JP3461091B2 - Integrated circuit input circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input circuit of an integrated circuit capable of supporting a single power source and a plus / minus power source.

[0002]

2. Description of the Related Art Conventionally, there has been a surround circuit for obtaining a surround or an echo by adding an audio signal and a signal obtained by delaying the audio signal by a predetermined time. In such a circuit, the surround amount and the echo amount are changed by changing the delay time according to the digital signal from the microcomputer. Such a circuit is constructed as shown in FIG. In FIG. 3, the microcomputer 1 generates a digital signal according to a desired surround amount by operating an operation panel (not shown). The digital signal is applied to the digital processing circuit 3 of the surround circuit 2, and the digital processing circuit 3 controls the delay time S5 by decoding the digital signal or the like, and sets the surround amount.

[0003]

The digital signal a generated by the microcomputer 1 has a lower power supply voltage of 0 V and an upper power supply voltage of 5 V, for example, as shown in FIG. It is a signal. In addition, the power source of the surround circuit 2 is, for example, a single 5 V power source (not shown).
2B, the upper power supply voltage of the digital processing circuit 3 of the surround circuit 2 is 0V and the lower power supply voltage thereof is 5V. Therefore, the level of the digital signal matches the operating voltage of the digital processing circuit 3, and the digital signal can be directly applied from the microcomputer 1 to the surround circuit 2.

However, the power supply for the surround circuit is
If necessary, as shown in FIG. 2C, there may be a case of connecting to a plus / minus power source of ± 4.5V. In that case, the upper power supply voltage of the digital processing circuit 3 is + 0.5V, and the lower power supply voltage thereof is -4.5V. Therefore, the level of the digital signal and the power supply voltage of the digital processing circuit 3 do not match, and the digital signal cannot be directly applied from the microcomputer 1 to the surround circuit 2. In the case of applying the digital signal, the digital signal must be level-shifted and then applied, and there is a problem that an external circuit is required.

[0005]

SUMMARY OF THE INVENTION The present invention is an input circuit of an integrated circuit to which a digital signal is applied, said integrated circuit comprising:
A circuit connected to the outside of the circuit to generate the digital signal.
A reference voltage generating circuit for generating a reference voltage based on the lower power supply voltage used in the circuit, a first transistor to which the digital signal is applied to the base, and an emitter commonly connected to the emitter of the first transistor. A second transistor having the base to which the reference voltage is applied, a voltage generating circuit which generates a voltage obtained by boosting a lower power supply voltage used in the integrated circuit by a predetermined voltage, and an output signal of the first transistor. , An output stage circuit for generating a voltage of one of the output voltage of the voltage generating circuit and the lower power supply voltage of the integrated circuit in a circuit in a subsequent stage.

Further, the reference voltage generating circuit includes the first voltage generating circuit.
When the output signal of the transistor increases, the base voltage of the second transistor increases, and when the output signal of the first transistor decreases, the base voltage of the second transistor decreases. Again, enter
A ratio of the output current to the output current is set smaller than 1, and a current mirror circuit for inverting the output signal of the first transistor to the reference voltage generation circuit is provided.

Furthermore, the reference voltage is the digital signal.
It is characterized by having a hysteresis characteristic with respect to a signal . According to the present invention, a reference voltage is generated based on a lower power supply voltage of a circuit that generates a digital signal, and the first and second transistors are turned on / off based on the reference voltage.
Since the output signal having one of the lower power supply voltage of the integrated circuit and the voltage obtained by boosting the lower power supply voltage by a predetermined voltage is generated according to the output signal of the first transistor, the power supply voltage of the integrated circuit is set to a single value. Digital signals can be applied directly to the integrated circuit, whether it is a positive or negative power source.

[0008]

1 is a view showing an embodiment of the present invention, in which 4 is a first external terminal to which a digital signal a from the microcomputer 1 is applied, and 5 is an external terminal on a base. A first transistor to which a digital signal from 4 is applied, 6 is a second transistor whose emitter is commonly connected to the first transistor 4, and 7 is a microcomputer 1
A second external terminal connected to the ground terminal of the second external terminal, a resistor 8 connected in series between the second external terminal 7 and the base of the second transistor 6, first and second diodes 10a and 10b. The reference voltage generating circuit, 11 is diode-connected, and the third transistor through which the collector current of the first transistor 5 flows, 12 is the third transistor 1
A fifth transistor which is mirror-connected to 1 and which supplies a collector current to the resistor 9 and the first and second diodes 10a and 10b, and 13 which is mirror-connected to a third transistor and which supplies a collector current to the resistor 14, 1
5 is a voltage generating circuit for boosting a predetermined voltage from the lower power supply voltage, 16 is a sixth transistor which is on / off controlled by the terminal voltage of the resistor 14, 17 is a constant current source, and 18 is an output current of the constant current source 17. A first current mirror circuit for inverting, 19
Is a second current mirror circuit that inverts the output current of the first current mirror circuit 18 and supplies it to the resistor 9, the first and second diodes 10a and 10b, and 20 and 21 are the upper and lower power supply voltages of the surround circuit 2. The first and second power supply terminals are applied. The same elements as those in FIG. 3 are designated by the same reference numerals.

