Methods and apparatus for reducing power usage of a transmitter and receiver coupled via a differential serial data link

Abstract

Methods and apparatus are disclosed for using in-band signal(s) over a differential serial data link to reduce power usage of a transmitter and receiver coupled by the link.

1 . For use with a transmitter, a receiver and a differential serial data link including at least two lines connecting the transmitter and receiver, a method comprising: 
 determining a voltage difference between the at least two lines of the differential serial data link to eliminate common mode noise present on the at least two lines;    determining if an absolute value of the voltage difference between the at least two lines of the differential serial data link is less than a threshold; and    transitioning at least a portion of the receiver from a first state to a second state if the absolute value of the voltage difference between the at least two lines of the differential serial data link is less than the threshold for at least a predefined time period.    
   
   
       2 . A method as defined in  claim 1  wherein the first state is a normal power state and the second state is a reduced power state.  
   
   
       3 . A method as defined in  claim 1  further comprising transitioning at least a portion of the transmitter from the first state to the second state.  
   
   
       4 . A method as defined in  claim 1  wherein determining if the absolute value is less than the threshold comprises: 
 developing a signal representative of the absolute value of the voltage difference between the at least two lines; and    integrating the developed signal to develop an integrated signal; and    wherein transitioning at least the portion of the receiver from the first state to the second state comprises:    signaling the at least a portion of the receiver to enter the second state if the integrated signal falls below the threshold.    
   
   
       5 . A method as defined in  claim 4  further comprising discharging an RC circuit; and wherein the integrated signal is a voltage associated with the RC circuit.  
   
   
       6 . A method as defined in  claim 5  further comprising transitioning the at least a portion of the receiver from the second state to the first state when further communication is expected from the transmitter.  
   
   
       7 . A method as defined in  claim 6  wherein the transitioning of the receiver from the second state to the first state is performed by: 
 charging the RC circuit; and    if the voltage associated with the RC circuit passes the threshold, signaling the at least a portion of the receiver to exit the second state.    
   
   
       8 . A method as defined in  claim 1  further comprising transitioning at least a portion of the transmitter from a normal power state to a reduced power second state.  
   
   
       9 . A method as defined in  claim 8  wherein transitioning at least the portion of the transmitter from the normal power state to the reduced power state occurs in response to detecting an absence of data to transmit in a queue associated with the transmitter.  
   
   
       10 . For use with a transmitter, a receiver, and a differential serial data link including at least two lines connecting the transmitter and receiver, a method comprising: 
 determining a voltage difference between the at least two lines of the differential serial data link to eliminate common mode noise present on the at least two lines;    developing a signal representative of an absolute value of the voltage difference between the at least two lines at the receiver;    integrating the developed signal to develop an integrated signal; and    determining whether at least a portion of the receiver is to enter a reduced power state based on a comparison of the integrated signal and a threshold.    
   
   
       11 . A method as defined in  claim 10  further comprising discharging an RC circuit; and wherein the integrated signal is a voltage associated with the RC circuit.  
   
   
       12 . A method as defined in  claim 11  further comprising transitioning the at least a portion of the receiver from the reduced power state to the normal power state when further communication is expected from the transmitter.  
   
   
       13 . A method as defined in  claim 12  wherein the transitioning of the receiver from the reduced power state to the normal power state is performed by: 
 charging the RC circuit; and    if the voltage associated with the RC circuit exceeds the threshold, signaling the at least a portion of the receiver to exit the reduced power state.    
   
   
       14 . For use with a transmitter, a receiver and a differential serial data link connecting the transmitter and receiver, a method comprising: 
 detecting a first in-band signal received via the differential serial data link, wherein detecting the first in-band signal comprises eliminating common mode noise from the in-band signal;    transitioning at least a first portion of the receiver from a normal power state to a reduced state in response to the first in-band signal;    detecting a second in-band signal received at the receiver via the differential serial data link; and    transitioning at least a second portion of the receiver from the normal power state to the reduced power state in response to the second in-band signal.    
   
   
       15 . A method as defined in  claim 14  wherein the first in-band signal is a lack of a substantial voltage difference on the differential serial data link which occurs for at least a first time period.