High-Speed USB ULPI Transceiver-less Link Logic

Abstract:

A link logic called High-speed USB ULPI Transceiver-less Link Logic to connect USB device without using the USB transceiver is presented. It can save costs related to platform design, reduce the board size design, and provide a flexible way of implementing the USB connection for inter-chip communication.

1.   Introduction

After more than 10 years since its birth on 1994, the USB (Universal Serial Bus) has become a real universal bus from desktop/laptop computer to consumer electronics, to industrial and to everywhere. Due to the popularity of the USB, many devices are implemented using the USB interface. Although the USB protocol is plug-and-play, in many system designs, the USB devices are sold on a circuit board to provide a full feature to end customers, and are not removable from the system.

The general connection for such a system is shown in Figure 1.  The USB protocol requires that the USB transfer data through differential signals, with strict signal requirements. This is called the USB Physical layer signal protocols [1].  The electrical signal transfer is usually through a USB Transceiver (called USB PHY, for handling USB physical layer signal transfer). In 2004, the ULPI specification [3] was released and it quickly became the most popular HS USB PHY interface standard.

Figure 1. General USB Connection through USB ULPI PHY

Therefore, in this case, both the USB Host and the USB Device have to include an USB PHY into their chip or an extra USB PHY device is required at the board level for the USB Physical level connection. In either of these cases, the cost and the complexity of the whole system is increased. For such inter-chip connection, if there is no need to plug and/or remove the device, there should be other way to implement that connection.

The USB organization presented a standard called the High-Speed Inter-Chip USB Specification [2] in an attempt to solve this problem without using PHY for those inter-chip connections. It needs new design logic for both the USB Host and the USB Device. Therefore, it only partially solves this problem.

In addition, the HS IC USB standard works only for new designs or devices designed with the HS IC USB standard.  There are still many legacy devices or USB chips on market. Therefore, there is a need to address such legacy devices’ connection to a host system. Similarly, an IC USB for the legacy USB device connection is needed.

2.   HS USB ULPI TLL

The HS USB ULPI TLL can solve the above problem for the legacy USB devices connection without the need of USB PHY. It is called the High-Speed USB Transceiver-less Link Logic (HS USB ULPI TLL).

Figure 2 describes the connection with the HS USB TLL. The standard interface between the USB Host/Device controller and the PHY are ULPI interface.

Figure 2 HS USB...