JPH0360216A - Logic circuit - Google Patents

Abstract

PURPOSE:To prevent an accident that a circuit malfunctions due to supply sequence of a power supply by making a constant voltage circuit work only when both negative and positive voltage power supplies operate and the voltages of both power supplies are impressed on it. CONSTITUTION:The constant voltage circuit 3a is constituted of resistors R1 to R3 and bipolar transistors Q1, Q2, and other part excepting the resistor R1 whose one end is connected to the positive voltage power supply VCC is connected to the middle point between the negative voltage power supply VEE and a ground terminal GND. A circuit current flows in this constant voltage circuit 3a and its starts normal operation when both the negative and positive voltage power supply VEE, VCC are impressed on this circuit. Thus, a current mode logic circuit which is independent of the power supply sequence and executes stable operation can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a logic circuit, and particularly to a logic circuit including a current switching type logic circuit whose logic amplitude is controlled by a constant voltage circuit.

[Prior Art] Current switching type logic circuits are widely used as typical bipolar basic logic circuits, and are particularly popular as basic circuits of high-speed logic LSIs. However, it is rare to construct an entire system using only current-switching logic circuits, and when current-switching logic circuits are used, they usually include a TTL logic level circuit that operates on a positive voltage power supply,
Circuits that operate at the ECL logic level that operate on a negative voltage power supply are mixedly used in the same system.

Therefore, the LSI used in such a system
In this case, LS mainly based on current switching type logic circuit
Even if the input/output part is
TT to ECL logic level to CL logic level or vice versa
It becomes necessary to incorporate a TTL-ECL level conversion circuit for converting to the L logic level. In that case, the circuit type between the two shells is constructed as shown in FIG. That is, as shown in the figure, the TTL-ECL level conversion circuit 2
is supplied with power from both the positive voltage power supply VCC and the negative voltage power supply VER, and the current switching type logic circuit 1 is configured to be supplied with power from the negative voltage power supply VEE. Also,
Bipolar transistor Q1. A constant voltage circuit 3C composed of Q2 and R□ to R5 is connected between the negative voltage power supply EE and the ground terminal GND, and the constant voltage obtained between the emitter of the transistor Q2 and the power supply VER is a current switching type logic circuit. 1, and the ECL circuit portion of the TTL-ECL level conversion circuit 2. The reference voltage source of the constant voltage circuit 3 is the base-emitter forward voltage VBE of Ql, and the constant voltage applied to the current switching type logic circuit 2 is given by .beta.BE(1+R2/R1).

Note that the voltage generated by the constant voltage circuit 3 is normally used in common for a plurality of current switching type logic circuits and the ECL circuit portion of the TTL-ECL level changing circuit.

[Problem M to be solved by the invention] Bipolar integrated circuits are generally based on pn junction isolation, in which the substrate of the integrated circuit is connected to the lowest potential on the circuit, and the isolation region of the resistor is connected to the highest potential on the circuit. Because it is
Depending on the order in which the power is turned on, excessive circuit current may temporarily flow, which may cause abnormal phenomena. For example, in the circuit shown in Figure 3, if the highest potential is applied later, or for some other reason. Therefore, if the highest potential is temporarily cut off, the isolation region of the resistor will no longer be biased in the opposite direction, so there will be no isolation effect on the resistor.

However, the constant voltage circuit 3 and the current switching type logic circuit 1 themselves are normally biased and start operating normally. Therefore, normal current flows through the resistors included in these circuits, but if the voltage drop across these resistors is large, the junction between the isolation region becomes forward biased and abnormal current flows. It will flow. As a result, a voltage drop also occurs within the substrate, causing thyristor operation including the substrate, and in this case, a phenomenon occurs in which the normal state is not restored even if the highest potential is applied again.

[Means for Solving the Problems] A logic circuit of the present invention includes a current switching type logic circuit powered by a negative voltage power supply VEE, a TTL-ECL level conversion circuit powered by a negative voltage power supply VEE and a positive voltage power supply VCC, and The constant voltage circuit includes a constant voltage circuit for applying a predetermined voltage to the constant current source circuit of these circuits, and the constant voltage circuit is configured to be powered by a negative voltage power source and a positive voltage power source, and is a dual chamber source. It is configured to operate only when a voltage of .

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. As shown in the figure, the current switching type logic circuit 1 operates only with the negative voltage power supply VER, while the TTL-ECL level conversion circuit 2 receives power from both the positive voltage power supply VCC1 and the negative voltage power supply VEE.

