JP2009044517A - Amplification circuit, and remote controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce dark noise sound, harsh on the ears, during a sounding halt time. <P>SOLUTION: An amplifier mute circuit 2 shifts a potential of a node a21 based on a control signal C to change a potential difference between a +IN terminal and a -IN terminal of a power amplifier IC. In the case that the potential difference is <Vd, a differential amplifier circuit 1 outputs a signal amplifying an AC signal S and an amplifier circuit 100 performs amplifying operation. In the case that the potential difference is equal to or greater than Vd, the differential amplifier circuit 1 outputs a saturation voltage, and the amplifier circuit 100 stops the amplifying operation. Furthermore, quality is improved in a remote controller having the amplifier circuit 100. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an amplifier circuit including a differential amplifier circuit that amplifies a potential difference between a normal input terminal and an inverting input terminal, an amplifier mute circuit that stops an amplification operation, and a remote control device using the amplifier circuit.

In many cases, a remote controller for a water heater has an amplifier circuit and a speaker built therein, and various sounds are output during operation. Some amplifier circuits include a differential amplifier circuit and an amplifier mute circuit. The differential amplifier circuit can set an arbitrary gain by connecting a resistor to the outside.
The conventional amplifier mute circuit cuts off a signal line for inputting an AC signal as various sounds, thereby providing a sound generation stop time during which the differential amplifier circuit does not amplify the AC signal.

Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for preventing pop noise output from an amplifier circuit by stopping power supply to a differential amplifier circuit when the power is turned on. Since the power supply is turned on / off by a control signal having an audible frequency or higher, the rise time of the power supply voltage supplied to the amplifier circuit is moderated by the effect of the capacitor connected in parallel to the power supply line of the amplifier circuit.
JP-A-8-237035

The technique described in Patent Document 1 removes a pop sound when the power is turned on. For this reason, the pop sound when the power is turned off is also annoying.
The differential amplifier circuit also has a gain in the sound generation stop time, and amplifies dark noise generated inside. For this reason, not only the pop sound when the power is turned off but also the dark noise sound during the sound generation stop time is annoying.

  In view of the above problems, an object of the present invention is to provide an amplifier circuit that can reduce the generation of dark noise sound during the sound generation stop time, and a remote control device using the same.

The amplifier circuit according to claim 1 saturates the output voltage of the differential amplifier circuit by setting the potential difference to a predetermined value or more by amplifying the potential difference between the normal input terminal and the inverting input terminal. And an amplifier mute circuit for stopping the amplification operation.
According to another aspect of the present invention, the amplifier circuit includes a differential amplifier circuit that amplifies the potential difference between the non-inverting input terminal and the inverting input terminal, an AC signal is input to the non-inverting input terminal, and the inverting input terminal is grounded. In some cases, the differential amplifying circuit includes an amplifier mute circuit that amplifies a potential difference and masks an AC signal when the potential difference is set to a predetermined value or more.
According to the above configuration, since the amplifier mute circuit that saturates the output voltage and stops the amplification operation or the amplifier mute circuit that masks the input AC signal is provided, the annoying dark noise sound of the sound generation stop time is reduced. can do.

The amplifier circuit according to claim 2 is the amplifier circuit according to claim 1, wherein the differential amplifier circuit has an AC signal voltage applied to the normal input terminal, and the amplifier mute circuit has the inverting input terminal grounded. Sometimes, the amplification operation is performed, and the amplification operation is stopped when the absolute value of the potential applied to the inverting input terminal is shifted to a predetermined value or more.
According to the configuration, the amplification operation of the differential amplifier circuit can be easily stopped.

The amplifier circuit according to claim 3 is the amplifier circuit according to claim 1, wherein the differential amplifier circuit operates with a single power source, and an AC signal voltage to which a bias voltage is added is applied to the normal rotation input terminal. The amplifier mute circuit performs an amplification operation when the inverting input terminal is set near the bias voltage, and stops the amplification operation when the potential applied to the inverting input terminal is changed to a predetermined value or more. It is characterized by that.
According to the above configuration, in particular, if the bias voltage is set low, the inverting input terminal set in the vicinity of the bias voltage when the amplification operation is stopped, and the normal rotation input terminal to which the AC signal to which the bias voltage is added is applied. Is amplified. For this reason, the AC signal voltage is amplified. For example, the bias voltage is obtained by (input resistance × bias current).

