JPH09181598A - Field programmable gate array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the capacity of a programmable logic cell(PLC) without adding a lookup table(LUT) adding layer to a circuit network by including decoder circuit arrangement capable of operating so as to increase the number of inputs to each PLC in the PLC and connecting the decoder circuit arrangement, to an LUT. SOLUTION: An PLC 200 includes a look-up table(LUT) 202 connected to the decoder circuit arrangement 203. The arrangement 203 includes a multiplexer(MUX) 204 and a decoder circuit 206. The arrangement 203 connected to the PLC 200 increases the number K of inputs of the PLC 200 in relation with the addition of an LUT circuit network. When the LUT 202 is an 8-bit LUT (m=3) and the circuit 206 has five inputs (L=5) for instance, the PLC 200 is provided with capacity for executing a Boolean function having eight inputs at maximum (K=8=3+5) and the arrangement 203 increases the number K of inputs of the PLC 200 by a coefficient L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a programmable logic device formed on an integrated circuit semiconductor chip,
In particular, it relates to a logic cell that is part of a field programmable gate array chip.

[0002]

BACKGROUND OF THE INVENTION Integrated circuits (ICs) have traditionally performed one function or functions defined in software programming. However, in each case, the logic configuration that performed the function was determined during IC design. More recently, integrated circuits have been developed in which the logic configuration can be changed after manufacture. For example, field programmable gate arrays (FPGAs) have been developed that allow users to establish logic functions. Typically, this logic function is performed in a programmable function unit (PFU). The PFU typically includes various logic circuit elements (e.g., AND gates, OR gates, NANDs) that can be connected in the desired arrangement to perform the desired logic and memory functions.
Gate, NOR gate, flip-flop, look-up table memory, multiplexer, register, latch, 3-state buffer). For example, typical logic functions include combinatorial logic, adders, counters and other datapath functions. Combinatorial logic is typically implemented using a look-up table (LUT), whereas sequential logic is typically implemented using storage elements (registers) such as flip-flops and latches.

As mentioned above, each logic cell (or PLC: programmable logic cell) uses a look-up table (LUT) to perform combinatorial logic functions. LUTs typically use static random access memory (RAM) to perform Boolean functions according to the combinatorial logic functions of each PLC.
Note that "K" will indicate the maximum number of inputs that can be implemented in the individual PLCs of the FPGA connected to the Boolean network. Typically, as the value of K increases, it is required to execute the application circuit (the circuit implemented in the FPGA chip) (P
The number of levels (eg depth) of the LUT (similar to LC) is reduced, which eliminates time delays (increases circuit speed). Therefore, it may be desirable to have a PLC with a large K value.

For example, FIG. 1 shows a block diagram of a LUT 152 of a prior art PLC 150. Specifically, LUT1
52 is a 16-bit RAM that allows the PLC 150 to perform Boolean functions up to 4 inputs (eg, K = 4)
It is. FIG. 2 shows the F and G of the prior art PLC 160.
3 shows a block diagram of LUTs 162 and 164. F and G LUTs 162 and 164 are both 16-bit RA
M, and the PLC 160 has five inputs A1, A2, A3, A4 and A5 (K = corresponding to the circuit configuration of the PLC 160).
The Boolean functions up to 5) can be performed (inputs A2, A3 and A4 are common to both F and G LUTs). FIG. 3 shows the above described F connected to an 8-bit H LUT 172 that allows the PLC 170 to perform some Boolean function up to 9 inputs (A1 through A9) (K = 9) in relation to its circuit configuration. And G LU
FPGA PLC with T162 and 164 outputs
17 shows a block diagram of 170.

Therefore, the specific size (RAM) of the LUT in the PLC and their circuit configuration are
Determine the K value of C. For example, the PLC 150 (FIG. 2) described above includes a 16-bit RAM F and G LUT 162 and 1 with a 32-bit combined size that provides a K value of 5.
64 are provided. In contrast, the PLC 170 described above
(FIG. 3) is (F and G LUT inputs (A1 to A4
And A6 to A9) are independent of each other)
It has an equivalent 16-bit RAM F and G LUT with a 32-bit bond size that provides the value. further,
F and G LUTs 162 and 164 to increase K value
Additional LUTs can be added to the output terminals of. For example, the H-LUT 17 added to the PLC 170 (FIG. 3)
2 worked to increase the K value by 1. However, adding additional LUTs to the PLC increases signal propagation time (eg, reduces circuit speed), which is a disadvantage for most circuit applications. Further, F
As the number of PLC levels in the PGA increases, so does the size and cost of the FPGA.

