Structural testing of integrated circuits
An integrated circuit (IC) that is operable in scan test and functional modes includes scan-in pads, scan-out pads, scan chains, a compressor, a decompressor, a test control register, and a scan controller. The scan controller includes a multiple input shift register (MISR), an inverter, and multiple logic gates. The scan-in and scan-out pads receive scan test data and masking signals, respectively. The decompressor provides decompressed scan test data to the scan chains, which generate functional responses based on the decompressed scan test data. The compressor provides compressed functional responses to the scan controller. The logic gates receive the compressed functional responses and the masking signals from the compressor and the corresponding scan-out pads, respectively, and generate corresponding masked signals. The masking signals mask non-deterministic values in the decompressed functional responses. The MISR receives the masked signals and generates an error free signature.
1. An integrated circuit operable in scan test and functional modes when connected to an automated test equipment (ATE) for testing the integrated circuit, the integrated circuit comprising:
a first set of input/output (IC) pads, connectable to the ATE for receiving a plurality of test patterns when the integrated circuit is in the scan test mode;
a decompressor, connected to the first set of IO pads, for receiving and decompressing the plurality of test patterns and generating a corresponding plurality of decompressed test patterns when the integrated circuit is in the scan test mode;
a plurality of scan chains, connected to the decompressor, for receiving the plurality of decompressed test patterns and generating a corresponding plurality of test responses when the integrated circuit is in the functional mode;
a compressor, connected to the plurality of scan chains for receiving and compressing the plurality of test responses and generating a plurality of compressed test responses when the integrated circuit is in the scan test mode;
a second set of IO pads, connectable to the ATE for receiving a plurality of masking signals when the integrated circuit is in the scan test mode;
a scan controller, connected to the compressor, including:
a plurality of logic gates, wherein each logic gate has a first input terminal connected to the compressor for receiving a compressed test response of the plurality of compressed test responses, a second input terminal connected to an IC pad of the second set of IO pads for receiving a masking signal of the plurality of masking signals, and an output terminal for outputting a masked signal based on a logic state of the masking signal when the integrated circuit is in the scan test mode; and
a multiple input shift register (MISR) having a clock input terminal connected to the ATE, for receiving a tester clock signal, and a plurality of input terminals, wherein each of the plurality of input terminals is connected to a corresponding output terminal of a logic gate of the plurality of logic gates, for receiving masked signals generated by each of the plurality of logic gates and generating a signature such that a non-deterministic value of a compressed test response of the plurality of compressed test responses is masked when the integrated circuit is in the scan test mode;
a test control register connected to the scan controller for generating a test mode select signal to configure the second set of IO pads as at least one of input and output pads; and
a first set of buffers, wherein each buffer of the first set of buffers has a first input terminal connected to a corresponding IO pad of the second set of IO pads for receiving a masking signal of the plurality of masking signals, a second input terminal connected to the test control register for receiving the test mode select signal, and an output terminal connected to the second input terminal of a corresponding logic gate of the plurality of logic gates for outputting the masking signal based on a logic state of the test mode select signal.
2. The integrated circuit of claim 1 , wherein the scan controller further includes an inverter having an input terminal connected to the test control register for receiving the test mode select signal and an output terminal for outputting an inverted test mode select signal.
3. The integrated circuit of claim 2 , further comprising a second set of buffers, wherein each buffer of the second set of buffers has a first input terminal connected to the compressor for receiving a compressed test response of the plurality of compressed test responses, a second input terminal connected to the output terminal of the inverter for receiving the inverted test mode select signal, and an output terminal connected to a corresponding IO pad of the second set of IO pads for outputting the compressed test response based on a logic state of the test mode select signal.
4. The integrated circuit of claim 3 , wherein each buffer of the second set outputs a compressed test response of the plurality of compressed test responses when the test mode select signal is at logic low state, and wherein each IO pad of the second set of IO pads is configured as an output of the integrated circuit when the integrated circuit is in the functional mode.
5. The integrated circuit of claim 1 , wherein each buffer outputs a masking signal of the plurality of masking signals when the test mode select signal is at a logic high state, and wherein each IO pad of the second set of IO pads is configured as an input to the integrated circuit when the integrated circuit is in the scan test mode.
6. The integrated circuit of claim 1 , wherein the masked signal includes the compressed test response when the masking signal is at a logic high state and includes a logic low state signal when the masking signal is at a logic low state.
7. The integrated circuit of claim 1 , wherein each logic gate of the plurality of logic gates comprises an AND gate.
8. The integrated circuit of claim 1 , wherein each IO pad of the first and second sets of IO pads simultaneously receives a test pattern of the plurality of test patterns and a masking signal of the plurality of masking signals, respectively, in one tester clock signal cycle when the integrated circuit is in the scan test mode.