JPS62224116A - Electronic circuit - Google Patents

Abstract

PURPOSE:To obtain an electronic circuit capable of high speed response by connecting a constant current circuit to an emitter of a transistor (TR) in operation to form an emitter follower and connecting a base to the constant current circuit at non-operation so as to open the emitter. CONSTITUTION:A switch S11 is thrown as shown in solid lines at normal operation and a constant current circuit CS11 is connected to the emitter of a TR Q11. When an input signal Vin is at a high level, the TR Q11 is turned on, an output signal Vout goes to a high level and the voltage level in this case is decided by a value Vcc-Vbe Q11. In bringing the output impedance to a high impedance, the switch circuit is driven to connect the constant current circuit CS11 to the base. A diode D11 applies low level clamp of the base and a resistor R11 decides the impedance viewed from the input side. Since no Schottky diode nor Schottky TR is employed, the circuit integration by the minute process is facilitated.

Description

[Detailed Description of the Invention] Field of Application in CPI Industry] The present invention relates to an electronic circuit suitable for application to an output circuit of a logic circuit such as a TTL circuit, and particularly to an electronic circuit suitable for application to an output circuit of a logic circuit such as a TTL circuit.
This paper relates to circuit technology that is effective when used as an interface with logic circuits.

[Conventional technology]

TTL circuits are often used as logic circuits, and are described in "Digital System Design" (7th edition published on March 1, 1970, published by CQ Publishing, I), p. 21-30.
)It is described in. Its outline is that it consists of a transistor that switches the direction of current in response to level changes in a digital input signal, and an output circuit that obtains a logical output.

By the way, the logic circuit to which the output signal of the TTL circuit is supplied is not uniform, and an example thereof is a logic circuit formed of C-MO8) transistors.

In this case, if the logic level of the output signal of the TTL circuit is low and the logic level of the C-MOS logic circuit is high, the logic level will not be transmitted.

The present inventors conducted various technical studies in order to accurately transmit the above-mentioned logic level. Although the following is not a publicly known technique, it is a technique that has been studied by the present inventors, and its outline is as follows.

FIG. 4 shows an example of an output circuit applied to a TTL circuit, and the input signal Vin is a digital signal.

When the input signal Vin is normal, the transistor Q
1 operates in the on state and drives transistor Q4, and the voltage drop across resistor R causes transistors Q2. Turn off Qs.

When the input signal Vin is at a low level, the transistor Q is turned off, turning off the transistor Q4, and
Transistors Q, ,Q are driven to obtain a high level output signal Vout.

When the output impedance is set to a zero level, the switches S, , S are turned on, and the transistors Q, , Q3 are turned off.

Although the circuit operation as described above is performed and a logical output is obtained, studies by the present inventors have revealed that there are problems as described below.

[Problem that the invention seeks to solve]

First, the high level of the output signal becomes the voltage level of Vc6-2 Vbe, and the power supply Vcc becomes 5■ and 3.6Vbe.
■It is to decrease to a degree. Since the C-MO8 logic circuit requires an input signal of 3.5 square meters or more, it becomes difficult to drive the C-MOS logic circuit accurately at this level.

The second is transistor Q for high-speed response.

~Q4 is a Schottky transistor, diode D,
, D are Schottky diodes.

Currently, electronic circuits are made into semiconductor integrated circuits (hereinafter referred to as ICs) through miniaturization processes, but Pur
Forming a Schottky diode with e Al is difficult. However, unless a Schottky diode is used, the switching speed cannot be increased due to the effect of base charge accumulation.

Currently, TTL circuits are required to be driven up to around 30MHz, but if Schottky diodes are not used,
Driving at high frequencies as described above becomes difficult.

Furthermore, there is a problem that transistors Q, , Q, may be turned on at the same time, causing a through current to flow.

An object of the present invention is to provide an electronic circuit that can be formed by a miniaturization device process without using Schottky transistors, Schottky diodes, etc., and that can respond at high speed.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief summary of typical inventions disclosed in this application is as follows.

That is, an input signal is supplied to the base of the bipolar transistor through a parallel circuit of a resistor and a diode, and a constant current circuit is connected to the emitter of the transistor by driving a switch circuit to function as an emitter follower. Drive in the non-saturation region to achieve high-speed response. Historically, when the transistor is not in operation, the switch circuit is driven to connect the constant current circuit to the base, putting the emitter in an open state and making the output impedance high.

