JPH0379120A - Input protecting circuit - Google Patents

Abstract

PURPOSE:To attain effective input protection by providing an input protection resistance which is interposed between an external input terminal and an internal circuit, and a pull-up or pull-down resistance which has one terminal connected to a specific power source and the other terminal connected between the external input terminal and input protection resistance. CONSTITUTION:The input protecting circuit consisting of the input protection resistance R1 is connected between an input part 2 and the internal circuit 3 and the pull-up resistance R2 which has one terminal connected to the high- potential power source VCC is connected between an input pad 2 and the input protecting circuit 1. The pull-down resistance R3 which has one terminal connected to a low-potential voltage VSS is connected between the input pad 2 and input protecting circuit 1. The input protection resistance R1 and pull-up (pull-down) resistance R2 (R3) are therefore not in voltage division relation, so the value of the input protection resistance R1 can be set irrelevantly to the value of the pull-up (pull-down) resistance R2 (R3).

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Field of Application Conventional Technology Problems to be Solved by the Invention (Figure 3.4) Means for Solving the Problems Example of Action (Example of the Present Invention) Figure 1.2) Effects of the invention [Summary] Regarding the input protection circuit, an input protection circuit that can set the value of the input protection resistor regardless of the value of the pull-up resistor or pull-down resistor, and can perform effective input protection. The purpose is to provide an input protection resistor inserted between an external input terminal and an internal circuit, one end of which is connected to a predetermined power supply, and the other end of which is connected between the external input terminal and the input protection resistor. A pull-up or pull-down resistor is connected between the two.

[Industrial application field]

The present invention relates to an input protection circuit, and more particularly to an input protection circuit in which the value of an input protection resistor can be set independently of the value of a pull-up (or pull-down) resistor.

In recent years, the degree of integration of semiconductor circuits has been increasing with advances in microfabrication technology. On the other hand, miniaturization of circuits tends to reduce electrostatic breakdown resistance, and for this reason, so-called ESD (Electro 5 tatic
Discharge) countermeasures are becoming increasingly important. The stress of electrostatic discharge as described above causes deterioration or destruction of integrated circuits. The main mechanism is thermal destruction, but depending on the discharge process and device structure, destruction may occur by whichever is the weaker mechanism. In order to improve this breakdown voltage, each input/output terminal is provided with a protection circuit. In the case of MOS devices, the gate insulating film is the most easily destroyed, and in the case of Sin, 7
It is said that gate breakdown occurs when an electric field of MV/cm or more is applied and the power consumption during that time is about 2 μJ. Therefore, a circuit that clamps the voltage is required to protect this. In the MO3 type integrated circuit, a relatively large source/drain is connected to the output terminal, so this serves as a protection circuit. Although some care is required to form the source/drain pn junction, it usually has a good E.
It is necessary to intentionally provide a protection circuit to one input terminal that has an SD withstand voltage.

[Conventional technology]

Figure 3.4 is a diagram showing an example of a conventional input protection circuit. Figure 3 is an input protection circuit that has a pull amplifier resistor that pulls up the input signal and transmits it to the internal circuit, and Figure 4 pulls down the input signal. This is an input protection circuit with a pull-down resistor that transmits the signal to the internal circuit. In Fig. 3, 1 is an input protection circuit consisting of an input protection resistor R1 inserted between an input pad (external input terminal) 2 and an internal circuit 3, and one end of the pull-up resistor R2 is connected to the high potential side power supply. It is connected to VCC, and the other end is connected between the input protection resistor R1 and the internal circuit 3. Similarly, in the input protection circuit 4 having a pull-down resistor R3 as shown in FIG. 4, one end of the pull-down resistor R3 is connected to the low potential side power supply Vss (GND), and the other end is connected to the input protection resistor R1 and is connected between.

According to such a configuration, even if, for example, an excessive input current is applied to the input pad 2, the input protection circuit 1 can appropriately protect the internal circuit 3.

