Transmission Comparison between Micro-coaxial Harness Jumper and Low-transmission-loss Board Connections
1) Reference specifications for internal loss value ; loss budget
2) Typical internal connection method of USB4 (20 Gbps (10 GHz) / Lane)
3) Transmission Comparison test results between micro-coaxial harness jumper and low-transmission-loss board connections
4) I-PEX micro-coaxial connectors for high-speed transmission
5) Test conditions
As the usage of large-capacity memory devices increases, high-resolution images and videos can be enjoyed more easily on consumer products such as PCs, tablets and smartphones. As a result, the amount of information that needs to be processed on these devices has dramatically increased and the signal speed in the device has been getting faster and faster.
However, the higher the speed of the transmitted signal, the greater the transmission loss, such as conductor loss and dielectric loss, etc., that occurs in the transmission path, making signal transmission more difficult. Therefore, depending on the transmission standards, there are reference specifications for the internal loss value called the loss budget.
For example, in the case of the USB4 (*1) specification Ver. 1.0 [Thunderbolt 4 (*2)], which is a 20 Gbps (10 GHz)/lane high-speed transmission, the loss budget is specified as -7.5 dB for each of Device A, the cable, and Device B, as shown in the image below.
* 1: USB4 is the name of the standard defined by the USB-IF standards organization.
* 2: Thunderbolt 4 is a high-speed data transmission technology developed by Intel.
Board designers have more flexibility in designing their boards if they can transmit high-speed signals over a longer distance on the board within a loss budget of -7.5 dB. (1) High-speed signals such as USB4 can be transmitted by using a low-transmission-loss board if the transmission distance is to a certain extent. However, the longer the transmission distance, the greater the loss that occurs in the transmission path, and it becomes more difficult to transmit signals within the loss budget. Therefore, if the transmission path is long, it is necessary to take measures to suppress the loss that generated in the transmission path.
Although it is possible to extend the transmission distance by using an ultra-low-transmission-loss board, it may lead to a significant cost increase for mass production of the products. Other measures to extend the required transmission distance while suppressing loss may be: (2) use a jumper transmission path suitable for high-speed transmission, or (3) use a Retimer IC that corrects the attenuated signal waveform and reproduces the original waveform.
In this section, we conducted a transmission loss comparison test between (1) a low-transmission-loss board and (2) a micro-coaxial harness jumper.
Transmission comparison test results between micro-coaxial harness jumper and low-transmission-loss board connections
- Transmission loss comparison
CABLINE®-VS II micro-coaxial harness jumper < Low-transmission-loss board
- Transmittable distance (USB4 (Thunderbolt 4) specification (at 20 Gbps (10 GHz) / Lane)
CABLINE®-VS II micro-coaxial harness jumper > Low-transmission-loss board
1. Transmission by micro-coaxial harness jumper: 2 inches, 4 inches, 8 inches, 10 inches
2. Transmission by low-transmission-loss board: 2 inches, 4 inches
The maximum transmission length with a loss of -7.5 dB in each transmission path calculated from the above results (reference)
It was confirmed that the CABLINE®-VS II micro-coaxial harness jumper can transmit a distance about two to three times longer than the transmission using a low-transmission-loss board at any transmission speed.
I-PEX offers a number of micro-coaxial connectors with EMC shielding and a mechanical locking feature, suitable for jumper connection for USB4 [20 Gbps (10 GHz)/Lane]
- CABLINE®-VS II (used in test on this page)
0.5 mm pitch, horizontal mating type
- CABLINE®-CA II
0.4 mm pitch, horizontal mating type (narrow space type)
- CABLINE®-CA II PLUS
0.4 mm pitch, horizontal mating type (Wider Space type)
0.4 mm pitch, right angle vertical mating type
Low-transmission-loss board *
- Permittivity: 3.7
(* The permittivity of a general FR-4 board is about 4.7 to 5.0)
- Specifications of micro-coaxial harness:
- Transmission method: Differential transmission
- Test equipment: Network analyzer Keysight technologies E5071C
- Measured frequency : 20 MHz～20 GHz
- Measured Position :1,2,3,4 (G,S,S,G)
Low-transmission-loss boards of different lengths (2, 4, 8, and 10 inches) and CABLINE®-VS II micro-coaxial harness jumpers were made and insertion loss was compared.