Data compression circuit and method for testing memory devices

Abstract

A test circuit detects defective memory cells in a memory device. The test circuit includes a test mode terminal adapted to receive a test mode signal. An error detection circuit includes a plurality of inputs and an output, each input coupled to some of the plurality of memory cells. The error detection circuit develops an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data. A control circuit is coupled to the test mode terminal, the error detection circuit, and the memory cells. The control circuit is operable responsive to the test mode signal being active to apply the data of accessed memory cells to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary values.

1. A test circuit for detecting defective memory cells in a plurality of memory cells in a memory device, the test circuit comprising:
 a test mode terminal adapted to receive a test mode signal;  
 an error detection circuit including a plurality of inputs and an output, each input coupled to some of the plurality of memory cells, the error detection circuit developing an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data, the error detection circuit comprising: 
 a first data compression circuit including first and second pairs of complementary inputs adapted to receive first and second complementary data signals, respectively, and having a pair of outputs;  
 a second data compression circuit including first and second pairs of complementary inputs adapted to receive third and fourth complementary data signals, respectively, and having a pair of outputs;  
 a third data compression circuit including a first pair of complementary inputs coupled respectively to the outputs of the first data compression circuit, and a second pair of complementary inputs coupled respectively to the outputs of the second data compression circuit and having a pair of outputs;  
 a logic gate having an output and having inputs coupled respectively to the outputs of the third data compression circuit, and  
 
 a latch having a set input coupled to the output of the logic gate and an output coupled to a data terminal of the memory device; and  
 a control circuit coupled to the test mode terminal, the error detection circuit, and the memory-cells, the control circuit operable responsive to the test mode signal being active to apply the data of accessed memory cells to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary values.  
 
     
     
       2. The test circuit of  claim 1  wherein the memory cells are located in a plurality of arrays, each array coupled to an input of the error detection circuit and the control circuit simultaneously accessing at least one memory cell in each of the plurality of arrays. 
     
     
       3. The test circuit of  claim 1  wherein the error detection circuit comprises the data signals applied on its inputs and develops the error signal in response to the compressed data. 
     
     
       4. The test circuit of  claim 1  wherein the plurality of memory cells are located in a plurality of arrays. 
     
     
       5. A test circuit for detecting defective memory cells in a plurality of memory-cell arrays in a memory device, the test circuit comprising:
 a test mode terminal adapted to receive a test mode signal;  
 an external clock terminal adapted to receive an external clock signal having a frequency;  
 a clock multiplier circuit having an input coupled to the external clock terminal, the multiplier circuit developing an internal clock signal on an output in response to the external clock signal, the internal clock signal having a frequency greater than the frequency of the external clock signal;  
 an error detection circuit including an output coupled to a terminal of the memory device, a clear terminal adapted to receive a clear signal, an enable signal adapted to receive an enable signal, and further including a plurality of inputs, each input coupled to one of the plurality of memory-cell arrays, the error detection circuit operable, when the enable signal is active, to develop an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data, and to drive the error signal inactive responsive to the clear signal, the error detection circuit comprising: 
 a first data compression circuit including first and second pairs of complementary inputs adapted to receive first and second complementary data signals, respectively and having a pair of outputs;  
 a second data compression circuit including first and second pairs of complementary inputs adapted to receive third and fourth complementary data signals, respectively and having a pair of outputs;  
 a third data compression circuit including a first pair of complementary inputs coupled respectively to the outputs of the first data compression circuit, and a second pair of complementary inputs coupled respectively to the outputs of the second data compression circuit, and having a pair of outputs;  
 a logic gate having an output and having inputs coupled respectively to the outputs of the third data compression circuit; and  
 
 a latch having an input coupled to the output of the logic gate and an output coupled to a data terminal of the memory device; and  
 a control circuit coupled to the test mode terminal, the output of the clock multiplier circuit, and the memory-cell arrays, the control circuit operable, when the test mode signal is active, responsive to the internal clock signal to apply the data of accessed memory cells in the arrays to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary values, the control circuit applying the data of accessed memory cells to the error detection circuit until all memory cells in the arrays have been accessed, and activating the clear signal after the data of a predetermined number of memory cells has bean applied to the error detection circuit.  
 
