Level shifting CMOS I/O buffer
First Claim
1. An output buffer circuit comprising:
- an input stage receiving a data signal, wherein the input stage includes a data signal voltage level shifter, and the data signal voltage level shifter outputs a voltage shifted data signal on a data signal path out of the input stage;
a first predrive stage including a first buffer being operatively driven by the voltage shifted data signal and including a second buffer being operatively driven by the voltage shifted data signal;
a second predrive stage comprising a signal combining circuit, said second predrive stage operatively driven by each output of the first and second buffers of the first predrive stage; and
an output driving stage operatively driven by an output of the second predrive stage.
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Abstract
A low power CMOS bidirectional I/O buffer that translates low voltage core logic level signals into the higher voltage logic level signals. A first predrive stage is provided, comprising buffers (e.g., CMOS inverters) for tuning and balancing the circuit and the core signal combining circuit of a second predrive stage, thereby enabling IC designers to reduce the size of transistors in the level-shifting stage and providing more flexibility in the tuning of the predrive circuitry to synchronize or balance the logical transitions of the complementary transistors of the output driving stage. The invention provides a faster balanced level-shifting output buffer which enables higher frequency operation.
44 Citations
20 Claims
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1. An output buffer circuit comprising:
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an input stage receiving a data signal, wherein the input stage includes a data signal voltage level shifter, and the data signal voltage level shifter outputs a voltage shifted data signal on a data signal path out of the input stage;
a first predrive stage including a first buffer being operatively driven by the voltage shifted data signal and including a second buffer being operatively driven by the voltage shifted data signal;
a second predrive stage comprising a signal combining circuit, said second predrive stage operatively driven by each output of the first and second buffers of the first predrive stage; and
an output driving stage operatively driven by an output of the second predrive stage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 17, 18)
a first transistor referenced to a first voltage, said first transistor comprising a p-channel field effect transistor (PFET); and
a second transistor referenced to ground, said second transistor comprising an n-channel field effect transistor (NFET).
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17. The output buffer circuit of claim 1, wherein each of the voltage level shifter and the first buffer and the second buffer is sized so that the data signal will propagate through the output buffer circuit faster than if the output buffer circuit were operably constructed without the first buffer and the second buffer.
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18. The output buffer circuit of claim 8, wherein the first logic gate is a NAND-gate, and the second logic gate is a NOR-gate.
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14. An interface circuit for translating a lower-voltage-logic signal into a higher-voltage-logic signal, comprising:
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a level-shifter operatively driven by said lower-voltage-logic signal;
two tuning inverters, each of the two tuning inverters being operatively driven by the same output of said level-shifter;
a signal combining circuit operatively driven by an output from each one of said two tuning inverters, said signal combining circuit being adapted to tristate the output of the interface circuit; and
an output driving circuit operatively driven by said signal combining circuit, said output driving circuit being adapted to drive said higher-voltage-logic signal out of the interface circuit. - View Dependent Claims (15, 16)
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19. An interface circuit for translating a data signal from a lower-voltage-logic to a higher-voltage-logic, the circuit comprising:
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a first voltage level shifter including cross-wired transistors, and the first voltage level shifter being operatively driven by said data signal being received as a lower-voltage-logic signal, the first voltage level shifter outputting a level-shifted complemented data signal, the level-shifted complemented data signal being the logical complement of the data signal level-shifted to the higher-voltage-logic;
a first tuning inverter, being operatively driven by said level-shifted complemented data signal;
a second tuning inverter, being operatively driven by said level-shifted complemented data signal;
a signal combining circuit operatively driven by the output of the first tuning inverter and by the output of the second tuning inverter, said signal combining circuit being adapted to control a tristate output driving circuit of the interface circuit; and
the tristate output driving circuit being adapted to drive the said data signal out of the interface circuit at the higher-voltage-logic. - View Dependent Claims (20)
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Specification