Power saving circuit having a keeper stage to hold a signal line in a weakly held state
AssigneeIntel Corporation
InventorsGregory Rose, James R. Feddeler, Zahid Ahsanullah
Life of this patent
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Abstract
Power saving method is achieved by weakly holding a signal line in its last in time state, which is responsive to and may be overcome by the state of an external signal. During sleep mode, the weakly held signal line state tracks and holds the external signal using alternatively a controllable weak pull-up or pull-down device, such that weakly held state may be driven to a different state by the external driving signal with slight power consumption. When sleep mode is off, the keeper function is disabled and the signal line maybe driven alternatively internally or externally depending upon the state of an enable line.
Claims23
An apparatus comprising:
- a Universal Serial (USB) device to connect to a USB host, the USB device comprising:
- an internal signal line connectable to an external signal line that couples to the USB host;
- and
- a keeper stage comprising at least one controllable weak pull-up device and at least one controllable weak pull-down device, the keeper stage to hold the internal signal line in a weakly held state responsive to changes in a state of the external signal line that occur after a powering down, in which control of the at least one controllable weak pull-up device comprises a logical NAND of a SLEEP signal and a signal on the internal signal line, and control of the at least one controllable weak pull-down device comprises a logical NOR of an inverted SLEEP signal and the signal on the internal signal line.
A method comprising:
- after powering down a Universal Bus (USB) device, sensing a state of an external signal coupled to a USB host;
- storing the state of an external signal in an internal signal weakly held on a stored state by a keeper stage having at least one controllable weak pull-up device and at least one controllable weak pull-down device, the weakly held internal signal being responsive to changes in the state of the external signal;
- and
- controlling the at least one weak pull-up device with a logical NAND of the internal signal and a SLEEP signal, and controlling the at least one weak pull-down device with a logical NOR of an inverse of the SLEEP signal and the internal signal.
A Universal Serial Bus (USB) device having an internal signal line to connect to a USB host through an external signal line, the USB device comprising:
- an output buffer stage to drive the internal signal line and the external signal line;
- a keeper stage to maintain a state of the internal signal line in a weakly held state;
- and
- a processor;
- wherein the USB device operates in at least three states:
- (a) when both the output buffer stage and the keeper stage are disabled, the USB device listens to the USB host through the external signal line,
- (b) when the output buffer stage is enabled, the USB device drives the external signal line to send a signal to the USB host, and
- (c) when the USB device is powered down, the keeper stage is enabled to hold the internal signal line in a weakly held state responsive to changes in the external signal line, and the processor is awakened when the USB host drives the external signal line to a different state.
Dependencies are inferred from the claim text.