JPH10242390A - Semiconductor integrated circuit device with input/ output protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To incorporate an input/output protection circuit in a semiconductor integrated circuit device by reducing the capacitance of a capacitor. SOLUTION: An input/output protection circuit 20 is constituted of two stages of CR filter circuits 21 and 22, thus achieving equivalent filter characteristics and at the same time reducing the capacitance of a capacitor as compared with the configuration of the CR filter circuit with only one stage and hence incorporating the input/output protection circuit 20 in a semiconductor integrated circuit device 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor integrated circuit device provided with an input / output protection circuit for performing input / output protection.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, in a circuit device having a semiconductor integrated circuit device 2 and an external component 3 mounted on a printed circuit board 1, the semiconductor integrated circuit device 2 is exposed to static electricity.
An input / output protection circuit 5 that protects from a surge or the like is provided between the input / output terminal 4 and the semiconductor integrated circuit device 2.

The input / output protection circuit 5 comprises an external capacitor 5a and an external resistor 5b. The input / output protection circuit 5 can absorb static electricity, surge, etc. The malfunction and destruction of the circuit device 2 can be prevented, and the reliability thereof can be ensured.

[0004]

In order to reduce the size of an electronic device, it is conceivable to integrate the input / output protection circuit 5 in the semiconductor integrated circuit device 2. However,
The input / output protection circuit 5 shown in FIG.
Since the capacitance value of a is large, when the input / output protection circuit 5 is formed on a semiconductor substrate by integration, the area for forming the capacitor 5a becomes large, which leads to an increase in cost. Therefore, there is a problem that it is difficult to integrate the input / output protection circuit 5 in the semiconductor integrated circuit device 2 to perform integration.

The present invention has been made in view of the above problems, and has as its object to realize an input / output protection circuit that can be built in a semiconductor integrated circuit device while achieving the same performance as a conventional input / output protection circuit. .

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a resistor (21b,
The input / output protection circuit (20) is characterized in that a plurality of CR filter circuits (21, 22) each including a capacitor (22b) and a capacitor (21a, 22a) are connected in series.

As described above, the CR filter circuit (21, 2
2) are connected in series in a plurality of stages to form the input / output protection circuit (20), thereby realizing the same performance as the conventional input / output protection circuit and reducing the capacitance value of the capacitor. The output protection circuit (20) can be realized as an integrated circuit together with the internal circuit (30). In the input / output protection circuit (20), specifically, a connection portion between the other end of the capacitor (21a, 22a) and one end of the resistor (21b, 22b) is provided. CR with the input part and the other end of the resistor (21b, 22b) as the output part
The filter circuits (21, 22) can be configured by connecting a plurality of stages in series. In this case, the input section of the first stage CR filter circuit (21) is connected to the input / output terminal (4), The output of the CR filter circuit (22) of the stage can be connected to the internal circuit (30).

According to the third aspect of the present invention, the capacitor (21) of the first stage CR filter circuit (21) is provided.
The capacitance value of a) is made larger than the capacitance value of the capacitor (22a) of the second stage CR filter circuit (22), or the first stage CR filter circuit (21) as in the invention according to claim 4. ), The resistance of the resistor (21b) is made larger than the resistance of the resistor (22b) of the second stage CR filter circuit (22), so that the input / output protection circuit ( 20) It is possible to increase the resistance.

In the case where the CR filter circuit is constituted by two stages as in an embodiment to be described later, claim 3
The second stage CR filter circuit described in No. 4 is a final stage CR filter circuit.
It becomes a filter circuit.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. In the present embodiment, as shown in FIG. 2, the input / output protection circuit 20 is composed of two stages of CR filter circuits 21 and 22. The first CR filter circuit 21 includes a capacitor 21 having one end connected to a ground terminal.
a and a resistor 21b having one end connected to the other end of the capacitor 21a and the input / output terminal 4. The second CR filter circuit 22 includes a capacitor 22a having one end connected to the ground terminal, and a resistor 22b having one end connected to the other end of the capacitor 22a.

The input / output protection circuit 20 will be described in comparison with the conventional input / output protection circuit 5 shown in FIG. The characteristics of the input / output protection circuit can be determined by the filter characteristics. In this case, the filter characteristics can be obtained from the filter characteristic calculation models shown in FIGS.
That is, an input / output between the discharge resistance (output resistance of the static electricity generator) 41 of the electrostatic discharge tester and the gate capacitance 42 of the internal circuit of the semiconductor integrated circuit device connected to the input / output protection circuit 20 (or 5). A filter characteristic calculation model to which the protection circuit 20 (or 5) is connected is set, and the input / output protection circuit 20 (or 5), the output resistor 41, and the gate capacitance 42 are regarded as one filter circuit. The filter characteristics of the input / output protection circuit can be obtained from the filter characteristics of the circuit.

