JPH0823236A - Non-inverse amplifier cirucit - Google Patents

Abstract

PURPOSE:To satisfactorily reduce the click voltage that is generated when a power supply is applied without muting the output side even if a two power supply OP (operational amplifier) is used and then the power current given from a single power supply is applied to the operational amplifier. CONSTITUTION:When a power supply is applied, the voltage divided by the resistors R8 and R9 is applied to the inverse input of an OP via a capacitor C1. Meanwhile the preceding divided voltage is applied to the non-inverse input of the OP via a diode D1 as the intra-active area voltage. Thus no inversion phenomenon occurs. The voltage applied to the non-inverse input is lower than the voltage applied to the inverse input via a capacitor C4 by a degree equal to the voltage drop of the D1. Thus the OP output is satisfactorily reduced when the power supply is applied. The difference between the voltage applied to the non-inverse input and the voltage applied to the inverse input is gradually reduced in response to the charging of the C1. Thus the OP output gradually increases. As a result, the click voltage is satisfactorily reduced at the output terminal OUT of a non-invers amplifier circuit when the power supply is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-inverting amplifier circuit, which is suitable as a headphone amplifier for amplifying an audio signal, for example.

[0002]

2. Description of the Related Art Generally, a non-inverting amplifier circuit shown in FIG. 7 is known as an audio signal amplifier circuit. This amplifier circuit is composed of a dual power supply type operational amplifier, and a power supply voltage from a single power supply is supplied to this operational amplifier. In this figure, reference sign OP is the operational amplifier, the non-inverting input of which is connected to the input terminal IN of the amplifier circuit via the capacitor C1, and the resistor R1 is provided between the non-inverting input and the power supply terminal Vcc. A resistor R2 is connected between the grounds. A bias voltage is applied to the operational amplifier OP by these resistors R1 and R2. The output of the operational amplifier OP is connected to the output terminal OUT of the amplifier circuit via a capacitor C2, a resistor R3 is provided between the output of the operational amplifier OP and the inverting input, and a series connection is provided between the inverting input and the ground. The connected resistor R4 and capacitor C3 are connected. Then, the resistors R3 and R4 and the capacitor C4 provide a negative feedback to the operational amplifier OP. Resistors R5 and R6 are connected between the input terminal IN and the ground and between the output terminal OUT and the ground, respectively.

In the non-inverting amplifier circuit configured as described above, when the power is turned on, the charging current flows through the capacitor C1 via the resistors R1 and R5. Then, the voltage at the connection point between the capacitor C1 and the resistor R1 is applied to the non-inverting input of the operational amplifier OP. As shown in FIG. 8, the applied voltage gradually rises after the power is turned on and the resistance R1
When the resistance values of R2 and R2 are the same, Vcc / 2 approaches. Here, Vcc is the voltage of the power supply terminal Vcc.
The bias voltage divided by the resistors R1 and R2 is
Naturally, it is the voltage in the active region described later.

By the way, the above-mentioned operational amplifier OP is a dual power supply type operational amplifier, and when connected as shown in FIG. 9, the output voltage is close to Vcc because the operational amplifier does not operate normally when the input voltage is near 0 volt. It becomes a value. Then, when the input voltage is gradually increased, the operational amplifier normally operates at a certain point. As a result, after the output voltage suddenly drops to around 0 volt at the above-mentioned point, the output voltage becomes the same voltage as the input voltage and gradually increases.
Such an abrupt increase in the input voltage near 0 volt may be referred to as an operational amplifier inversion phenomenon. Further, as described above, the region of the input voltage in which the operational amplifier normally operates is referred to as a normal operation region or active region of the operational amplifier. This normal operation region is a region where the operational amplifier operates as an operational amplifier, that is, a region where the difference between the inverting input and the non-inverting input is amplified and output, and the region where the inversion phenomenon occurs is the inverting input and the non-inverting input. This is a region where the output voltage sticks to V CC regardless of the difference between As shown in FIG. 7, if a dual power supply type operational amplifier is used as the operational amplifier OP and a power supply voltage is supplied from a single power supply, the output voltage of the operational amplifier OP changes as shown in FIG. Output terminal O of the amplifier circuit
The output voltage at the UT changes as shown in FIG. 11 and becomes the click voltage. In this way, when the output voltage accompanied by a click when the power is turned on is converted into a voice, a click sound is generated, which makes the sound difficult to hear.