[0006]

SUMMARY OF THE INVENTION The present invention provides a plurality of PLCs.
And each PLC is directed to a field programmable gate array including a decoder circuit arrangement operable to increase the number of inputs (K) to each PLC. This decoder circuit arrangement is connected to each LUT of each PLC in the process so that the number of inputs of the PLC is
It is increased by the corresponding number of inputs of the decoder circuit arrangement described above.

Each decoder circuit arrangement is preferably a PLC.
A multiplexer circuit connected to the LUT. Further, a decoder circuit having a plurality of input terminals and an output terminal connected to the address selector of the multiplexer circuit is provided. In a preferred embodiment, the multiplexer circuit has a first input terminal connected to the output terminal of the LUT,
2-to-1 with second input terminal connected to default value
Includes MUX. The 2-to-1 MUX address selector is connected to and controlled by the above-mentioned decoder circuit. Therefore,
The decoder circuit arrangement of the present invention has a LUT in a circuit network FPGA.
FPGA without the need to add additional layers of
Increase the capability of each PLC by increasing the maximum number of inputs (K) in the Boolean network associated with. The above features of the present invention will be readily apparent and understood by reference to the following detailed description of one embodiment of the device according to the present invention taken in conjunction with the accompanying drawings.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, like reference numbers identify identical or equivalent components. FIG.
Shows a portion of a programmable logic cell (PLC) 200 including a look-up table (LUT) 202 connected to a decoder circuit arrangement 203 of the present invention. The decoder circuit arrangement 203 in the simplest embodiment includes a multiplexer (MUX) 204 and a conventional decoder circuit 206. PLC200 in an integrated circuit of a commercially available FPGA, such as an ORCA FPGA commercially available from AT & T.
Those skilled in the art will understand that In general, providing the decoder circuit arrangement 203 to the PLC 200 has the ability to increase the number of inputs (K) of the PLC 200 without the drawbacks described above in connection with the addition of additional layers of LUT circuitry.

Referring to FIG. 4, as an example, LUT 20
2 is of the 2 ^m- bit class, so m inputs 2
It is possible to implement a Boolean network with 08 (eg K = m). For example, the LUT 202 has a 16-bit class (2
^{If m} = 16, m = 4), then it is adapted to implement a Boolean network with up to 4 inputs (K = 4). LU
The output line 210 of the T202 is preferably a 2: 1 MUX2.
No. 04 is connected to the first input terminal 212. MUX
The second input terminal 214 of 204 is connected to the default value (0). The address selector terminal 218 of the MUX 204 is connected to the decoder circuit 206. As is well known, such a decoder circuit 206 is a device that converts a combination of input signals into one output signal corresponding to an input combination signal. By way of example, the decoder circuit 206 is adapted to have an L input line 220. Therefore, this decoder circuit 206 outputs a logic signal to its output terminal (line 220) depending on the combination value of the L input 220.
It operates to have either a high (1) or a logic low (0) output. Those skilled in the art will appreciate that the conversion scheme of the decoder circuit 206 can be easily configured to have a logic high (1) or a logic low (0) output value depending on a specific input combination value of the decoder circuit 206. Recognize.

Further, as in the conventional case, a value (for example, 0 to 1) input to the address selector 218 of the MUX 204.
Which input terminal (212 or 214) is the output terminal Y
Has the power to decide which should be connected to. Preferably, MUX 204 is adapted to be active low (0) so that the output of decoder circuit 206 (line 2
When 20) is a logic low (0), the first input terminal 212 of MUX 204 is connected to its output Y. For example, the output of the decoder circuit 206 is a logic low (0).
Then, the Y output value of the MUX 204 becomes equal to the output value of the LUT 202 via the output line 210. If the output of the decoder circuit 206 is logic high (1), MUX2
The Y output value of 04 is equal to the default value (0) of the second input terminal 214.

Thus, as described above with respect to FIG. 4, PLC 200 is provided with m + L inputs (K = m + L), thereby providing the ability to perform Boolean functions with maximum m + L inputs therein. For example, L
If the UT 202 is an 8-bit LUT (m = 3) and the decoder circuit 206 is configured to have 5 inputs (L = 5), the PLC 200 will have a maximum of 8 inputs (K =
The ability to perform Boolean functions with 8 = 3 + 5) is provided. Therefore, the decoder circuit layout 203 is
It operates to increase the number of inputs (K) in C200 by a factor of (L).

