Abstract:
An interface between USB devices employs isolation techniques to provide electrical isolation of a USB signal for transmission of the USB signal between the devices. Unidirectional isolator channels are utilized to transmit the USB signals, and a selection of an isolator channel operating in an intended direction is performed by either direction control logic or a USB hub function. Logic may be employed to detect a device attempting to initiate a USB signal. The logic operates to enable a transmitter on a receiving side and isolate the USB signal through an isolator channel operating in a transmission direction.

Description:
RELATED APPLICATION 
     This application claims priority to U.S. application Ser. No. 11/881,281, entitled “USB Integrated Bidirectional Digital Isolator,” filed on Jul. 26, 2007, the content of which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     Isolation of digital signals communicated between devices is needed to reduce safety hazards as well as for noise robustness factors. Shock and fire hazards may result from digital signals that are not isolated. Additionally, excess noise may be introduced into the digital signals as a result of insufficient isolation. Thus, electrical isolation of digital signals being transmitted between devices, while still allowing the digital signal to be transmitted across an interface between the devices, is a necessary requirement. 
     Interface components, operating to communicate digital signals between devices, may be utilized to isolate the digital signals. Isolator channels are components for electrically isolating digital signals and may be employed in interface components for such a purpose. Isolator channels are uni-directional components, while digital signals may be bi-directional. Thus, one isolator channel may be utilized to transmit a digital signal in one direction, while a second isolator channel is needed to transmit the digital signal in an opposite direction. For example, the first isolator channel may be used for communication from a transmitter to a receiver, while the second isolator channel may be used for communication from the receiver to the transmitter. 
     When a digital signal reaches an interface between devices, it is necessary to determine the intended direction of the signal to allow for an isolator channel operating in the intended direction to be utilized to electrically isolate the digital signal. Thus, a need exists for a process and component to manage and control the direction of the signal across the interface. 
     SUMMARY 
     A digital signal, such as a universal serial bus (USB) signal, is communicated between two or more devices, such as USB devices, across an interface. The interface operates to receive, isolate, and transmit the digital signal. Isolator channels or isolation techniques are employed at the interface to electrically isolate the devices while still allowing the transmission of the digital signal. The isolator channels or isolation techniques are managed by either direction control logic or a USB hub function, to control the direction of the signal across the interface. 
     The direction logic may detect an initiation of a transmission of the signal and enable a transmitter on the receiving side. For High Speed USB interfaces, a hub controller operates to determine an intended direction of a USB signal and utilize an isolator operating in the intended direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary and the following detailed description are better understood when read in conjunction with the appended drawings. Exemplary embodiments are shown in the drawings; however, it is understood that the embodiments are not limited to the specific methods and instrumentalities depicted herein. In the drawings: 
         FIG. 1  is a diagram illustrating an exemplary interface component that communicates and electrically isolates a digital signal between two low speed or full speed USB devices; 
         FIG. 2  is a timing diagram illustrating an exemplary frame of a digital signal communicated across an interface between two devices; 
         FIG. 3  is a flowchart illustrating an additional exemplary method of communicating a digital signal across an isolated USB interface; 
         FIG. 4  is a diagram illustrating an exemplary isolator component for providing electrical isolation between a USB host and a USB device; and 
         FIG. 5  is a diagram illustrating an additional exemplary isolator component for providing electrical isolation between a USB host and a USB device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram illustrating an exemplary low and full speed USB interface component  100  that communicates and electrically isolates bi-directional digital signals between two devices. This exemplary component  100  may be utilized in low and full speed USB applications, such as USB 1.1. The component  100  may be utilized between USB devices, such as between a USB host and a USB device or between two USB hosts. 
     The low and full speed USB isolation component  100  may operate to communicate and electrically isolate a digital signal between two devices, such as device  140   a  and device  140   b . Bi-directional communication ports  110   a  and  110   b  may act as the link between the devices  140   a  and  140   b  and the interface component  100 . The bi-directional communication ports  110   a  and  110   b  may operate to transmit and receive the digital signal between the two devices  140   a  and  140   b . The digital signal may be a USB data signal, for example. Other types of digital signals may be communicated between the devices  140   a  and  140   b  across the low and full speed USB isolation component  100 . Moreover, the USB isolation component  100  may include additional bidirectional communication ports. Two ports,  110   a  and  110   b , are shown only as an exemplary embodiment, as illustrated in  FIG. 1 . 
