JPH0457514A - Electromagnetic wave suppression type integrated circuit - Google Patents

Abstract

PURPOSE:To suppress an electromagnetic wave radiating externally from the inside of the circuit and to reduce noise due to electromagnetic wave interference by connecting 1st and 2nd output means in parallel and using an output control means so as to control the output state of the 2nd output means. CONSTITUTION:When an output control means 10 activates the output state of a 2nd output means 12, an output signal OUT fed from an internal circuit is outputted to an output terminal via 1st and 2nd output means 11,12. On the other hand, after the output signal OUT is made stable, the output control means 10 inactivates the output state of the 2nd output means 12 and an output signal fed from the internal circuit is outputted to the output terminal 7 via the 1st output means 11. Thus, an electromagnetic wave radiating from the output terminal 7 is minimized and noise due to electromagnetic wave interference is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention suppresses electromagnetic interference noise radiated to the outside,
The present invention relates to an electromagnetic wave suppressing integrated circuit suitable for incorporating various integrated circuits into the same system.

[Prior Art] In recent years, as various systems have become larger, various integrated circuits have been incorporated into the same system, and this trend is expected to further advance in the future.

FIG. 3 is a circuit diagram showing an oscillation circuit as an example of a conventional integrated circuit.

As shown in FIG. 3, the input signal XTAL 1 input from the input terminal 1 is input to one input terminal of the NOR gate 7 via a resistor 8 and a transfer gate consisting of a P channel transistor 3 and an N channel transistor 4. is input. Further, the input signal XTALI is fed back to the one input terminal of the NOR gate 7 via the resistor 8 and the inverter 30, and is also supplied to the ground GND via the resistor 8 and the N-channel transistor 6.

The control signal 5TOP is input to each gate of the P-channel transistor 3 and the N-channel transistor 6, and
It is input to the gate of N-channel transistor 4 via inverter 5 . Further, the control signal 5TOP is input to the other input terminal of the NOR gate 7. The input signal XTAL2 inputted from the input terminal 2 is inputted to the one input terminal of the NOR gate 7 via the resistor 9.

In the conventional oscillation circuit configured as described above, the control signal 5TOP is set to low level, and the transistors 3 and 4 are
By turning on the transistor 6 and turning off the transistor 6, the output signal OUT is oscillated from the NOR gate 7. In this case, since a predetermined time is required until the oscillation of the output signal OUT becomes stable, it is necessary to use an inverter 30 for feedback with a relatively large drive capacity.

[Problems to be Solved by the Invention] However, in the conventional oscillation circuit described above, after the oscillation is stabilized, the drive capacity of the feedback inverter 30 is larger than necessary, so that the output signal OUT
The change is steep. Since the signal changes abruptly in this way, there is a drawback that electromagnetic waves generated within the circuit are directly radiated from the output terminal. When a plurality of such integrated circuits are incorporated into the same system, there is a problem in that electromagnetic waves are emitted from each integrated circuit, and noise caused by electromagnetic wave interference induces malfunctions in other electronic devices.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide an electromagnetic wave suppressing integrated circuit that can suppress electromagnetic waves radiated from inside the circuit to the outside, and that can reduce noise caused by electromagnetic wave interference.

[Means for Solving the Problems] The electromagnetic wave suppressing integrated circuit according to the present invention has a first circuit connected between an internal circuit and an output terminal and configured by a logic gate.
a second output means connected in parallel with the first output means and constituted by a logic gate;
and output control means for controlling the output state of the output means.

[Operations] In the present invention, it is preferable that the first output means is constituted by a logic gate with a relatively small drive capacity, and the second output means is constituted by a logic gate with a relatively large drive capacity. When the output state of the second output means is activated by the output control means, the output signal supplied from the internal circuit is output to the output terminal via the first and second output means. In this case, since the drive capability is large, it is possible to sufficiently cope with an unstable period until the output signal stabilizes, such as immediately after signal oscillation. On the other hand, after the output signal becomes stable, the drive ability is too high as it is, so the change in the output signal becomes steep.

Therefore, after the output signal becomes stable, the output state of the second output means is made inactive by the output control means. Thereby, the output signal supplied from the internal circuit is outputted to the output terminal via the first output means. In this case, since the drive ability of the first output means is relatively small, it is possible to alleviate a sharp change in the output signal, and it is possible to suppress electromagnetic waves radiated from the output terminal to a minimum. Therefore, noise caused by electromagnetic interference can be significantly reduced, and malfunctions of other electronic devices can be prevented from being caused by such noise caused by electromagnetic interference.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an oscillation circuit according to a first embodiment of the present invention. In FIG. 1, the same parts as in FIG. 3 are designated by the same reference numerals, and detailed explanations of those parts will be omitted.