[Effect]

According to the above means, high-speed response is possible without using a Schottky transistor or a Schottky diode, and since a single bipolar transistor is used, the 71 level of the output signal is determined by Vcc-Vbe. It is possible to achieve the object of the present invention, which is to obtain an electronic circuit that can be formed by a miniaturization process by making the voltage level high and the output signal high.

[Embodiment 1] Hereinafter, a first embodiment of an electronic circuit to which the present invention is applied will be described with reference to FIG.

Note that FIG. 1 is a circuit diagram showing the basic circuit configuration of the electronic circuit.

The feature of this embodiment is that the bipolar transistor is driven in a non-saturation region to enable high-speed response.

Transistor Q++ corresponds to transistor 1 in the present invention, and includes resistor R11 and diode D11.
A digital input signal Vin is supplied through the parallel circuit. During normal use, the switch S11 is switched as shown by the solid line to connect the constant current circuit CS, , to the emitter of the transistor QII.

That is, the transistor QII is made an emitter follower.

When the input signal vin is at high level, the transistor Qt
+ operates in the on state, and the output signal Vout becomes high level. At this time, the voltage level is Vcc-vbeQ
It is determined by ll. Since the voltage level of the power supply Vcc is 5V, the voltage level of the output signal Vout is about 4.3V. Even if the next stage is a C-MO8 logic circuit, it can be sufficiently driven.

In order to make the output impedance non-impedance, the switch circuit is driven and the constant current circuit CS is connected to the base. The input signal Vin is connected to the switch circuit S
The diode D11 clamps the base at a low level, and the resistor R11 determines the impedance seen from the input side.

(1) A constant current circuit is connected to the emitter of bipolar transistor 1 via a switch circuit to form an emitter follower, and an input signal is supplied to the base via a resistor to obtain an output signal from the emitter, thereby connecting the bipolar transistor to the power source. Since the voltage drop between the output terminal and the emitter becomes Vbe, it is possible to obtain the effect that the voltage level of the output signal becomes a high level determined by Vcc-Vbe.

(2) According to (11) above, the transistor is driven in a non-saturation region, thereby achieving the effect of enabling high-speed response.

(3) By connecting a constant current circuit to the base via a switch circuit and turning off the transistor, the current path of the output circuit is cut off, and the output impedance can be easily and quickly changed to no impedance. The effect is that it can be done.

(4) Since the above effects can be obtained without using a Schottky diode or a Schottky transistor, the effect of facilitating IC fabrication through a miniaturization process can be obtained.

(5) The above (4) provides the effect that production costs can be significantly reduced.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to FIG.

The feature of this embodiment is that the electronic circuit is configured to be able to transmit signals in both directions and to increase the level of the output signal.

11 is a switch circuit, and when the control signal Vc is at a high level, the transistor Q! 1 is turned on, and the voltage drop across the resistor R□ causes the transistor Q□ to be turned on. Resistor R76, diode D□, D2! A current path is formed, and the transistor Qzs is turned on. Transistor Q! Since the base voltage of No. 3 is fixed at a predetermined voltage level, it can be regarded as a constant current circuit. A constant current circuit is now connected to the emitter of transistor Q+t.

As a result, the voltage level at terminal 3 of transistor Q r
It is now supplied as an input signal to the base of t, and an output voltage is obtained via the resistor R31.

And the transistor Qll is the Vb of the transistor Q.
It becomes reverse biased by e and is forced off.

On the other hand, when the control signal Vc is changed to low level, the reference voltage Vref turns on the transistor Qta, and the voltage drop across the resistor R2 causes the transistor Q2 to turn on.
4 operates in the on state. Resistor R22, diode D
A current path of 23 r D 24 is formed, and the transistor Q□ operates in an on state.

Similarly to the above, a constant current circuit is connected to the emitter of transistor Q, and transistor Q becomes an emitter follower. Transistor Q++ is driven by input signal Vin, and output signal Vout is obtained from its emitter. At this time, although the output signal You t is supplied to the base of the transistor Q+t, its emitter is at the voltage level of the input signal Vin, so that it is reverse biased.

