JPH0794987A - Integrated circuit for sound output - Google Patents

Abstract

PURPOSE:To obtain a sound outputting integrated circuit capable of preventing the deterioration of a distortion ratio and the generation of a practical problem even at the time of using low power supply voltage by controlling the level of a sound line output so as not to exceed a prescribed level. CONSTITUTION:When a sound signal is inputted to the base of a transistor(TR) T9, its base potential is made higher than the base potential of a TR T8, the conductive quantity of the TR T9 is increased and that of the TR T8 is reduced. Since the ratio of currents flowing into TRs T6, T7 to currents flowing into the TRs T8, T9 are changed in accordance with the level of an AGC detection input to a differential pair 34, a difference between the collector currents of TRs T12, T13 is allowed to flow into a reference circuit 44 through a resistor R5, so that a sound line signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output integrated circuit, and more particularly to an audio output integrated circuit which is used, for example, in a VTR or the like and which performs a predetermined process on an audio signal and outputs it as an audio line output.

[0002]

2. Description of the Related Art In consumer high-fidelity VTRs, integration of ICs has progressed during recording / reproduction processing of high-fidelity audio signals, and circuits for input control signal processing, noise reduction, modulation / demodulation, and output signal processing are each constructed by a one-chip IC. It is supposed to be done. The number of these circuit elements has exceeded 6000, and the current consumption has increased significantly. Therefore, conventionally, the power consumption is reduced by operating with separate power supplies, such as 9 V or more for the input control signal processing, noise reduction, and output signal processing circuits and 5 V for the modulation / demodulation circuits. . This is also the limit of the package power, and it also generates a lot of heat.

On the other hand, when outputting the audio VTR hi-fi system, a reference output to front and rear -9 dB _S, the maximum output, in the state in which the strain rate was kept below 0.3% + 10DB _S
It is necessary to set, and to satisfy this, 9V
The above voltage is required. For this reason, in the conventional audio output integrated circuit 1 shown in FIG.
Is supplied with a voltage from a 5V power source 3, while an input switching circuit 4, a noise reduction circuit 5, an amplifier 6, and a switching circuit 7 are provided.
And the voltage was supplied from the 10V power supply 9 to the amplifier circuit section 8.

As a result, the audio signal output from the input switching circuit 4 or the modulation / demodulation circuit 2 is noise-removed by the noise reduction circuit 5, and then input to the amplification circuit section 8 via the amplifier 6 and the switching circuit 7. In the amplifier circuit section 8, the audio signal is amplified by the amplifier 8a or 8b and output as the L channel output or the R channel output, and is also mixed by the mixer 8c, and the mixed audio signal is given to the AGC amplifier 8d. AG
The C amplifier 8d outputs an audio signal amplified by a predetermined gain by the signal from the AGC detection circuit 8e, and this is output as an RF audio output via the amplifier 8f.

The configuration of the noise reduction circuit 5 is shown in FIG.
Shown in. The output signals of the input switching circuit 4 and the modulation / demodulation circuit 2 are input to the (+) input terminal of the operational amplifier 5b via the switch 5a, and the (-) input terminal of the operational amplifier 5b is output from the operational amplifier 5b via the switch 5c. CC
Output from A (Current Condrol Amp) 5d is given. The output signal from the operational amplifier 5b is given to the modulation / demodulation circuit 2 as an FM recording signal, the high frequency component is de-emphasized by the NR emphasis circuit 5e, and the high frequency component is weighted by the weighting circuit 5f. The audio signal output from the weighting circuit 5f is then rectified by the rectification circuit 5g, the rectified signal is converted into a current by the VI conversion circuit 5h, and the converted current is given to the CCA 5d. CCA5d
Has a characteristic as shown in FIG. 22, and the degree of amplification changes depending on the input current. The audio signal output from the NR emphasis 5e is amplified by the CCA 5d, the amplified audio signal is given to the switch 5c, and is output to the amplifier 6. The switches 5a and 5c are connected to the terminals C2 and C4 when the video tape is reproduced, and are connected to the terminals C1 and C3 except when the video tape is reproduced.

