JPH0833436B2 - Integrated circuit test method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an integrated circuit test method applicable to an LSI or the like.

[Prior art and its problems]

Conventionally, various test pattern generators have been devised, but as a generator for random number input, a device for generating a test pattern by directly inputting a generated random number or by uniform conversion has been mainly proposed. For example, in the case of a circuit with 24 inputs, when a random number is AD-converted and generated as a test pattern, a set of 24 "1" s or "0" s is formed as one test pattern. Therefore, the number of "1" s in the set (hereinafter abbreviated as "weight") is taken on the horizontal axis, and the "weight"
FIG. 1 shows the distribution in the case where 3000 sets of test patterns are generated by the uniform random number generation device, with the vertical axis representing the occurrence probability corresponding to.

From the figure, it can be seen that the distribution is a binomial distribution as long as the input is a uniform random number.

Further, when the uniform conversion, that is, the appearance probabilities of "1" and "0" are simply changed, it is nothing but the distribution obtained by moving the distribution in FIG. 1 in the horizontal axis direction.

However, in the above method, the distribution of the "weight" is 2
Since it is a term distribution, if you want to generate as few test patterns as possible and test it, even if you want to generate patterns with various weights, with a pattern limited as a probability distribution,
There are many things that are difficult to generate. For example, if a test pattern with 20 "0" s and 4 "1" s occurs in a binomial distribution, it is approximately 0.03%.
, That is, it appears only three times in 10,000 patterns.

The same thing can be said about the “weight” in the reverse direction that is translated even if a uniform transformation is added.
This tendency becomes more remarkable as the number of inputs increases. For example AND
Conventionally, it cannot be applied to the case where the gate and the OR gate are configured and the ratios thereof are different.

[Object of the Invention]

In consideration of this point, the present invention has an object to freely control the weight of a test pattern by external data such as circuit data to facilitate testing of an integrated circuit.

[Outline of Invention]

The present invention provides a random number distribution conversion device that controls the distribution of random numbers generated in the subsequent stage of a uniform random number generation device, and further provides a test pattern generation device that outputs a specific logical value with a predetermined probability according to this random number distribution. It is characterized in that the movement of the logical value appearance probability distribution in the weight axis direction and its shape change are controlled by external binary values.

〔The invention's effect〕

According to the present invention, it is possible to freely set the "1" probability distribution by controlling the movement amount and the change of the distribution shape of the probability distribution by the external binary value, and the integrated circuit test time is greatly shortened. It

For example, for an integrated circuit that includes AND gates and OR gates at a predetermined ratio, the ratio of the appearance probabilities at both ends of the weight axis is calculated according to the ratio of the two, and the amount of movement in the weight axis direction is set to Balance according to the ratio, and then change the distribution shape from the binomial distribution to concave shape to set the magnitude of the appearance probability at each end and generate a test pattern that finishes the test in an extremely short time. You can

Example of Invention

An embodiment of the present invention will be described in detail below with reference to the drawings.

The outline of the apparatus will be described. First, a conversion function is prepared, and this is defined as G ₁ (X). Here specifically And

Here, a uniform random number is generated between -1 and 1, and (1)
Converting by the formula, and letting it be P, that is, the generated random number is γ ₀ , Becomes This is the reference value.

Furthermore, as a conversion function Define and prepare. (Α and β are control parameters described later) Then, a test pattern sequence is generated by uniform random numbers. If the random numbers generated with the number of elements of the test pattern sequence being 24 are γ ₁ to γ ₂₄ converted pattern elements Q _{1 to} Q ₂₄ , Becomes

Next, according to (2), the test pattern is generated from the determined Q _{1 to} Q ₂₄ by the determined P and (4). The method is that if the generated test patterns are T _{1 to} T ₂₄ , Is defined. By repeating (1) to (5) according to this method, test patterns are generated one after another.

Here, a supplementary explanation will be given regarding α and β which have been expressed by the equation (3). First of all, α is a parameter for controlling the parallel shift of the probability distribution in the horizontal axis direction in FIG. 1, that is, the “weight”, to the left and right.
The role of this parameter is to carry out the above-mentioned uniform change. Fig. 2 shows that α is β = 5.0 and Fig. 2 is α = 1.0.
(A) and α = 1.0 (b). This is an example of changing. This determines the left-right balance with respect to the center of weight (12 occurrences of "1"). Next, β is a parameter that changes the distribution shape. FIG. 3 shows an example in which β is changed. In the figure, when α = 0.0, β = 10.0
As can be seen from Fig. 3 where (a) and β = 0.1 (b), the size relationship between the center (peak part) of the probability distribution and both ends by changing the distribution shape, and the ratio Is controlled. FIG. 4 shows an example of the apparatus. In FIG. 4, a uniform random number group γ ₀ , γ ₁ ... γ ₂₄ input as basic inputs from the uniform random number generator 10 and external parameters α, β input from the external data input circuit 11 are random number distribution converters. type 12, further initially entered gamma ₀ also the conversion function device 13 of the formula (1) type, gamma ₁ to? ₂₄ are output are respectively converted from the conversion function 14 of the formula (3) type. This output sequence P, Q ₁ , Q ₂ ..., Q ₂₄ is further added to the test pattern generator 15
And the final test patterns T _{1 to} T ₂₄ are generated by the conversion of the formula (5) type.

 The above flow chart is shown in FIG.

Furthermore, the test patterns T _{1 to} T ₂₄ are input to the test circuit 16. PI ₁ , PI ₂ ..., PIn are the input terminals. If the circuit under test is an AND, OR gate, do the following.

Explaining the 2-input AND gate beforehand, the input is "00",
The output is "0" for the three patterns "01" and "10". And the output becomes "1" only for the input "11". That is, the output "0" appears with a probability of 3/4. In the case of a 2-input OR gate, on the contrary, only the input "00" outputs "1".

Therefore, if the circuit under test is mainly composed of AND and OR logic circuits,
Is determined, and β is determined from the occupancy ratio of the AND system and the OR system with respect to the previous input pin. And "1" such as β = 0.1 in Fig. 3
If the test pattern is generated with the appearance probability distribution, the test circuit can be efficiently tested, and the test is completed in an extremely short time.

The present invention is not limited to the above embodiment, and various conversion functions can be used, for example. Also, the random numbers are not limited to those that generate -1 to 1 as numerical values,
The logic "1" may be generated at random short time intervals, and the time intervals may correspond to random numbers.

[Brief description of drawings]

Fig. 1 shows the weight on the horizontal axis, the probability on the vertical axis, and the "weight" -probability distribution curve of the test pattern generated by 24 uniform random numbers for pattern elements (the total number of "1" s and "0" s). ,
FIG. 2 is a diagram showing a “weight” -probability distribution curve of a test pattern generated by changing only α, FIG. 3 is a diagram in which only β is changed, FIG. 4 is a device configuration diagram of the present invention, FIG. 5 is a flow chart of the present invention.

Claims (1)

[Claims] 1. A random number generator and a random number distribution converter for controlling the distribution of random numbers generated based on a conversion function having the number of occurrences of a predetermined logical value and the envelope shape of its occurrence probability distribution as parameters. A test pattern generator for outputting a specific logical value with a predetermined probability according to the random number distribution, and by changing the two parameters, the center of the envelope of the occurrence probability distribution with respect to the central value of the number of occurrences. Test method for an integrated circuit, which comprises generating a test pattern in which the movement of the pattern and its envelope shape are controlled and inputting the test pattern into the integrated circuit.