Three input field programmable gate array logic circuit configurable as a three input look up table, a D-latch or a D flip-flop
View Patent ↗A field programmable gate array logic cell includes a logic circuit having three inputs and at least one output and a plurality of multiplexers having inputs and outputs. The logic circuit also includes a plurality of programmable elements coupled between the three inputs and at least one output of the logic circuit and the inputs and outputs of the plurality of multiplexers such that a plurality of sequential logic units and combinatorial units can be realized by programming selected ones of the programmable elements, the sequential logic units may include a flip-flop.
1. A programmable logic cell, capable of receiving a first input signal, a second input signal, and a third input signal, and providing an output signal, comprising:
a first multiplexer having a first input, a second input, an output, and a selector;
a NAND gate having a first input, a second input, and an output, wherein the first input of the NAND gate receives the output from the first multiplexer;
a second multiplexer having a first input, a second input, an output, and a selector;
a third multiplexer having a first input coupled to the output of the second multiplexer, a second input, an output providing the output signal for the programmable logic cell, and a selector;
a plurality of programmable elements coupled to the first multiplexer, the second multiplexer, and the third multiplexer such that the combination of the first multiplexer, the second multiplexer, the third multiplexer, and the NAND gate together perform each one of a set of functions depending on which of the plurality of programmable elements are programmed, said set of functions comprising:
a D flip-flop,
a D latch, and
a LUT capable of implementing any three input logic function.
2. The programmable logic cell in claim 1 wherein:
the selector for the first multiplexer and the selector for the second multiplexer are both coupled to receive the second input signal; and
the selector for the third multiplexer is coupled to receive the third input signal.
3. The programmable logic cell in claim 1 wherein:
the first multiplexer, the second multiplexer, and the third multiplexer each comprise:
a first tri-state buffer having an input accepting the first input to the multiplexer, a selector, and an output coupled to the output of the multiplexer, and
a second tri-state buffer having an input accepting the second input to the multiplexer, a selector, and an output coupled to the output of the multiplexer;
wherein the selector of the first tri-state buffer receives an inverted signal to that received by the selector of the second tri-state buffer.
4. The programmable logic cell in claim 1 wherein:
the programmable elements comprise flash transistors.
5. The programmable logic cell in claim 1 wherein:
the programmable elements comprise antifuse elements.
6. The programmable logic cell in claim 1 wherein:
the programmable elements comprise MOS transistors.
7. The programmable logic cell in claim 1 wherein:
a first programmable element programmably couples the first input signal to ground;
a second programmable element programmably couples the second input signal to ground; and
a third programmable element programmably couples the third input signal to ground.
8. The programmable logic cell in claim 1 wherein:
a first programmable element programmably couples the first input signal to VCC; and
a third programmable element programmably couples the third input signal to VCC.
9. The programmable logic cell in claim 1 which further comprises:
a first inverter, a second inverter, and a third inverter,
a first pair of programmable elements to programmably insert the first inverter in series with the first input signal;
a second pair of programmable elements to programmably insert the second inverter in series with the second input signal; and
a third pair of programmable elements to programmably insert the third inverter to in series with the third input signal.
10. The programmable logic cell in claim 1 wherein:
when a D flip-flop is enabled, programmable elements enable:
a first feedback loop coupling the output of the NAND gate to an input of the first multiplexer, and
a second feedback loop coupling the output of the third multiplexer to an input of the second multiplexer; and
when the LUT is enabled, programmable elements disable the first feedback loop and the second feedback loop.
11. A field programmable gate array containing a plurality of programmable logic cells, each programmable logic cell accepting a first input signal, a second input signal, and a third input signal, and providing an output signal and comprising:
a first multiplexer having a first input, a second input, an output, and a selector;
a NAND gate having a first input, a second input, and an output, wherein the first input of the NAND gate receives the output from the first multiplexer;
a second multiplexer having a first input, a second input, an output, and a selector;
a third multiplexer having a first input coupled to the output of the second multiplexer, a second input, an output providing the output signal for the programmable logic cell, and a selector;
a plurality of programmable elements coupled to the first multiplexer, the second multiplexer, and the third multiplexer such that the combination of the first multiplexer, the second multiplexer, the third multiplexer, and the NAND gate together perform each one of a set of functions depending on which of the plurality of programmable elements are programmed, said set of functions comprising:
a D flip-flop,
a D latch, and
a LUT capable of implementing any three input logic function.
12. field programmable gate array in claim 11 wherein:
the selector for the first multiplexer and the selector for the second multiplexer are both coupled to receive the second input signal; and
the selector for the third multiplexer is coupled to receive the third input signal.
13. The field programmable gate array in claim 11 wherein:
the first multiplexer, the second multiplexer, and the third multiplexer each comprise:
a first tri-state buffer having an input accepting the first input to the multiplexer, a selector, and an output coupled to the output of the multiplexer, and
a second tri-state buffer having an input accepting the second input to the multiplexer, a selector, and an output coupled to the output of the multiplexer;
wherein the selector of the first tri-state buffer receives an inverted signal to that received by the selector of the second tri-state buffer.
14. The field programmable gate array in claim 11 wherein:
the programmable elements comprise flash transistors.
15. The field programmable gate array in claim 11 wherein:
the programmable elements comprise antifuse elements.
16. The field programmable gate array in claim 11 wherein:
the programmable elements comprise MOS transistors.
17. The field programmable gate array in claim 11 wherein:
a first programmable element programmably couples the first input signal to ground;
a second programmable element programmably couples the second input signal to ground; and
a third programmable element programmably couples the third input signal to ground.
18. The field programmable gate array in claim 11 wherein:
a first programmable element programmably couples the first input signal to VCC; and
a third programmable element programmably couples the third input signal to VCC.
19. The field programmable gate array in claim 11 wherein each programmable logic cell further comprises:
a first inverter, a second inverter, and a third inverter,
a first pair of programmable elements to programmably insert the first inverter in series with the first input signal;
a second pair of programmable elements to programmably insert the second inverter in series with the second input signal; and
a third pair of programmable elements to programmably insert the third inverter to in series with the third input signal.
20. The field programmable gate array in claim 1 wherein:
when a D flip-flop is enabled, programmable elements enable:
a first feedback loop coupling the output of the NAND gate to an input of the first multiplexer, and
a second feedback loop coupling the output of the third multiplexer to an input of the second multiplexer; and
when the LUT is enabled, programmable elements disable the first feedback loop and the second feedback loop.