Referring now to FIGS. 5a-5c, another preferred embodiment of the decoder circuit 206 of FIG. 4 is shown. FIG. 5a shows a decoder circuit 206 in the form of a conventional NAND gate 222 having an L input terminal. FIG. 5b has L input terminals, each input terminal being 2 to 1
Shown is a decoder circuit 206 in the form of a NAND gate 224 connected to a MUX 226. Each 2-to-1 multiplexer 226 has a respective input terminal 228, 230 associated with a common node 232, here an intermediate node 232, which input terminal 230 is a conventional inverter 234.
Address selector 236 of MUX 226 is 1 bit
Static random access memory (RAM) 23
8 is connected and controlled. FIG. 5c shows the MUX 226 of FIG. 5b composed of first and second transistors 240 and 242, the base of each transistor 240, 242 being connected to a 1-bit static RAM 238, which is either activated or deactivated. . It will be appreciated that the decoder circuit 206 of FIG. 4 can be configured in a number of circuit schemes (eg, NAND gate 224 may be replaced by an AND gate) and should not be limited to that shown in FIG. .

FIG. 6 illustrates yet another preferred embodiment of a decoder circuit arrangement 245 in PL 250 according to the present invention. In the decoder circuit arrangement 245, the second input terminal 214 of the MUX 204 is a 1-bit static RAM 252.
4 is connected to the decoder circuit arrangement 20 of FIG.
Substantially the same as 3. The provision of RAM 252 provides the user with the ability to adapt MUX 204 to have a default value of either 0 or 1.

FIG. 7 shows an example of providing the decoder circuit arrangement of the present invention to an existing FPGA. In FIG. 7, the above A
The provision of the decoder circuit arrangement 245 of FIG. 6 to the PLC 300 of the T & T ORCA FPGA is shown. For convenience, the two LUTs 302,3 on top of the ORCA PGA
It should be understood that only 04 is shown. LU
T302 and 304 are 16-bit LUTs, and each LU
T302 and 304 are equipped with four inputs (m = 4). The three inputs of each LUT 302, 304 are connected together (A1, A2 and A3) and therefore the LUT
The total number of inputs of 302 and 304 is 5 (m =
5, A0, A1, A2, A3 and A4). Each LUT30
The outputs of 2 and 304 are connected to the 2: 1 multiplexer 306 via lines 308 and 310, respectively.
The output of MUX 306 is sent via line 312 to MUX2 described above.
No. 04 is connected to the first input terminal 212. Therefore, the decoder circuit arrangement 245 described above is
Given the ability of the PGA to work cooperatively with the PLC 300, it operates to increase the number of inputs of the PLC 300 by L (the number of inputs of the decoder circuit 206), as described above. For example, if the decoder circuit 206 is adapted to have 3 inputs (L = 3), the total number of inputs (K) of the PLC 300 will be 8 (K = 8 = 5 + 3 = m + L).

Referring now to FIG. 8, the PL of the above-mentioned ORCA FPGA providing the decoder circuit 351 of the present invention.
Another preferred embodiment of C350 is shown. PLC3
50 is two 2 to 1 MUX30 of PLC300 of FIG.
Substantially the same as PLC 300 of FIG. 7, except that a 4 to 1 MUX 360 is provided as opposed to 6,204. The PLC 350 is the 16-bit LUT 30 described above.
2 and 304, each output of LUTs 302 and 304 (lines 303 and 305) is coupled to the first and second input terminals 362 and 362 of MUX 360 via lines 352 and 354, respectively.
Has been input to 364. The L input decoder circuit 206 is connected to the first address selector terminal 372 of the MUX 360, and the input terminals 366 and 368 of the MUX 360 are
It is connected to a 1-bit static RAM 373 which operates to provide a default value of either 0 or 1.

In operation, if the output of the decoder circuit 206 is active low (0), the output of the MUX 360 (Y).
Depends on the value input to the second address selector terminal 374, through the input terminals 362 and 364.
Either 302 or the output value of the LUT 304 is selected. Therefore, the output (Y) of MUX360 is LU
It has a value of either T302 or LUT304.
If the output of the decoder circuit 206 is inactive (1), the MU
The output (Y) of X360 becomes equal to the output of RAM 373 via the input terminals 366 and 368.

The decoder circuit arrangement 351 described above is an FPG.
Can be connected to any A LUT, FPGA
It can be seen that it should not be limited to the two LUTs on the top of the. Therefore, as described above, each decoder circuit arrangement used for a particular PLC is effective in correspondingly increasing the number of inputs (K) of that particular PLC.