In the case of the conventional input / output protection circuit 5 shown in FIG. 5, its transfer function is expressed by equation 1 from the filter characteristic calculation model of FIG.

[0013]

(Equation 1)

In this equation 1, Rx is the discharge resistance 41
, Cg is the capacitance value of the gate capacitance 42 of the internal circuit,
R is the resistance value of the external resistor 5b, and C is the external capacitor 5b.
This is the capacitance value of a. Here, in the conventional input / output protection circuit 5 shown in FIG.
00000 pF, and the resistance value R of the external resistor 5b is 1 KΩ. When Rx = 150Ω and Cg = 1 pF,
The filter characteristics of the input / output protection circuit 5 are as shown in FIG. 4, and the cutoff frequency fc of the filter is equal to the transfer function V
Since the cut-off frequency fc is 10.6 KHz, the cut-off frequency fc is obtained at the frequency at which out / Vin is reduced by 3 dB.

On the other hand, in the case of the input / output protection circuit 20 of the present embodiment, its transfer function is expressed by Equation 2 from the filter characteristic calculation model of FIG.

[0016]

(Equation 2)

In equation (2), Rx is the discharge resistance 41
, Cg is the capacitance value of the gate capacitance 42 of the internal circuit,
C1 is the capacitance value of the capacitor 21a, C2 is the capacitor 2a
2a, R1 is the resistance of the resistor 21b, and R2 is the resistance of the resistor 22b. Here, for example, Rx = 150
Ω, Cg = 1 pF, C1 = 1000 pF, C2 = 100
Assuming that 0 pF, R1 = 15 kΩ and R2 = 1 kΩ, FIG.
As shown in FIG. 5, the cutoff frequency fc of the filter can be made equal to that of the conventional input / output protection circuit 5 shown in FIG.

As described above, the conventional input / output protection circuit 5
The capacitance value of the capacitor 5a used for the
In contrast to F, the capacitance values of the capacitors 21a and 21b used in the input / output protection circuit 20 of this embodiment are both 1000 pF, and the capacitance value of the capacitor can be reduced to 1/50. Here, in the semiconductor integrated circuit device, the circuit area occupied by the resistor is extremely smaller than the circuit area occupied by the capacitor, and the circuit area of the capacitor is proportional to the capacitance value of the capacitor. And the input / output protection circuit 20 according to the present embodiment,
Identical formation conditions (such as using the same capacitor thickness)
When the integrated circuit is formed on a semiconductor substrate, the occupied area of the input / output protection circuit 20 according to the present embodiment is approximately 1/50 of that of the conventional input / output protection circuit 5.

Therefore, as in the present embodiment, a two-stage CR
By configuring the input / output protection circuit 20 with the filter circuits 21 and 22, it is possible to realize a filter characteristic equivalent to that of a case where a CR filter circuit is configured in a single stage and to reduce the capacitance value of the capacitor much. Thus, the input / output protection circuit 20 can be realized by an integrated circuit. FIG.
1 shows a specific configuration in which the input / output protection circuit 20 is built in the semiconductor integrated circuit device 10. The input / output protection circuit 20 is provided between the input / output terminal 4 and the internal circuit 30, and is formed integrally with the internal circuit 30 on a semiconductor substrate. The semiconductor integrated circuit device 10 is mounted on the printed circuit board 1 together with other external components 3.

In the input / output protection circuit 20, when static electricity, surge, or the like is applied through the input / output terminal 4, a voltage larger than that of the second CR filter circuit 22 is applied to the first CR filter circuit 21. As a result, a large current flows through the first CR filter circuit 21. Therefore, the immunity of the first CR filter circuit 21 must be improved more than the immunity of the second CR filter circuit 22.

Therefore, the capacitance value of the capacitor 21a of the first CR filter circuit 21 is
It is preferable that the resistance value of the resistor 21b of the first CR filter circuit 21 be larger than the capacitance value of the resistor 22b of the second CR filter circuit 22. The number of CR filter circuits constituting the input / output protection circuit 20 is not limited to two, but may be three or more. Specifically, a CR filter circuit in which the connection between one end of the resistor and the capacitor in the first stage CR filter circuit is used as an input unit and the other end of the resistor is used as an output unit,
Connect more than one stage in series. By increasing the number of stages of the CR filter circuit in this manner, the capacitance value of the capacitor can be reduced, and the area occupied by the input / output protection circuit 20 can be further reduced.