     
     
       6. The test circuit of  claim 5  wherein the control circuit simultaneously accesses at least one memory cell in each of the plurality of arrays and applies the data stored in the accessed memory cells it associated inputs of the error detection circuit. 
     
     
       7. The test circuit of  claim 5  wherein the error detection circuit compresses the data applied on its inputs and develops the error signal in response to the compressed data. 
     
     
       8. A memory device, comprising:
 an address bus;  
 a control bus;  
 a data bus;  
 a test mode terminal adapted to receive a test mode signal;  
 an address decoder coupled to the address bus;  
 a control circuit coupled to the control bus;  
 a read/write circuit coupled to the data bus;  
 an array coupled to the address decoder and read/write circuit, the array including a plurality of memory cells; and  
 a test circuit coupled to the data bus, comprising: 
 an error detection circuit including a plurality of inputs and an output, each input coupled to some of the plurality of memory cells, the error detection circuit developing an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data, the error detection circuit comprising: 
 a first data compression circuit including first and second pairs of complementary inputs adapted to receive first and second complementary data signals, respectively, and having a pair of outputs;  
 a second data compression circuit including first and second pairs of complementary inputs adapted to receive third and fourth complementary data signals, respectively and having a pair of outputs;  
 a third data compression circuit including a first pair of complementary inputs coupled respectively to the outputs of the first data compression circuit, and a second pair of complementary inputs coupled respectively to the outputs of the second data compression circuit, and having a pair of outputs;  
 a logic gate having an output and having inputs coupled respectively to the outputs of the third data compression circuit; and  
 
 
 a latch having a set input coupled to the output of the logic gate and an output coupled to a data terminal of the memory device; and  
 a control circuit coupled to the test mode terminal, the error detection circuit, and the array, the control circuit operable responsive to the test mode signal being active to apply the data of accessed memory cells to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary values.  
 
     
     
       9. The memory device of  claim 8  wherein each memory cell comprises:
 an access transistor having a gate terminal coupled to a respective word line associated with each row of memory cells in the array, and a drain terminal coupled to one of a respective pair of complementary digit lines associated with each column of memory cells and a source terminal; and  
 a capacitor having a first plate coupled to the source terminal, and a second plate coupled to receive a reference voltage.  
 
     
     
       10. The memory device of  claim 8 , further including a plurality of arrays. 
     
     
       11. A test system for detecting defects in a memory device having address, data and control buses a memory cell array having a plurality of memory cells arranged in rows and columns, and a test mode terminal adapted to receive a test mode signal, the test system comprising:
 an error detection circuit including a plurality of inputs and an output, each input coupled to some of the plurality of memory cells, the error detection circuit developing an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data, the error detection circuit comprising: 
 a first data compression circuit including first and second pairs of complementary inputs adapted to receive first and second complementary data signals, respectively, and having a pair of outputs;  
 a second data compression circuit including first and second pairs of complementary inputs adapted to receive third and fourth complementary data signals, respectively, and having a pair of outputs;  
 a third data compression circuit including a first pair of complementary inputs coupled respectively to the outputs of the first data compression circuit, and a second pair of complementary inputs coupled respectively to the outputs of the second data compression circuit and having a pair of outputs;  
 a logic gate having an output and having inputs coupled respectively to the outputs of the third data compression circuit; and  
 
 a latch having a set of input coupled to the output of the logic gate and an output coupled to a data terminal of the memory device;  
 a control circuit coupled to the test mode terminal, the error detection circuit, and the memory-cells, the control circuit operable responsive to the test mode signal being active to apply the data of accessed memory cells to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary value; and  
 a memory tester coupled to the address, data, and control buses of the memory device and to the test method terminal, the memory tester activating the test mode signal to place the memory device into a test mode, storing a predetermined test pattern of data in the memory cells, and detecting a defect in the memory device when the error signal goes active.  
 
     
     
       12. The system of  claim 11  wherein the memory tester sequentially applies separate predetermined test patterns of data that are stored in the memory cells, the memory tester determining at least once after applying a respective test pattern and before applying a subsequent test pattern whether the error signal is active. 
     
