JP2001168658A - Sound output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in a low output power mode. SOLUTION: This circuit is provided with a noninverted amplifier 12 of a SEPP configuration to which a sound signal is supplied, an attenuating means 28 attenuating the output signal of the noninverted amplifier up to its input level, an inverted amplifier 14 of a SEPP configuration to which the output signal that is subjected to level adjustment by the attenuating means is supplied, a gain adjustment amplifier 30 connected to the preceding stage of the noninverted amplifier, a speaker 16 connected between the noninverted amplifier and an output of the inverted amplifier, a switching means 32 connected to the inverted amplifier side and a voltage detection circuit 34 detecting an input level to the gain adjustment amplifier. When the input level becomes below a prescribed level, the switching means is controlled by a voltage detection output so that the speaker can be driven only by the output of the noninverted amplifier. Thus, power consumption in a low output power mode (SEPP drive mode) can be reduced more drastically than in a BTL drive mode for which the noninverted amplifier and the inverted amplifier are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output circuit having a BTL configuration. Specifically, at low output, the load can be driven using only one amplifier of the BTL configuration, so that power consumption at low output can be reduced.

[0002]

2. Description of the Related Art In order to obtain a high output with a low power supply voltage, a BTL (Bridge Tied Load or Bala
There is known an output circuit having a non-transformerless configuration. In the BTL-structured audio output circuit, a speaker as a load is connected between the output of the non-inverting amplifier and the output of the inverting amplifier.
In this case, an amplitude twice as large as that described above can be obtained.

FIG. 3 shows a conventional example. As described above, the audio output circuit 10 includes the non-inverting amplifier 12, the inverting amplifier 14, and the speaker 16 as a load connected between the respective amplifier outputs.

The non-inverting amplifier 12 has an amplifier 22 whose non-inverting terminal (+) serves as an input terminal 26 to which an audio signal is supplied. A resistor Ra is connected to the inverting terminal (-), and the output signal of the amplifier 22 is fed back to the inverting terminal side via the resistor Rb. Operate.

On the other hand, the inverting amplifier 14 has an inverting terminal (-) of the amplifier 24 grounded via a resistor Rd.
The non-inverting terminal (+) is grounded. Then, the output signal Sb of the amplifier 24 is fed back to the inverting terminal via the resistor Re, so that the entire amplifier operates as an inverting amplifier as is well known.

The output signal Sa of the non-inverting amplifier 12 is supplied to an amplifier 2 constituting the non-inverting amplifier 14 through a resistance attenuating means (resistance dividing means) 28 using a resistor Rc and a resistor Rd.
4 non-inverting terminals. The resistance voltage dividing means 28 attenuates the voltage amplified by the amplifier 22 and
This allows the audio signal to be supplied to the inverting terminal side of the amplifier 24 at the same level as the input level.

A speaker 16 functioning as a load is connected between the output terminal Pa of the non-inverting amplifier 12 and the output terminal Pb of the inverting amplifier 14.

With this configuration, each of the amplifiers 22 and 24
4B, the output signal Sa obtained at the output terminal Pa is as shown in FIG. 4A, and the output signal Sb obtained at the output terminal Pb is as shown in FIG. 4B. Ideally double power supply voltage 2B
And the output power of the combined output signal So is four times as high. Therefore, a high-output audio output circuit with low power supply voltage driving can be realized.

[0009]

FIG. 2 is a characteristic diagram showing a relationship between the output power Po (watt) to the speaker 16 and the power consumption Pd (watt), and a curve La represents a curve of the BTL configuration shown in FIG. Is the case. As shown by the curve La, the output power Po is about 10 watts and the maximum power consumption Pd
(Approximately 10 watts), and as the output power Po decreases, the power consumption Pd also decreases. However, the output power P
Even if o becomes about 5 watts, the power consumption Pd does not decrease so much and is about 9 watts. At this level of output power, power consumption should be further reduced.

[0010] By the way, in order to effectively use limited resources, designs are being adopted to minimize energy consumption of products. In particular, when the New Energy Conservation Law is enforced, all products shipped after the year 2003 are subject to regulation under the New Energy Conservation Law.