[Problem to be solved by the invention]

However, in such a conventional input protection circuit, a pull-up resistor R1 or a pull-down resistor R2 is connected between the input protection circuit 1 and the internal circuit 3, so for example, the input protection circuit shown in FIG. In the protection circuit 1, unless the value of the input protection resistor R2 is set sufficiently small compared to the value of the pull-up resistor R1 (threshold voltage of the first stage inverter of the circuit 3), "
There was a problem in that even if an L" level signal was input, the first stage inverter of the internal circuit 3 did not invert, and the value of the input protection resistor R1 could not be increased. In other words, the input IN of the internal circuit 3 had an input protection voltage. Since the voltage divided by R1 and pull amplifier resistor R2 is input, the input protection resistor R
The resistance value of 1 must be determined in relation to the resistance value of the pull-up resistor R2, and it has been difficult to set the input protection resistor R1 to a sufficiently large resistance value for input protection. The above problem is exactly the same even in the input protection circuit 1 having the pull-down resistor R3 shown in FIG.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an input protection circuit that can set the value of the input protection resistor regardless of the value of the pull-amplifier resistor or pull-down resistor, and can provide effective input protection.

[Means to solve the problem]

In order to achieve the above object, the input protection circuit according to the present invention includes an input protection resistor inserted between an external input terminal and an internal circuit, one end of which is connected to a predetermined power supply, and the other end of which is connected to the external input terminal and the internal circuit. It includes a pull amplifier or pull-down resistor connected between the input protection resistor and the input protection resistor.

[Function] In the present invention, an input protection resistor is inserted between the external input terminal and the internal circuit, one end of the pull-up or pull-down resistor is connected to the power supply terminal, and the other end is connected between the external input terminal and the input protection resistor. connected to.

Therefore, the input protection resistor and pull-up (pull-down)
Since there is no voltage division relationship with the resistor, the value of the input protection resistor can be set regardless of the value of the pull-up (pull-down) resistor, making chip protection effective.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

Fig. 1.2 is a diagram showing an embodiment of the input protection circuit according to the present invention. In explaining this embodiment, the same components as those of the conventional example shown in Fig. 3.4 are given the same reference numerals. are doing.

FIG. 1 shows an input protection circuit having a pull amplifier resistor R2. In this figure, an input protection circuit 1 consisting of an input protection resistor R1 is connected between the input pad 2 and the internal circuit 3, and the input protection circuit 1 is connected between the input pad 2 and the internal circuit 3. A pull amplifier resistor R2 having one end connected to VCC is connected to the input protection circuit 1. On the other hand, FIG. 2 shows an input protection circuit having a pull-down resistor R3, and in this figure as well, the input protection circuit 1 is connected between the input pad 2 and the internal circuit 3, as in the case of FIG. A pull-down resistor R whose one end is connected to VSl+ is connected between the input pad 2 and the input protection circuit 1.
3 is connected.

In the above configuration, when an "L" level signal is input to the input pad 2, an "L" level signal is input to the internal circuit 3 regardless of the values of the input protection resistor R1 and pull-up resistor R2. . Therefore, the resistance value of the input protection resistor R1 can be freely set.

Further, the same can be said of the pull-down resistor R3 shown in FIG. 2, one end of which is grounded to VSS.

As described above, according to this embodiment, the value of the input protection resistor can be set to a value that is related to (larger than) the value of the pull-up (pull-down) resistor, so it is extremely useful in practice for chip protection.

Fig. 3.4 is a diagram showing a conventional input protection circuit, Fig. 3 is a circuit diagram of an input protection circuit having a pull-up resistor R2, and Fig. 4 is a circuit diagram of an input protection circuit having a pull-down resistor R3. It is a diagram.

〔Effect of the invention〕

According to the present invention, the value of the input protection resistor can be set regardless of the value of the pull-up resistor or pull-down resistor, and effective input protection can be achieved.

[Brief explanation of drawings]

FIG. 1.2 is a diagram showing an embodiment of the input protection circuit according to the present invention. FIG. A circuit diagram of an input protection circuit having the following: 1... Input protection circuit, 2... Input pad (input terminal of strike part), 3...
...Internal circuit, R1...Input protection resistor, R2...Pull-up resistor, R3...Pull-down resistor, Vcc...--High potential side power supply , VSS...Low potential side power supply. Figure 1 Figure 3 A circuit diagram of a conventional input protection circuit with a pull-up resistor R2 Figure 3 A circuit diagram of a conventional human protection circuit with a pull-down resistor R3 Figure 4

Claims (1)

[Claims] An input protection resistor inserted between an external input terminal and an internal circuit, one end of which is connected to a predetermined power supply, and the other end of which is connected between the external input terminal and the input protection resistor. An input protection circuit comprising: a connected pull-up or pull-down resistor;