Therefore, when the audio signal output from the input switching circuit 4 is recorded, the operational amplifier 5b has a configuration shown in FIG.
When an audio signal including a plurality of frequencies as shown in (A) is input, the operational amplifier 5b outputs the signal shown in FIG. 23 (B). This signal is recorded on a video tape (not shown) as an FM recording signal, de-emphasized as shown in FIG. 23 (C) in the NR emphasis circuit 5e, and the weighting circuit 5f.
In FIG. 24, weighting is applied as shown in FIG. A current based on the signal shown in FIG. 24A is given to the CCA 5d as a control current, whereby the NR
The output signal from the emphasis circuit 5e is amplified as shown in FIG. The signal shown in FIG. 23B is output from the modulation / demodulation circuit 2 during reproduction, and the switch 5c is connected to the terminal C4 at this time, so that the operational amplifier 5b operates as a buffer and the operational amplifier 5b operates as shown in FIG.
The signal shown in (B) is output. Therefore, even during reproduction, the signal shown in FIG. 24 (B) is output from the CCA 5d. Incidentally, the hiss noise generated at the time of reproducing the tape is reduced when the signal shown in FIG. 23B output from the operational amplifier 5b is de-emphasized by the NR emphasis 5e.

On the other hand, when a voice signal is recorded, when a signal having a single frequency as shown in FIG. 25 (A) is applied from the input switching circuit 4 to the operational amplifier 5b, the operational amplifier 5b outputs the signal as shown in FIG. 25 (B). Signal is output to the modulation / demodulation circuit 2, the NR emphasis circuit 5e and the weighting circuit 5f. Then, the NR emphasis circuit 5e and the weighting circuit 5f respectively output the signals shown in FIGS. 25 (C) and 26 (A), and the CCA 5d outputs the signals shown in FIG. 26 (B). As can be seen from FIG. 26B, the level of the frequency signal subjected to de-emphasis and weighting is almost the same as the level of the frequency signal not subjected to de-emphasis and weighting, and for a single frequency signal, , NR emphasis circuit 5e and weighting circuit 5f may or may not be present.
The output from 5d has little effect. When reproducing the single frequency signal recorded on the tape, the signal shown in FIG. 25 (B) is output from the operational amplifier 5b in the same manner as described above, whereby the signal shown in FIG. 26 (B) is output from the CCA 5d. Is output.

FIG. 27 shows the L channel and R channel output characteristics with respect to the input to the input switching circuit 4 included in the audio output integrated circuit 1. From this, the maximum output voltage is 20
It can be seen that it is dB (11 dB _S ). On the other hand, the maximum output voltage characteristics with respect to the working voltage of the amplifiers 8a and 8b are shown in FIG. 28, and it can be seen that the maximum output voltage with respect to the power supply voltage of 10V is 11 dB _S. Therefore, the amplifier circuit section 8 operates sufficiently with the power supply voltage of 10V.

[0009]

However, such a conventional audio output integrated circuit 1 requires two kinds of power supply voltages, and has a large chip size so that the circuit element can withstand the voltage of 10V. There was a problem that it had to be converted. Therefore, a main object of the present invention is to provide an audio output integrated circuit which can lower the power supply voltage and can be miniaturized.

[0010]

According to a first aspect of the present invention, in an audio output integrated circuit which amplifies an audio signal and outputs it as an audio line output, the amplification degree is adjusted according to the output level of the audio line output. It is an integrated circuit for audio output characterized by the above. A second aspect of the present invention is an audio output integrated circuit which outputs, as an audio line output, an audio signal from which noise has been removed by the noise removing means, wherein the noise removing means removes the high frequency component of the recorded audio signal with the high frequency raised. A de-emphasis means for suppressing, a signal generating means for generating a control signal based on a recorded audio signal, a limiter for limiting a level of the control signal above a predetermined level, and a limiter for an audio signal in which a high frequency component is suppressed by the de-emphasis means. It is an integrated circuit for audio output, comprising an amplifying means for amplifying according to a control signal whose level is limited.