Therefore, the above-mentioned audio output circuit which can be driven with a low power supply voltage is also applicable, but at present, such a BTL-structure audio output circuit has not taken sufficient measures to save power as described above. . It is necessary to design such that the power consumption is reduced because the audio output circuit having the BTL configuration can be used.

In view of the above, the present invention solves such a conventional problem, and proposes an audio output circuit in which sufficient power saving measures are taken.

[0013]

According to a first aspect of the present invention, there is provided an audio output circuit including a non-inverting amplifier having a SEPP configuration to which an audio signal is supplied and a non-inverting amplifier having the SEPP configuration. Attenuating means for attenuating the output signal to the input level thereof, an inverting amplifier having a SEPP configuration to which the output signal whose level has been adjusted by the attenuating means is supplied
A gain adjustment amplifier connected before the non-inverting amplifier, a load connected between the outputs of the non-inverting amplifier and the inverting amplifier, switching means connected to the inverting amplifier, The detection means for detecting the input level, and the switching means is controlled by the output of the detection means so that the load is driven only by the output of the non-inverting amplifier when the input level falls below a predetermined level. It is characterized by having been made.

According to the present invention, when the output power to the speaker, which is a load, falls below a predetermined value, the BTL drive mode is switched to drive by one non-inverting amplifier, that is, the SEPP drive mode, and the power consumption at that time is switched. Reduce.

[0015]

Next, an embodiment of an audio output circuit according to the present invention will be described in detail with reference to the drawings. According to the present invention, the power consumption at the time of low output can be reduced by switching to the mode (SEPP drive mode) of driving the speaker as a load by two amplifiers at the time of low output from the BTL drive mode at which the speaker is driven by two amplifiers. It was made.

FIG. 1 shows a case where the present invention is applied to an audio output circuit 10 having a two-channel configuration of L and R. Since the configurations of the L channel and the R channel are the same, only the configuration of one channel will be described.

In this embodiment, the audio output circuit 10
In order to obtain a high output with a low power supply voltage, an output circuit having a BTL configuration is used. The BTL audio output circuit includes a non-inverting amplifier 12, an inverting amplifier 14, and a speaker 1 as a load connected between the respective amplifier outputs.
6.

The non-inverting terminal (+) of the operational amplifier constituting the non-inverting amplifier 12 and the other amplifier 22 is an input terminal 26.
The audio signal is supplied here. The resistor Ra is connected to the inverting terminal (-), and the output signal of the amplifier 22 is fed back to the inverting terminal side via the resistor Rb, whereby the amplifier 12 operates as a non-inverting amplifier. The amplifier 22 is, as is well known, a SEPP (Single
An Ended Push Pull) amplifier is used.

On the other hand, the inverting amplifier 14 has an amplifier 24 of the SEP configuration, and its inverting terminal (-) is connected to the resistor Rd.
And the non-inverting terminal (+) is grounded. Then, the output signal Sb of the amplifier 24 is fed back to the inverting terminal side via the resistor Re, so that the amplifier 14 operates as an inverting amplifier.

The output signal Sa of the non-inverting amplifier 12 is supplied to the amplifier 2 constituting the non-inverting amplifier 14 via a resistance attenuating means (resistance dividing means) 26 using a resistor Rc and a resistor Rd.
4 non-inverting terminals. This resistance voltage dividing means 26 attenuates the voltage amplified by the amplifier 22 and
This allows the audio signal to be supplied to the inverting terminal side of the amplifier 24 at the same level as the input level. A speaker 16 as a load is connected between the output terminal Pa of the non-inverting amplifier 12 and the output terminal Pb of the inverting amplifier 14.

This embodiment further has the following configuration. Switching means 32 is provided between the output terminal Pb of the inverting amplifier 14 and the speaker 16, and is inverted in the BTL drive mode in which the two amplifiers, ie, the non-inverting amplifier 12 and the inverting amplifier 14 drive the speaker 16. Terminal a so that the amplifier 14 is connected to the speaker 16
And in a mode in which the speaker 16 is driven by only one amplifier, in this example, the non-inverting amplifier 12 (hereinafter referred to as a SEPP drive mode), the terminal b is switched to the ground.

