the decision module 24 automatically determines whether the video signal is analog or serial digital and provides a select signal to the video switch 14 accordingly. The output from the video switch 14 is the video signal from the video input path 13, 15 selected by the decision module 24 for further processing by the instrument. Also input to the switch 14 is a manual switch override control signal that overrides the output from the decision module 24 if desired by a user.

#The serial digital video receiver 16-22 may be contained within a standard serial digital video receiver chip set that provides the information signals to the decision module 24 indicated above. The decision module 24 determines whether a serial digital video signal is present at the video input. If there is, the output from the serial digital video receiver is output by the video switch 14, otherwise the output from the video switch is from the analog video buffer 12. As an example, if a phase locked loop (PLL) in the serial digital video receiver chip set reports a video lock, then a variable lock is set to “1”, otherwise it is “0”. The following routine may be used to filter some glitches out of lock. 1 if (lock) { if (countSdVideoLock < INTEGRATION_COUNT) { countSdVideoLock++; if (countSdVideoLock >= INTEGRATION_COUNT) { detSdVideoStd = SdStd_Unknown; // digital video is locked, but the standard is not yet known // } } } else { if (countSdVideoLock > 0) CountSdVideoLock-; if (countSdVideoLock == 0) detSdVideoStd = SdStd_Unlocked // digital video is unlocked // }