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Multirate video clock generator asserts lowest jitter

Posted: 16 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:clock generator multi-rate? video? LMH1982 lowest jitter?

According to National Semiconductor Corp., the LMH1982 multi-rate video clock generator with genlock delivers high-definition (HD) clock output jitter as low as 40ps peak-to-peak.

The clock generator provides reference clocks for video A/D converters, D/A converters and FPGA transceivers. The reference clocks ensure a system's 3Gbit/s (3G), HD and standard-definition (SD) serial digital interface (SDI) output jitter complies with the Society of Motion Picture and Television Engineers (SMPTE) video standards.

The LMH1982's high-integration and 5mm x 5mm package size simplifies the design of video cameras, digital recorders and a wide range of video editing and post-production equipment. The clock generator can replace discrete and FPGA phase-lock loops (PLLs) with multiple voltage-controlled crystal oscillators (VCXOs), while offering low total power dissipation of 250mW. Only one external VCXO is required to operate the LMH1982.

The device can generate two simultaneous SD and HD output clocks and an output top of frame (TOF) timing pulse. In genlock mode, these output signals can be phase-locked to H and V sync signals applied to either of the reference ports.

The LMH1982's low-jitter output clocks are capable of driving FPGA serializers without the need for additional clock cleansing. The device's integrated PLLs can synchronize the output clocks to an analog timing reference from National's LMH1981 multi-format video sync separator or a digital timing reference from a SDI deserializer. The use of an external loop filter offers additional configurability to optimize rejection of reference input timing jitter.

Offered in a 32-pin LLP package, the LMH1982 3G/HD/SD multi-rate video clock generator provides two simultaneous low-voltage differential signaling (LVDS) output clocks with selectable frequencies for SD (27MHz or 67.5MHz) and HD (74.25MHz, 74.25/1.001MHz, 148.5MHz or 148.5/1.001MHz) resolutions. The LMH1982 supports NTSC/525i, PAL/625i, 525p, 625p, 720p, 1080i and 1080p video timing. An I2C compatible bus interface is included for programming device registers and reading device status. The LMH1982 operates from 3.3V and 2.5V supplies. Price is set at $24.95 each for 100-unit quantities. Samples are available now, with high-volume quantities scheduled at the end of May 2008.

- Gina Roos

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