State retention power gated cell for integrated circuit

A method for recovering from a low power period, the method comprising:

• supplying a gated supply voltage (206) to a power gated circuit (202) and to a first end of a switch (210) during a non-low power period before the low power period;
• supplying a local power supply voltage (214) to a retention circuit (204) coupled to the power gated circuit, the local power supply voltage (214) coupled to a second end of the switch (210), wherein the switch (210) is closed during the non-low power period and open during the low power period, and the local power supply voltage (214) is coupled to a non-gated power supply (208) via an isolation element (212) during the low power period;
• saving, at the retention circuit (204), during the low power period, state information reflecting the state of the power gated circuit (202) before the low power period started;
• and
• recovering from the low power period by closing the switch (210) and providing the gated supply voltage to the power gated circuit (202);
• wherein recovering from the low power period further comprises isolating, at the isolation element (212), the non-gated power supply (208) from the local power supply (214).

An integrated circuit, comprising:

• a first power grid (102) coupled to a gated power supply (206) that is shut down during a low power period;
• a power gated circuit (202) coupled to the first power grid during at least a portion of a non-low power period;
• a retention circuit (204) coupled to the power gated circuit during at least a portion of the non-low power period, wherein the retention circuit stores, during the low power period, state information of a state of the power gated circuit before the low power period started;
• a second power grid (304) coupled to a non-gated power supply (208) that does not shut down during the low power period;
• and
• a local power supply rail (214) coupled to the first power grid via a power supply switch (210) and coupled to the second power grid via an isolation element (212);
• wherein the local power supply rail is coupled to the retention circuit and supplies the gated supply voltage to the retention circuit during the non-low power period, and supplies the non-gated power supply to the retention circuit during the low power period;
• wherein the isolation element isolates the non-gated power supply from the local power supply rail during the non-low power period.