LM1881: Video Sync Separator

LM1881: Video Sync Separator

The LM1881 Video sync separator extracts timing information including composite and vertical sync, burst or back porch timing, and odd and even field information from standard negative going sync NTSC, PAL (1) and SECAM video signals with amplitude from 0.5-V to 2-V p-p. The integrated circuit is also capable of providing sync separation for non- standard, faster horizontal rate video signals. The vertical output is produced on the rising edge of the first serration in the vertical sync period. A default vertical output is produced after a time delay if the rising edge mentioned above does not occur within the externally set delay period, such as might be the case for a non-standard video signal.

The LM1881 is designed to strip the synchronization signals from composite video sources that are in, or similar to, the N.T.S.C. format. Input signals with positive polarity video (increasing signal voltage signifies increasing scene brightness) from 0.5 V (p-p) to 2 V (p-p) can be accommodated. The LM1881 operates from a single supply voltage between 5-V DC and 12-V DC. The only required external components besides a power supply decoupling capacitor at pin 8 and a set current decoupling capacitor at pin 6, are the composite input coupling capacitor at pin 2 and one resistor at pin 6 that sets internal current levels. The resistor on pin 6 (that is, Rset) allows the LM1881 to be adjusted for source signals with line scan frequencies differing from 15.734 kHz. Four major sync signals are available from the I/C; composite sync including both horizontal and vertical scan timing information; a vertical sync pulse; a burst gate or back porch clamp pulse; and an odd and even output. The odd and even output level identifies which video field of an interlaced video source is present at the input. The outputs from the LM1881 can be used to gen-lock video camera/VTR signals with graphics sources, provide identification of video fields for memory storage, recover suppressed or contaminated sync signals, and provide timing references for the extraction of coded or uncoded data on specific video scan lines.

 

Features

  • AC Coupled Composite Input Signal
  • >10-kΩ Input Resistance
  • <10-mA Power Supply Drain Current
  • Composite Sync and Vertical Outputs
  • Odd and Even Field Output
  • Burst Gate or Back Porch Output
  • Horizontal Scan Rates to 150 kHz
  • Edge Triggered Vertical Output
  • Default Triggered Vertical Output for Non- Standard Video Signal (Video Games-Home Computers)

Applications

  • Video Cameras and Recorders
  • Broadcasting Systems
  • Set-Top Boxes
  • Home Entertainment
  • Computing and Gaming Applications

 

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