     
       13. A computer system, comprising:
 a data input device;  
 a data output device; and  
 computing circuitry coupled to the data input and output devices, the computing circuitry including a memory device having a data terminal adapted to receive a data signal and having a plurality of memory cells arranged in rows and columns, each memory cell storing a bit of data, and a test circuit having a test mode terminal adapted to receive a test mode signal, the test circuit comprising:  
 an error detection circuit including a plurality of inputs and an output, each input coupled to some of the plurality of memory cells, the error detection circuit developing an active error signal on an output when the binary value of data on at least one input is different from predetermined binary values of data, the error detection circuit comprising: 
 a first data compression circuit including first and second pairs of complementary inputs adapted to receive first and second complementary data signals, respectively, and having a pair of outputs;  
 a second data compression circuit including first and second pairs of complementary inputs adapted to receive third and fourth complementary data signals, respectively, and having a pair of outputs;  
 a third data compression circuit including a first pair of complementary inputs coupled respectively to the outputs of the first data compression circuit, and a second pair of complementary inputs coupled respectively to the outputs of the second data compression circuit, and having a pair of outputs;  
 
 a logic gate having an output and having inputs coupled respectively to the outputs of the third data compression circuit; and  
 a latch having a set input coupled to the output of the logic gate and an output coupled to a data terminal of the memory device; and  
 a control circuit coupled to the test mode terminal, the error detection circuit, and the memory cells, the control circuit operable responsive to the test mode signal being active to apply the data of accessed memory cells to the associated inputs of the error detection circuit such that the error detection circuit drives the error signal active when the binary value of the data stored in at least one accessed memory cell is different from predetermined binary values.  
 
     
     
       14. The computer system of  claim 13  wherein the memory cells are located in a plurality of arrays. 
     
     
       15. An error detection circuit for detecting defective memory cells in a plurality of memory cells in a memory device, the plurality of memory cells arranged in a plurality of memory- cell arrays, the error detection circuit adapted to receive a test mode signal and being coupled to each memory - cell array and to a terminal of the memory device, the error detection circuit operable when the test mode signal is active to simultaneously receive data from at least one memory cell in each of the plurality of memory - cell arrays and to apply an active error signal on the terminal when the data is different from expected values, the error detection circuit including a plurality of data compression circuits coupled to progressively compress the data received from the at least one memory cells and generate a data compression signal having a value indicative of the result of the data compression, and the error detection circuit generating the error signal responsive to the data compression signal.    
     
     
       16. The error detection circuit of  claim 15  wherein the data compression signal comprises a complementary pair of signals and wherein the error detection circuit further includes a logic gate coupled to the receive the complementary signals and having an output, and further including a latch coupled to the output of the logic gate and an output coupled to the terminal of the memory device.  
     
     
       17. The error detection circuit of  claim 15  wherein the memory cells are located in a plurality of arrays, each array coupled to the error detection circuit and the error detection circuit simultaneously receiving data from at least one memory cell in each of the plurality of arrays.  
     
     
       18. A memory device, comprising:
   an address bus;        a control bus;        a data bus;        a test mode terminal adapted to receive a test mode signal;        an address decoder coupled to the address bus;        a control circuit coupled to the control bus;        a read/write circuit coupled to the data bus;        a plurality of memory - cell arrays coupled to the address decoder and read/write circuit, the arrays including a plurality of memory cells; and        an error detection circuit for detecting defective memory cells in each array, the error detection circuit adapted to receive the test mode signal and being coupled to each memory - cell array and to one of the address, control, and data busses, the error detection circuit operable when the test mode signal is active to simultaneously receive data from at least one memory cell in each of the plurality of memory - cell arrays and to apply an active error signal on one of the address, control, and data busses when the data is different from expected values, the error detection circuit including a plurality of data compression circuits coupled to progressively compress the data received from the at least one memory cells and generate a data compression signal having a value indicative of the result of the data compression, and the error detection circuit generating the error signal responsive to the data compression signal.      
     
     
       19. The memory device of  claim 18  wherein the data compression signal comprises a complementary pair of signals and wherein the error detection circuit further includes a logic gate coupled to the receive the complementary signals and having an output, and further including a latch coupled to the output of the logic gate and an output coupled to the terminal of the memory device.  
     
