The present invention relates generally to electronic circuits, and more particularly to a multiple voltage supply switch to selectively apply one of a plurality of voltage supplies to an output.
Often in integrated circuit design, one or more of the components of an integrated circuit or system will need to be powered by different voltages or the circuit or system will perform different functions depending upon the voltage applied to the component. For example, the cells of a memory array or system will perform different functions or can be placed in different modes of operation depending upon the voltage level applied to the gates of passgate transistors controlling the operation of the memory cells or devices in the array. To place selected memory cells in a programming mode, a high voltage may be applied to the gate of the passgate transistor controlling the selected memory cells. A second, different voltage level may be applied to the gate of the passgate transistor during an erase verify operation and a third voltage level may be applied to the gate of the passgate transistor for a normal read operation of the memory cells. A need therefore exists to multiplex a plurality of analog voltage supplies onto a common bus to control the operation of memory cells in a memory system or to connect to components operating at various voltage levels.
One known arrangement for multiplexing three different voltage supplies onto a common bus is to use two two-way analog switches connected in series. Two of the voltage supplies, V1 and V2, would be connected to inputs of the first analog switch. The output of the first analog switch would be connected to one input of the second analog switch and the third voltage supply, V3, would be connected to another input of the second analog switch. The first analog switch can then be operated to connect either V1 or V2 to the input of the second analog switch. The second analog switch can then be operated to connect the output of the first analog switch (V1 or V2) or V3 to its output.
A switch leg or path through a two-way analog switch typically includes at least two p-channel devices or field effect transistors in series between the voltage supply and the output of the switch. Therefore, for the arrangement described above, V1 or V2 would be connected through at least four p-channel devices to be connected to the output of the second two-way analog switch. Each of the p-channel devices introduces some amount of IR drop or voltage drop (voltage=current (I)xc3x97resistance (R)) which may adversely affect the performance of this switching arrangement for use in high current applications.
Accordingly, for the reason stated above, and for other reasons that will become apparent upon reading and understanding the present specification, there is a need for a multiple voltage supply switch that has minimal IP drop between the input and the output of the switch and that exhibits good performance characteristics for high current applications.
In accordance with the present invention, a multiple voltage supply switch includes a plurality of switching device pairs. Each switching device pair is connectable between an associated one of a plurality of voltage supplies and an output of the switch. Each switching device pair includes a first switching device connected to the associated one of the plurality of voltage supplies and a second switching device connected in series between the first switching device and the output of the switch. Both the first and second switching devices are activated to connect the associated one of the voltage supplies to the output of the switch and at least one of the first or the second switching devices of each of the other switching device pairs is inactivated to disconnect the voltage supply associated with each of the other switching device pairs from the output of the switch.
In accordance with another aspect of the present invention, a system includes a multiplex voltage supply switch and a plurality of voltage supplies connected to the multiplex voltage supply switch. The system further includes at least one device operating on voltages of different levels that is connected to an output of the multiplex supply switch. The multiplex switch alternatively applies a selected one of the plurality of voltage supplies to the at least one device to cause the device to perform different predetermined operations in response to the level of the voltage supply applied. The system may include a control circuit to select the voltage supply to be applied to the device according to the desired function or operation to be performed. The control circuit may be controlled by an algorithm. The multiplex switch includes a plurality of switch paths, one switch path between each of the plurality of voltage supplies and an output of the multiplex switch. Each switch path includes only two switching devices to minimize an IR drop across the switch path.
In accordance with a further aspect of the present invention, a method of alternatively applying one of a plurality of voltage supplies to a device, in response to an operation or function to be performed by the device, includes connecting each of a plurality of voltage supplies to one of a plurality switching device pairs of a multiplex switch; selecting one of the plurality of voltage supplies to be connected to an output of the multiplex switch by activating a first switching device and a second switching device of the switching device pair associated with the one of the plurality of voltage supplies; and selectively inactivating at least one of a first or a second switching device of each of the other switching device pairs to disconnect an associated one of the plurality voltage supplies not selected to be connected to the output of the multiplex switch.