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audio/videoZONE Products for the week of April 21, 2008
National Semiconductor Says…
LMH1982: Low-Jitter Clock Generator for Professional and Broadcast Video
Multi-Rate Clock Generator’s High-Integration and Miniature Size Simplify Video Equipment Design
A new multi-rate video clock generator with genlock from National Semiconductor Corp. delivers high-definition (HD) clock output jitter as low as 40 ps peak-to-peak. The LMH1982 provides reference clocks for video analog-to-digital converters (ADCs), digital-to-analog converters (DACs) and field-programmable gate array (FPGA) transceivers. These reference clocks ensure a system’s 3-Gbps (3G), HD and standard-definition (SD) serial digital interface (SDI) output jitter is in compliance with the Society of Motion Picture and Television Engineers (SMPTE) video standards.
The LMH1982’s high-integration and small 5 mm by 5 mm package size simplifies the design of video cameras, digital recorders and a wide range of video editing and post-production equipment. The LMH1982 can replace discrete and FPGA phase-lock loops (PLLs) with multiple voltage controlled crystal oscillators (VCXOs), while offering low total power dissipation of 250 mW. 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 an SDI deserializer. The use of an external loop filter offers additional configurability to optimize rejection of reference input timing jitter.
EN-Genius Says…
The video designer needs to completely read the data sheet for this part to get a full understanding of what it can do for him. Suffice it to say that with an external 27 MHz voltage-controlled crystal oscillator and external loop filter (that is unfortunate) the LMH1982 will produce the necessary horizontal and vertical LVDS output clocks for:
- NTSC
- PAL
- 525 progressive
- 625 progressive
- SMPTE 296M standards
- SMPTE 274M standards
This is as complete a solution that could be out there for manufacturers of broadcast and professional video equipment as well as video capture and display equipment.
I do pick an argument that whoever tagged the product adding “… with Genlock.” Whoever that was does not understand what genlock is. It is not a loop of any kind. I remember being at an outside broadcast (in US, remote) at horse racing at Newmarket in the UK. I was responsible for a camera (Marconi Mk III) that was dodgy at best. When the camera output over a UHF link to the main outside broadcast vehicle (scanner in BBC parlance) on the other side of the course was selected to network ,then the syncs from this camera were genlocked to by the scanner and the whole network synchronization was dependent on this one sorry piece of equipment. What National have here is an AFC, automatic frequency control, loop...not genlock.
This is a key building block for multi-standard SD/HD products and it will do extremely well. I am sorry that National management doesn’t seem to recognize how important the video industry, and NAB in particular, is to get their message out to video designers. Nevertheless the product will almost self-select into PCBs and the pricing is where I would expect, and like, it to be. The package is well chosen for high volumes but may be difficult for small production runs.
The LMH1982 is in production in LLP-32 priced at $24.95 in 100-piece lots. An evaluation board is available.
Data Sheet
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