JPH0818366A - IC for audio - Google Patents

Abstract

(57) [Abstract] [Purpose] In an audio IC, it is used both as a capacitor for a low-frequency enhancement circuit and a capacitor for volume control. [Structure] Low-frequency boosting circuit 20 and level limiting circuit 30
And a level detection circuit 41. This detection circuit 4
Terminal T16 to which capacitor C5 for time constant 1 is connected
, The terminal T18 to which the switch S1 is connected, and the switch S2
A terminal T17 connected to each other, a switch element Q43, and a resistor R46 are provided. When switch S1 is operated,
The detection output of the detection circuit 41 controls the low-frequency enhancement circuit 20 to control the low-frequency level of the audio signals L and R output. When the switch S2 is operated, the level of the output audio signals L and R is controlled by controlling the level limiting circuit 30 by the detection output of the detection circuit 41, and the switch element Q43 is controlled to detect the detection output. Change the constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio IC suitable for use in headphone stereos and the like.

[0002]

2. Description of the Related Art In a so-called headphone stereo or the like, a powerful reproduced sound can be obtained by enhancing a low frequency range during reproduction. Therefore, some headphone stereos are provided with a low-frequency boost circuit.

On the other hand, when the headphone stereo is being listened to, if the volume is increased more than necessary, the user (listener) may not be able to hear the surrounding sound, or may annoy the surrounding people. Therefore, some headphone stereos are also provided with a volume limiting circuit.

FIG. 4 shows an example of a headphone stereo provided with such a low frequency band boosting circuit and a volume limiting circuit. In this figure, the portion surrounded by the chain line is a one-chip IC as the reproducing IC 10,
The mark indicates the external connection pin.

That is, at the time of reproduction, the left and right channel reproduction heads 1L and 1R reproduce the left and right channel audio signals L and R from the cassette tape (not shown), and the signals L and R are reproduced. Amplifiers 11L and 11R → adding circuits 12L and 12R → variable resistors R1 and R2 for volume adjustment → output amplifiers 14L and 14
Headphones (earphones) 2L through the R signal line,
It is supplied to 2R.

Reference numeral 20 designates a low frequency band boosting circuit. That is, in this example, the amplifier 21 is provided, the capacitor C1 is connected between the input terminal and the ground, and the resistor R21 and the capacitor C2 are connected between the output terminal and the ground.
And a series circuit of are connected to form a low-pass filter 22. The signals L and R from the equalizer amplifiers 11L and 11R are sent to the amplifier 21 through the resistors R11 and R12.
Is supplied to the low frequency component SLOW of the added signal (monaural signal) of the signals L and R, and the low frequency component SLOW is supplied to the addition circuits 12L and 12R.

Therefore, in the adder circuits 12L and 12R, the low-frequency component SLOW from the low-pass filter 22 is added to the audio signals L and R from the equalizer amplifiers 11L and 11R, so that the low-frequency components from the adder circuits 12L and 12R are low. Will be extracted.

However, in this case, the low-pass filter 22
Is connected to the output terminal of the variable resistance circuit 23, and the signals L and R from the amplifiers 14L and 14R are transferred to the resistor R13 and
It is supplied to the detection circuit (rectifier circuit) 24 through R14.
The detection circuit 24 includes a capacitor C3 for time constant (smoothing) and a switch S1 for on / off of low-frequency enhancement.
When the switch S1 is turned on, the voltage VDBB indicating the DC level of the added signal of the signals L and R is taken out from the detection circuit 24, and this detection voltage VDBB is supplied to the variable resistance circuit 23 as its control voltage. Supplied.

When the switch S1 is on,
The resistance value of the variable resistance circuit 23 is controlled by the detection voltage VDBB, and the low frequency component S supplied to the adder circuits 12L and 12R.
LOW level is controlled. Therefore, the adder circuit 12
The frequency characteristics of the audio signals L and R output from the L and 12R (low-frequency characteristics of the audio signals L and R) change corresponding to the levels of the signals L and R, for example, as shown by the solid line in FIG. . In this case, the capacitance of the capacitor C3 (time constant due to C3) is set to be short, and the response of the low-frequency enhancement processing is made relatively fast.