First, the surround circuit 2 is operated by a single power supply, and the first power supply terminal 20 receives a power supply voltage VDD1 (for example,
5 V) is applied and the second power supply terminal 21 is grounded. When the microcomputer 1 is not generating a digital signal, the constant current source 17
Output current of the first and second current mirror circuits 18 and 1
It is supplied to the resistor 9 and the first and second diodes 10 a and 10 b via 9. Further, in such a state, the first and second transistors 5 and 6 which are differentially connected to each other.
Are turned on, the collector current of the first transistor 5 is mirror-connected to the third and fourth transistors 1.
Resistor 9 and diodes 10a and 10 through 1 and 12
b.

First and second diodes 10a and 10b
Is turned on when a current is supplied, the ON voltage of the first and second diodes 10a and 10b is VD, the resistance value of the resistor 9 is R9, the collector current of the fourth transistor 12 is Ic12, and the second current is Assuming that the output current of the mirror circuit 19 is I19, the base voltage VB of the second transistor 6 is VB = 2 × VD + R9 × (Ic12 + I19).
Becomes The base voltage VB of the second transistor 6 is
For example, a digital signal a from the microcomputer 1
2 has a level of 0V and 5V as shown in FIG. 2A, it is set to 2.5V, which is a half of 0V and 5V.

In such a state, when the digital signal a is applied from the microcomputer 1 to the base of the transistor 5 via the first external terminal 4, the first transistor 5 of the first transistor 5 responds to the rising of the digital signal a. The collector current increases. As the collector current of the first transistor 5 increases, the collector current of the fourth transistor 12 increases. If the increased collector current of the fourth transistor 12 is Ic12 ′, the base voltage Vb ′ of the second transistor 6 is Vb ′ = 2 × VD + R9 ×
(Ic12 '+ I19). However, Ic12 '> I
It is c12. Therefore, the base voltage of the second transistor 6 rises when the digital signal rises.

By changing the emitter resistance of the fourth transistor 12, the mirror ratio of the third and fourth transistors 11 and 12 that are mirror-connected is reduced, and the collector current of the fourth transistor 12 changes at the first speed. It becomes slower than the changing speed of the collector current of one transistor 5. As a result, the speed at which the base voltage of the second transistor 6 rises is set slower than the rising speed of the digital signal a, so that when the base voltage Vb ′ of the second transistor 6 becomes 3V, the first transistor 5 turns on. ,
The second transistor 6 is turned off.

The collector current of the first transistor 5 is the mirror current of the third and fifth transistors 11 and 13.
It is also supplied to the resistor 14 via. First transistor 5
The collector current of the fifth transistor 13 when only one is turned on is supplied to the resistor 14. The sixth transistor 16 is turned on by the terminal voltage of the resistor 14 generated according to the collector current. As a result, the first power supply terminal 21 is grounded, and the collector voltage of the sixth transistor 16 becomes 0V.

Further, when the digital signal a of the microcomputer 1 falls, the collector current of the first transistor 5 decreases. The collector current of the first transistor 5 passes through the third and fourth transistors 11 and 12 and
The resistor 9 and the first and second diodes 10a and 10b are supplied. Therefore, the collector current of the fourth transistor 12 is reduced, and assuming that the reduced collector current is Ic12 ″, the base voltage Vb ″ of the second transistor 6 is Vb ″.
= 2 × VD + R9 × (Ic12 ″ + I19), where Ic12 ″ <Ic2. Therefore, when the digital signal a falls, the base voltage of the second transistor 6 drops. When the base voltage of the second transistor 6 drops to 2V, the first transistor 5 turns off and the second transistor 6 turns on.

Therefore, the collector current of the first transistor 5 becomes 0, and the collector current of the fifth transistor 13 becomes 0. Therefore, no current flows through the resistor 14 and no voltage drop occurs in the resistor 14. Therefore, the sixth transistor 16 is turned off, and the collector voltage of the sixth transistor 16 becomes the output voltage of the voltage generation circuit 15. In this case, the sixth
The collector voltage of the transistor 16 becomes 5V. As a result, the output signal b from the collector of the sixth transistor 16 becomes a signal having levels of 0 V and 5 V as shown in FIG.

Therefore, the on / off operation of the first and second transistors 5 and 6 is performed regardless of the power supply voltage VDD1.
Since the microcomputer 1 is operated based on the reference voltage generated from the lower power supply voltage and the output signal of the first transistor 5 is supplied to the resistor 14 in the current mode, 0 V and 5 V are input to the input digital signal. A digital signal can be obtained.