Incidentally, the single power supply type operational amplifier does not have the above-mentioned inversion phenomenon unlike the dual power supply type operational amplifier, and when connected as shown in FIG. 9, an output voltage of the same voltage as the input voltage is obtained. To be However, the single power supply type operational amplifier is often distorted when the output load impedance is low, and is often unsuitable for amplifying an audio signal. Therefore, conventionally, the dual power supply type operational amplifier is used as the operational amplifier OP as described above, and the signal level is small.
When the output impedance of the amplifier circuit may be high, the signal obtained from the output terminal OUT is muted by the transistor only when the power is turned on.

[0006]

As described above, in a non-inverting amplifier circuit using a dual power supply type operational amplifier and supplying a power supply voltage from a single power supply, a click voltage is generated when the power is turned on. It was muted due to such reasons. By the way, when this non-inverting amplifier circuit is a headphone amplifier, even if the signal obtained from this amplifier is grounded by a transistor as a mute circuit, the impedance of the transistor is sufficiently compared with the impedance of the headphone. Since it is not low, it was difficult to sufficiently reduce the above-mentioned click sound at power-on.

According to the present invention, as described above, even if a dual power supply type operational amplifier is used and a power supply voltage from a single power supply is supplied to the operational amplifier, the click voltage at power-on is not muted as in the conventional case. It is an object of the present invention to provide a non-inverting amplifier circuit capable of sufficiently reducing the above.

[0008]

A non-inverting amplifier circuit according to the present invention for solving the above problems and achieving the above object is
A non-inverting amplifier circuit configured by a dual power supply type operational amplifier, which is adapted to be supplied with a power supply voltage from a single power supply,
Between the first resistor and the second resistor for dividing the voltage of the single power supply and applying the bias voltage to the non-inverting input of the operational amplifier, the connection point of these resistors and the input terminal of the non-inverting amplifier circuit. A capacitor connected to the third resistor, a third resistor and a fourth resistor for dividing the voltage of the single power source, and a diode connected between the voltage dividing point and the non-inverting input of the operational amplifier. , A capacitor connected between the voltage dividing point and the inverting input of the operational amplifier, the diode is connected in the forward direction from the voltage dividing point to the non-inverting input, and the first Resistance and second
So that the ratio of the resistance value of the third resistor to the resistance value of the fourth resistor becomes equal to the ratio of the resistance value of the third resistor to the fourth resistor.
The resistance value of the resistor is selected.

[0009]

In the non-inverting amplifier circuit configured as described above,
When the power is turned on, the voltage divided by the third resistor and the fourth resistor is applied to the inverting input of the operational amplifier via the capacitor, and the third input is applied to the non-inverting input.
Since the voltage divided by the first resistance and the fourth resistance is applied through the diode, the voltages of the inverting input and the non-inverting input are within the normal operation region. Therefore, the click voltage due to the inversion phenomenon described above is sufficiently reduced.
When the power is turned on, the third resistor and the fourth resistor are connected as described above.
The voltage divided by the resistor is applied to the inverting input via the capacitor. Therefore, the voltage applied to the inverting input is higher than the voltage applied to the non-inverting input by the amount of the voltage drop in the forward direction of the diode, so that the output voltage of the op-amp at the time of power-on is sufficient. It becomes a low voltage. By the way, when the output voltage of the operational amplifier suddenly rises when the power is turned on, the output voltage at the output terminal of the non-inverting amplifier circuit becomes the click voltage.