However, when the switch S1 is off,
The variable resistance circuit 23 is turned on, and the low-pass filter 22
The low frequency component SLOW from is not supplied to the adder circuits 12L and 12R. Therefore, the frequency characteristics of the audio signals L and R output from the adder circuits 12L and 12R become flat, for example, as indicated by the broken line in FIG.

Reference numeral 30 indicates a volume limiting circuit. That is, on the output side of the adder circuits 12L and 12R, the variable resistance circuits 13L and 13R are connected in parallel to the signal lines of the signals L and R, respectively. Furthermore, the amplifiers 14L and 14
Signals L and R from R are supplied to the detection circuit 31 through the signal lines of the resistors R3 and R4 → the switch S2 for turning on / off the volume limit → the capacitor C4. When the switch S2 is on, the detection circuit 31 outputs , The voltage VAVLS indicating the DC level of the added signal of the signals L and R is extracted, and this detection voltage VAVLS is supplied to the variable resistance circuits 13L and 13R as its control voltage. C5 is a capacitor for time constant.

Therefore, when the switch S2 is on, the variable resistance circuits 13L and 13R are driven by the detection voltage VAVLS.
Of the audio signals L and R supplied from the adder circuits 12L and 12R to the variable resistors R1 and R2 are limited to a predetermined level as shown by the solid line in FIG. That is, the AGC control is performed on the audio signals L and R to limit the volume. In this case, the capacitance of the capacitor C5 (time constant due to C5) is set to a relatively large value so that the change when the sound volume is reduced becomes gentle.

When the switch S2 is off, the variable resistance circuits 13L and 13R are off and the adder circuit 12
The audio signals L and R from L and 12R are supplied to the variable resistors R1 and R2 as they are, that is, the volume is not limited.

Further, when both the switches S1 and S2 are turned on, the signal level in the middle-high range is limited to the level shown by the solid line, as shown by the chain line in FIG. Will be increased to a level. The capacitor C4
Is for preventing the volume limitation from being performed more than necessary by the enhanced low frequency component when the low frequency enhancement and the volume limitation are turned on.

As described above, according to the headphone stereo of FIG. 4, the low frequency range can be enhanced during reproduction, and a powerful reproduced sound can be obtained. Further, it is possible to prevent the volume from becoming unnecessarily loud and inaudible to the surrounding sounds, or to avoid annoying the people around.

[0016]

However, the IC shown in FIG.
In 10, it is necessary to connect capacitors C3 and C5 to the detection circuits 24 and 31, respectively, which is not preferable for the IC.

The present invention has been conceived in view of the above points.
It is intended to omit the capacitor C3 in C10.

[0018]

Therefore, in the present invention, when the reference numerals of the respective parts are made to correspond to the embodiments described later, the low frequency component SLOW of the input audio signals L and R is low.
A low-frequency boosting circuit 20 for boosting and outputting, a level limiting circuit 30 for limiting the levels of the output audio signals L, R, and a detection circuit 41 for detecting the levels of the output audio signals L, R, A terminal T16 connected to the time constant capacitor C5 of the detection circuit 41, a terminal T18 connected to the first switch S1, a terminal T17 connected to the second switch S2, a switch element Q43, When the switch element Q43 is turned on, it has a resistor R46 connected in parallel with the capacitor C5, and when the first switch S1 is operated, the detection output of the detection circuit 41 causes
The low-frequency boosting circuit 20 is controlled to control the low-frequency level of the output audio signals L and R, and when the second switch S2 is operated, the level limiting circuit 30 is controlled by the detection output of the detection circuit 41. Output audio signals L and R are limited in level, and the switching element Q43
Is controlled to change the time constant of the detection output.

[0019]

The capacitor C5 acts as a capacitor for the time constant when forming the detection output for enhancing the low frequency range, and also as a capacitor for the time constant when forming the detection output for limiting the volume.