According to a third aspect of the present invention, a suppressing means for suppressing the level of the audio signal from which noise has been removed by the noise removing means according to the control signal, and a signal for generating a control signal based on the audio signal suppressed by the suppressing means. The generating means includes a limiter for limiting the level of the control signal above a predetermined level, and an amplifying means for amplifying the audio signal whose level is suppressed by the suppressing means according to the control signal whose level is restricted by the limiter. And an audio output integrated circuit for outputting the audio signal as an audio line output.

[0012]

According to the first invention, for example, the output of the AGC amplifier is detected by, for example, the AGC detection circuit, and the detected output is fed back to the AGC amplifier. As a result, the output level of the AGC amplifier is adjusted. Therefore, the audio line output does not exceed the predetermined level, and the distortion rate does not decrease even if the audio input level is high. On the other hand, the decrease in the dynamic range due to such level adjustment is about 10 dB, and there is no practical problem.

According to the second aspect of the present invention, the audio signal whose high frequency band is raised and recorded on the tape, for example, is suppressed in the high frequency band by the de-emphasis circuit, and the suppressed audio signal is input to, for example, the CCA. The high-frequency-raised audio signal is also input to, for example, a weighting circuit, where the high-frequency-increased audio signal is rectified by, for example, a rectifying circuit and then, for example, V-I.
It is converted into electric current by the conversion circuit. The current converted by the VI conversion circuit is given to the CCA as a control current through the limiter, and the amplification degree is determined by this. Therefore,
The amplification degree of CCA does not rise above a predetermined value, and the audio signal amplified by such CCA is output as an audio line output.

According to the third aspect of the invention, the noise-free audio signal is applied to, for example, the (+) terminal of the operational amplifier. The (−) terminal and the output terminal of the operational amplifier are connected via, for example, the first CCA, and thereby the audio signal output from the operational amplifier is suppressed in proportion to the amplification degree of the CCA. The audio signal output from the operational amplifier is rectified by, for example, a rectifying circuit, and the rectified audio signal is converted into a current by, for example, a VI conversion circuit. Then, the converted current determines the amplification degree of the first CCA. The audio signal output from the operational amplifier is also, for example, the second signal.
CCA, and amplified to a predetermined level. However, since the output current of the VI conversion circuit is input to the second CCA via the limiter, the amplification degree of the second CCA does not rise above a predetermined value, and the second CCA causes The amplified audio signal is output as an audio line output.

[0015]

According to the first aspect of the present invention, since the audio line output does not exceed a predetermined level, an audio output integrated circuit having sufficient characteristics can be obtained even at a constant power supply voltage such as 5V. According to the second and third aspects of the invention, the amplification degree of the amplification means never rises above a predetermined value.
For example, an audio output integrated circuit having sufficient characteristics can be obtained even at a constant power supply voltage such as 5V.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the detailed description of the following embodiments made with reference to the drawings.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an audio output integrated circuit 10 of this embodiment includes input switching circuits 12a and 12b. Of these, the low frequency audio signal for the L channel is input to the input switching circuit 12a from the tuner, line or external, and the low frequency audio signal for the R channel is input to the input switching circuit 12b from the tuner, line or external. The input is switched by this input switching circuit 12a or 12b. The audio signals respectively output from the input switching circuits 12a and 12b are then input to the amplifiers 16a and 16b via the noise reduction circuits 14a and 14b, and the high frequencies are raised by the noise reduction circuits 14a and 14b, and the modulation / demodulation circuit 18 And is recorded on a video tape (not shown) as an FM recording signal.

The FM recording signal reproduced from the video tape (not shown) is demodulated by the modulation / demodulation circuit 18,
Noise is removed by the noise reduction circuits 14a and 14b, and the noises are input to the amplifiers 16a and 16b. The audio signals amplified by the amplifiers 16a and 16b are input to the switching circuits 22a and 22b directly or after being mixed with the normal audio signals by the mixing circuits 20a and 20b. The normal voice signal is also directly input to the switching circuits 22a and 22b. The audio signals output from the switching circuits 22a and 22b are then input to the AGC amplifiers 26a and 26b included in the amplification circuit section 24a. Input switching circuits 12a and 12b, noise reduction circuits 14a and 14b, amplifiers 16a and 16b, demodulation circuit 1
8. Switching circuits 22a and 22b and amplifier circuit 24a
Is supplied with a power supply voltage of 5V from the 5V power supply 28.

