High Speed Digital Design
As video and comms increase in resolution and bandwidth, this places greater need on the requirement for high speed digital design of PCBs. Omnitek have performed a number of PCB designs with speeds of 12GHz and beyond. The following section reviews 12G SDI PCB design.
The emerging 4K and UHD video formats have set challenges for broadcast equipment manufacturers who now must develop new products that support the myriad of video interfaces that are being adopted in order to stay in the market place. Some manufacturers have offered quad 3G-SDI interfaces to ‘dip their toe in the water’ while others are facing head on the challenges that come from adopting the 12G-SDI interface and pushing the boundaries of what is possible with FR4 PCB substrate, FPGA design and product testing.
For a lot of manufacturers facing this challenge raises more questions that are not that easy to answer.
We have researched, modelled and experimented with different approached to answer the questions raise by 12G-SDI and have implemented sophisticated solutions in our own products and we wish to share some of our findings to aid all those preparing to embrace the 12G-SDI challenge.
At 6 GHz (the fundamental frequency component of 12G-SDI) the effect of PCB design on the signal becomes more significant than at 1.5 GHz (the fundamental frequency of 3G-SDI signals). Things such as PCB substrate dielectric losses, conductor skin effect, mutual inductance, capacitive effects as well as surface roughness all have a greater effect on the quality of the 12G-SDI signal arriving at the chip.
The 12G-SDI PCB Design Guidelines White Paper (available as part of our Design Services) covers areas such as choice of PCB substrate, connector types, PCB trace type and layout and cabling to ensure that signal quality, jitter management and PSU noise are taken into considerations.
One of the significant challenges of 12G-SDI signal measurement is how to accurately and repeatedly measure waveform amplitude because without this measurement values of rise time and fall time cannot be made. Due to the high 3rd and 5th harmonic frequencies of the 6GHz fundamental frequency (relative to the bandwidth of the BNC and cable) the signal actually sent by currently available transmitters is effectively a distorted sine wave. Making accurate amplitude measurements of signals like this depends on the measurement technique used.
The 12G-SDI Physical Layer Analysis using the Ultra 4K Tool Box White Paper discusses these aspects of physical layer analysis using the Omnitek Ultra 4K Tool Box in comparison to the Teledyne LeCroy SDA 820Zi-A high-end oscilloscope and shows that the results are comparable and well within acceptable tolerances.
Omnitek’s SDI IP and knowledge of 12G-SDI / 4K design implementation, uses within the Omnitek Ultra 4K Tool Box itself, allows customers to get their products to market very quickly while removing the risk of physical designs that just don’t work at 12G.