[0020]

[Embodiment] Also in FIG. 1, a portion surrounded by a chain line is a one-chip IC as the reproducing IC 10,
~ T25 indicates the external connection pin. And head 1
The signal system of the audio signals L and R from L and 1R to the headphone acoustic units 2L and 2R is configured as described above. In addition, the low-pass filter 2 of the low-frequency boosting circuit 20.
2 and the variable resistance circuit 23 are also configured as described above in this example, and the low-pass component SLOW from the low-pass filter 22 is supplied to the addition circuits 12L and 12R.

The IC 10 is provided with a detection circuit 41. This detection circuit 41 corresponds to the detection circuit 24 and the detection circuit 31 of FIG. 4, and a capacitor C5 having a relatively large capacity for the time constant is externally attached to the IC 10.

The audio signals L and R from the amplifiers 14L and 14R are supplied to the detection circuit 41 through the resistors R13 and R14, and the signals L and R from the amplifiers 14L and 14R are supplied to the resistors R3 and R4. And capacitor C4
Is also supplied to the detection circuit 41. In this way, the detection voltages VDBB and DAVLS are extracted from the detection circuit 41, the detection voltage VDBB is supplied to the variable resistance circuit 23 as its control voltage, and the detection voltage VAVLS is supplied to the variable resistance circuit 1.
It is supplied to 3L and 13R as its control voltage.

Further, the IC 10 is provided with a grounded-emitter transistor Q41, the collector of which is connected to the output terminal of the low-pass filter 22, and the base of which is connected to the resistor R.
41, R42 is pulled up and resistor R4
1, between the connection midpoint of R42 and the ground, low-frequency boost on
The switch S1 for turning off is connected.

Further, the IC 10 is provided with another emitter-grounded transistor Q42, Q43.
Is connected to the voltage line of the control voltage VAVLS from the detection circuit 41, the base is pulled up by the resistors R43 and R44, and the volume between the connection midpoint of the resistors R43 and R44 and the ground is increased. A switch S2 for turning on / off the limit is connected.

Further, the collector of the transistor Q43 is connected to the hot side of the capacitor C5 through the resistor R46, and its base is connected through the resistor R45 to the resistors R43 and R44.
It is connected to the connection midpoint of.

According to such a configuration, the resistors R13, R
Since the audio signals L and R are supplied to the detection circuit 41 by 14 and the resistors R3 and R4, the detection voltages VDBB to VAVLS are formed in the detection circuit 41.

The switch S1 is turned off and the switch S2 is turned on.
When is off, the bass boost and volume limit are not performed. That is, in this case, since the switch S1 is off, the transistor Q41 is on, and therefore, the low-frequency component SLOW from the low-pass filter 22 is bypassed and is not supplied to the adder circuits 12L and 12R. Not done

Further, since the switch S2 is off, the transistor Q42 is on, so that the detection voltage VAVLS from the detection circuit 41 is bypassed and the variable resistance circuit 1 is bypassed.
Since it is not supplied to 3L and 13R, the variable resistance circuit 13
L and 13R are turned off, and the audio signals L and R from the adder circuits 12L and 12R are directly variable resistors R1 and R1.
Supplied to R2. Therefore, the volume is not limited.

However, the switch S1 is turned on and the switch S2 is turned on.
When is off, the low frequency range is boosted and the volume is not limited. That is, in this case, since the switch S1 is on, the transistor Q41 is off, and therefore
Since the low-frequency component SLOW from the low-pass filter 22 is supplied to the adding circuits 12L and 12R, the adding circuits 12L and 1L
Low frequency enhancement of the audio signals L and R from 2R is performed.

At this time, since the resistance value of the variable resistance circuit 23 is controlled according to the detection voltage VDBB, the frequency characteristics of the audio signals L and R from the adder circuits 12L and 12R are shown by the solid line in FIG. 2, for example. Signal L,
It changes according to the level of R. Further, since the switch S2 is off, the transistor Q43 is on. Therefore, the resistor R46 is connected in parallel to the capacitor C5 through the transistor Q43, so that the detection voltage V
The time constant of DBB is short.

Further, at this time, since the switch S2 is off and the transistor Q42 is on, the sound volume is not limited as described above.