The amplifier circuit according to claim 5 is characterized in that, when the potential difference is shifted to a predetermined value or more, the potential applied to the inverting input terminal gradually changes between the ground potential and the predetermined potential. .
According to the said structure, an unpleasant pop sound can be further removed.

The amplifier circuit according to claim 6 is characterized in that the potential applied to the inverting input terminal gradually changes between a ground potential and a predetermined potential based on a D / A conversion signal input from the outside. And
According to the said structure, it can set so that an electric potential may change gradually with a D / A conversion signal. As a result, since the D / A converter inside the CPU can be used, the number of parts used is reduced.

The amplifier circuit according to claim 7 is characterized in that the potential applied to the inverting input terminal gradually changes between a ground potential and a predetermined potential based on a predetermined time constant.
According to the said structure, it can set so that an electric potential may change gradually by changing resistance value and a capacitance.

A remote control device according to an eighth aspect is characterized in that the amplifier circuit according to any one of the first to seventh aspects is used for amplifying a sound whose sound generation time is shorter than the sound generation stop time.
According to the above configuration, since the dark noise sound during the sound generation stop time can be reduced and the pop sound can be removed, the quality of the remote control device is improved.

  The present invention includes an amplifier mute circuit that saturates the output voltage and stops the amplification operation, or an amplifier mute circuit that masks the input AC signal, thereby reducing annoying dark noise sound during the sound generation stop time. Can do. In particular, the invention according to claim 5 can remove an annoying pop sound.

(First embodiment)
FIG. 1 is a circuit diagram of an amplifier circuit 100 according to the first embodiment of the present invention. The amplifier circuit 100 includes a differential amplifier circuit 1 and an amplifier mute circuit 2 and drives a speaker SP connected to the outside. The differential amplifier circuit 1 includes a power amplifier IC, a resistor R11, capacitors C11 to C16, and an arbitrary element Z11.

The + IN terminal of the power amplifier IC is connected to a terminal 11 to which an AC signal S such as a buzzer sound or a synthesized voice that is to be generated from the speaker SP is input from the outside. The -IN terminal of the power amplifier IC is connected to the node a21 of the amplifier mute circuit 2.
The OUT terminal of the power amplifier IC is connected to the ground via a series circuit of a capacitor C13 and a resistor R11, and is connected to the ground via a series circuit of the capacitor C14 and an external speaker SP.
A parallel circuit of capacitors C15 and C16 is connected between the GND terminal and the V + terminal of the power amplifier IC, and the GND terminal of the power amplifier IC is connected to the ground. The V + terminal of the power amplifier IC is connected to a + 12V terminal for power supplied from outside via a resistor R1. The short-circuit terminal J1 is for short-circuiting the resistor R1.
A series circuit of an arbitrary element Z11 and a capacitor C11 is connected to both GAIN terminals of the power amplifier IC, and is a terminal for controlling the gain. The BYP terminal of the power amplifier IC is connected to the ground via the capacitor C12.

  For the power amplifier IC, the GAIN terminal is for gain control, the -IN terminal is for inverting input, the + IN terminal is for forward rotation input, the GND terminal is for grounding, and the OUT terminal is for output of the power amplifier The V + terminal is for power supply and the BYP terminal is for ripple removal.

For example, when NJM386B manufactured by New Japan Radio Co. is used for the power amplifier IC having a gain Av of 26 [db] (TYP) and the speaker SP having an impedance of 8Ω is used, the resistor R11 is 10Ω and the capacitor C11. Is 10 μF, capacitor C12 is 47 μF (electrolytic capacitor), capacitor C13 is 0.047 μF, capacitor C14 is 220 μF (electrolytic capacitor), capacitor C15 is 100 μF (electrolytic capacitor), and capacitor C16 is 0.1 μF.
An arbitrary value resistor or jumper wire is used for the arbitrary element Z11. Depending on the design value of the series circuit of the resistor (Z11) and the capacitor C11, the gain Av of the power amplifier IC can be set to any value from 20 times to 200 times.

Many audio power amplifier ICs having a mute function are expensive. NJM386B which does not have a mute function is low in price and is advantageous for cost reduction.
The NJM386B can perform a single power supply operation with a positive power supply voltage, the input terminal is configured to be compared with the ground, and the output voltage is automatically designed to be about ½ of the power supply voltage.

