Application of USB-C Technology in the Commercial AV Market: Considerations and Solutions

Table of Contents

Introduction to USB-C Technology

USB-C technology is a shortened term for USB Type-C, which is a completely new form of USB interface. USB is a type of hot-swappable transmission bus, and Type-C can be seen as a new form of this transmission bus. This article will present the use of Type-C technology in current products, covering aspects such as its physical structure, protocol support, and considerations.

Introduction to USB-C Pin

Figure 1

The diagram shown in Figure 1 represents a schematic of the Type-C connector pins. From the diagram, you can see a total of 24 pins, including: 2 sets of ground pins, 2 sets of power pins, 2 sets of D+ and D- pins, 4 sets of Tx/Rx differential pairs, and 2 sets of CC/SUB lines. The specific functions of these pins are as follows:

Table 1

Introduction to PD Protocol

Figure 2

Note: Power Supply Port refers Host/DFP Downstream Port, Sink Port refers Device/UFD Upstream Port.

The PD (Power Delivery) protocol, which stands for USB-PD, is a charging protocol used to specify how charging voltage and current should be delivered between a charger, charging cable, and the device being charged. It can be simplified as what people commonly refer to as “fast charging.” The communication process for PD is as depicted in Figure 2 and primarily involves the following steps:

  1. When a Downstream Facing Port (DFP) detects a device plugged into its CC pins, it initially provides 5V power through Vbus.
  2. Through the CC pins, the DFP actively initiates communication and declares its power capabilities (recommended values in the protocol are 5V/3A, 9V/3A, 12V/3A, 15V/3A, 20V/3A). The host or device can request a role swap.
  3. Once both sides agree on the parameters, they inform each other.
  4. USB enumeration begins (USB enumeration involves the negotiation of various parameters related to data transfer, but it’s not detailed here).

Considerations for USB-C in the Commercial AV Market

Type-C Performance and Cable Length

In Type-C connectors, there are a total of 4 sets of Tx/Rx (transmit/receive) lines used for high-speed differential signal transmission. In different product designs, the definition of Type-C functionality and performance characteristics can be determined based on the product’s needs and usage scenarios. The specific functions and video performance of Type-C may vary. AVA‘s products primarily belong to the category of personal use KVM Docking products. Our products are designed to meet the highest standards, supporting the maximum benchmark of MST dual displays at 4K@60 with 4:4:4 chroma subsampling, equivalent bandwidth. Additionally, our products also support various resolutions, high refresh rates (up to 240Hz without exceeding the overall bandwidth), and widescreen resolutions.

Table 2

In addition to the video specifications, it’s important to consider cable length for video and USB configuration solutions. The table above specifies the standard cable lengths for each product. If the Type-C interface is extended to a USB 2.0 interface, the maximum cable length defined by the USB 2.0 protocol is 4 meters.

If the Type-C interface is extended to a USB 3.0 interface, and each lane is used to transmit a 5Gbps video data rate (for example, 4K@30), the USB 3.0 protocol specifies a cable length of 2 meters.

To support actual transmission bandwidth of up to 10Gbps, such as MST dual 4K@60 video, the USB protocol specification dictates a cable length of 1 meter.

In practical engineering use, it’s essential to ensure cable transmission efficiency and then perform specific cable length measurements. For certain specialized cables, it may be possible to exceed the standard cable lengths defined in the protocol.

Negotiating Power Delivery Capability in the PD Protocol

The PD (Power Delivery) protocol is a charging protocol, and the specific protocol details were introduced in Section 1.2, “Introduction to the PD Protocol.” This subsection primarily focuses on considerations related to the PD protocol.

The PD protocol recommends a total of five voltage/current combinations: 5V/3A, 9V/3A, 12V/3A, 15V/3A, and 20V/3A. The Type-C Vbus port can accept a maximum voltage of 20V, a maximum current of 5A, and can deliver a maximum power of 100W. Under normal circumstances, it is advisable to adhere to the recommended voltage/current values specified in the PD protocol.

Type-C Cable

Common Types of USB-C Cables

Table 3

Notes: The three types of cables corresponding to a, b, and c in Table 2 are common types of Type-C cables. Pay special attention to the highlighted portions in the notes.

Type-C Cable Transmission Rate

The claimed transmission speed of Type-C cables generally refers to the maximum transmission speed supported for USB signals and video signals.

Table 4

For Alt 2Lane DP mode, if the requirement is for DP (DisplayPort) to support a maximum resolution of 4K@30Hz, each Lane’s DP signal speed is at 5.4Gbps. In this case, cables that meet the USB 3.1 Gen 1 standard can transmit the signal (USB 3.1 Gen 1 operates at 5Gbps, slightly below 5.4Gbps, and does not affect transmission performance).

If the requirement is to achieve 2Lane DP resolutions of 4K@60Hz and above, or to transmit USB 3.1 Gen 2 data, then cables that meet the USB 3.1 Gen 2 standard are needed, which have a maximum transfer speed of 10Gbps.