Multiplexer with level shifter
AssigneeApple Inc.
InventorsGreg M. Hess, Naveen Javarappa, James E. Burnette, II
Life of this patent
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Abstract
A level shifting multiplexer is disclosed. In one embodiment, a multiplexer is coupled to receive a first input signal from circuitry in a first power domain and a second input signal from circuitry in a second power domain. The multiplexer is configured to output a selected one of the first and second input signals to circuitry in the second power domain. The multiplexer also includes a level shifter circuit. When the first input signal is selected, the level shifter circuit may be enabled. When enabled, the level shifter circuit may level shift the first signal such that its voltage swing corresponds to that of the second voltage domain. The multiplexer may also include isolation circuitry configured to inhibit the level shifter.
Claims11
An apparatus comprising:
- a level shifter circuit coupled between a first input node in a first voltage domain and an output node in a second voltage domain, wherein the level shifter circuit is configured to receive a first input signal on the first input node, wherein the level shifter is configured to drive an output signal corresponding to the first input signal on the output node responsive to a first state of a select signal;
- a first pull-up transistor configured to pull the output node up to an operating voltage of the second voltage domain responsive to a second state of the select signal and a first state of a second input signal;
- a pull-down transistor configured to pull the output node down to a ground voltage responsive to a second state of the select signal and a second state of the second input signal;
- and
- isolation circuitry coupled to receive an isolation signal, wherein the isolation circuitry is configured to inhibit the level shifter circuit from driving the output node when the isolation signal is asserted.
A method comprising:
- a multiplexer selecting a first signal received from a first functional unit operating in a first voltage domain;
- level shifting and outputting the first signal to a second functional unit operating in a second voltage domain;
- selecting, using the multiplexer, a second signal received from a third functional unit operating in the second voltage domain;
- and
- outputting the second signal to the second functional unit
- wherein the method further comprises:
- receiving a selection signal from a circuit operating in the second voltage domain;
- selecting, using the multiplexer, the first signal responsive to the selection signal being in a first state;
- selecting, using the multiplexer, the second signal responsive to the selection signal being in a second state;
- inhibiting level shifting of the first signal responsive to receiving an isolation signal;
- and
- inhibiting level shifting of the first signal responsive to receiving the selection signal in the second state.
A circuit comprising:
- a level shifter configured to receive a first input signal from a first voltage domain to provide an output signal in a second voltage domain;
- a first transistor coupled to an output of the level shifter and configured to pull the output node up in response to a second input signal in the second voltage domain, wherein the output of the level shifter is in the second voltage domain;
- a second transistor coupled to the output and configured to pull the node down in response to a second input signal;
- and
- an isolation circuit coupled to the level shifter, wherein the isolation circuit is configured to inhibit the level shifter circuit from providing the output signal in the second voltage domain responsive to receiving an isolation signal;
- wherein the first transistor, the second transistor, and the level shifter are further controlled response to a select signal that selects between the first input signal and the second input signal.
Dependencies are inferred from the claim text.