Next, the amplifier mute circuit 2 includes a transistor TR, resistors R21 to R26, and a capacitor C21. The base of the transistor TR is connected to the ground via a resistor R22, and further connected to a terminal 12 to which a control signal C is input from the outside via a resistor R21.
The emitter of the transistor TR is connected to the ground. The collector of the transistor TR is connected to the + 5V terminal for power supply via the resistor R23.
The node a21 is connected to the collector of the transistor TR via the resistor R24, connected to the + 5V terminal via the resistor R25, connected to the ground via the capacitor C21, and connected to the ground via the resistor 26. The

Next, the operation of the amplifier circuit 100 will be described.
An AC signal S is input to the + IN terminal of the power amplifier IC of the differential amplifier circuit 1. The peak value of the AC signal S is minute compared to the voltage of 5V.
The potential at the + IN terminal of the power amplifier IC has a predetermined bias voltage so that the AC signal S can be amplified without distortion. The bias voltage is set low.
The power amplifier IC amplifies the potential difference between the + IN terminal and the −IN terminal with a gain Av. The AC signal S is set to a value necessary for driving the speaker SP.

When the -IN terminal of the power amplifier IC is changed to the bias potential, the -IN terminal (inverted input terminal) set near the bias voltage when the amplification operation is stopped and the AC signal S to which the bias voltage is added are applied. The potential difference from the + IN terminal (normal input terminal) is set to be less than Vd. Vd is a value obtained by dividing the saturation voltage by the gain Av.
The power amplifier IC amplifies the AC signal S (AC signal voltage) with a gain Av and drives the speaker SP.

  The capacitor C14 cuts the direct current component of the output voltage from the power amplifier IC. Resistor R11 and capacitors C13, C15, and C16 prevent abnormal oscillation. The capacitor C12 removes a ripple of the power supply voltage supplied to the V + terminal of the power amplifier IC.

When the −IN terminal of the power amplifier IC is shifted to a predetermined positive potential or higher, the potential difference between the + IN terminal and the −IN terminal is set to Vd or higher.
Since the power amplifier IC amplifies Vd with the gain Av, the power amplifier IC outputs a saturated voltage saturated near the ground potential from the OUT terminal. In the path from the OUT terminal to the speaker, there is a capacitor C14 for cutting a direct current component. Only the AC voltage component is produced from the speaker.
The saturation voltage is a DC voltage near the power supply voltage + 12V or near the ground potential, and has no AC signal component. Since there is no sound from the speaker, the differential amplifier circuit 1 stops the amplification operation. In other words, the AC signal S is masked if the potential difference is set to Vd or more.

  FIG. 2 is a waveform diagram of the control signal C. The control signal C is a square wave composed of an L level of 0 [V] and an H level near the voltage + Ea [V]. The voltage + Ea [V] is set to a voltage higher than a value that can turn on the transistor TR. An external CPU changes the potential of the node a21 of the amplifier mute circuit 2 based on the control signal C.

When the control signal C is at the L level, the transistor TR is turned off, and a parallel resistance component composed of the resistor R25 and the series circuit of the resistors R23 and R24 is formed.
The potential of the node a21 gradually increases with a time constant T1 based on the capacitor C21, the resistor R26, and the parallel resistance. The time constant T1 is calculated by C21 · {R26 // (R25 // (R23 + R24))}. However, Rx // Ry indicates a parallel resistance value composed of Rx and Ry.
The potential of the node a21 is a voltage obtained by dividing the voltage + 5V by the resistance value of the parallel resistance and the resistor R26, and the −IN terminal of the power amplifier IC is transited to a predetermined positive potential or higher.

On the other hand, when the control signal C is at the H level, the transistor TR is turned on, and a parallel resistance component including the resistors R24 and R26 is formed.
The potential of the node a21 gradually decreases with a time constant T2 based on the capacitor C21 and the parallel resistance. The time constant T2 is calculated by C21 · {R26 // (R24 // (R23 + R25))}.
The potential of the node a21 becomes a bias potential, and the -IN terminal of the power amplifier IC is changed to the bias potential.

