LMH1981 Datasheet, PDF (11/24 Pages) National Semiconductor (TI) – Multi-Format Video Sync Separator

LMH1981
www.ti.com
SNLS214H – APRIL 2006 – REVISED MARCH 2013
APPLICATION INFORMATION
GENERAL DESCRIPTION
The LMH1981 is designed to extract the timing information from various video formats with vertical serration and
output the syncs and relevant timing signals in CMOS logic. Its high performance, advanced features and easy
application make it ideal for broadcast and professional video systems where low jitter is a crucial parameter.
The device can operate from a supply voltage between 3.3V and 5V. The only required external components are
bypass capacitors at the power supply pins, an input coupling capacitor at pin 4, and a precision R_EXT resistor at
pin 1. Refer to the test circuit in Figure 2.
R_EXT Resistor
The R_EXT external resistor establishes the internal bias current and precise reference voltage for the LMH1981.
For optimal performance, R_EXT should be a 10 kΩ 1% precision resistor with a low temperature coefficient to
ensure proper operation over a wide temperature range. Using a R_EXT resistor with less precision may result in
reduced performance (like worse jitter performance, increased propagation delay variation, or reduced input sync
amplitude range) against temperature, supply voltage, input signal, or part-to-part variations.
NOTE
The R_EXT resistor serves a different function than the “R_SET resistor” used in the LM1881
sync separator. In the older LM1881, the R_SET value was adjusted to accommodate
different input line rates. For the LMH1981, the R_EXT value is fixed, and the device
automatically detects the input line rate to support various video formats without electrical
or physical intervention.
Automatic Format Detection and Switching
Automatic format detection eliminates the need for external programming via a microcontroller or R_SET resistor.
The device outputs will respond correctly to video format switching after a sufficient start-up time has been
satisfied. Unlike other sync separators, the LMH1981 does not require the power to be cycled in order to ensure
correct outputs after a significant change to the input signal. See START-UP TIME for more details.
50% Sync Slicing
The LMH1981 features 50% sync slicing on HSync to provide accurate sync separation for video input
amplitudes from 0.5 V_PP to 2 V_PP, which enables excellent HSync jitter performance even for improperly
terminated or attenuated source signals and stability against variations in temperature. The sync separator is
compatible with SD/EDTV bi-level and HDTV tri-level sync inputs. Bi-level syncs will be sliced at the 50% point
between the video blanking level and negative sync tip, indicated by the input's sync timing reference or “O_H” in
Figure 9. Tri-level syncs will be sliced at the 50% point between the negative and positive sync tips (or positive
zero-crossing), indicated by O_H in Figure 10.
VIDEO INPUT
The LMH1981 supports sync separation for CVBS, Y (luma) from Y/C and YP_BP_R and G (sync on green) from
GBR with either bi-level or tri-level sync, as specified in the following video standards.
• Composite Video (CVBS) and S-Video (Y/C):
– SDTV: SMPTE 170M (NTSC), ITU-R BT.470 (PAL)
• Component Video (YP_BP_R/GBR):
– SDTV: SMPTE 125M, SMPTE 267M, ITU-R BT.601 (480I, 576I)
– EDTV: ITU-R BT.1358 (480P, 576P)
– HDTV: SMPTE 296M (720P), SMPTE 274M (1080I/P), SMPTE RP 211 (1080PsF)
The LMH1981 does not support RGB formats that conform to VESA standards used for PC graphics.
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