In the input / output protection circuit 20, when the signal input from the input / output terminal 4 is very small, it is necessary to prevent the input signal from attenuating. For this reason,
In a multi-stage CR filter circuit, it is necessary to reduce the resistance value of the resistor connected in series, increase the capacitance value of the capacitor accordingly, reduce the input impedance, and prevent the input signal from attenuating. preferable.

Further, in the internal circuit 30 of the semiconductor integrated circuit device 10, a high frequency signal serving as noise may be generated due to a cause such as crosstalk. In this case, the resistance 2 in the first and second CR filter circuits 21 and 22
By setting the resistance values of the first and second capacitors 1b and 22b and the capacitance values of the capacitors 21a and 22a to predetermined values, when a high-frequency signal having a frequency equal to or higher than the cutoff frequency appears in the output of the internal circuit 30, the high-frequency signal is input to the The signal can be cut off to some extent.

Note that there is a CR filter circuit in which one end of a resistor is connected to an input / output terminal and a capacitor is connected to the other end of the resistor. For example, as shown in FIG. 2, it is more preferable to connect the capacitor 21a to the input / output terminal 4 and connect the resistor 21b to the connection point between the input / output terminal 4 and the capacitor 21a.

[Brief description of the drawings]

FIG. 1 shows an input / output protection circuit 20 according to an embodiment of the present invention.
FIG. 1 is a diagram showing a configuration in which is incorporated in a semiconductor integrated circuit device 10.

FIG. 2 shows an input / output protection circuit 20 according to an embodiment of the present invention.
FIG. 3 is a diagram showing the configuration of FIG.

3 is a diagram showing a circuit model for calculating filter characteristics of the input / output protection circuit 20 shown in FIG. 2 and a conventional input / output protection circuit 5. FIG.

4 is a diagram illustrating filter characteristics of the input / output protection circuit 20 shown in FIG. 2 and a conventional input / output protection circuit 5. FIG.

FIG. 5 is a diagram showing a conventional configuration in which an input / output protection circuit 5 is externally attached to a semiconductor integrated circuit device 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Printed circuit board, 10 ... Semiconductor integrated circuit device, 20 ...
Input / output protection circuit, 21... First CR filter circuit, 22
... Second CR filter circuit, 21a, 22a... Capacitors, 21b, 22b.

Claims (4)

[Claims] An input / output protection circuit (20) is provided between an input / output terminal (4) and an internal circuit (30), and the internal circuit (30) and the input / output protection circuit (20) are provided on a semiconductor substrate. A semiconductor integrated circuit device integrally formed thereon, wherein the input / output protection circuit (20) includes resistors (21b, 22).
b) and a capacitor (21a, 22a)
A semiconductor integrated circuit device comprising a plurality of filter circuits (21, 22) connected in series. 2. An input / output protection circuit (20) is provided between an input / output terminal (4) and an internal circuit (30), and the internal circuit (30) and the input / output protection circuit (20) are mounted on a semiconductor substrate. A semiconductor integrated circuit device integrally formed on the input / output protection circuit, wherein the input / output protection circuit (20) includes a capacitor (21a, 22a) having one end connected to a ground terminal, and a capacitor (21a, 22a) having one end. 22a) and a resistor (21b, 22b) connected to the other end of the capacitor (21a).
a, 22a) and a CR filter circuit (21, 22) in which a connection between the other end of the resistor (21b, 22b) is an input portion and the other end of the resistor (21b, 22b) is an output portion.
Are connected in series at a plurality of stages. An input section of a first stage CR filter circuit (21) is connected to the input / output terminal (4), and an output of a final stage CR filter circuit (22) is provided. A semiconductor integrated circuit device, wherein a unit is connected to the internal circuit (30). 3. The capacitance value of a capacitor (21a) of a first stage CR filter circuit (21) is larger than the capacitance value of a capacitor (22a) of a second stage CR filter circuit (22). 3. The semiconductor integrated circuit device according to claim 1, wherein 4. The resistance value of a resistor (21b) of a first-stage CR filter circuit (21) is changed to a second-stage CR filter circuit (2).
3. The semiconductor integrated circuit device according to claim 1, wherein the resistance value of the resistor (2b) is larger than the resistance value of the resistor (2b).