Further, the switch S1 is off and the switch S2 is
When is on, the low range is not boosted, but the volume is limited. That is, in this case, since the switch S1 is off and the transistor Q41 is on, as described above,
There is no low range enhancement.

However, at this time, since the switch S2 is on, the transistor Q42 is off, and therefore the detection voltage VAVLS from the detection circuit 41 is the variable resistance circuit 13.
Since the control signals are supplied to L and 13R, the levels of the audio signals L and R supplied from the adder circuits 12L and 12R to the variable resistors R1 and R2 are predetermined as shown by the solid lines in FIG. Limited to level. That is,
AGC control is performed on the audio signals L and R to limit the volume.

At this time, since the switch S2 is on and the transistor Q43 is off, the resistor R46 is no longer connected in parallel to the capacitor C5, and the time constant of the detection voltage VAVLS is long.

Further, the switch S1 is turned on and the switch S2 is turned on.
When is on, both low-frequency boosting and volume limiting are performed. That is, in this case, since the switch S1 is on and the transistor Q41 is off, the low frequency band enhancement is performed as described above. Further, since the switch S2 is on and the transistor Q42 is off, the sound volume is limited as described above. At this time, since the switch S2 is on and the transistor Q43 is off, the capacitor C5 is connected to the resistor R4.
Since 6 is no longer connected in parallel, the time constant of the detection voltage VAVLS is long. That is, the time constant is suitable for volume limitation.

[0036]

According to the present invention, the detection circuit 24 for enhancing the low frequency range and the detection circuit 31 for limiting the volume are made common, and the capacitor C3 of the detection circuit 24 and the detection circuit 3 are provided.
Since one capacitor C5 is shared, one capacitor C3 can be omitted, that is, the number of capacitors externally attached to the IC 10 can be reduced. Therefore, as a result, it is possible to reduce the cost of the headphone stereo, reduce the number of manufacturing steps, and improve the reliability. Moreover, the number of external connection pins of the IC 10 does not increase.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an example of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the circuits of FIGS. 1 and 4.

FIG. 3 is a characteristic diagram for explaining the operation of the circuits of FIGS. 1 and 4.

FIG. 4 is a connection diagram for explaining the present invention.

[Explanation of symbols]

 1L Playhead (for left channel) 1R Playhead (for right channel) 2L Headphone (for left channel) 2R Headphone (for right channel) 10 Playback IC 13L Variable resistance circuit (for left channel) 13R Variable resistance circuit (right channel) 20 Low-frequency booster circuit 22 Low-pass filter 23 Variable resistance circuit 30 Volume limiter circuit 41 Detection circuit C5 Time constant capacitor S1 switch (Low-frequency booster on / off) S2 switch (Volume limiter on / off)

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 21, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Therefore, when the switch S2 is turned on, the variable resistance circuits 13L and 13L are caused by the detection voltage VAVLS.
The resistance value of R is controlled, and the levels of the audio signals L and R supplied from the adder circuits 12L and 12R to the variable resistors R1 and R2 are limited to a predetermined level, for example, as shown by the solid line in FIG. . That is, the AGC control is performed on the audio signals L and R to limit the volume. In this case, the capacitance of the capacitor C5 (time constant due to C5) is set to a relatively large value, and the noise due to the amplitude change of the signals L and R is
The shaking phenomenon is reduced .

Claims (1)

[Claims] 1. A low-frequency enhancing circuit for enhancing and outputting a low-frequency component of an input audio signal, a level limiting circuit for limiting the level of the output audio signal, and a level of the output audio signal. A detection circuit for detecting the voltage, a terminal to which a time constant capacitor of the detection circuit is connected, a terminal to which the first switch is connected, a terminal to which the second switch is connected, and a switch element, And a resistor connected in parallel to the capacitor when the switch element is turned on. When the first switch is operated, the low-frequency boost circuit is controlled by the detection output of the detection circuit. Control the low frequency level of the output audio signal, and when the second switch is operated, the level limit circuit is controlled by the detection output of the detection circuit. And with limiting the level of the audio signal the output, the audio IC for controlling the switch elements so as to change the time constant of the detection output.