As shown in FIG. 1, this embodiment is an oscillation circuit constructed by connecting a control unit 10 instead of the inverter 30 in FIG. 3. The control unit 10 is configured as follows. That is, the inverter 11 is connected between the resistor 8 and the NOR gate 7. The inverter 11 used has the minimum driving ability to maintain oscillation. On the other hand, the clocked inverter 12 for feedback is connected in parallel with the inverter 11, and its output state is controlled by a control signal MODE supplied from the outside. Further, this clocked inverter 12 has a relatively large drive capacity. In this case, the clocked inverter 12 receives the control signal M
It becomes active when ODE is at "1'level" and becomes inactive when control signal MODE is at "O" level.

Furthermore, the control signal MODE is at the "1" level until the oscillation of the oscillation circuit is stabilized, and after the oscillation is stabilized, it is at the "0" level.
level.

Next, the operation of the oscillation circuit configured as described above will be explained.

The control signal MODE remains “until the oscillation of the oscillation circuit stabilizes.
1" level, the clocked inverter 12 becomes active during this period, and the output of the control unit 10 becomes the output of the inverter 11 and clocked inverter 12 connected in parallel. Therefore, the oscillation at the start of oscillation is During the predetermined time until the oscillation circuit stabilizes, this oscillation circuit has a relatively large drive capacity and can sufficiently cope with the instability of the output signal OUT.On the other hand, after the output signal OUT of the oscillation circuit stabilizes, the control The signal MODE becomes "0" level, the clocked inverter 12 becomes inactive, and the output of the control unit 10 becomes equal to the output of the inverter 11. In this case, the inverter 11 has a minimum Since it uses a drive capacity of

Therefore, according to this embodiment, by controlling the output state of the clocked inverter 12 using the control signal MODE, sufficient drive capability can be obtained during the period until the oscillation is stabilized, and after the oscillation is stabilized, the signal High frequency components radiated from the output terminal due to the change can be suppressed to a minimum. As a result, noise caused by electromagnetic interference can be significantly reduced, and malfunctions of other electronic devices due to this noise can be prevented.

FIG. 2 is a circuit diagram showing an output buffer circuit according to a second embodiment of the present invention. In this embodiment, the conventional general output buffer circuit driver inverter is replaced with a control unit 20 in the same manner as in the first embodiment.

As shown in FIG. 2, the control unit 20
1 and a clocked inverter 22 are connected in parallel. The output state of the clocked inverter 22 is controlled by the control signal MODE. Data signals DATA supplied from an internal circuit (not shown) are commonly input to inverters 21 and 22, and the outputs of inverters 21 and 22 are output to output terminal 25.

Furthermore, diodes 23 and 24 are connected between the power supply VDD and the ground GND and the output terminal 25 in opposite directions.

In the output buffer circuit configured as described above, as in the first embodiment, the clocked inverter 22 is configured to have a relatively large drive capacity, and the inverter 11 is configured to have the minimum required drive capacity. Use what you have. If it is not necessary to consider noise due to electromagnetic interference, the control signal MODE is set to "1" level to activate the clocked inverter 22. On the other hand, if it is necessary to take measures against noise, the control signal MODE is set to "0" level to make the clocked inverter 22 inactive. Thereby, the high frequency components radiated from the output terminal 25 due to changes in the output signal can be suppressed to a minimum as necessary, and noise due to electromagnetic wave interference can be significantly reduced.

[Effects of the Invention] As explained above, according to the present invention, the first output means and the second output means are connected in parallel, and the output state of the second output means is controlled by the output control means. Therefore, electromagnetic waves radiated from inside the circuit to the outside can be suppressed, and noise caused by electromagnetic wave interference can be reduced. As a result, it is possible to prevent other electronic devices from malfunctioning due to electromagnetic interference noise, and it is possible to provide a highly reliable integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an oscillation circuit according to a first embodiment of the present invention, FIG. 2 is a circuit diagram showing an output buffer circuit according to a second embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional oscillation circuit. FIG. 2 is a circuit diagram showing a circuit. 1.2; input terminal; 3; P channel transistor; 4.
6; N-channel transistor, 5.11°21,30;
Inverter, 7; NOR gate, 8° 9; Resistor, 10,
20; Control unit, 2, 22; Clocked inverter, 23. 24; Diode, 25; Output terminal 1.2゜3゜4.6i 5.30i 8,9i Kanorunstai〉Bark NOR Riichito resist jrL

Claims (1)

[Claims] (1) A first output means connected between the internal circuit and the output terminal and constituted by a logic gate; and a second output means connected in parallel with the first output means and constituted by a logic gate. , and output control means for controlling the output state of the second output means.