JPS59169225A - Integrated circuit - Google Patents

Abstract

PURPOSE:To improve the protecting effect of an IC without deteriorating the electrical characteristics by connecting the drains and gates of two MOSFETs having higher threshold voltage than the operating voltage of an output buffer MOSFET to the drain of said output buffer MOSFET. CONSTITUTION:Two MOSTRs having threshold voltage higher than the operating voltage of an output buffer MOS transistor TR1 are provided at the drain side of said TR1. Then the gates and drains of MOSTR3 and 4 are connected to the drain side of the TR1, and the sources of the TR3 and TR4 are connected to an earth terminal and a power supply terminal of high voltage VC respectively. Thus the satisfactory protecting effect is secured for both TR3 and TR4 having high threshold voltage without affecting the circuit operation, the characteristics or load Rl of the TR1 and the pellet size respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an MO8 integrated circuit, particularly an output buffer, an OMO
8) Regarding transistor protection circuits.

There are buffers in which the output is configured with one MOS transistor, but in such a single λDS output buffer, if the drain size of the MOS transistor cannot be increased due to the characteristics, as shown in FIG. The MOS transistor 2 will be protected by connecting the diode 2 of PJOS to the drain of the transistor PJOS. Normally, the drain size of a single MOS transistor, which does not require a large output current, is small. Therefore, the current capacity of the drain, which functions as a protection diode, becomes small.

From this, when positive and negative electrostatic pulses are applied to the output terminal, there is no current path for the positive electrostatic pulse. Therefore, the breakdown voltage is determined by the reverse breakdown voltage of the diode 2, and protection against electrostatic breakdown is also reduced. On the other hand, for a good electrostatic pulse, the current path flows through the diode 2 in the forward direction, so it acts as a protection for the single MO transistor 1, but normally the size of the diode 2 MO8) Depends on the drain width of the transistor. Therefore, the small size of the drain of the small output current single MOS transistor means that the size of the protection diode 2 is small. The discharge current of static electricity is small. As described above, the protection circuit shown in FIG. 1 has the disadvantage that it is less effective against electrostatic damage caused by high voltage, especially for MOS transistors that require only a small output current.

Therefore, in order to further strengthen the electrostatic breakdown strength, a protection circuit as shown in FIG. 2 has been proposed. This protection circuit has a resistor rD on the drain side of the single MO8) transistor 1 in Figure 1.
are connected in series.

This resistor rD functions to limit the current when positive and negative electrostatic pulses are applied to the output terminal, thereby relaxing the voltage applied to the single MO8) transistor l and the diode 2. Ru. However, the resistance rη on the drain side
Since they are connected in series, the output current drops more than necessary.

Conversely, if an attempt is made to prevent the output current from decreasing, the pattern size will inevitably increase.

An object of the present invention is to provide a single MO8 output buffer transistor device with a sufficient protective effect without deteriorating the electrical characteristics of the device.

In the present invention, two MOS transistors having a threshold higher than the operating voltage of the output buffer transistor are prepared, their drains are connected to the drain of the output buffer transistor, and the source is connected to the power supply terminal. They are characterized by being connected to each other.

Hereinafter, explanation will be given according to examples.

FIG. 3 shows an embodiment of the present invention.

Two MOS transistors having a threshold voltage higher than the operating voltage of this transistor l are provided on the drain side of the output buffer 77M0S transistor 1, and the gate and drain of each MOS transistor 3 and 4 are connected to the output buffer MO8.
) is connected to the drain side of transistor 1, the source of MOS) transistor 3 is connected to the ground terminal, and the source of MOS) transistor 4 is connected to the power supply terminal of high potential VC.

As mentioned above, the threshold voltages of the MOS transistors 3 and 4 must be set higher than the operating voltage of the single MO8 output buffer transistor 1.

By doing this, a single MO8) with a high threshold voltage can be obtained.
The transistor 3.4 does not affect the circuit operation, the characteristics of the output backer transistor 1, or the load Re, and since it can be placed near the bonding pad on the pattern, it does not affect the pellet size. Nor.

Next, the principle of operation will be explained.

FIG. 4 shows a current path when a positive electrostatic pulse is applied to the output terminal with respect to ground potential. In this case, since the gate HC positive potential of the single MO transistor 3 having a high threshold voltage is applied, this transistor 3 is turned on and current flows to the ground potential. FIG. 5 shows a current path when a negative electrostatic pulse is applied to the output terminal with respect to ground potential. In this case, current flows through the diode 2 to the output terminal. Furthermore, the breakdown of the MOS transistor 3 with a higher threshold voltage protects the 9MO8 output buffer transistor l. FIG. 6 shows a current path when a positive electrostatic pulse is applied to the output terminal for a high potential. In this case, since a positive potential is applied to the gate of the MOS transistor 4 having a high value voltage, this transistor 4 is turned on and current flows to a high potential.

As described above, the destruction prevention effect according to the present invention is excellent.

Although this embodiment is shown using an N-channel MOS transistor, it can also be applied to a P-channel MO8 transistor.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing a conventional protection circuit, Figure 3 is a circuit diagram showing an embodiment of the present invention, and Figures 4, 5, and 6 are detailed explanations of the present invention. This is a diagram of the end. Engineering: Output huffer MOS transistor, 2.
...Output buffer MO8) Drain side diode of transistor, 3,4...MOS) transistor with high threshold voltage. Fig. 1 Tea 21 vr Fig. 3 No. 4 Kuni Ushi 5 Inter 6 ■

Claims (1)

[Claims] The drain of the insulated gate transistor for output KM is higher than the operating voltage of the insulated gate transistor for output. An integrated circuit characterized in that the gates and drains of first and second transistors having comparable threshold voltages are connected, and the sources of the first and second transistors are connected to the first and second power supply terminals, respectively. circuit.