Patent ID: 8421516

Claim:
Apparatus providing an interface between a first voltage domain and a second voltage domain, first voltage components in said first voltage domain connected to a first voltage supply and second voltage components in said second voltage domain connected to a second voltage supply, said apparatus comprising: a level shifter configured to receive the second supply voltage and an input signal from said first voltage domain and to level shift said input signal to provide an output signal for passing to said second voltage domain; and a control signal generator configured to generate a second voltage control signal in said second voltage domain to said level shifter mean in response to at least one first voltage control signal from a controller coupled to receive the first supply voltage in said first voltage domain, wherein said level shifter is configured to be in a retention state when said second voltage control signal has a first value, in which said output signal provided by said level shifter is held constant at the same value as the value of the output signal before the level shifter was configured to be in the retention state, wherein said level shifter is configured to be in a transmission state when said second voltage control signal has a second value, in which said output signal depends on said input signal, and wherein said control signal generator is configured, if while generating said second voltage control signal with said first value said controller becomes not actively driven by said first voltage supply, to maintain said second voltage control signal at said first value.