To further illustrate the present invention, by way of example, an 8-input combinatorial logic function is shown in Table A.
Those skilled in the art will appreciate that this feature typically has too many variables for the intended application, and therefore must be "broken down" into a smaller set of features. Table B shows three less combinatorial functions that occur with commercially available software such as SIS 1.1 from UC Berkley. The combination of the three functions shown in Table B is logically equivalent to the functions shown in Table A as shown below.

[0018]

[Table 1]

[Table 2]

The above-described logic function shown in Tables A and B provides the above-mentioned prior art AT & T which provides two PLCs (LC400 and PLC420) as shown in FIG.
It can be implemented in an ORCA FPGA.
In PLC400, LUT T3 and T4 (40
2) supplies the "tmp1" cover output and the LUT T1
And T0 (404) provide the "tmp2" cover output, and LUTs T3 and T2 (402) and LUTs T1 and T0 (404) have four inputs (a1, a3, respectively).
a5, a6, a7) are provided. tmp1 and t
The mp2 cover output is the LUT of the PLC 420, respectively.
Inputs to T3 and T2 (406) and additional inputs (a2, a4, a8) to LUT T3 and T2 (406).
Is provided. LUT T3 and T of PLC 420
2 (406) provides the'y 'cover output (line 422). The FPGA circuit arrangement of FIG. 9 described above is used to provide a PLC 400, 420 to provide a'y 'cover with 8 inputs.
It is noted that it required two levels of. Therefore, the above-mentioned input signals (a1 to a8) are output from the PLC 400, 420 before the'y 'cover output signal is generated.
Had to handle by one level. Therefore, as mentioned above, the additional PLC420 level not only increases the signal propagation time and cost of the FPGA, but also the PLC42.
This results in an increase in the overall size of the FPGA required to accommodate zero.

In contrast to the prior art FPGA of FIG. 9, FIG. 10 illustrates the above A which provides the decoder circuit arrangement of the present invention.
1 shows a PLC 450 of a T & T ORCA FPGA. P
The LC450 each has the above-mentioned 5 inputs (m = 5).
LUT T3 with a1, a3, a5, a6 and a7
And T2 (452) and LUTs T1 and T0 (454)
Contains. The'tmp1 'output from LUT T3 and T2 (452) is connected to a 2: 1 MU456,
The'tmp2 'outputs from T T1 and T0 (454) are connected to a 2: 1 MU 458. The MUX 456 is an address selector 457 connected to the decoder circuit 460.
The MUX 458 includes an address selector 459 connected to the decoder circuit 462. Each MUX45
The outputs of 8,460 (lines 470 and 472) are each connected to a NAND gate 464 whose output provides a'y 'cover. Decoder circuits 460 and 46
2 has the above-mentioned three inputs (L = 3) a2 and a4, respectively.
And a8 are provided. In particular, the decoder circuit 460
Is adapted to be active low (0) when the inputs a2, a4 and a8 are 010 respectively, and the decoder circuit 462 has the inputs a2, a4 and a8 101 respectively.
It is adapted to become active low (0) at.

Therefore, the FPG of FIG. 10 according to the present invention
The A circuit arrangement provides an equivalent'y 'output with the same 8 inputs (K = 8, a1 to a8) compared to the prior art FPGA circuit arrangement of FIG. However, the FPGA circuit layout of FIG. 10 is similar to that of the prior art FPGA of FIG.
In contrast to the circuit arrangement requiring two PLCs 400, 420, the use of only one PLC 450 achieves the same result as above. Therefore, the FPGA circuit arrangement (FIG. 10) of the present invention has a smaller overall size and a reduced delay time (the input signal is one PLC4).
PLC 40 only).
Prior art FPG requiring two levels of 0 and 420
There is an advantage that the cost of the circuit is reduced as compared with the A circuit arrangement.

What has been disclosed herein is merely an application of the principles of the invention. Other arrangements and methods may be provided by those skilled in the art without departing from the spirit and scope of the invention.

[Brief description of the drawings]

FIG. 1 shows a block diagram of a programmable logic cell of prior art circuitry.

FIG. 2 shows a block diagram of a programmable logic cell of another prior art circuit configuration.

FIG. 3 shows a block diagram of a programmable logic cell of another prior art circuit configuration.

FIG. 4 shows a programmable logic cell implementing a decoder circuit arrangement embodying the invention.

5A is another circuit configuration 1 of the decoder circuit arrangement of FIG.
Is shown.

5B is another circuit configuration of the decoder circuit arrangement of FIG.
Is shown.

5C is another circuit configuration of the decoder circuit arrangement of FIG.
Is shown.