The TTL-ECL level conversion circuit receives the output of the ECL logic level from the current switching type logic circuit 1, converts it to the TTL logic level and outputs it to the outside, or receives a signal of the TTL logic level from the outside and converts it to the ECL logic level. It is converted to a logic level and output to the current switching type logic circuit 1.

The constant voltage circuit 3a is composed of resistors R1 to R5 and bipolar transistors Ql and Q2, and the end thereof is connected to a positive voltage power supply V.
The other parts except for the resistor R1 connected to CC are connected between the negative voltage power supply VER and the ground terminal GND.

The output voltage of the constant voltage circuit 3a is used to keep the logic level of the current switching type logic circuit 1 constant. TTL
-ECL The ECL circuit portion of the level conversion circuit also receives constant voltage from this constant voltage circuit or from a constant voltage circuit of the same type.

Next, the operation of the circuit of this embodiment will be explained. First, considering the case where only the negative voltage power supply VER is applied,
Since the bias current due to the resistor R1 does not flow, the constant voltage circuit 3a does not operate, and the emitter potential of the transistor Q2 becomes
The voltage becomes the same potential as VER, and no current flows through the current switching type logic circuit 1. Therefore, since a voltage drop does not occur across the resistors in each of these circuits, no abnormal current will flow even if isolation to the resistors is not performed normally due to no positive voltage being applied. Then, normal operation starts immediately when the positive voltage power supply VCC is applied.

Next, when only the positive voltage power supply VCC is applied, a small current flows between the base and collector of the transistor Q2 of the constant voltage circuit 3a via the resistor R1;
No current flows through the other portions of the integrated circuit, and no current flows through the current switching type logic circuit 1 portion, which occupies most of the integrated circuit, because the negative voltage power source VEE of the main power source is not applied thereto. In addition, the positive voltage power supply VC required to separate the resistors
Since C has already been given, no abnormal behavior will occur.
Normal operation is started by the next applied negative voltage power supply VEE.

That is, in the logic circuit of the present invention, the necessary power supply of the constant voltage circuit is reduced so that the circuit current flows and all circuits start normal operation only when both the negative voltage power supply VEE and the positive voltage power supply VCC are applied. is taken from both VER and VCC. Therefore, even when one power supply voltage is applied, there is no voltage drop across the circuit resistance, and abnormal currents are prevented from occurring in the middle of the process due to the resistance not being separated. Accidents such as malfunctions can be prevented by adjusting the input order.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a more simplified constant voltage circuit 3b is used, and even in this circuit, the base of the transistor Q1
The logic amplitude of the current switching type logic circuit 1 is controlled by a voltage obtained by boosting the inter-emitter forward voltage by the ratio of the resistors R3 and R2, and the operation is basically the same as that of FIG. 1.

[Effects of the Invention] As explained above, the present invention provides a logic circuit composed of a current switching type logic circuit and a TTL-ECL level conversion circuit.
The power required by the constant voltage circuit that controls the logic amplitude of the logic circuit of the ECL circuit part of the L level conversion circuit, that is, the circuit current, is supplied from both the negative voltage power supply VEE and the positive voltage power supply VCC, and the voltage of both power supplies is Since the current in the constant voltage circuit starts flowing only when the voltage is applied,
According to the present invention, even if one of the power supply voltages is applied, no current flows through the constant voltage circuit and the circuit portion that waits for the operation of this circuit to start its operation. Therefore, according to the present invention, it is possible to prevent the occurrence of abnormal current in the middle of the process due to resistances not being properly separated, and to obtain a current switching type logic circuit that operates stably regardless of the power supply order. It will be done.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing embodiments of the present invention, and FIG. 3 is a circuit diagram showing a conventional example. 1... Current switching type logic circuit, 2... TTL
-ECL level conversion circuit, 3a to 3c...constant voltage circuit, VCC...positive voltage power supply, VEE...
Negative voltage power supply, GND...ground terminal, 1 2...bipolar transistor, R. ~R8...Resistance.

Claims (1)

[Claims] (1) A current switching type logic circuit powered by a negative voltage power supply, a TTL-ECL level conversion circuit powered by a negative voltage power supply and a positive voltage power supply, and the current switching type logic circuit and the TTL-ECL level conversion circuit. In a logic circuit comprising a constant voltage circuit for applying a predetermined voltage to each of the constant voltage circuits, the constant voltage circuit is powered by a negative voltage power supply and a positive voltage power supply and operates only when the voltages of both power supplies are applied. A logic circuit characterized by: