Apparatus and method for a programmable logic device having improved look up tables
AssigneeAltera Corporation
InventorVincent Leung
Life of this patent
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Abstract
A programmable logic device including a plurality of logic elements organized in an array. Each of the logic elements includes an N-stage Look Up Table structure having 2N configuration bit inputs and a Look Up Table output. The first stage of the Look Up Table includes 2N tri-state buffers coupled to receive the 2N configuration bit inputs respectively. A decoder, configured from logic gates, is coupled to receive to one or more Look Up Table select signals and to generate a set of control signals to control the 2N tri-state buffers so that one or more of the 2N configuration bit inputs is selected by the first stage. The configuration bits are then provided to subsequent muxing stages in the Look Up Table.
Claims25
A programmable logic device, comprising:
- a look up table (LUT) having sixteen configuration bit inputs, wherein a first stage of the LUT comprises:
- tri-state buffers coupled to receive the configuration bit inputs;
- a decoder coupled to receive one or more select signals and to control the tri-state buffers so that a subset consisting of four of the configuration bit inputs is selected by the first stage.
A look up table, comprising:
- a tri-state buffer stage that receives configuration bits;
- a decoder coupled to the tri-state buffer stage that selects one or more of the configuration bits in response to a first set of one or more select signals;
- one or more muxing stages coupled to the output of the tri-state buffer stage that multiplexes the selected configuration bits in response to a second set of one or more select signals and generates a look up table output signal;
- and
- wherein the tri-state buffer stage is configured to receive 16 configuration bits and the decoder is configured to generate a first select signal and a second select signal to select 4 of the 16 configuration bits.
A method of fabricating a programmable logic device, comprising:
- fabricating a look up table (LUT) having sixteen configuration bit inputs, wherein a first stage of the fabricated LUT includes tri-state buffers coupled to receive the configuration bit inputs;
- and
- fabricating a decoder coupled to receive one or more select signals and to control the tri-state buffers so that four of the configuration bit inputs are selected by the first stage.
Dependencies are inferred from the claim text.