Level shifter with memory interfacing two supply domains

A method for providing a first signal from a first section of a circuit powered by a first power supply to a second section of the circuit powered by a second power supply, the method comprising:

• receiving the first signal from the first section of the circuit, wherein a level of the first signal is based on the first power supply;
• generating a second signal according to the first signal, wherein a level of the second signal is based on the second power supply;
• providing the second signal to the second section of the circuit;
• holding the second signal at a constant level while powering down the first power supply.

A level shifter comprising:

• an input terminal configured to receive an input from a first voltage domain corresponding to a first supply voltage;
• an output terminal configured to provide an output according to the input to a second voltage domain corresponding to a second supply voltage;
• a latch powered by the second supply voltage and having an input, and having an output coupled to the output terminal;
• a first transistor having a channel coupled between the input of the latch and a reference voltage, and having a control terminal coupled to the input terminal;
• a second transistor having a channel coupled between the output of the latch and the reference voltage, and having a control terminal;
• an inverter powered by the first supply voltage and having an input coupled to the input terminal, and having an output coupled to the control terminal of the second transistor;
• and
• a reset circuit coupled to the output terminal and configured to receive a reset signal, wherein the reset circuit is operable to reset the output of the level-shifter when the reset signal is asserted.

A system comprising:

• a first circuit powered by a first supply voltage and having an input and an output;
• a second circuit powered by a second supply voltage and having an input and an output;
• an interface circuit having a first input coupled to the output of the first circuit, a second input coupled to the output of the second circuit, a first output coupled to the input of the second circuit, and second output coupled to the input of the first circuit, wherein a first section of the interface circuit is powered by the first supply voltage and a second section of the interface circuit is powered by the second supply voltage;
• wherein the interface circuit is operable to transfer data from the first circuit to the second circuit through the first input and the first output, and transfer data from the second circuit to the first circuit through the second input and the second output;
• wherein the interface circuit is operable to:
• maintain at the first output a signal level corresponding to a state of the first input representative of the data, even when the first supply voltage is powered off;
• and
• maintain at the second output a signal level corresponding to a state of the second input representative of the data, even when the second supply voltage is powered off.

A system comprising:

• a latch powered by a first supply voltage and having an input and an output;
• a control circuit coupled to the latch and configured to receive an input signal, and further configured to control the input of the latch and the output of the latch according to the input signal, wherein a section of the control circuit which is configured to control the output of the latch is powered by a second supply voltage;
• and
• a reset circuit operable to reset the output of the latch while the first power supply and the second power supply are powering up;
• wherein an output signal generated at the output of the latch in response to the input signal remains at a level corresponding to a state of the input signal even when the second supply voltage is powered down.