(Comparative example)
FIG. 3 is a schematic diagram of an amplifier circuit 500 of a comparative example. The amplifier circuit 500 of the comparative example includes a differential amplifier circuit 51 and a power supply control unit 52. The differential amplifier circuit 51 has the same circuit configuration as the differential amplifier circuit 1 (FIG. 1), and only the outline thereof is shown. The difference from the differential amplifier circuit 1 is that the -IN terminal of the power amplifier IC is connected to the ground instead of the node a21 of the amplifier mute circuit 2.
Based on the control signal C, the power controller 52 supplies or cuts off power to the V + terminal of the power amplifier IC of the differential amplifier circuit 51.

FIG. 4A is a waveform diagram of the voltage of the synthesized speech output from the amplifier circuit 500 of the comparative example. The horizontal axis of the scale is observed in the time range of 1 [s], and the vertical axis is observed in the range of 0.5 [v].
The amplifier circuit has a sound generation time H2 in which sound is generated from the speaker and a sound generation stop time in which there is no sound from the speaker. The sound generation stop time includes a start time H1 and an end time H3. The start time H1 is a predetermined time before the start of generation of synthesized speech, and the end time H3 is a predetermined time after the end of generation of synthesized speech.
A synthesized voice composed of a buzzer sound and a message voice is generated at the pronunciation time H2. At the start time H1 and the end time H3, a pop sound that sounds “buzz” is generated.
FIG. 4B is a waveform diagram of the voltage of the synthesized speech output from the amplifier circuit 100 according to the first embodiment. No pop sound is generated at the start time H1 and the end time H3.

(Second Embodiment)
FIG. 5 is a circuit diagram of the amplifier circuit 110 according to the second embodiment of the present invention. The amplifier circuit 110 includes a differential amplifier circuit 1 and an amplifier mute circuit 3. The difference from FIG. 1 is that an amplifier mute circuit 3 is used instead of the amplifier mute circuit 2. The amplifier mute circuit 3 includes resistors R31 and R32 and a capacitor C31, and uses fewer components than the amplifier mute circuit 2.
The terminal 13 to which the D / A conversion signal G is input from the outside is connected to the node a31 via the resistor R32, and is connected to the ground via the resistor R31. The node a31 is connected to the ground via the capacitor C31 and is connected to the −IN terminal of the power amplifier IC of the differential amplifier circuit 1.

  6A is a voltage waveform diagram of the D / A conversion signal G. FIG. An external CPU performs digital / analog conversion based on a program to generate a D / A conversion signal G. The D / A conversion signal G is a stepped waveform that intermittently changes in the range from 0 [V] to the voltage + Eb [V]. The voltage + Eb [V] is set to a value that allows the potential difference between the normal input terminal and the inverting input terminal of the power amplifier IC to be equal to or greater than Vd. An external CPU arbitrarily raises or lowers the potential of the node a31 of the amplifier mute circuit 3 (FIG. 5) based on the D / A conversion signal G.

FIG. 6B is a voltage waveform diagram of a signal on the node a31. The amplifier mute circuit 3 smoothes the waveform and converts the D / A conversion signal G into a signal on the node a31. Resistors R31 and R32 and capacitor C31 constitute a high-frequency cutoff filter.
The CPU program is designed so that the potential on the node a31 gradually increases at the start time H1 (FIG. 4), becomes constant near the voltage + Eb [V] at the sound generation time H2, and gradually decreases at the end time H3. Is done.

In the amplifier mute circuit 3, the potential of the node a31 transitions based on the D / A conversion signal G.
As in the first embodiment, if the potential difference between the + IN terminal and the −IN terminal of the power amplifier IC is equal to or greater than Vd, the differential amplifier circuit 1 stops the amplification operation. If it is less than Vd, the differential amplifier circuit 1 performs an amplification operation.

The D / A conversion signal G is input from an external CPU. By changing the CPU program, changes in the start time H1, the sound generation time H2, the end time H3, and the like can be arbitrarily and easily set.
Further, since the D / A converter inside the CPU can be used, the number of parts used is reduced, which is advantageous for cost reduction and size reduction.