6 shows the decoder circuit arrangement of FIG. 4 with a 1-bit static RAM operable to determine the input default value of the multiplexer of the decoder arrangement.

7 shows the decoder circuit arrangement of FIG. 6 used in a programmable logic cell having first and second look-up tables.

8 shows the decoder circuit arrangement of FIG. 7 including a 4 to 1 multiplexer.

FIG. 9 shows a prior art FPGA with two programmable logic cells cascaded together.

FIG. 10 illustrates an FPGA having one programmable logic cell that includes a decoder circuit arrangement embodying the invention.

[Explanation of symbols]

 202 LUT 204 MUX 206 decoder circuit 208 m input 210 output line 214 input terminal

Claims (15)

[Claims] 1. An integrated circuit comprising a field programmable gate array, comprising: (a) at least one lookup table having a plurality of input terminals and one output terminal; and (b) at least one lookup table. A decoder circuit arrangement connected to the output terminal, said decoder circuit arrangement comprising (i) an address selector terminal,
A multiplexing circuit having at least one input terminal connected to an output terminal of the at least one lookup table; and (ii) a decoder having a plurality of input terminals and connected to an address selector of the multiplexing circuit. An integrated circuit comprising a circuit. 2. The integrated circuit according to claim 1, wherein the multiplexing circuit comprises a first input terminal connected to an output terminal of the at least one look-up table and a second input terminal connected to the default value. A two-to-one multiplexer having an input terminal, the two-to-one multiplexer including the decoder circuit for the first and second multiplexers.
An integrated circuit having the address selector connected to the decoder circuit for selectively connecting the output terminal of the multiplexer between the input terminals of. 3. The integrated circuit according to claim 2, wherein the decoder circuit arrangement further comprises a 1-bit static RAM connected to the second input terminal and operable to provide the default valve. circuit. 4. The integrated circuit according to claim 1, wherein the decoder circuit has a plurality of input terminals and an output terminal connected to an address selector of the multiplexing circuit.
An integrated circuit including an ND logic gate. 5. The integrated circuit according to claim 4, wherein each input terminal of the NAND gate is connected to a 2: 1 multiplexer. 6. The integrated circuit according to claim 5, wherein each said 2 to 1 multiplexer includes a 1-bit static RAM connected to its respective address selector. 7. A field programmable gate array integrated circuit having a large number of programmable logic cells, each programmable logic cell comprising: (a) a plurality of look-up tables each having a plurality of input terminals and one output terminal; (B) a first multiplexer circuit having an input terminal connected to each output terminal of each look-up table, and (c) a decoder circuit arrangement connected to an output terminal of the first multiplexing means. And the decoder circuit layout is
(I) a second multiplexer circuit having an input connected to the output of the first multiplexing means, and (ii) having a plurality of inputs and connected to an address selector of the second multiplexing means. A field programmable gate array integrated circuit comprising a decoder circuit. 8. The field programmable gate array according to claim 7, wherein the first multiplexing means is a 2-to-1 multiplexer having respective input terminals connected to the first and second look-up tables. Field programmable gate array. 9. The field programmable gate array according to claim 8, wherein said second multiplexing means is connected to an output of said first 2: 1 multiplexer.
A field programmable gate array including a second 2 to 1 multiplexer having an input to the decoder and an address selector connected to the decoder circuit. 10. The field programmable gate array according to claim 9, wherein 1-bit static RA is used.
M is a field programmable gate array connected to the second input of the second 2: 1 multiplexer. 11. The field programmable gate array according to claim 10, wherein the decoder circuit has a plurality of input terminals and one output terminal connected to an address selector of the second 2-to-1 multiplexer.
Field programmable gate array including AND logic gates. 12. The field programmable gate array according to claim 11, wherein each input terminal of the NAND gate is connected to a 2: 1 multiplexer. 13. A field programmable gate array integrated circuit having a large number of programmable logic cells, each programmable logic cell comprising: (a) a plurality of look-up tables each having a plurality of input terminals and one output terminal; (B) a plurality of multiplexer circuits each having an input terminal connected to an output terminal of the look-up table; (c) a plurality of decoder circuit arrangements each connected to the multiplexer circuit address selector; ) A field programmable gate array integrated circuit, comprising a logic control circuit each having a plurality of input terminals connected to the output terminals of the multiplexer circuits and one output terminal. 14. The field programmable gate array according to claim 13, wherein the logic control circuit is a NAND gate. 15. The field programmable gate array according to claim 14, wherein each of the multiplexer circuits is a 2: 1 multiplexer.