JPH0129095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor-transistor logic circuit in which a phase splitter section is formed of a PNP transistor and an NPN transistor.

FIG. 1 shows a commonly used low power Schottky transistor-transistor logic circuit (abbreviated as LSTTL). This circuit has a low threshold voltage for logic levels and a low noise margin. Q2 is a phase splitter.

An advanced draw power shot logic circuit (abbreviated as ALSTTL) as shown in Fig. 2, which is an improved version of the LSTTL shown in Fig. 1, has also been developed, but the phase splitter section of this circuit is By configuring NPN transistors Q1 and Q2, the threshold voltage Vth at the input is increased to increase the noise margin.

However, the gain of the phase splitter section becomes large, and the falling time during switching becomes short and steep. This means that when considering only the switching time, it becomes smaller and the high speed of ALSTTL can be obtained. However, the steepness during switching may cause large undershoot or ringing.
A real problem is that reflection occurs between the ALSTTL and the circuit connected to the output of the ALSTTL, which is undesirable in terms of switching characteristics.

The present invention was devised to solve the above-mentioned drawbacks of the conventional circuit, and its purpose is to connect a PNP type transistor and an NPN type transistor between the output of the input circuit section and the input of the output transistor circuit section. It is an object of the present invention to provide a transistor-transistor logic circuit which is provided with a phase splitter to improve switching characteristics and can maintain a high threshold voltage.

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 3 shows a transistor-transistor logic circuit 1 of the present invention. This logic circuit is input circuit section 2
, an output transistor circuit section 3, and an input circuit section 1
The phase splitter section 4 is composed of a PNP transistor Q7 and an NPN transistor Q8, which are interposed between the output of the output transistor Q7 and the input of the output transistor circuit section 3.

The input circuit section 2 exhibits high impedance with respect to one logic level of the input logic signal and low impedance with respect to the other logic level. For example, as shown in FIG. 3, the base is connected to the input terminal 5. The collector of the PNP transistor Q3 is connected to a reference potential, for example, the ground potential, and the emitter thereof is connected to a DC power supply Vcc via a resistor R1. The emitter of transistor Q3 becomes the output of input circuit section 2.

The output transistor circuit section 3 consists of a first output transistor circuit section 3a and a second output transistor circuit section 3b, and the first output transistor circuit section 3a has, for example, a base that becomes an input of the circuit section, It consists of an NPN transistor Q4 whose emitter is connected to a reference potential, such as the ground potential, and whose collector is connected to the output terminal 6. Further, the second output transistor circuit section 3b connects, for example, the base of the transistor Q5 (which is the input of the circuit section 3b) of the Darlington-connected NPN transistors Q5 and Q6 to the power supply Vcc via the resistor R2, and Connect the emitter of transistor Q5 to transistor Q6.
and to the emitter of a transistor Q6 via a resistor R4, and the emitter is connected to an output terminal 6.

The base of the PNP transistor Q7 and the base of the NPN transistor Q8 constituting the phase splitter section 4 are connected to each other, and the transistor Q
The emitter of transistor Q3 is connected to the output of the input circuit section, that is, the emitter of transistor Q3. The collector of the transistor Q7 is connected to the emitter of the transistor Q8, one end of a resistive element (for example, a resistor, an active pull-down circuit) R5 (the other end is connected to a reference potential, for example, ground potential), and the first output transistor circuit section. 3a (the first input of the output transistor circuit section), that is, the transistor Q4
connected to the base of. The collector of the transistor Q8 is the input of the second output transistor circuit section 3b (second input of the output transistor circuit section),
That is, it is connected to the base of transistor Q5. In order to speed up the switching off of the transistors Q7 and Q8 of this phase splitter section 4, if necessary, a unidirectional element such as A diode is connected.

Next, the operation of the circuit of the present invention will be explained.

When the input logic signal supplied to the input terminal 5 becomes low level, the transistor Q3 turns on,
In response to this, transistors Q7 and Q8 of the phase splitter section 4 turn off. Therefore, the first
The transistor Q4 of the output transistor circuit is turned off, while the Darlington-connected transistors Q5 and Q6 are turned on. As a result of this,
A high level logic signal appears at the output terminal 6.

Subsequently, when a high level logic signal is input to the input terminal 5, the transistor Q3 is turned off, the transistor Q7 is turned on, and the transistor Q8 is turned on. Therefore, the transistor Q4 turns on, and the Darlington-connected transistors Q5 and Q6 turn off, so that the output terminal 6
A low level logic signal appears.

In the circuit of the present invention that operates in this way,
Since the phase splitter section 4 is composed of a PNP type transistor Q7 and an NPN type transistor Q8, the gain is equivalently lowered in the phase splitter section 4, and the transistor Q4 of the first output transistor circuit section 3a The driving current of is the resistance R
1. Power will be supplied via transistor Q7 which is turned on. Therefore, the steepness of the falling characteristic during switching is alleviated, and the time delay in switching is reduced. In other words, the switching characteristics are improved. Therefore, in conventional circuits, problems caused by the steepness of the drop, such as undershoot and ringing, can be avoided by providing means such as clamping means, which had to be provided in order to suppress such problems to an acceptable limit in conventional circuits. It can be removed without being installed. Furthermore, there is no generation of noise caused by the above-mentioned defects, which is convenient for driving the next stage circuit.

In the above circuit, a PNP type transistor is
If you change the NPN transistor to a PNP transistor, configure the circuit by reversing the polarity of the power supply supplied to it, and also reverse the logic signal level supplied to it, you can create this circuit as described above. It is possible to generate a logic operation equivalent to that of a circuit that is similar to that of a conventional circuit.

In summary, according to the present invention, the following effects can be obtained.

The steepness of switching can be alleviated without any time delay in switching.

Therefore, problems that occur in conventional circuits,
For example, undershoot and ringing can be removed.

It does not generate noise and is advantageous for driving subsequent stages.

[Brief explanation of drawings]

FIG. 1 is a conventional LSTTL circuit diagram, FIG. 2 is a conventional ALSTTL circuit diagram, and FIG. 3 is a TTL circuit diagram of the present invention. In the figure, 1 is a transistor-transistor logic circuit, 2 is an input circuit section, 3 is an output transistor circuit section, 3a is a first output transistor circuit section, 3b
is the second output transistor circuit section, Q7 is PNP
type transistor, Q8 is an NPN type transistor.

Claims (1)

[Claims] 1. A first conductivity type having a base to which an input signal is applied, an emitter connected to a first power source via a first resistor, and a collector connected to a second power source. a second transistor of one conductivity type having an emitter connected to the emitter of the first transistor; a base connected to the base of the second transistor; a phase splitter section consisting of a third transistor of an opposite conductivity type having a collector connected to the first power supply via a resistor and an emitter connected to the collector of the second transistor; A fourth transistor of an opposite conductivity type has a base connected to the emitter of the transistor No. 3 and an emitter connected to the second power supply, and outputs a desired output signal from the collector of the fourth transistor. A transistor-transistor logic circuit characterized by having an output circuit section.