Fuse selection of predecoder output

• US 4,720,817 A
• Filed: 02/26/1985
• Issued: 01/19/1988
• Est. Priority Date: 02/26/1985
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Childers, Jimmie D.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/706,057
• Time in Patent Office: 1,057 Days
• Field of Search: 365/200, 365/96, 365/230, 371/11
• US Class Current: 365/200
• CPC Class Codes: G11C 29/80 with improved layout
• CPC Class Codes: G11C 8/10 Decoders

Abstract

A fuse selectable decoder for a redundant row of memory elements in an array includes a redundant decode select circuit (38) for receiving predecoder inputs from predecode lines (28), (30), (32) and (34). The predecode lines are output from predecoders (20), (24) and (26) which decode an eight bit address word. The redundant decode select circuit (38) is programmed by fuse select circuit (40) that selects the address of a defective one of the rows of memory elements in an array (10). The redundant decode select circuit (38) selects one line out of each of the predecode lines (28), (30), (32) and (34) for input to an AND gate (112) for selecting the redundant row (12).

Claims

1. A defect tolerant memory device, comprising:

an array of memory elements arranged in rows and columns, each of said rows having a control input for activation thereof, said rows addressable by an external address having n bits received at terminals of said device, said array having 2ⁿ rows;

a row of redundant memory elements disposed adjacent said array and having a redundant control input for activation thereof;

a plurality of predecode means each for receiving m adjacent bits of the n bits of said address from said terminals and predecoding the m bits from a binary format into one of 2^m mutually exclusive output;

final decode means for receiving the 2^m outputs from each of said predecode means and outputting 2ⁿ mutually exclusive decode outputs, each of said 2ⁿ decode outputs interfaced with said control input of one of the rows in said array;

deactivation means for selectively deactivating one of said 2ⁿ decode outputs from said final decode means; and

redundant decode means for receiving the 2^m outputs from each of said predecode means and being selectively programmable to activate the redundant control input to said redundant row of memory elements when said address from said terminals corresponding to the deactivated one of the rows in said array is input to said predecode means.

2. The defect tolerant memory of claim 1 wherein n is an even number.

3. The defect tolerant memory of claim 1 wherein m is equal to two.

4. The defect tolerant memory of claim 1 wherein said deactivation means comprises a series fuse connected between each of said 2ⁿ decode outputs from said final decode means and the corresponding one of the rows in said array.

5. The defect tolerant memory of claim 1 wherein each of the said decode means comprises one of 2^m decoders for receiving m bits in a binary format and outputting 2^m mutually exclusive decode outputs.

6. The defect tolerant memory of claim 1 wherein said final decode means comprises logic circuit means associated with each of the control inputs on the rows in said array and having a plurality of input lines, each of said input lines associated with each of said predecode means and one of the 2^m output lines therefrom, said logic circuit means outputting a signal when the signals applied to said plurality of inputs is at a predetermined state.

7. The defect tolerant memory of claim 6 wherein said logic circuit means comprises a multiple input NAND gate.

8. The defect tolerant memory of claim 1 wherein said redundant decode means comprises:

select means associated with the 2^m outputs of each of said predecode means, each of said select means selecting one of the 2^m output lines associated therewith; and

logic circuit means having a plurality of inputs, each of said inputs connected to the output of each of said select means, said logic circuit means outputting a signal to the redundant control input of said redundant row when the state of the selected 2^m output lines of each of said predecode means is in a predetermined logic state.

9. The defect tolerant memory of claim 8 wherein each of said select means comprises:

pass gate means connected to each of the associated 2^m output lines from the associated one of said predecode means, the outputs of each of said pass gate means in each of said select means connected to a common node for input to one of the plurality of inputs of said logic circuit means, each of said pass gate means in the normally open state such that the associated 2^m lines are not interconnected to said common node; and

programming means for controlling said pass gate means to selectively activate only one of said pass gate means to selectively interconnect one of the associated 2^m output lines to said common node.

10. The defect tolerant memory of claim 9 wherein said programming means comprises:

control circuit means associated with each of said pass gate means for controlling said pass gate means to either interconnect the associated one of the 2^m outputs to said common node or inhibit interconnection therewith; and

a programming fuse interfaced with said control circuit means for each of said pass gate means in each of said select means, opening of said fuse activating said pass means to interconnect the associated one of the 2^m outputs to said common node.

11. The defect tolerant memory of claim 8 and further comprising terminating means for terminating said common node to a predetermined logic state when said pass gate means associated with said common node are in the normally opened state, activation of any of said pass gate means deactivating said terminating means.

12. A defect tolerant memory device, comprising:

an array of memory elements arranged in rows and columns, each of said rows having a control input for activation thereof, said rows addressed by an external row address applied to terminals of said device having n bits, said array having 2ⁿ rows;

a row of memory elements disposed adjacent said array and having a redundant control input for activation thereof;

a plurality of predecoders each for receiving m adjacent bits of the n address bits from said terminals and predecoding the m bits from a binary format into one of 2^m mutually exclusive outputs;

final decode means associated with each of the control inputs for activation thereof, each of said final decode means for receiving a select one of the 2^m outputs from each of said predecoders and outputting a decode signal to activate the associated one of said rows, said decode signal occurring when the logic state of the select ones of the 2^m outputs are equal to a predetermined logic state;

deactivation means associated with each of said final decode means for inhibiting output of said decode signal, said deactivation means selected to deactivate a defective one of said rows;

select means associated with each of said predecoders for selecting one of the 2ⁿ outputs associated therewith, said select means in a normally unselected state;

programming means for determining which of said associated 2^m predecode outputs is selected by each of said select means; and

redundant decode means associated with said redundant row control input for receiving the outputs of said select means and outputting a redundant decode signal when the logic state of the outputs of each of said select means is equal to a predetermined logic state.

13. The defect tolerant memory of claim 12 wherein said deactivation means comprises a series fuse disposed between each of said final decode means and the control input of the associated one of said rows, opening of said fuse preventing activation of the associated one of said rows.

14. The defect tolerant memory of claim 12 wherein each of said select means comprises a pass gate associated with each of the 2^m predecode outputs that are input to said select means and connected between the associated one of said 2^m predecode outputs and a common node, said programming means operable to switch one of said pass gates in each of said select means from a nonconducting to a conducting state to place the signal on the associated one of said 2^m predecode outputs onto the said common node, said common node connected to said redundant control input.

15. The defect tolerant memory of claim 14 and further comprising means for holding said common node on each of said select means to a predetermined potential when all of said pass gates are in the nonconducting mode, said programming means controlling said inhibiting means to remove said predetermined potential from said common nodes in each of said select means when one of said pass gates in each of said select means is selected.

16. The defect tolerant memory of claim 14 wherein said programming means comprises:

a control circuit for controlling said pass gates; and

a fuse interfaced with said control circuit, said control circuit forcing said pass gate to the nonconducting mode when said fuse is intact and forcing the associated one of said pass gates to the conducting mode when said fuse is open.

17. The defect tolerant memory of claim 12 wherein said redundant code means comprises an AND gate having a plurality of inputs, each input associated with each of said predecoders and the 2^m outputs therefrom.

18. The defect tolerant memory of claim 12 wherein said final decode means each comprise an AND gate having a plurality of inputs, each of said inputs associated with one of the 2^m outputs of each of said predecoders.