LMH1981MTSLASHNOPB datasheet(11/24 Pages) TI1

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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 REXT resistor at

pin 1. Refer to the test circuit in Figure 2.

REXT Resistor

The REXT external resistor establishes the internal bias current and precise reference voltage for the LMH1981.

For optimal performance, REXT should be a 10 kΩ 1% precision resistor with a low temperature coefficient to

ensure proper operation over a wide temperature range. Using a REXT 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 REXT resistor serves a different function than the “RSET resistor” used in the LM1881

sync separator. In the older LM1881, the RSET value was adjusted to accommodate

different input line rates. For the LMH1981, the REXT 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 RSET 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 VPP to 2 VPP, 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 “OH” 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 OH in Figure 10.

VIDEO INPUT

The LMH1981 supports sync separation for CVBS, Y (luma) from Y/C and YPBPR 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 (YPBPR/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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