Enhanced control in scan tests of integrated circuits with partitioned scan chains
A test controller implemented in an integrated circuit (IC) with partitioned scan chains provides enhanced control in performing scan tests. According to an aspect, a test controller can selectively control scan-in, scan-out and capture phases of scan tests for different scan chains of the IC to be independent. The number of pins required to interface the test controller with an external tester is less than the number of partitions that the test controller can support. According to another aspect, an IC includes a register corresponding to each partition to support transition fault (or LOS) testing. According to another aspect, an IC with partitioned scan chains includes serial to parallel and parallel to serial converters, thereby minimizing the external pins required to support scan tests.
1. An integrated circuit (IC) comprising:
a plurality of memory elements operable as a plurality of scan chains, said plurality of scan chains grouped into a plurality of partitions whereby scan chains of each partition are enabled together via a corresponding partition enable signal, each scan chain connected to a Test Data Input to receive test data; and
a test controller including a plurality of blocks, each block corresponding to one of said plurality of partitions, each block including
a delay register storing digital data therein having a input receiving a digital data input and an output generating a digital data output,
a count register storing a digital count therein having an input connected to said output of said corresponding delay register and an output generating a digital data output,
a delay element having a first input receiving said digital data stored in a corresponding delay register, a second input and an output generating a digital data output having a predetermined state a predetermined time after receiving an input at said second input, said predetermined time corresponding to said digital data stored in a corresponding delay register,
a counter having a trigger input connected to said output of said delay element and a count output generating a digital output corresponding to a count therein, said counter counting beginning upon receipt of a predetermined state at said trigger input,
a comparator connected to said count register and said counter comparing said digital count stored in said count register with said count of said counter and generating a match signal when said digital count stored in said count register matches said count of said counter;
an inverter having an input connected to receive said match signal of said comparator and an output, and
an AND gate having a first input connected to receive said output of said delay element, a second input connected to receive said output of said inverter and an output generating said partition enable signal to a corresponding partition of scan chains,
said plurality of blocks of said test controller disposed serially from a first block through a last block whereby said input of said delay register of said first block receives said Test Data Input, said input of said delay register of each subsequent block receives said output of said count register of a prior block, said input of said delay element of said first block receives a global start signal and said input of said delay element of each subsequent block receives said match signal of said comparator of a prior block; and said Test Data Input being received from a set of pins connected to an external tester, wherein the number of said set of pins is less than the number of said plurality of scan chains.
2. The integrated circuit (IC) of claim 1 , wherein:
each of said blocks of said test controller except said first block further includes
a logic bypass register storing a single bit therein having an input connected to said output of said corresponding count register and an output connected to said input of said delay register of said subsequent block, and
a multiplexer having a first input receiving said global start signal, a second input receiving said match signal of said comparator of said prior block, a control signal receiving said single bit stored in said bypass register and an output connected to said trigger input of said delay element, said multiplexer outputting either said first input or said second input on said output dependent upon a digital state of said single bit stored in said corresponding bypass register.
3. The integrated circuit (IC) of claim 1 , wherein:
each of said blocks of said test controller further includes an AND gate having a first input receiving a global master clock, a second input receiving said corresponding partition enable signal and an output supplying a clock input to said corresponding partitions of scan chains.
4. The integrated circuit (IC) of claim 1 , wherein:
each of said blocks of said test controller further includes an AND gate having an input receiving a global scan enable signal, a second input receiving said corresponding partition enable signal and an output supplying an enable input to said corresponding partition of scan chains.