On the other hand, the surround circuit 2 is operated with a plus / minus power supply, and the first power supply terminal 20 receives the power supply voltage + VD.
D2 is applied, and the second power supply terminal 21 has the power supply voltage −VDD.
The case where 2 is applied will be described. Even if the surround circuit 2 is operated with a plus / minus power supply, the reference voltage applied to the base of the second transistor 6 is generated based on the lower power supply voltage of the microcomputer 1. The output signal of the first transistor 5 is generated in the current mode and supplied to the resistor 14. Therefore, the operation of the first and second transistors 5 and 6 is equal to the power supply voltage ± VDD1.
Irrelevant to Therefore, the first and second transistors 5
The on / off operations of 6 and 6 and the operation of the sixth transistor 16 associated therewith are the same as those when the surround circuit 2 is operated by a single power source.

Next, the operation when the sixth transistor 16 is turned on / off will be described. When the sixth transistor 16 is turned on / off, the output voltage of the voltage generation circuit 15 appears at the collector of the sixth transistor 16. In this case, for example, the first
It is assumed that a voltage of + 4.5V is applied to the power supply terminal 20 and a voltage of -4.5V is applied to the second power supply terminal 21.
The voltage generation circuit 15 generates an output voltage by boosting the voltage of the second power supply terminal by 5V. Therefore, when the sixth transistor 16 turns on, the collector voltage of the sixth transistor 16 becomes −4.5V, and when the sixth transistor 16 turns off, its collector voltage becomes 0.5V. Therefore, when the input digital signal a as shown in FIG. 2A is applied, the output signal b from the sixth transistor 16 is as shown in FIG.
As in (e), the signal has the levels of -4.5V and + 0.5V.

By the way, in FIG. 1, as described above,
The base voltage of the second transistor 6 is set to the first transistor 5
The reference voltage is changed according to the level of the input digital signal by changing the collector voltage according to the collector current. As a result, the input circuit of FIG. 1 has a hysteresis characteristic for the input digital signal. Therefore, even if noise is applied to the input line or the level of the input digital signal changes, the circuit of FIG. 1 is prevented from malfunctioning and erroneously generating an output signal.

The operation of the surround circuit 2 has been described above. However, not only the surround circuit 2 but also a circuit having an input circuit for receiving a digital signal and capable of using a single power source or a plus / minus power source as a power source, The circuit of FIG. 1 can be applied.

[0021]

According to the present invention, the base voltage of the second transistor is set based on the lower power supply voltage of the microcomputer, and the output signal of the output circuit is generated from the lower power supply voltage of the integrated circuit. It is generated according to the output voltage of the circuit. As a result, the level of the digital signal is converted to a level according to the power supply voltage of the integrated circuit and then transmitted to the circuit in the subsequent stage, so that the digital signal can be directly applied to the integrated circuit. Therefore, an input circuit of an integrated circuit which can be applied to a single power source or a plus / minus power source can be provided, and it is not necessary to use an external circuit controlled by a digital signal.

Further, since the base voltage of the second transistor is changed according to the output signal of one of the first and second transistors which are commonly connected to the emitters, a hysteresis characteristic is generated in the input circuit of the integrated circuit. It is possible to prevent malfunction due to fluctuations in the input signal.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing each signal in FIG.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

4 First external terminal 5 First transistor 6 Second transistor 7 Second external terminal 8 Reference voltage generation circuit 9, 14 resistance 10a, 10b diode 11 Third transistor 12 Fourth transistor 13 Fifth transistor 15 Voltage generation circuit 16th transistor 17 constant current source 18 First current mirror circuit 19 Second current mirror circuit 20 First power supply terminal 21 Second power supply terminal

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Claims (4)

(57) [Claims] 1. An input circuit of an integrated circuit to which a digital signal is applied, the input circuit being connected to the outside of the integrated circuit to generate the digital signal.
A reference voltage generating circuit for generating a reference voltage based on a lower power supply voltage used in the generating circuit, a first transistor to which the digital signal is applied to the base, and an emitter commonly connected to the emitter of the first transistor. And a second reference voltage applied to the base.
A transistor, a voltage generation circuit that generates a voltage obtained by boosting a lower power supply voltage used in the integrated circuit by a predetermined voltage, and an output voltage of the voltage generation circuit and the integrated circuit according to an output signal of the first transistor An input circuit of an integrated circuit, comprising: an output stage circuit for generating a voltage of one of the lower power supply voltage to a circuit in a subsequent stage. 2. The reference voltage generating circuit increases the base voltage of the second transistor when the output signal of the first transistor increases, and decreases the output signal of the first transistor when the output signal of the first transistor decreases. 2. The base voltage is reduced to claim 1.
An input circuit of the integrated circuit described. 3. A current mirror circuit, wherein a ratio of an output current to an input current is set to be smaller than 1 and a current mirror circuit for inverting an output signal of the first transistor to the reference voltage generating circuit is provided. An input circuit of the integrated circuit described. 4. The input circuit of an integrated circuit according to claim 1, wherein the reference voltage has a hysteresis characteristic with respect to the digital signal .