US 6,320,408 B1Granted

Dual-sided undershoot-isolating bus switch

AssigneePericom Semiconductor Corp.

InventorDavid Kwong

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Abstract

Both buses connected to a bus switch are protected from undershoots. A bus switch transistor is an n-channel metal-oxide-semiconductor (MOS) with its source connected to a first bus and its drain connected to a second bus. An enable gate drives the gate node of the bus switch transistor high to enable or low to disable. Undershoot sensing circuits are attached to the first and second bus. When a low-going transition is detected by an undershoot sensing circuit, an n-channel connecting transistor is turned on, connecting the bus with the low-going transition to the gate node through a grounded-gate n-channel transistor. If an undershoot occurs, it is coupled to the gate node. Since both the gate and source of the bus switch transistor are coupled to the undershoot, the gate-to-source voltage never reaches the transistor threshold and the bus switch transistor remains off.

Claims20

Dependent claims

A bus switch with undershoot protection on both ports comprising:

a bus-switch transistor controlled by a gate node that controls current conduction between a first port and a second port;
a first detector, coupled to the first port, for activating a first signal in response to a low-going transition detected on the first port;
a first fixed-gate transistor coupled to conduct an undershoot on the first port to a first node;
a first connecting transistor coupled to conduct the undershoot from the first node to the gate node when the first signal is activated;
an enable gate, receiving an enable signal, for driving an enabling voltage onto the gate node to enable conducting by the bus-switch transistor, and for driving a disabling voltage onto the gate node to isolate the first port from the second port;
a second detector, coupled to the second port, for activating a second signal in response to a low-going transition detected on the second port;
a second fixed-gate transistor coupled to conduct an undershoot on the second port to a second node;
and
a second connecting transistor coupled to conduct the undershoot from the second node to the gate node when the second signal is activated, whereby undershoots are conducted through fixed-gate and connecting transistors to the gate node to prevent channel conduction by the bus-switch transistor.

6 more elements

An undershoot-protecting bus switch comprising:

bus switch means for selectively connecting and isolating a first bus from a second bus in response to a control gate;
first fixed-gate transistor means, coupled between the first bus and a first node, for conducting an undershoot on the first bus to the first node;
first connecting transistor means, coupled between the first node and the control gate, for coupling the undershoot from the first node to the control gate, the first connecting transistor means responsive to a first gate;
second fixed-gate transistor means, coupled between the second bus and a second node, for conducting an undershoot on the second bus to the second node;
second connecting transistor means, coupled between the second node and the control gate, for coupling the undershoot from the second node to the control gate, the second connecting transistor means responsive to a second gate;
first signaling transistor means for activating the second gate of the second connecting transistor means when the undershoot is detected on the second bus;
second signaling transistor means for activating the first gate of the first connecting transistor means when the undershoot is detected on the first bus;
enable gate means for driving the control gate with an enabling signal when the bus switch means is to connect the first bus to the second bus, and for driving a disabling signal onto the control gate when the first bus is to be isolated from the second bus;
first isolating transistor means, in the enable gate means, for isolating the disabling signal from the control gate when the undershoot is detected on the first bus;
second isolating transistor means, in the enable gate means, for isolating the disabling signal from the control gate when the undershoot is detected on the second bus.

7 more elements

Dependencies are inferred from the claim text.