The present invention relates to a Serial Bus transceiver interface, particularly although not exclusively for use in a Universal Serial Bus (USB) device.
It is well known to employ a bus to carry signals within and between electronic devices. The definition of one such bus, the Universal Serial Bus (USB) is described in the following reference document—Universal Serial Bus Specification Revision 1.1 published by the USB Implementation Forum. The USB standard provides specifications for a host, a device and the cabling which links them. Amongst other requirements of the standard, a USB host must be capable of detecting the speed of those devices with which it is communicating. There are four possible such states as set out in the table of FIG. 1 below.
The USB standard has become very popular with manufacturers of personal computers in particular. More recently and particularly with the expansion of the Internet, it is becoming even more necessary for a computer to be connected, at least part of the time, to a telephone line to permit the transfer of data such as electronic mail. In the case of a laptop computer, it is often not convenient or possible to connect to a fixed telephone line. Thus, interfaces have been developed to allow a mobile telephone to be connected to a computer. Such interfaces can place severe demands on a lightweight battery-powered device such as a mobile telephone where considerations of size and complexity of circuitry together with power consumption are very important.