Further, a gain adjusting amplifier 30 is connected to a path preceding the non-inverting amplifier 12 and to which an audio signal is supplied. The gain adjustment amplifier 30 is for switching the amplifier gain between the BTL drive mode and the SEPP drive mode. In the BTL drive mode, the input audio signal is output as a through signal (its gain is 0 dB).
In the EPP drive mode, the gain is adjusted so that the input audio signal is output with an increase of about 6 dB.

This is because when the mode is switched from the BTL drive mode to the SEPP drive mode, even if an audio signal of the same level is input, the level is reduced by 6 dB in principle, so that the same level is maintained even when the mode is switched. is there.

The audio signal supplied to the terminal 26 is supplied to a voltage detection circuit 34 for level detection together with the gain adjustment amplifier 30.
To detect the input level (voltage).
Detection output C when input level falls below reference level
The switching means 32 is controlled by TL to switch to the terminal b side, and to switch to the SEPP drive mode.

The voltage detection output CTL is further supplied to a gain adjustment amplifier 30 as a gain adjustment signal. When the voltage detection output CTL is obtained, that is, when control is performed in the SEPP drive mode, the output gain of the input audio signal is adjusted to increase by about 6 dB for the above-described reason.

In this embodiment, the voltage detection output CTL is further supplied to the inverting amplifier 14 as a power supply control signal. As a result, the power supply + B of the amplifier 24 is cut off in the SEPP drive mode, so that the power consumption of the inverting amplifier 14 can be reduced by disabling the amplifier 24. Of course, the amplifier 24 can be driven as it is. This is because if the amplifier 24 is in the driving state, it is not necessary to consider the rise of the amplifier 24 when the switching means 32 is switched.

The voltage detection output CTL is provided not only on the L channel side but also on the switching means 3 provided on the R channel side.
2. It is also supplied to the gain adjustment amplifier 30 and the amplifier 24 and is controlled in the same manner as the L channel. Therefore, in this embodiment, the audio signal on the R channel side is also supplied to the voltage detection circuit 34, and the voltage detection output CTL is obtained when the audio signal on either the L or R channel falls below the reference value. I have.

Although the voltage detection circuit 34 detects the level of the input audio signal, the voltage detection output CTL may be obtained separately from the signal from the manual terminal 36. That is, it is possible to forcibly switch to the SEPP drive mode by this manual signal.

Now, in this configuration, the relationship between the output power Po and the power consumption Pd when the loudspeaker 16 is driven by a single amplifier, that is, the non-inverting amplifier 12 by switching the switching means 32 is as shown by a curve Lb in FIG. become. Therefore, for example, comparing the power consumption Pd in the BTL drive mode when the output power Po is 5 watts with the power consumption Pd in the SEPP drive mode, the former is about 9 watts, while the latter is about 9 watts. It will be 4.5 watts. In other words, it can be seen that even with the same output power, the power consumption can be reduced by about half when in the SEPP drive mode than in the BTL drive mode.

Therefore, in this embodiment, when the output power drops to about 5 watts in the BTL drive mode, the power consumption is reduced by automatically switching from the BTL drive mode to the SEPP drive mode. It is.

Here, the impedance R of the speaker 16
When L is 8Ω and the output voltage of the terminals Pa and Pb is, for example, 8 volts, the output power Po becomes 8 watts.
When the gain of the amplifiers 22 and 24 is, for example, 20 dB, the input voltage to the amplifiers 22 and 24 is about 0.8 volt. According to this example, the output power Po is 5
At about watts, the input voltage to terminal 26 is about 0.6 volts.

Therefore, when the output power Po is 5 watts and is set to a reference value for switching from the BTL drive mode to the SEPP drive mode, the input voltage of the audio signal supplied to the terminal 26 at that time is about 0.6 volt. Becomes
Therefore, the level set value of the voltage detection circuit 34 is 0.6 volt. When the input voltage becomes 0.6 volt or less, a voltage detection output CTL is obtained. The gain of the gain adjustment amplifier 30 is increased by about 6 dB with the voltage detection output CTL, and at the same time, the switching means 32 is switched to the terminal b. The state transits to the SEPP drive mode. In addition, the power supply + B of the amplifier 24 is turned off.