     USB isolation component  100  may isolate USB low and full speed interfaces by examining the data stream between two devices  140   a  and  140   b , which may be USB devices. A transition from an idle state to a non-idle state in a digital signal may serve as an indication that a frame is beginning (a transmission is being initiated by device  140   a  or  140   b ), which may thus indicate the direction of transmission of the digital signal. An isolator channel operating in the desired direction may then be utilized to electrically isolate the digital signal in the direction of transmission. 
     Isolator channels  130  may be uni-directional isolator channels that operate to provide high-volt electrical isolation to digital signals. The means of isolation may be, but are not limited to, capacitive, magnetic, optical, or acoustical means. 
     Transceivers  150   a  and  150   b  operate to transmit and receive digital signals from devices  140   a  and  140   b . For example, transceivers  150   a  and  150   b  may transmit and receive USB signals, from USB devices. Transceivers  150   a  and  150   b  may be USB-specific transceivers. Oscillator  160  may operate at a sufficiently high frequency to meet the timing requirements of the USB protocol. 
     Direction/line state control logic  120  may be used to determine a direction of the digital signal. The digital signal may be a bi-directional digital signal, for example a bi-directional USB signal. Upon determination of the direction of the digital signal, direction/line state control logic  120  may provide the digital signal to one of the isolator channels  130   a - 130   f  operating in the determined direction. Six isolator channels,  130   a - 130   f , are shown in the exemplary embodiment illustrated in  FIG. 1 . However, fewer or more isolator channels  130  may be included depending on the particular application. 
     To determine the direction of the digital signal, direction/line state control logic  120  monitors the data stream. Direction/line state control logic  120  detects a change in the digital signal from an idle state to a non-idle state. When a change is detected, direction/line state control logic  120  may determine the device  140   a  or  140   b  transmitting the digital signal. Direction/line state control logic  120  may then operates to enable the transceiver  150   a  or  150   b  to drive the device  140   a  or  140   b  receiving the digital signal. The transceiver  150   a  or  150   b  may then transmit the digital signal to the receiving device  140   a  or  140   b.    
     Direction/line state control logic  120  may further transmit the digital signal to one of the isolator channels  130   a - 103   f  that operates in the determined transmission direction of the digital signal. Moreover, direction/line state control logic  120  may perform subsequent monitoring operations to determine the end of transmission of the digital signal. When the transmission is complete, the transceiver  150   a  or  150   b  driving the receiving device  140   a  or  140   b  may then be disabled. 
     For example, while monitoring the data stream, direction/line state control logic  120  may detect a change from an idle state to a non-idle state in a digital signal from device  140   a . With this detection, it may be determined that the digital signal is being transmitted from device  140   a  to device  140   b . Direction/line state control logic  120  may transmit the digital signal to an isolator channel  130   a - 130   f  operating in the direction from device  140   a  to device  140   b . After isolation of the digital signal, direction/line state control logic  120  may then operate to enable the transceiver  150   b  associated with device  140   b  to transmit the isolated digital signal to device  140   b . A subsequent monitoring operation may indicate the end of transmission of the digital signal. Direction/line state control logic  120  may then disable the transceiver  150   b  driving the device  140   b.    
       FIG. 2  is a timing diagram illustrating an exemplary frame of the digital signal being communicated across the low and full speed USB isolation component  100  of  FIG. 1 . An idle (J) transition to a non-idle (K) transition may be detected by direction/line state control logic  120 . Upon detection of the transition, the appropriate transceiver  150   a  or  150   b  is enabled to drive the receiving device  140   a  or  140   b , the digital signal is isolated by an isolator channel  130  operating in the transmission direction of the digital signal, and the digital signal is transmitted to the receiving device  140   a  or  140   b . The end of the transmission may be determined by detecting an SEO symbol. The direction/line state control logic  120  may wait a pre-determined number of cycles, such as 3 bit-times, before disabling the transceiver and returning the isolator channel  130  to a non-driven state. 
       FIG. 3  is a flowchart illustrating an additional exemplary method of communicating a digital signal across a USB isolation component  100  of  FIG. 1 . The USB isolation component  100  operates to isolate the digital signal to provide electrical isolation between the devices  140   a  and  140   b . The digital signal is being transmitted from a transmitting device to a receiving device, and the devices may be any USB devices  140   a  or  140   b  or other devices capable of transmitting and receiving digital data. 
