JPS62176321A - Input noise shutting off system - Google Patents

Abstract

PURPOSE:To protect the entire circuit of the titled system from the noise attended with an output circuit switching by disconnecting a signal from an input terminal during the transient period of the output circuit. CONSTITUTION:The input of an exclusive OR circuit is connected to each input/ output of n-set of output circuits 11, 12-1n capable of being operated simultaneously and an output of exclusive OR circuits 21, 22-2n connects to a NOR circuit 3. When at least one of the n-set of output circuits 11-1n is in the transient state, the output of the NOR circuit 3 goes to '0' to interrupt latch circuits 61-6m inserted between input terminals 41-4m and an internal circuit 5. In applying the system to an input terminal susceptible to a noise, the circuit is protected from the noise at the time of output circuit switching.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for blocking noise generated by transient current when an output circuit switches from entering from an input terminal in a semiconductor integrated circuit. [Prior Art] Generally, in logic integrated circuits, there are malfunctions caused by simultaneous operation of multiple outputs. This is because large transient currents caused by many output circuits operating simultaneously cause the GND level of the logic integrated circuit to fluctuate, and noise enters isometrically from the input terminals, causing the circuit to malfunction. It is something that leads to.

Conventionally, as a means of protecting circuits from the adverse effects of this kind of simultaneous operation of output circuits and stabilizing their operation, consideration has been taken to prevent transient currents of a plurality of output circuits from concentrating at a single time.

This is achieved by inserting delay circuits 82 to 8n with mutually different signal width delay times in front of multiple output circuits 11.12 to 1o that may operate simultaneously, as shown in Figure 4. It has been.

[Problem that the invention seeks to solve]

The conventional method described above has the following two drawbacks.

First, the amount of delay to be set in the delay circuit must be determined in accordance with the period during which a transient current is flowing through the output circuit, that is, the period during which the output value of the output circuit is changing. Generally, the transient period of an output circuit changes depending on the load connected to the output circuit. Therefore, when this method is applied, it is necessary to design a delay circuit according to the output load conditions, which makes circuit design difficult.

Second, this method cannot be applied unless the time at which the output signal from the internal circuit reaches the delay circuit before the output circuit changes.

[Means for solving problems]

In the input noise cutting force type of the present invention, when the output circuit is in a transient period, the output transient state detection circuit outputs a signal indicating this, and the signal propagates the signal between the input terminal and the internal circuit. This attempts to stabilize circuit operation by cutting off the route.

1. Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a time chart 1- showing the operation of the circuit of FIG.

n output circuits that may operate simultaneously 11.12
．． . ~
The output of 2n is connected to the NOR circuit 3. When at least one of the n output circuits 11 to 1n is in the transition period, the output value of the NOR circuit 3 becomes "0" as shown in time chart I in FIG. 4m and the internal circuit 5 are cut off.

By applying the gravity method to input terminals that are susceptible to noise, such as those connected to flip-flop clocks and resets, the circuit can be protected from noise during output circuit switching.

Furthermore, two circuits shown in FIG. 3 will be introduced as application examples that increase the effects of the present invention. 4A shows a circuit in which a delay circuit is inserted between the output terminal of the output circuit and the exclusive logic circuit, and FIG. 2B shows a circuit in which a hysteresis circuit is inserted in place of the delay circuit. Both have the effect of compensating for the deviation between the actual transient period of the output circuit and the transient state display signal output from the exclusive OR circuit.

〔Effect of the invention〕

As explained above, the present invention has the effect of protecting the circuit from noise caused by output circuit switching by cutting off the signal from the input terminal during the output circuit transition period.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
Time chart showing the operation shown in Fig. 3 (a>, (b))
4 is a circuit diagram of another embodiment of the present invention, and FIG. 4 is a circuit diagram of a conventional example. 11, 12. ~l n-output circuit, 21.22°~
20... Exclusive OR circuit, 3... NOR circuit, 5
...internal circuit, 61. ~6m...Latch circuit. Male 1 figure, lv7m) 7/ 7-13 □ Ward 2

Claims (1)

[Claims] By taking the exclusive OR of the input signal and output signal of the output circuit, a signal indicating that the output circuit is in a transient state is obtained, and this signal is used to determine the signal propagation path between the input terminal and the internal circuit. An input noise shielding method characterized by blocking noise generated due to output circuit operation from entering from the input terminal by shielding the input terminal.