Wordline driver for a non-volatile memory device, a non-volatile memory device and method
View Patent ↗A wordline driver, for a non-volatile memory device, comprises a wordline driver output, a first power source, adapted to provide an erase level voltage for erasing portions of the non-volatile memory device, a second power source, adapted to provide read and program level voltages for reading and programming portions of the non-volatile memory device and first switching means, including an isolation transistor, adapted to connect the wordline driver output to a one of the first and second power sources dependent upon an operating mode of the wordline driver. The wordline driver further comprises a programmable switch controller for providing a variable control signal to a control electrode of the isolation transistor. The programmable switch controller is arranged to set the variable control signal to a value dependent upon the operating parameters of the non-volatile memory device and such that the endurance of the isolation transistor is maximised.
1. A wordline driver for a non-volatile memory device, the wordline driver comprising:
a wordline driver output;
a first power source, adapted to provide an erase level voltage for erasing portions of the non-volatile memory device;
a second power source, adapted to provide read and program level voltages for reading and programming portions of the non-volatile memory device;
first switching means adapted to connect the wordline driver output to a one of the first and second power sources dependent upon an operating mode of the wordline driver, the first switching means including an isolation transistor adapted to selectively connect the second power source and the wordline driver output; and
a programmable switch controller for providing a variable control signal to a control electrode of the isolation transistor, the programmable switch controller being arranged to set the variable control signal to a value dependent upon at least one operating parameter of the non-volatile memory device, and wherein the programmable switch controller further comprises:
a voltage reference having an output; and
a control loop connected between the output of the voltage reference and the control electrode of the isolation transistor and configured to adapt the output of the voltage reference to provide the variable control signal to the control electrode of the isolation transistor.
2. A wordline driver for a non-volatile memory device, the wordline driver comprising:
a wordline driver output;
a first power source, adapted to provide an erase level voltage for erasing portions of the non-volatile memory device;
a second power source, adapted to provide read and program level voltages for reading and programming portions of the non-volatile memory device;
first switching means, including an isolation transistor, adapted to connect the wordline driver output to a one of the first and second power sources dependent upon an operating mode of the wordline driver; and
a programmable switch controller for providing a variable control signal to a control electrode of the isolation transistor, the programmable switch controller being arranged to set the variable control signal to a value dependent upon at least one operating parameter of the non-volatile memory device, wherein the programmable switch controller comprises:
a voltage reference having an output; and
a control loop connected between the output of the voltage reference and the control electrode of the isolation transistor and configured to adapt the output of the voltage reference to provide the variable control signal to the control electrode of the isolation transistor.
3. The wordline driver of claim 2 , wherein the control loop comprises:
a first transistor, substantially identical to said isolation transistor, and configured for providing a compensation voltage to the control loop for adapting the output of the voltage reference; and
a second switching means, adapted to switch the first transistor in and out of said control loop in dependence upon an operating mode.
4. The wordline driver of claim 3 , wherein the control loop further comprises an operational amplifier having:
an output coupled to said control electrode of the isolation transistor for providing the variable control signal;
a first input selectively coupled to the output of said voltage reference; and
a second input coupled to a first current electrode of the first transistor in dependence on the second switching means.
5. The wordline driver of claim 4 , wherein a control electrode of said first transistor is connected to the control electrode of said isolation transistor and to the output of the operational amplifier, and a second current electrode of said first transistor is connected to a third power source.
6. The wordline driver of claim 5 , wherein the second switching means is a changeover switch comprising two inputs and a single output, wherein the single output of said changeover switch is connected to the second input of the operational amplifier, one of the two inputs is connected to the output of the operational amplifier and the other of the two inputs is connected to the first current electrode of the first transistor, such that the changeover switch is operable to switch the first transistor in and out of said control loop.
7. The wordline driver of claim 5 , wherein the programmable switch controller further comprises:
a bypass transistor, connected between the third power source and the control electrode of the isolation transistor; and
a read select input connected to a control electrode of the bypass transistor and to an enable input of the operational amplifier, such that the read select input is operable to disable the operational amplifier and connect the control electrode of the isolation transistor to the third power source during a read operating mode.
8. The wordline driver of claim 2 , wherein the voltage reference is a programmable voltage reference.
9. The wordline driver of claim 8 , wherein the programmable voltage reference is a Digital-to-Analog converter.
10. The wordline driver of claim 9 , wherein the Digital-to-Analog converter is a resistor network Digital-to-Analog converter.
11. The wordline driver of claim 10 , wherein the resistor network Digital-to-Analog converter comprises:
a plurality of resistors connected in series across a power supply and having a plurality of output taps, wherein a node between two of said plurality of resistors is an output tap providing a fractional voltage of said power supply; and
a multiplexer for selecting a one of the output taps for output.
12. The wordline driver of claim 11 , wherein the plurality of resistors comprises a predetermined number of resistors, the predetermined number being selected such that a minimum desired output voltage and a suitable range of further output voltages, up to a maximum desired voltage, is provided.
13. The wordline driver of claim 2 , wherein the at least one operating parameter of the non-volatile memory device includes an operating mode of the non-volatile memory device.
14. The wordline driver of claim 13 , wherein the operating mode of the wordline driver is one of:
a read operating mode, a program operating mode or an erase operating mode.
15. A non-volatile memory device comprising the wordline driver according to claim 2 .
16. In a wordline driver of a non-volatile memory device, a method comprising:
selectively connecting a wordline driver output of the wordline driver to one of a first power source or a second power source dependent upon an operating mode of the wordline driver, the first power source adapted to provide an erase level voltage for erasing portions of the non-volatile memory device and the second power source adapted to provide read and program level voltages for reading and programming portions of the non-volatile memory device; and
providing, from a programmable switch controller of the wordline driver, a variable control signal to a control electrode of an isolation transistor adapted to selectively connect the second power source to the wordline driver output, the variable control signal being set to a value dependent upon at least one operating parameter of the non-volatile memory device, and wherein providing the variable control signal comprises adapting, via control loop of the programmable switch controller, an output of a voltage reference to provide the variable control signal to the control electrode of the isolation transistor.
17. The wordline driver of claim 1 , wherein the programmable switch controller further comprises:
an operational amplifier comprising an output coupled to said control electrode of the isolation transistor for providing the variable control signal;
a bypass transistor, connected between a third power source and the control electrode of the isolation transistor; and
a read select input connected to a control electrode of the bypass transistor and to an enable input of the operational amplifier, such that the read select input is operable to disable the operational amplifier and connect the control electrode of the isolation transistor to the third power source during a read operating mode.
18. A non-volatile memory device comprising the wordline driver according to claim 1 .