Transistor Q12 is turned off. Output signal Vou
The voltage level at t becomes a high level output signal determined by Vcc-VbeQo.

(6) Transistor Qll, which transmits signals in one direction, and transistor Q+t, which transmits signals in the other direction, are selectively driven by a switch circuit, and when one transistor is in operation, the other transistor is driven by a decrease in its Vbe. Since the switch is configured to be turned off, the effect is that bidirectional signal transmission becomes possible.

(7) When transistor Qu is driven based on the input signal, the voltage level of the output signal is Vcc-Vbe.
As determined by , we get a high level output signal,
This effect can be obtained.

(8) The effect that the C-MOS logic circuit can be reliably driven by the force described above can be obtained.

(9) According to (7) above, it can be used as an interface for CPU and memory circuits that need to be connected to a data bus and exchange signals, thereby increasing added value.

[Embodiment 3] Next, a third embodiment of the present invention will be described with reference to FIG.

In this embodiment, the electronic circuit described above is applied as an interface for a single board computer.

21 is a parallel type A/D converter, resistor R1 amplifier A,
It is composed of a gate circuit G, an encoder E, etc. The details of this circuit operation are described in "Design of A-D/D-A Conversion Circuit" (3rd edition published on May 20, 1981, published by CQ Publishing, ap121-123). However, the analog input signal Va is obtained as the digital output signal vb.

11 is the switch circuit, and 12 is the electronic circuit. The digital output signal Vd is supplied to the data bus B via the electronic circuit 12. 13 is C-MOS
) A memory circuit such as a ROM or RAM formed of transistors, and sends and receives recording signals and read signals in both directions via the electronic circuit 12.

The CPU 14 is formed of C-MOS transistors,
The electronic circuit 12 bidirectionally sends and receives the digital output signal Vd and the like.

Note that B2 is a control bus, and B is an address bus.

By applying the electronic circuit 12 as described above, bidirectional transmission of various digital signals becomes possible, and since the level of the output signal becomes high as described above, C
- A MOS load circuit can be driven accurately.

Although the invention made by the present inventor has been specifically explained based on examples above, the present invention is not limited to the above examples, and can be modified in various ways without departing from the gist of the invention. Needless to say. For example, a load resistor may be provided at each collector of the transistor Q++ + Q+t to obtain an output signal separate from the above output signal.

In the above description, the present inventors have mainly explained the case where the present invention is applied to an output circuit of a TTL circuit, but the present invention is not limited thereto, and can be used for a two-way communication device, an impedance converter, etc.

The present invention can be widely used at least when driving a load circuit composed of C-MOS transistors.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

In other words, during normal operation, a constant current circuit is connected to the emitter of the bipolar transistor by driving a switch circuit to form an emitter follower circuit that can operate in a non-saturation region, and when the output impedance is set to high impedance, the above switch circuit is used. By connecting the constant current circuit to the base of the transistor through the transistor and cutting off the current path of the transistor, the output signal can be set to a high level and a high-speed response can be achieved.

Fig. 1 is a circuit diagram showing a first embodiment of an electronic circuit to which the present invention is applied, Fig. 2 is a circuit diagram showing a second embodiment of the above electronic circuit, and Fig. 3 is a circuit diagram showing an application example of the above electronic circuit. FIG. 4, a block diagram of a single board computer, shows a circuit diagram of an output circuit that was considered prior to the present invention.

Q +t -Q ts...transistor, D, ~D,
4...Diode, CS,... Constant current circuit, V
in...input signal, Vout...output signal, Vc.
...Control signal, 12--Electronic circuit, 11--Switch circuit, 13--Memory circuit, 14-CPU.

Agent: Patent Attorney Katsuo Ogawa 'No. IFi!
J Figure 4

Claims (1)

[Claims] 1. a transistor that obtains an output signal from a first output terminal in response to an input signal supplied to the first control terminal;
When the first transistor is in operation, a constant current circuit is connected to the first output terminal to configure the first transistor as an emitter follower, and when the first transistor is not in operation, the constant current circuit is connected to the first output terminal. 1. An electronic circuit comprising: a switch circuit connected to a control terminal to make the output impedance of the transistor of 1 above high impedance.