     
       20. A test system for detecting defects in a memory device having address, data and control buses, a memory- cell array having a plurality of memory cells arranged in rows and columns, and a test mode terminal adapted to receive a test mode signal, the test system comprising:      an error detection circuit coupled to the test mode terminal and being coupled to the memory - cell array and to one of the address, control, and data busses, the error detection circuit operable when the test mode signal is active to receive from accessed memory cells and to apply an active error signal on one of the address, control, and data busses when the data is different from expected values, the error detection circuit including a plurality of data compression circuits coupled to progressively compress data from accessed memory cells.      
     
     
       21. The test system of  claim 20  wherein the memory tester sequentially applies separate predetermined test patterns of data that are stored in the memory cells, the memory tester determining at least once after applying a respective test pattern and before applying a subsequent test pattern whether the error signal is active.  
     
     
       22. A computer system, comprising:
   a data input device;        a data output device; and        computing circuitry coupled to the data input and output devices, the computing circuitry including a memory device including,      an address bus;        a control bus;        a data bus;        a test mode terminal adapted to receive a test mode signal;        an address decoder coupled to the address bus;        a control circuit coupled to the control bus;        a read/write circuit coupled to the data bus;        a plurality of memory - cell arrays coupled to the address decoder and read/write circuit, the arrays including a plurality of memory cells; and        an error detection circuit for detecting defective memory cells in each array, the error detection circuit adapted to receive the test mode signal and being coupled to each memory - cell array and to one of the address, control, and data busses, the error detection circuit operable when the test mode signal is active to simultaneously receive data from at least one memory cell in each of the plurality of memory - cell arrays and to apply an active error signal on one of the address, control, and data busses when the data is different from expected values, the error detection circuit including a plurality of data compression circuits coupled to progressively compress the data from the at least one memory cells and generate a data compression signal having a value indicative of the result of the data compression, and the error detection circuit generating the error signal responsive to the data compression signal.        
     
     
       23. The computer system of  claim 22  wherein the data compression signal comprises a complementary pair of signals and wherein the error detection circuit further includes a logic gate coupled to the receive the complementary signals and having an output, and further including a latch coupled to the output of the logic gate and an output coupled to the terminal of the memory device.  
     
     
       24. A method of detecting defective memory cells in a memory device including a plurality of memory- cell arrays, the method comprising:      placing the memory device in a test mode;        storing test data in the memory cells in the plurality of arrays;        accessing memory cells in at least some of the arrays;        progressively compressing the data stored in the accessed memory cells to generate a compression signal;        generating an error signal responsive to the data compression signal;        storing the error signal;        placing the error signal on a terminal of the memory device; and        detecting a defective memory cell responsive to the error signal being active.      
     
     
       25. The method of  claim 24  wherein storing test data in the memory cells in the plurality of arrays includes transferring the same binary value of data to all memory cells in the arrays.  
     
     
       26. The method of  claim 24  wherein placing the memory device in a test mode occurs after the step of storing test data.  
     
     
       27. A method of detecting defective memory cells in a memory device, comprising:
   writing test data to the memory cells;        reading the test data from the memory cells;        compressing the data stored in the accessed memory cells a first time to generate a first set of data compression signals;        compressing the first set of data compression signals to generate an output data compression signal;        generating an error signal responsive to the output data compression signal; and        detecting a defective memory cell responsive to the error signal.      
     
     
       28. The method of  claim 27  wherein writing test data to the memory cells comprises writing the same binary value to all the memory cells.  
     
     
       29. A method of detecting defective memory cells in a memory device, comprising:
   writing test data to the memory cells;        reading the test data from the memory cells;        an error detection circuit for detecting defective memory cells in each array, the error detection circuit adapted to receive the test mode signal and being coupled to the memory - cell arrays and to one of the address, control, and data buses, the error detection circuit operable when the test mode signal is active to receive data from accessed memory cells and to apply an active error signal on one of the address, control, and data busses when the data is different from expected values, the error detection circuit including a plurality of data compression circuits coupled to progressively compress data form accessed memory cells and generate a data compression signal having a value indicative of the result of the data compression, and the error detection circuit generating the error signal responsive to the data compression signal.