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LMH1980 bảng dữ liệu(PDF) 11 Page - Texas Instruments |
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LMH1980 bảng dữ liệu(HTML) 11 Page - Texas Instruments |
11 / 22 page LMH1980 www.ti.com SNLS263A – JULY 2007 – REVISED MARCH 2013 APPLICATION INFORMATION GENERAL DESCRIPTION The LMH1980 is designed to extract the timing information from various video formats with standard and non- standard vertical serration and output the syncs and relevant timing signals in CMOS logic. Its advanced features and easy application make it ideal for consumer, professional, and industrial video systems where sync timing needs to be extracted from SD, HD, and PC video signals. The device can operate from a supply voltage between 3.3V and 5V. The only required external components are bypass capacitors between the VCC and GND pins, input coupling capacitor (CIN) from the signal source to the VIN pin, and a fixed-value 1% precision resistor between the REXT and GND pins. Refer to the test circuit in Figure 2. REXT Resistor The precision external resistor (REXT) establishes the internal bias current and precise reference voltage for the LMH1980. 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 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 used with the LMH1980 serves a different function than the “RSET resistor” used with other previous sync separators, like the LM1881. For the LM1881, the RSET value needed to be adjusted externally to support different input line rates. For the LMH1980, 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 adjusting an external RSET resistor or programming via a microcontroller. The device outputs will respond correctly to a switch in video format after a sufficient start-up time has been satisfied, usually within 1 to 2 fields of video. Unlike other sync separators, the LMH1980 does not require the power to be cycled in order to produce correct outputs after a significant change to the input signal. See START-UP TIME for more details. Fixed-Level Sync Slicing The LMH1980 uses fixed-level sync slicing for video inputs with an amplitude from 0.5VPP to 2VPP, which allows for proper sync separation even for improperly terminated or attenuated input signals. The fixed-level sync slicing threshold is nominally 70 mV above the clamped sync tip. This means that for a minimum video input signal amplitude of 0.5VPP, the slicing level is near the mid-point of the sync pulse amplitude. This slicing level is independent of the input signal amplitude; therefore, for a 2VPP input, the slicing level occurs at 12% of the sync pulse amplitude. INPUT CONSIDERATIONS The LMH1980 supports sync separation for analog CVBS, Y (luma) from Y/C and YPBPR, and G (sync on green) from GBR/RGsB, as specified in the following video standards. • Composite Video (CVBS) and S-Video (Y/C): – 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) • PC Graphics (RGsB): – VESA Monitor Timing Standards and Guidelines Version 1.0, Revision 0.8 • Non-Standard Video: Copyright © 2007–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LMH1980 |
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