In the embodiment described above, the present invention is applied to the audio output circuit having a two-channel configuration, but the number of channels is not limited. This is because the greater the number of channels, the more remarkable the power saving effect of the present invention.

In the embodiment shown in FIG.
2 is applied to the audio output circuit 10 configured to return to the input stage of the inverting amplifier 14, but the present invention can be applied to an audio output circuit of another type. That is, the audio signal of the positive phase and the negative phase is formed in advance by the preceding amplifier, and the audio signal of the positive phase is input to the non-inverting amplifier,
The present invention can also be applied to an audio output circuit having a BTL configuration in which a non-inverting audio signal is supplied to a non-inverting amplifier to drive a speaker.

Similarly, an audio signal is supplied to a non-inverting amplifier, and the audio signal is inverted in phase by an inverter, and then supplied to the non-inverting amplifier to drive a speaker to a BTL audio output circuit. This invention can also be applied to the present invention.

[0036]

As described above, according to the present invention, the BTL
In the audio output circuit having the configuration, the drive mode of the speaker as the load is changed from the BTL drive mode to the SE by the output power.
The mode is switched to the PP drive mode.

According to this, even with the same output power, B
Since the power consumption can be reduced by about half in the SEPP drive mode than in the TL drive mode, the power consumption can be reduced by switching the drive mode at a predetermined output power or lower to the SEPP drive mode. Can be significantly reduced.

Therefore, the audio output circuit according to the present invention is extremely suitable for application to an audio output system for driving a plurality of speakers on a plurality of channels.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment when an audio output circuit according to the present invention is applied to an audio output system having a two-channel configuration.

FIG. 2 is a characteristic diagram showing a relationship between output power and power consumption.

FIG. 3 is a connection diagram of a conventional audio output circuit.

FIG. 4 is a waveform chart for explaining the operation.

[Explanation of symbols]

10: audio output circuit, 12: non-inverting amplifier, 1
4 ... inverting amplifier, 16 ... speaker, 22, 24
... Amplifier, 30 ... Gain adjustment amplifier, 32 ...
.Switching means, 34 ... voltage detection circuit

Continued on the front page F-term (reference) 5J069 AA02 AA16 AA17 AA21 AA23 AA41 AA51 CA36 FA04 FA18 HA25 HA39 HA40 KA01 KA04 KA17 KA47 KA49 KA55 KA62 MA21 SA06 TA01 TA02 5J092 AA02 AA16 AA17 GRA HAA GRA KA01 KA04 KA17 KA47 KA49 KA55 KA62 MA21 SA06 TA01 TA02 VL01 VL02 VL06 VL08

Claims (6)

[Claims] 1. A non-inverting amplifier having a SEPP configuration to which an audio signal is supplied, attenuating means for attenuating an output signal of the non-inverting amplifier to its input level, and an output signal whose level has been adjusted by the attenuating means is supplied. An inverting amplifier having a SEPP configuration, a gain adjustment amplifier connected in front of the non-inverting amplifier, a load connected between the outputs of the non-inverting amplifier and the inverting amplifier, and a switching means connected to the inverting amplifier. Detecting means for detecting an input level to the gain adjustment amplifier; and, when the input level falls below a predetermined level, the load is driven only by the output of the non-inverting amplifier.
An audio output circuit, wherein the switching means is controlled by an output of the detection means. 2. The audio output circuit according to claim 1, wherein said load is a speaker. 3. The gain adjustment amplifier is controlled such that when the load is driven only by the non-inverting amplifier, the value of the gain adjustment amplifier is increased by a predetermined value. The audio output circuit according to claim 1. 4. The audio output circuit according to claim 1, wherein the inverting amplifier is controlled so as not to operate when the load is driven only by the non-inverting amplifier. 5. An apparatus according to claim 4, wherein said inverting amplifier is controlled by an output of said detecting means.
The described audio output circuit. 6. The audio output circuit according to claim 1, wherein said attenuating means comprises a resistive voltage dividing means.