Apparatus for scannable D-flip-flop which scans test data independent of the system clock
First Claim
1. A scannable D-flip-flop circuit for processing data bits, said scannable D-flip-flop circuit comprising:
- (a) a first latch circuit coupled to a first input of said scannable D-flip-flop, said first latch circuit receives a first data input signal and a first clock signal and stores said first data input signal in response to said first clock signal during a normal mode of operation, said first latch having an output;
(b) a second latch circuit coupled to a second input of said scannable D-flip-flop, said second latch circuit receives a second data input signal and a second clock signal and stores said second data input signal in response to said second clock signal during a scan mode of operation, said second latch having an output;
(c) a third latch circuit having a data path and a feedback path wherein said data path is coupled to said output of said first latch circuit and said feedback path is coupled to said output of said second latch circuit, said third latch circuit receives said first data input signal and said first clock signal and stores said first data input signal in response to said first clock signal during said normal mode of operation, said third latch circuit receives said second data input signal and said second clock signal and stores said second data input signal in response to said second clock signal during said scan mode of operation, said third latch circuit is coupled to an output of said D-flip-flop.
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Abstract
The present invention discloses an apparatus for controlling and observing test data stored in scannable-D-flip-flops independent of a system clock, thereby making the scannable-D-flip-flops well suited for partial scanning Design-For-Test (DFT) techniques. Under the present invention, the scannable-D-flip-flop is comprised of two master latches and one slave latch such that the scannable-D-flip-flops may operate in a normal mode of operation or a scan/test mode of operation. During normal mode of operation, the first master latch operates together with the slave latch in response to the system clock. During the scan/test mode of operation, the second master latch operates together with the slave latch in response to a scan clock. Since the scanning of external test data is controlled by the scan clock, the conventional non-scannable D-flip-flops in the design, which are controlled by the system clock, maintain their previous states during a scanning operation. Also disclosed is a method for performance testing integrated circuits utilizing the scanning application of the scannable-D-flip-flops. This is accomplished by constructing a test circuit that spans the entire silicon die area. By using a special AC-TEST-MODE control signal, the scannable D-flip-flops are set to a "flow-through" mode to provide a direct path through the scannable flip-flops such that the test circuit forms an oscillator in which the frequency of the device can be measured.
136 Citations
12 Claims
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1. A scannable D-flip-flop circuit for processing data bits, said scannable D-flip-flop circuit comprising:
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(a) a first latch circuit coupled to a first input of said scannable D-flip-flop, said first latch circuit receives a first data input signal and a first clock signal and stores said first data input signal in response to said first clock signal during a normal mode of operation, said first latch having an output; (b) a second latch circuit coupled to a second input of said scannable D-flip-flop, said second latch circuit receives a second data input signal and a second clock signal and stores said second data input signal in response to said second clock signal during a scan mode of operation, said second latch having an output; (c) a third latch circuit having a data path and a feedback path wherein said data path is coupled to said output of said first latch circuit and said feedback path is coupled to said output of said second latch circuit, said third latch circuit receives said first data input signal and said first clock signal and stores said first data input signal in response to said first clock signal during said normal mode of operation, said third latch circuit receives said second data input signal and said second clock signal and stores said second data input signal in response to said second clock signal during said scan mode of operation, said third latch circuit is coupled to an output of said D-flip-flop. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification