USB isolator with advanced control features

Abstract

A USB-based isolator system conveys USB signals between a pair of galvanically isolated circuit systems and supports controlled enumeration by a downstream device on upstream USB signal lines. The isolator system provides a multi-mode voltage regulator to support multiple voltage supply configurations. The isolator system further provides control systems for each of the isolated circuit systems and provides robust control in a variety of start up conditions. Additionally, the isolator system includes refresh timers and watchdog mechanisms to support persistent operation but manage possible communication errors that can arise between the isolated circuit systems.

We claim: 
     
       1. An isolation system, comprising:
 a plurality ofone or more isolation devices bridging an isolation barrier between an upstream side and a downstream side of the isolation barrier, 
 a USB interface provided on an the upstream side of the isolation barrier, including a termination circuit having a pull up resistor, 
 an isolator transceiver coupling the USB interface to the isolation devices, and 
 an isolator transmitter provided on a the downstream side of the isolation barrier and configured to receive an enumeration transmit to the upstream side a control signal controlling which signal line of a pair of differential signal lines is to be connected to the pull up resistor, 
 wherein the enumeration isolation system is configured to propagate the control signal propagates through at least one of the one or more isolation devices to the upstream side and controls switching of the pull up resistor in the termination circuit. 
 
     
     
       2. The isolation system of  claim 1 , wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol and a separate from the at least one isolation device is provided for the enumeration control signal. 
     
     
       3. The isolation system of  claim 1 , wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol, and signals are encoded so the enumeration control signal can propagate through said isolation devices along with the D+ and D− data. 
     
     
       4. The isolation system of  claim 1 , wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol and are shared with the enumeration control signal. 
     
     
       5. The isolation system of  claim 1 , wherein the one or more isolation devices are unidirectional isolation devices. 
     
     
       6. The isolation system of  claim 1 , wherein the one or more isolation devices are bidirectional isolation devices. 
     
     
       7. The isolation system of  claim 1 , further comprising an input for a selection signal that identifies which one of the D+ and D− data lines is to be connected to the pull up resistor. 
     
     
       8. The isolation system of  claim 7 , wherein the input is provided on the upstream side of the isolation barrier. 
     
     
       9. The isolation system of  claim 7 , wherein the input is provided on the downstream side of the isolation barrier. 
     
     
       10. The isolation system of claim 1, further comprising a pulse generator to generate the control signal, wherein the control signal is a pulse signal.  
     
     
       11. The isolation system of claim 1, further comprising a refresh timer to maintain one side of the isolation system in a reception state for communication across the isolation barrier during a watchdog interval.  
     
     
       12. A method of communicating in a USB isolation system including a first side and a second side separated by an isolation barrier, comprising:
 transmitting, from the first side to the second side, a control signal across the isolation barrier through at least one isolation device; and   receiving the control signal from the first side; and   in response to receiving the control signal, controlling which signal line of a pair of differential signal lines is to be connected to a pull up resistor.    
     
     
       13. The method of claim 12, further comprising:
 at the first side, transmitting D+ and D− data signals of a USB protocol across the isolation barrier through a different isolation device than the one used to transmit the control signal.    
     
     
       14. The method of claim 12, further comprising:
 at the first side, transmitting D+ and D− data signals of a USB protocol across the isolation barrier through the same isolation device used to transmit the control signal.    
     
     
       15. The method of claim 14, further comprising:
 encoding the control signal with the data signals.    
     
     
       16. The method of claim 12, further comprising:
 receiving a selection signal that identifies which of a D+ and D− data lines is to be connected to the pull up resistor.    
     
     
       17. The method of claim 16, wherein the selection signal is received on the second side.  
     
     
       18. The method of claim 16, wherein the selection signal is received on the first side.  
     
     
       19. The method of claim 12, wherein the control signal is a pulse signal.  
     
     
       20. The method of claim 12, further comprising:
 maintaining one side of the USB isolation system in a reception state for communication across the isolation barrier during a watchdog interval.    
     
     
       21. An integrated circuit, comprising:
 an isolation barrier separating a downstream side and an upstream side of the integrated circuit; and   one or more isolation devices bridging an isolation barrier between the downstream and upstream sides,   the downstream side including an isolator transmitter to transmit a control signal through at least one of the one or more isolation devices to the upstream side,   the upstream side including
 a USB interface including a termination circuit having a pull up resistor, 
 an isolator receiver to receive the control signal transmitted by the isolator transmitter on the downstream side, and 
 a switch controller configured to control which signal line of a pair of differential signal lines is to be connected to the pull up resistor in the termination circuit according to the control signal.  
   
     
     
       22. The integrated circuit of claim 21, wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol that are separate from the isolation device(s) provided for the control signal.  
     
     
       23. The integrated circuit of claim 21, wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol, and signals are encoded so the control signal can propagate through said isolation devices along with the D+ and D− data.  
     
     
       24. The integrated circuit of claim 21, wherein isolation devices are provided for each of a D+ and D− data signal of a USB protocol and are shared with the control signal.  
     
     
       25. The integrated circuit of claim 21, wherein the one or more isolation devices are unidirectional isolation devices.  
     
     
       26. The integrated circuit of claim 21, wherein the one or more isolation devices are bidirectional isolation devices.  
     
     
       27. The integrated circuit of claim 21, further comprising an input for a selection signal that identifies which one of the D+ and D− data lines is to be connected to the pull up resistor.  
     
     
       28. The integrated circuit of claim 27, wherein the input is provided on the upstream side of the isolation barrier.  
     
     
       29. The integrated circuit of claim 27, wherein the input is provided on the downstream side of the isolation barrier.  
     
     
       30. The integrated circuit of claim 21, further comprising a pulse generator to generate the control signal, wherein the enumeration control signal is a pulse signal.  
     
     
       31. The integrated circuit of claim 21, further comprising a refresh timer to maintain one side of the integrated circuit in a reception state for communication across the isolation barrier during a watchdog interval.