     At  305 , an initiation for transmission of the digital signal from the transmitting device is detected. The detection may be done by monitoring the data stream of devices  140   a  and  140   b . A change from an idle to a non-idle state may signify transmission of a digital signal. The detection may be performed by direction/line state control logic  120 . 
     At  310 , upon detection of the transition, direction/line state control logic  120  operates to enable the transceiver  150   a  or  150   b  to drive the receiving device. For example, it may be detected by a change in transition of a digital signal that device  140   a  is transmitting the digital signal. Device  140   b  may then receive the digital signal. To achieve this transmission, transceiver  150   b , operating for device  140   b , is enabled to perform the transmission to device  140   b.    
     At  315 , the digital signal is transmitted in the detected and enabled direction. The transmission may include utilizing an isolator channel  130   a - 130   f  operating in the direction of the digital signal transmission. The uni-directional isolator channel  130  isolates the digital signal to provide electrical isolation between the device  140   a  and  140   b . Direction/line state control logic  120  utilizes a uni-directional isolator channel  130  operating in the desired direction. 
     At  320 , the isolated digital signal is transmitted to the receiving device  140   a  or  140   b  from the enabled transceiver  150   a  or  150   b.    
     At  325 , a completion of the digital signal transmission is detected by, for example, direction/line state control logic  120 . When the digital signal has been sent, the state of the signal changes from a non-idle state to an idle state. 
     At  330 , the transceiver driving the receiving device is disabled. Continuing the above example, transceiver  150   b , transmitting the digital signal to device  140   b , is disabled upon completion of the transmission. The disablement may occur after a predetermined number of cycles elapse after the detection. 
       FIG. 4  is a diagram illustrating an exemplary high speed USB isolator component  400  for providing electrical isolation between a High Speed USB host  440   a  and a USB device  440   b . A USB signal may be communicated between the USB host  440   a  and the USB device  440   b . This exemplary component  400  may be utilized in USB applications, such as USB 2.0. 
     The USB isolator component  400  may include bi-directional communication ports  410   a  and  410   b  for transmitting and receiving the USB signal between the two devices to USB physical layer components  450   a  and  450   b . A USB hub controller  420  may be connected to the USB physical layer components  450   a  and  450   b  for the purposes of retiming and repeating the USB signals and for determining a transmission direction of the USB signal. The USB hub controller  420  may be a multi-port device that allows for the connection of multiple devices. The USB hub controller  420  may determine the transmission direction of a digital signal to convey to isolator channels  430 . 
     The isolator channels  430  may isolate and transmit the USB signal in the determined direction. The isolator channels  430  may include multiple uni-directional isolator channels that operate to provide high-volt electrical isolation to digital signals. 
     The USB hub controller  420  serves as a repeater which serves to receive, retime, and repeat the USB signal. The signals in and out of the hub controller  420  are all uni-directional and can be easily isolated with uni-directional isolators, such as the isolator channels  430 . For this configuration, as shown in  FIG. 4 , separate direction control logic is not required as the hub function inherently provides the direction logic. 
     In an exemplary embodiment shown in  FIG. 5 , a second high speed USB isolator component  500  includes a physical layer component  450   a  as well as a clock data recovery (CDR) component  510  and a transceiver (XCVR) component  520 . In this embodiment, the isolator channels  430  are connected between the CDR component  510  and the XCVR component  520 . However, the USB hub controller  420  continues to inherently provide the USB digital signal direction and determine the transmission direction to convey to the isolator channels  430 . The isolator channels  430  may isolate and transmit the USB digital signal in the determined direction as described above with relation to  FIG. 4 . The CDR component  510  and the XCVR component  520  together may form the physical layer component  450   b  shown in  FIG. 4 . In some applications, it may be necessary or beneficial to split the physical layer component  450   b , as shown in  FIG. 5 , into the CDR component  510  and the XCVR component  520 . Alternatively, the physical layer component  450   a  may be split, or both components  450   a  and  450   b  may be split. 
     The foregoing examples are provided merely for the purpose of explanation and are in no way to be construed as limiting. While reference to various embodiments are shown, the words used herein are words of description and illustration, rather than words of limitation. Further, although reference to particular means, materials, and embodiments are shown, there is no limitation to the particulars disclosed herein. Rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.