4.1. Enabling PCB panel design
The following guidelines and requirements target general PCB panels. You can use FR4 stack-up to reduce costs or Rogers for better signalling on larger panels. Evaluate your stack-up requirements based on the attributes in the table below.
Ensure that your cables meet HDMI 2.1 certification. HDMI.org provides a list of compliant connectors and cables along with their providers. For the purpose of this guide, Intel uses Belkin cables with HDMI IP running 12-gigabits per second (Gbps) Fixed Rate Link (FRL).
|Trace||90-100 Ω Length matched||FR4, microstrip top/bottom layer||Keep stack-up targeting 90 Ω; to minimize reflection loss|
|Connectors & Cables||95 Ω||Surface mount||Use compliant connectors such Belkin HDMI 2.1 cables|
|Components||90 Ω||Surface mount||Reduce void by placement optimization|
Lowest Z possible
|2 layers||Partial to full Ground reference; full reference whenever possible|
|Ground plane||Lowest plane Z||NA||Full reference for signals|
HDMI 2.1 accommodates both Transition Minimized Differential Signaling (TMDS) and Fixed Rate Link (FRL) modes.
- TMDS supports legacy HDMI devices running on three data lanes and one clock lane.
- FRL runs on four data lanes.
On the receiver (RX), the TMDS clock path shares the FRL data lane.Therefore, on the PCB panel with Intel FPGA, you need a fanout buffer to split incoming RX signals to drive both paths to support both TMDS and FRL. At the schematic design level, one approach is to use an external fanout buffer. However, this additional fanout buffer increases system costs. Another approach is to use an integrated fanout buffer option with redriver at the RX side to recover signals at 19-decibel (dB) up to 12 Gbps.
HDMI 2.1 operates up to 12 Gbps with cable loss of up to 16dB. For cost optimization, use the redriver at the transmitter side.
|Insertion loss @12 Gbps||Z||Comment|
|DS125BR820||10dB||90 Ω||TX redriver|
|DS125MB203||18dB||90 Ω||RX redriver, integrated Fanout buffer|
The daughtercard panel size is small with high speed traces within 10 inches. If you target larger margin and desire for larger panel, you can opt for Meg6 material. Intel recommends a flex cable topology for signals up to 12 Gbps.
|Type FR4||Thick (T) um||Width (W) um||Height (H) um||Spacing (S) um||Dieletric Constant (Dk)|