JP3348679B2 - Semiconductor integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, and more particularly to a semiconductor integrated circuit capable of measuring transistor characteristics in an analog manner.

[0002]

2. Description of the Related Art FIGS. 2 and 3 are circuit diagrams showing a conventional example of a semiconductor integrated circuit.

First, in FIG. 2, TGa, TGb, TGa
Gc indicates a transfer gate, and when T1 = 1 or T1 is open, the transfer gate TG
Since a and TGb are open and the transfer gate TGc is closed, a normal output buffer operation is performed. When T1 = 0, the transfer gates TGa, TGa
Since Gb is closed and the transfer gate TGc is open, the output buffer level can be set at the test mode setting terminal T2 and the output current of the output buffer can be measured.

FIG. 3 is a circuit diagram of the test mode setting circuit shown in FIG. 2 using clocked inverters C1a to C1d in place of the transfer gates TGa, TGb and TGc.
This is realized by the st buffer. Also in this example, the test mode setting terminal T1 is opened during normal operation,
The clocked inverters C1a and C1b are closed, and when measuring the output current, the clocked inverters C1a and C1b are closed.
Was closed, and the clocked inverters C1c and C1d were opened.

[0005]

In the above-described conventional semiconductor integrated circuit, since the power supply and the ground of the output buffer are not separated, a current also flows through the transistor on the opposite side, and n
Vds-I of channel (or p-channel) transistor
There was a problem that ds measurement could not be performed.

It is an object of the present invention to provide a semiconductor integrated circuit in which transistor characteristics can be measured in an analog manner by separating a power supply and a ground of an output buffer in order to solve the above problem. .

[0007]

In order to achieve the above object, the present invention provides an internal logic circuit inside a chip and an output buffer for outputting a signal from an internal output terminal of the internal logic circuit to an external output terminal. A semiconductor integrated circuit comprising:
A first three-state buffer connected between one of the internal output terminals provided and the input terminal of the output buffer and switched between a normal output mode and a test mode; A second three-state buffer connected between a normal output mode and a test mode, and connected between an input terminal of the output buffer and an output terminal of the second three-state buffer, the normal output mode and the test mode The power supply and the ground of the output buffer are separated from the internal power supply and the internal ground inside the chip so that the transistor characteristics of the output buffer can be measured in an analog manner.

When the first and second three-state buffers are turned on, the changeover switch is turned off. When the first and second three-state buffers are turned off, the changeover switch is turned off. Are preferably in a conductive state.

Preferably, the output buffer comprises a first transistor connected in series between the power supply of the output buffer and the ground, and a second transistor having a different conductivity type from the first transistor.

Preferably, the changeover switch includes a third transistor and a fourth transistor having a different conductivity type from the third transistor.

It is preferable that the semiconductor device further includes a first pad disposed between the first transistor and the second transistor, and a second pad connected to an output side of the second three-state buffer. .

[0012]

As described above, in the semiconductor integrated circuit of the present invention, in particular, the test circuit is added to the output buffer, and the power supply / ground of the output buffer is separated from the internal power supply / ground, so that the transistor characteristics of the output buffer are improved. Can be measured in an analog manner.

[0014]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a semiconductor integrated circuit according to the present invention. This circuit is first connected to an internal logic circuit inside the chip, has two internal output terminals, and switches first and second output modes respectively.
3st buffers TB1 and TB2, and use first to fourth transistors Tr1, Tr2, Tr3 and Tr4. A pad A (first pad) is provided between the transistors Tr1 and Tr2, and a pad B (second pad) is provided on the third buffer TB2 side. Transistor Tr
A dedicated power supply (V) is provided on one side, and a dedicated ground (G) is provided on the transistor Tr2 side.

First, when TEST = 0, that is, when the test is not performed, the third buffers TB1 and TB2 enter the output mode, and the transistors Tr3 and Tr4 are turned off.
The transistors Tr1 and Tr2 operate as a normal output buffer.

When TEST = 1, the characteristics of the n-channel transistor are measured, that is, Vgs of Tr2 is measured.
If you want to measure Ids (current between drain and source) when Vds (voltage between drain and source) and Vds (voltage between drain and source) are set arbitrarily, apply an arbitrary voltage to pads A and B, If the voltage of (V) is set to the same potential as that of the pad A, no current flows through the p-channel transistor. Therefore, it is possible to measure the current flowing through the pad A. Similarly, in the case of the p-channel transistor, if an arbitrary voltage is applied to the pads A and B and the voltage of the dedicated ground (G) is set to the same potential as the pad A, no current flows through the n-channel transistor. This is possible by measuring the current flowing through A.

As described above, by setting the voltage of the dedicated power supply (V) or the dedicated ground (G) to the same potential as that of the pad A, it becomes possible to measure the transistor characteristics in an analog manner. As described above, in the semiconductor integrated circuit of the present invention, in particular, the power supply / ground of the output buffer is connected to the internal power supply,
By separating from the internal ground, transistor characteristics can be measured in an analog manner.

[0019]

As described above, since the semiconductor integrated circuit of the present invention enables analog transistor characteristics to be measured by an LSI tester, transistor characteristics can be measured without opening the device after assembly. This has the effect of becoming

Further, by adding the present test circuit to all output buffers, there is an effect that it is possible to measure a variation in transistor characteristics within a chip or between chips.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 Tr1 first transistor Tr2 second transistor Tr3 third transistor Tr4 fourth transistor TB1 first 3st buffer TB2 second 3st buffer V dedicated power supply G dedicated ground

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01R 31/28-31/3187 G01R 31/26 H01L 21 / 66,27 / 04 H03K 19/00

Claims (5)

(57) [Claims] 1. A semiconductor integrated circuit comprising: an internal logic circuit inside a chip; and an output buffer for outputting a signal from an internal output terminal of the internal logic circuit to an external output terminal. Connected between one of the internal output terminals and the input terminal of the output buffer, and switched between a normal output mode and a test mode.
A two-state buffer connected to the other internal output terminal and switched between a normal output mode and a test mode; an input terminal of the output buffer and an output of the second three-state buffer A switch connected between the output buffer and a normal output mode and a test mode, wherein a power supply and a ground of the output buffer are separated from an internal power supply and an internal ground inside a chip, and a transistor of the output buffer is provided. A semiconductor integrated circuit characterized in that characteristics can be measured in an analog manner. 2. When the first and second three-state buffers are turned on, the changeover switch is turned off. When the first and second three-state buffers are turned off, the changeover switch is turned off. 2. The semiconductor integrated circuit according to claim 1, wherein said changeover switch is turned on. 3. An output buffer comprising: a first transistor connected in series between a power supply and a ground of the output buffer; and a second transistor having a different conductivity type from the first transistor. 3. The semiconductor integrated circuit according to claim 1, wherein: 4. The semiconductor integrated circuit according to claim 1, wherein said changeover switch comprises a third transistor and a fourth transistor having a conductivity type different from that of said third transistor. . A first pad disposed between the first transistor and the second transistor; and a second pad disposed between the first transistor and the second transistor.
5. The semiconductor integrated circuit according to claim 1, further comprising a second pad connected to an output side of the three-state buffer.