A charging current flows through the first resistor or the like from the time when the power is turned on, and the capacitor is gradually charged. By this charging, the first resistor and the second resistor
The voltage at the connection point with the resistor rises, and the voltage obtained by subtracting the voltage drop due to the diode from the voltage divided by the third resistor and the fourth resistor, that is, to the non-inverting input when the power is turned on. When the applied voltage is exceeded, the applied voltage to the non-inverting input rises along the voltage at the connection point between the first resistor and the second resistor. Due to this rise, the difference in voltage between the non-inverting input and the inverting input gradually narrows, and as a result, the output voltage of the operational amplifier gradually rises. As described above, in this non-inverting amplifier circuit, the inversion phenomenon in the operational amplifier does not occur, and the output voltage of the operational amplifier gradually rises after the power is turned on. Therefore, the click voltage at the output terminal of this non-inverting amplifier circuit is sufficient. Is reduced to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the same reference numerals as those in FIG. 7 indicate the same parts, and thus detailed description thereof will be omitted. The non-inverting input of the operational amplifier OP is connected to the input terminal IN of the amplifier circuit via a resistor R7 and the capacitor C1 in series. Resistors R8 and R9 are connected in series between the power supply terminal Vcc and ground, and this connection point is connected to the non-inverting input via a diode D1 and to the inverting input via a capacitor C4. The resistance values of the resistors R1 to R4 are selected so that the resistance value ratio of the resistors R1 and R2 is equal to the resistance value ratio of the resistors R8 and R9.

The operation of the non-inverting amplifier circuit configured as described above will be described. The transient voltage applied to the non-inverting input when the power of the non-inverting amplifier circuit is turned on is shown by a solid line in FIG. The broken line shows the conventional one for reference. When the power is turned on, the voltage divided by the resistors R8 and R9 (Vcc / if the resistance values of R8 and R9 are the same)
2) is applied to the non-inverting input via the diode D1 connected in the forward direction. This applied voltage is within the above-mentioned normal operation region. The rising of this solid line is V
Lower than CC / 2 is due to the voltage drop across the diode D1. When the power is turned on, a charging current flows through the capacitor C1 as described with reference to FIG. 7, whereby the voltage at the connection point between the resistors R1 and R2 gradually rises. When this voltage becomes higher than the voltage divided by the resistors R8 and R9 minus the voltage drop of the diode D1, that is, the voltage applied to the non-inverting input, the voltage is applied to the non-inverting input. The voltage rises as the voltage at the connection point between the resistors R1 and R2 rises,
Reaches / 2.

The voltage divided by the resistors R8 and R9 is also applied to the inverting input via the capacitor C4. This voltage is within the normal operating range described above,
When the power is turned on, it is higher than the voltage applied to the non-inverting input by the voltage drop of the diode D1, and the output voltage of the operational amplifier OP becomes lower as shown by the solid line in FIG. The reason why it does not drop to 0 volt is due to the characteristics of the dual power supply type operational amplifier itself. Then, the capacitor C1 is gradually charged by the charging current flowing through the resistors R1 and R5 and the charging current flowing through the resistor R8, the diode D1 and the resistors R7 and R5, so that the non-inverting input is obtained. As described above, the voltage applied to the input voltage gradually increases and approaches the voltage applied to the inverting input. Along with this, the output voltage also rises as shown by the solid line. In FIG. 3, the broken line shows the output voltage of the operational amplifier OP in the conventional non-inverting amplifier circuit described with reference to FIG.

The solid line in FIG. 4 shows the voltage at the output terminal OUT of this non-inverting amplifier circuit, and the click voltage unlike the conventional one shown by the broken line is not generated. in this way,
In the above-described embodiment, the voltage applied to the non-inverting input and the inverting input of the operational amplifier OP is within the normal operation region when the power is turned on, so that the inversion phenomenon does not occur. When the power is turned on, the voltage applied to the non-inverting input is lower than that of the inverting input by the voltage drop of the diode D1, so that the output of the operational amplifier OP becomes sufficiently low when the power is turned on. The difference between the voltage applied to the non-inverting input and the voltage applied to the inverting input is
The output of the operational amplifier OP gradually increases because the output gradually decreases as the capacitor C1 is charged. As described above, in this non-inverting amplifier circuit, the click voltage at the output terminal OUT at power-on is sufficiently reduced.

In the equivalent circuit for an AC signal when the power source impedance is zero, the inverting input of the operational amplifier OP is connected to the output of the operational amplifier via the resistor R3, and the other is connected to the output of the operational amplifier OP via the capacitor C4. It is grounded by the parallel impedance of resistors R8 and R9. Therefore, the equivalent circuit of this circuit and the equivalent circuit of the circuit of FIG. 7 are the same, and therefore, the same operation is performed during the normal operation. Further, although the resistor R7 is used in the above embodiment,
It may be unnecessary depending on the selection of the resistance values of the resistors R1 to R4. Further, the resistor R5 may be unnecessary depending on the device connected to the input terminal IN.

