Method and system for reliable and secure memory erase
A memory device has a switch matrix with a power supply input, a control input and a power supply output, a random access memory with a power supply connection coupled with the power supply output of the switch matrix. The switch matrix has a capacitor being chargeable by a power supply and upon receiving a control signal through the control input, the switch matrix is designed to decouple the capacitor from the power supply and the random access memory and to couple the capacitor through the power supply output with the random access memory in reverse polarity thereby providing a negative power supply to the power supply output.
1. A memory device, comprising:
a switch matrix comprising a power supply input, a control input and a power supply output,
a random access memory having a power supply connection coupled with the power supply output of the switch matrix,
wherein the switch matrix comprises a capacitor being chargeable by a power supply coupled to the power supply input and wherein upon receiving a control signal through the control input, the switch matrix is designed to decouple the capacitor from the power supply input and the power supply output and to couple the capacitor through the power supply output with the random access memory in reverse polarity.
2. The memory device according to claim 1 , wherein the random access memory is a secure random access memory within an embedded system.
3. The memory device according to claim 1 , wherein the switch matrix comprises a first set of switches coupling the capacitor with the power supply input and a second set of switches for coupling the capacitor with the power supply output.
4. The memory device according to claim 3 , wherein the second set of switches comprises a first pair of switches configured to couple the capacitor with the power supply output in a first polarity and a second pair of switches configured to couple the capacitor with the power supply output in a second polarity, wherein the second polarity is a reverse polarity with respect to the first polarity.
5. The memory device according to claim 4 , wherein the switch matrix is controlled during normal operation to keep the first set of switches and the first pair of switches of the second set of switches closed while keeping the second pair of switches of the second set of switches open.
6. The memory device according to claim 5 , wherein upon receiving the control signal, the switch matrix is configured to open the first pair of switches of the second set of switches and the first set of switches and thereafter to close the second pair of switches of the second set of switches.
7. The memory device according to claim 6 , wherein switches of the second set of switches are controlled by a single switch control signal, wherein the first pair of switches is designed to operate faster than the second pair of switches.
8. The memory device according to claim 6 , wherein the first pair of switches is controlled by a first switch control signal and the second pair of switches is controlled by a second switch control signal, wherein for reversing a polarity of the capacitor, the first switch control signal is configured to be asserted before the second switch control signal.
9. The memory device according to claim 6 , wherein switches of the first set of switches are controlled to open after the first pair of switches of the second set of switches.
10. The memory device according to claim 1 , wherein the capacitor has a capacitance of about 10 times a total bit-cell capacitance of the random access memory.
11. The memory device according to claim 1 , wherein switches for coupling the capacitor in reverse polarity are sized for 3τ (tau).
12. A microcontroller comprising a memory device according to claim 2 , wherein the microcontroller forms the embedded system.
13. A hardware security module coupled with a memory device according to claim 2 .
14. A method for operating a memory device, comprising:
supplying a random access memory with a supply voltage via a switch matrix, wherein the switch matrix comprises a power supply input, a power supply output and a capacitor being charged by the supply voltage;
receiving a control signal indicating to erase the memory, and
upon receipt of the control signal to erase the memory, decoupling the capacitor from the power supply and the random access memory through the switch matrix and thereafter coupling the capacitor with the power supply output in reverse polarity.
15. The method according to claim 14 , wherein the random access memory is a secure random access memory within an embedded system.
16. The method according to claim 14 , wherein the switch matrix comprises a first set of switches coupling the capacitor with the power supply input and a second set of switches for coupling the capacitor with the power supply output, wherein the second set of switches comprises a first pair of switches configured to couple the capacitor with the power supply output in a first polarity and a second pair of switches configured to couple the capacitor with the power supply output in a second polarity, wherein the second polarity is a reverse polarity with respect to the first polarity.
17. The method according to claim 16 , further comprising when the control signal is not received, controlling the first set of switches and the first pair of switches of the second set of switches to be closed while keeping the second pair of switches of the second set of switches open.
18. The method according to claim 17 , wherein upon receiving the control signal, controlling the first pair of switches of the second set of switches and the first set of switches to open and thereafter to close the second pair of switches of the second set of switches.
19. The method according to claim 18 , wherein switches of the second set of switches are controlled by a single switch control signal, wherein the first pair of switches is designed to operate faster than the second pair of switches.
20. The method according to claim 18 , wherein the first pair of switches is controlled by a first switch control signal and the second pair of switches is controlled by a second switch control signal, wherein for reversing a polarity of the capacitor, the first switch control signal is asserted before the second switch control signal.
21. The method according to claim 18 , wherein switches of the first set of switches are controlled to open after the first pair of switches of the second set of switches are controlled to open.
22. The method according to claim 14 , wherein the capacitor has a capacitance of about 10 times a total bit-cell capacitance of the random access memory.
23. The method according to claim 14 , wherein switches for coupling the capacitor in reverse polarity are sized for 3τ (tau).