Taming the 12Gbs beast and how to T&M it with the Qx


Phillip Adams TV-Bay Magazine
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by Philip Adams and Paul Nicholls
Issue 107 - November 2015
The one thing you can say about working in the broadcast industry is that there isnt time to get bored! Hesitant, perhaps even frightened these days might be more accurate but bored, certainly not. Such is the case with the planned UHDTV roll out and the need for customers to invest in technology which will adapt as the technologies, proposals and standards evolve. For a company like PHABRIX the hiatus created by customers deciding where to place their investment money has produced a significant opportunity but also a problem: How to meet the evolving requirements of an industry with a suitably forward looking adaptable product available now!

The step from full HD to UHDTV is a very significant one. Current proposals see this as a three phase development. This phased approach is necessary due to the very significant technical hurdles at each stage. Phase one has begun, however ultimately UHDTV will provide a user experience incorporating:

- Higher spatial resolution: UHDTV1 (3840 x 2160), UHDTV2 (7680 x 4320)
- High Dynamic Range (HDR): camera and display technology taking the user experience from the current display technology reference luminance of 120 cd/m to over 10,000 cd/m
- High frame rates (HFR): 100/120Hz frame rates
- Wide Colour Gamut (WCG): A new colour space: Rec. 2020 with twice the CIE 1931 colour space area as full HD (Rec. 709)
- A new audio experience with opportunities for object based audio, 96 kHz sampling, and up to 22.2 surround sound

A quick scan of the table of UHDTV standards below gives a feel for the video payload requirements associated with UHDTV.

Handling these payloads alone and providing instrumentation is a difficult enough task. Add to this the complications of supporting coaxial SDI to 12Gbps, optical SDI to 12Gbs and 10G Ethernet with or without compression and the challenge is significant.

Timing is another factor. Technologies move on and the chipsets of 2012 by Moores Law are nowhere near a match for those available in 2015. A number of the key components utilized in the Qx only became available in February this year and despite our considerable IP evidenced in existing products a lot of development work has been required in order to integrate these new revolutionary devices into what is a totally new generation of product. However there have been rewards. Technologically we have released our new RTETM technology. This simple trademark belies the innovation behind the only currently available high end 12G capable real-time physical layer eye pattern analyser providing accurate SMPTE compliant measurements of eye amplitude rise time, fall time, overshoot, undershoot, timing and alignment jitter.

The holy grail of effective UHDTV SDI physical layer analysis is bandwidth. Without appropriate bandwidth youre in the dark. With over 30 GHz (5th harmonic of the 6GHz fundamental for 12G-SDI) analogue bandwidth on its front end, the Qx can deal with the demands of qualifying 12G interfaces accurately. More bandwidth than any other currently available Broadcast T&M manufacturer. Subtleties of PCB layout and SDI driver design can thus be explored with the Qx eye pattern display.

In addition, the latest crop of 12G-SDI chipsets have a new parameter to be adjusted: pre-emphasis. This typically boosts the high frequency energy of SDI outputs, adjustment of this control can only be understood in combination with an accurate eye diagram coupled with overshoot and undershoot measurement.
Noise floors are required to be much lower in a 12G-SDI world for accurate meaningful measurements to be taken. The PHABRIX Qx technology has previously unheard of low noise figures within its oscillators and measurement circuits. Use of both the SDI generation and physical layer analyser features simultaneously in the Qx is not a problem.

With the Advanced Jitter Generation and Analysis option (Q1/2016) SDI receiver performance can be thoroughly tested by the inclusion of output signal amplitude control exceeding the SMPTE specification of 800mV +/-10%. In addition comprehensive jitter insertion is provided along with pre-emphasis control affecting rise/fall times. The inclusion of jitter FFT instrumentation and a packaged solution to the automated measurement of both jitter tolerance and jitter transfer function will ensure that future SDI interfaces will be thoroughly tested in an automated environment with Qx technology.

Current cable length performance in the lab is up to 75m on standard Belden 1694A with 12G BNC connectors. With more expensive cable types we are achieving 100m.

At IBC this year we had a number of manufacturers wishing to use our RTETM technology to test their new products. The exercise was an interesting one and we undertook two separate tests qualified in comparison with two different high end oscilloscopes. The results presented in Figure 1 are from a manufacturers distribution amplifier which clearly suffers from a poor cable driver layout. Luckily the manufacturer was able to catch this one in time!

Figure 2 represents a second test undertaken with a manufacturer wishing to control pre-emphasis. As can be seen from the traces there is considerable overshoot and undershoot here which will again require layout changes to reduce the high frequency response of the SDI output circuitry.

There is nothing new here, if you have anything from £50,000 upwards to spend on a high end oscilloscope then you will see the same technology in action but who has that kind of money available these days? Thats where the Qx comes in offering the same real-time response as commercially available 30GHz oscilloscopes in addition to a whole host of other UHD specific features for a small fraction of the price.

With 4 separate 12 Gbps capable multi-rate inputs and outputs supporting payloads up to 48Gbps the Qx is well positioned to provide comprehensive UHDTV1/4k and UHDTV2/8k generation and analysis for all three phases of UHD development.

The first batch of Qx units are available this month very much focussed on tools for manufacturing. As we progress through 2016 a host of more advanced instrumentation addressing more general Broadcast related applications will be released.


Tags: iss107 | t&m | vidoe payloads | uhdtv | eye | phabrix | qx | agilent | tektronix | Phillip Adams
Contributing Author Phillip Adams

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