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, rich feature set, and easy application permit

use in critical systems where low jitter is a crucial parameter,

like in broadcast video and next-generation HDTV/DTV

equipment. The device can operate from a supply voltage

between 3.3V and 5V. The only required external compo-

nents are bypass capacitors at the power supply pins, an

input coupling capacitor at pin 4, and a R

Refer to the application circuit in Figure 2.

Internal Reference Voltage and R

EXT

The R

rent and precise reference voltage to assure proper opera-

tion of the LMH1981 over a wide temperature range. For

optimal performance, R

Ω 0.1% resistor

with a temperature coefficient under 100 ppm/˚C. See the

PCB LAYOUT CONSIDERATIONS section for more infor-

mation about the R

Note: The R

“R

(i.e.: LM1881). Previously, the R

accommodate different input scan line frequencies. The

R

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

device outputs will respond correctly to video format switch-

ing after a hold-off period has been satisfied. Unlike other

sync separators, the LMH1981 does not require the power to

be cycled in order to guarantee correct outputs after switch-

ing between video formats. See the Sync-Lock Condition

for Output Accuracy sub-section for details on sync-

locking.

Advanced Video Sync Processing

The LMH1981 features 50% sync slicing to provide accurate

and robust sync separation, even in the presence of irregular

sync amplitudes from attenuated or improperly terminated

sources and noise. Adaptive sync slicing provides excellent

output timing jitter and stability against variations in input

signal amplitude and temperature. The sync separator also

supports SDTV, EDTV, and HDTV formats, and is compat-

ible with bi-level and tri-level syncs. Bi-level syncs will be

sliced at the 50% point between the sync tip and video blank

level. Tri-level syncs will be sliced at the positive zero-

crossing of the tri-level sync signal, which is the 50% point

between the negative and positive sync tips.

Macrovision Compatibility

The LMH1981 is compatible with the Macrovision Video

Copy Protection System commonly used in VHS and DVD

video sources, which inserts pseudo-sync pulses in the

video blanking signal. These Macrovision-embedded pulses

will be effectively ignored by the sync separator, and the

outputs will not be affected.

VIDEO INPUT

Video Standards Supported

The LMH1981 supports sync separation for the following

standard video interfaces and formats:

•

Composite (CVBS) and S-Video (Y/C): NTSC, PAL,

SECAM

•

Component (YP

– SDTV with bi-level sync: 480i /60, 576i /50

– EDTV with bi-level sync: 480p /60, 576p /50

– HDTV with tri-level sync: 720p /60, 1080i /50/60, 1080p

/24/25/30/50/60

•

Computer Video: RGsB (Sync on green)

Video Input Requirements

The video input at pin 4 accepts Composite, Y from Y/C and

YP

bi-level sync or HD tri-level sync between 0.5 V

The video input signal should be AC coupled through a

coupling capacitor to minimize droop voltage and prevent

the signal at V

The video source should be properly terminated with 75

Ω to

ensure correct input amplitude and minimize video & sync

distortion due to reflections. In extreme cases, the LMH1981

can handle unterminated (2 V

V

LOGIC OUTPUTS

Most of the logic outputs are held high in the absence of a

video input signal, except for the odd/even field and video

format outputs, which both have special logic signaling for

different video formats, and composite sync output.

Sync-Lock Condition for Output Accuracy

When a new input signal is detected, the outputs will begin to

produce timing signals; however, these signals may not be

accurate until a hold-off period or “sync-lock condition” has

been satisfied. The sync separator requires some time to

identify the new video format and process the sync informa-

tion before the outputs are accurate. T

maximum period from when the new input signal starts, to

when the syncs are locked and the output signals are valid.

It is recommended that the outputs are used only after

T

Composite Sync Output

The composite sync output (pin 12) simply reproduces the

video input sync pulses below 0 mV (specified video blank-

ing level). This is obtained by clamping the video signal sync

tip to the internal clamp voltage at V

slicing to strip the sync signal. The resultant composite sync

logic signal is buffered out to pin 12. For both bi-level and

tri-level syncs, composite sync’s negative- and positive-

going edges are triggered from the 50% points of the input

sync’s leading negative- and positive-going edges, respec-

tively, with a propagation delay.

Horizontal Sync Output

The horizontal sync output (pin 7) produces an active low

horizontal sync logic signal with very low jitter on its leading

negative-going edge (reference edge). For bi-level sync sig-

nals, the horizontal sync leading edge is triggered from the

input sync leading edge reference with a propagation delay.

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