In the above embodiment, the case where the power supply voltage rises all at once when the power supply is turned on has been described. However, when the power supply voltage rises slowly, the resistor R when the power is turned on is used.
Since the voltage divided by 8 and R9 is low and the input voltage does not reach the normal operation region, the click voltage may occur due to the inversion phenomenon. 5 and 6 are suitable for the case where the rise of the power supply voltage is slow as described above, and the power supply current is supplied to the operational amplifier OP after the input voltage of the operational amplifier OP reaches the normal operation region. It was done. Note that, in FIGS. 5 and 6, the same reference numerals as those in FIG.

In the non-inverting amplifier circuit of FIG. 5, the power supply current is supplied to the operational amplifier OP through the Zener diode D2. Therefore, since the operational amplifier OP operates after the input voltage of the operational amplifier OP reaches the normal operation region, the click voltage can be reduced.
In the amplifier circuit of FIG. 6, the power supply current is supplied to the operational amplifier OP through the transistor Q1. R10 and R11 are resistors connected in series between the power supply terminal VCC and the ground, and the connection point is the transistor Q.
Connected to the base of 1. In the case of FIG. 6, when the power is turned on and the power supply voltage rises and the voltage across the resistor R10 reaches a predetermined value, the transistor Q1
Turns on. Therefore, since the operational amplifier OP operates after the input voltage of the operational amplifier OP reaches the normal operation region, the click voltage can be reduced.
In the case of using the Zener diode D2 as shown in FIG. 5, the dynamic range of the output is narrowed by the amount of the voltage drop due to the Zener diode D2.
With the transistor Q1 as described above, there is almost no effect.

[0018]

As described above, the non-inverting amplifier circuit of the present invention can sufficiently reduce the generation of the above-mentioned click voltage when the operation of the operational amplifier OP is started when the power is turned on.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a transient voltage applied to a non-inverting input of an operational amplifier at power-on in one embodiment of the present invention.

FIG. 3 is a diagram showing a transient voltage output from the output of the operational amplifier in one embodiment of the present invention when the power is turned on.

FIG. 4 is a diagram showing a transient voltage output from the non-inverting amplifier circuit according to the embodiment of the present invention when the power is turned on.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

FIG. 6 is a circuit diagram showing still another embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional example.

FIG. 8 is a diagram showing a transient voltage applied to a non-inverting input of an operational amplifier when the power is turned on in the conventional device.

FIG. 9 is a diagram for explaining the characteristics of this operational amplifier when a power supply voltage from a single power supply is supplied to the dual power supply type operational amplifier.

FIG. 10 is a diagram showing a transient voltage output from the output of an operational amplifier in a conventional device when the power is turned on.

FIG. 11 is a diagram showing a transient voltage output from a conventional non-inverting amplifier circuit when the power is turned on.

[Explanation of symbols]

OP operational amplifier C1, C2, C3, C4 capacitor IN input terminal Vcc power supply terminal R1, R2, R3, R4, R5, R6, R7, R8, R9, R1
0, R11 resistance OUT output terminal D1 diode D2 Zener diode Q1 transistor

Claims (1)

[Claims] 1. A non-inverting amplifier circuit configured by a dual power supply type operational amplifier so that a power supply voltage is supplied from a single power supply, wherein a voltage of the single power supply is divided to obtain a bias voltage of the operational amplifier. A first resistance and a second resistance applied to an inverting input, and a capacitor connected between a connection point of these resistances and an input terminal of this non-inverting amplifier circuit, wherein the voltage of the single power source And a fourth resistor for dividing the voltage, a diode connected between the voltage dividing point and the non-inverting input of the operational amplifier, and a diode connected between the voltage dividing point and the inverting input of the operational amplifier. And a diode connected in the forward direction from the voltage dividing point to the non-inverting input, and the ratio of the resistance values of the first resistor and the second resistor is
A resistance value of each of the first to fourth resistors is selected so as to be equal to a ratio of resistance values of the third resistor and the fourth resistor.