(Example of use)
A remote controller for a water heater includes the amplifier circuit of the first embodiment or the second embodiment and a speaker. For example, the user operates the temperature setting button of the remote control device to change the temperature setting of the water heater. Immediately after that, a synthesized voice consisting of a beeping sound and a message sound of “The hot water temperature has been changed” is generated.
The user's operation is not frequently performed, and the sound generation time H2 is shorter than the sound generation stop time. The dark noise sound during the sound generation stop time is particularly disturbing.
The amplifier circuit of the first embodiment or the second embodiment reduces the dark noise sound during the sound generation stop time and removes the pop sound. As a result, the operability is improved and the user does not hear a harsh sound, and the quality of the remote control device is improved.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications such as the following are possible.
For the differential amplifier circuit, it is possible to use a power amplifier IC that operates with two power supplies using positive and negative power supply voltages. This is because if the absolute value of the potential difference between the non-inverting input terminal and the inverting input terminal is set to Vd or more, the differential amplifier circuit outputs a saturation voltage, and the amplification operation of the amplifier circuit can be stopped.
When the inverting input terminal of the differential amplifier circuit is changed to a predetermined positive potential, the saturation voltage is close to the negative power supply voltage. When the input voltage is changed to the predetermined negative potential, the saturation voltage is Near positive power supply voltage.

  In an external circuit not shown, an input resistor is connected between the terminal 11 (the + IN terminal of the power amplifier IC) and the ground. An input resistance value of 3 [kΩ] is recommended because of circuit design requirements. In this case, the bias voltage is obtained by input resistance value (3 [kΩ]) × bias current (100 [nA]).

1 is a circuit diagram of an amplifier circuit according to a first embodiment of the present invention. It is a waveform diagram of a control signal. It is the schematic of the amplifier circuit of a comparative example. FIG. 6 is a waveform diagram of synthesized speech output from the comparative example and the amplifier circuit according to the first embodiment. It is a circuit diagram of the amplifier circuit which concerns on 2nd Embodiment of this invention. It is a wave form diagram of a D / A conversion signal and a signal on a node.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 51 Differential amplifier circuit 2, 3 Amplifier mute circuit S AC signal C Control signal G D / A conversion signal 11, 12, 13 Terminal 52 Power supply control part 100, 110, 500 Amplifier circuit R1, R11, R21-R26, R31, R32 Resistor C11-C16, C21, C31 Capacitor TR Transistor IC Power amplifier J1 Jumper line SP Speaker H1 Start time H2 Sounding time H3 End time T1, T2 Time constant Ea, Eb Predetermined voltage Vd Predetermined potential difference

Claims (8)

A differential amplifier circuit that amplifies the potential difference between the normal input terminal and the inverting input terminal;
An amplifier circuit comprising: an amplifier mute circuit that stops the amplification operation by setting the potential difference to a predetermined value or more and saturating the output voltage of the differential amplifier circuit. In the differential amplifier circuit, an AC signal voltage is applied to the forward rotation input terminal,
The amplifier mute circuit performs the amplification operation when the inverting input terminal is grounded, and the amplification operation when the absolute value of the potential applied to the inverting input terminal is changed to a predetermined value or more. The amplifier circuit according to claim 1, wherein the amplifier circuit is stopped. The differential amplifier circuit operates with a single power source, and an AC signal voltage with a bias voltage added to the normal rotation input terminal is applied,
The amplifier mute circuit performs the amplification operation when the inverting input terminal is set in the vicinity of the bias voltage,
The amplifier circuit according to claim 1, wherein the amplification operation is stopped when a potential applied to the inverting input terminal is changed to a predetermined value or more. A differential amplifier circuit that amplifies the potential difference between the normal input terminal and the inverting input terminal;
When an AC signal is input to the normal input terminal and the inverting input terminal is grounded, the differential amplifier circuit amplifies the potential difference, and the potential difference is set to a predetermined value or more. An amplifier circuit comprising an amplifier mute circuit for masking a signal. When the potential difference is shifted to a predetermined value or more,
4. The amplifier circuit according to claim 2, wherein the potential applied to the inverting input terminal gradually changes between a ground potential and the predetermined potential. 5.   3. The potential applied to the inverting input terminal gradually changes between a ground potential and the predetermined potential based on a D / A conversion signal input from the outside. The amplifier circuit according to claim 3.   The potential applied to the inverting input terminal gradually changes between a ground potential and the potential of the predetermined value based on a predetermined time constant. Amplification circuit. The amplifier circuit according to any one of claims 1 to 7,
A remote control device characterized in that it is used to amplify sound whose pronunciation time is shorter than the pronunciation stop time.

Images