Pushed-rule bit cells with new functionality
View Patent ↗A memory bit cell suitable for use in semiconductor integrated circuits that utilizes pushed design rules and layout geometries optimized by a semiconductor foundry for standard memory bit cells and edge-cell structures that provides a different functionality from that provided by the foundry standard bit cell. This different functionality is achieved by interconnecting the elements of one or a plurality of standard foundry bit cells and edge cells to implement a different circuit with different operation from the original bit cells and edge cells. The positioning and interconnection of the standard bit cells and edge cells are implemented in a manner so as to maintain the same periodic geometric proximity effects to the maximum degree possible. A preferred embodiment of this invention is to interconnect two standard foundry six-transistor SRAM bit cells and two edge cells to create a Ternary Content Addressable Memory bit cell with mask and compare functionality in addition to bit storage functionality.
1. A composite memory bit cell suitable for use in integrated circuits that utilize pushed layout rules comprising:
two foundry-supplied bit-cell layouts for two six-transistor SRAM bit cells, said foundry-supplied bit-cell layouts utilizing pushed layout rules, and
two foundry-supplied edge-cell layouts compatible with the layouts for said SRAM bit-cell layouts, and
minor bit-cell layout modifications and minor edge-cell layout modifications to enable functionality as data storage bits, mask bits and as compare transistors, and
interconnections between said two foundry-supplied bit-cell layouts and said two modified foundry-supplied edge-cell layouts to constitute the functionality of a Ternary Content Addressable Memory bit cell such that the first of said six-transistor SRAM bit cells stores the data bit, while the second of said six transistor SRAM bit cells stores the mask bit and the transistors in said modified edge-cell layouts comprise the compare function of the Ternary Content Addressable Memory, and
whereby said composite layout of said composite bit cell provides enhanced functionality with a layout that is optimized for area and performance by virtue of maintaining the salient layout features of the original foundry-supplied bit-cell and edge-cell layouts.
2. A composite memory bit cell suitable for use in an integrated circuit, the integrated circuit laid out using standard logic design rules, the composite memory bit cell comprising at least two pushed-rule memory bit cells laid out using pushed layout design rules, the composite memory bit cell implementing a logic function that is different than a logic function implemented by any of the pushed-rule memory bit cells.
3. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells comprise a six-transistor SRAM bit cell.
4. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells comprise a single-port SRAM bit cell.
5. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells comprise an eight-transistor SRAM bit cell.
6. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells are laid out in a manner that preserves geometric proximity characteristics of the pushed-rule memory bit cells.
7. The composite memory bit cell of claim 2 further comprising circuitry based on an edge cell associated with the pushed-rule memory bit cells.
8. The composite memory bit cell of claim 2 further comprising circuitry based on a strap cell associated with the pushed-rule memory bit cells.
9. The composite memory bit cell of claim 2 wherein the composite memory bit cell occupies less area than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
10. The composite memory bit cell of claim 2 wherein the composite memory bit cell consumes less power than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
11. The composite memory bit cell of claim 2 wherein the composite memory bit cell operates at a higher frequency than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
12. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells are foundry-supplied pushed-rule memory bit cells.
13. The composite memory bit cell of claim 2 wherein the pushed-rule memory bit cells are designed for a 28-nanometer or smaller process technology node.
14. The composite memory bit cell of claim 2 wherein the composite memory bit cell is a content addressable memory.
15. The composite memory bit cell of claim 2 wherein the composite memory bit cell is a ternary content addressable memory.
16. The composite memory bit cell of claim 2 wherein the composite memory bit cell is a register file memory.
17. The composite memory bit cell of claim 2 wherein the composite memory bit cell is a multi-port memory.
18. A ternary content addressable memory (TCAM) suitable for use in an integrated circuit, the integrated circuit laid out using standard logic design rules, the TCAM comprising an array of TCAM bit cells, each TCAM bit cell comprising:
a first pushed-rule memory bit cell for storing a data bit;
a second pushed-rule memory bit cell for storing a mask bit; and
compare circuitry coupled to the first and second pushed-rule memory bit cells, for comparing the data bit to an applied bit, wherein the mask bit determines whether to include the data bit in the comparison.
19. The TCAM of claim 18 wherein each of the first and second pushed-rule memory bit cells comprises an SRAM bit cell.
20. The TCAM of claim 19 wherein each of the first and second pushed-rule memory bit cells comprises a six-transistor SRAM bit cell.
21. The TCAM of claim 20 wherein the first pushed-rule memory bit cell is a mirror of the second pushed-rule memory bit cell.
22. The TCAM of claim 20 wherein the compare circuitry is based on an edge cell associated with the six-transistor SRAM bit cell.
23. The TCAM of claim 18 wherein the pushed-rule memory bit cells are laid out in a manner that preserves geometric proximity characteristics of the pushed-rule memory bit cells.
24. The TCAM of claim 18 wherein the composite memory bit cell occupies less area than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
25. The TCAM of claim 18 wherein the composite memory bit cell consumes less power than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
26. The TCAM of claim 18 wherein the composite memory bit cell operates at a higher frequency than a composite memory bit cell that implements the same logic function but laid out using standard logic design rules.
27. The TCAM of claim 18 wherein the pushed-rule memory bit cells are foundry-supplied pushed-rule memory bit cells.
28. The TCAM of claim 18 wherein the pushed-rule memory bit cells are designed for a 28-nanometer or smaller process technology node.