The audio signals input to the AGC amplifiers 26a and 26b are amplified here, and the output is detected by the AGC detection circuit 30. Then, the detected output is fed back to the AGC amplifiers 26a and 26b, whereby the amplification degree of the AGC amplifiers 26a and 26b is adjusted. A capacitor C and a resistor R connected in parallel are externally attached to the AGC detection circuit 30. The outputs of the AGC amplifiers 26a and 26b are also added directly or by the adder 31 to obtain an amplifier 32a having an amplification degree of 5 dB,
It is output from 32b and 32c. The amplifier 32
L channel output from a and R from amplifier 32b
An audio signal is output as an F audio output and as an R channel output from the amplifier 32c.

The AGC amplifiers 26a and 26b have a circuit configuration as shown in FIG. That is, the AGC amplifiers 26a and 26b are connected to the differential pairs 34, 36 and 38.
including. Two transistors T1 whose emitters are connected to each other and are grounded via a constant current source 40 are connected to the differential pair 34.
And T2 are included and their respective collectors are connected through resistors R1 and R2. A resistor R3 is connected to the base of the transistor T1, and the output of the AGC detection circuit 30 is input to the base of the transistor T1 via the resistor R3 and directly to the base of the transistor T2. The resistors R1 and R2 are connected to the emitter of a transistor T3 whose collector and base are connected, and a bias voltage of 5 V is applied to the collector of the transistor T3.

The collector of the transistor T1 is a differential pair 3
6 is connected to the bases of the transistor T4 forming the differential pair 38 and the transistor T5 forming the differential pair 38, and the collector of the transistor T2 is connected to the bases of the transistor T6 forming the differential pair 36 and the transistor T7 forming the differential pair 38. Connected. The emitters of the transistors T4 and T6 are connected to the collector of the transistor T8 whose emitter is grounded via the constant current source 42. A reference signal is input from the reference circuit 44 to the base of the transistor T8. Also, transistors T5 and T
The emitter of 7 is connected to the collector of a transistor T9 whose emitter is grounded via a constant current source 46. The voice signal and the reference signal are input to the base of the transistor T9. The emitter of the transistor T8 and the emitter of the transistor T9 are connected via the resistor R4. Further, a bias voltage of 5V is directly supplied to the collectors of the transistors T4 and T5, and
The collectors of 6 and T7 each have a transistor T
A bias voltage of 5V is supplied via 10 and T11.

The base of the transistor T10 is connected to the base of the transistor T12 to which a bias voltage is supplied to the emitter, which constitutes a current mirror circuit 48. Further, the base of the transistor T11 is also the transistor T13 whose bias voltage is supplied to the emitter.
Of the current mirror circuit 50. The collectors of transistors T12 and T13 are connected to the collectors of transistors T14 and T15, respectively, which form current mirror circuit 52, and the emitters of transistors T14 and T15 are grounded. The collector of the transistor T15 is connected to the reference circuit 44 via the resistor R5. The amplified audio signal and the reference signal are transferred to the transistor T15.
It is output from the connection point (point A) between the collector of R and the resistor R5.

When the output of the AGC detection circuit 30 is applied to the differential pair 34, the potential at the point B becomes higher than the potential at the point C, so that the potential at the point D becomes higher than that at the point E. On the other hand, when the base input of the transistor T9 becomes larger than the reference signal, the conduction amount of the transistor T9 increases and the transistor T9 increases.
A part of the emitter current of 9 is supplied to the constant current source 4 via the resistor R4.
Flow to 2. This reduces the conduction amount of the transistor T8. Transistors T10 and T11 have D
A part of the collector current of the transistor T8 and a part of the collector current of the transistor T9 flow according to the potentials of the points E and E, and the transistors T10 and T1 respectively.
A current equal to the conduction amount of 1 flows through the transistors T12 and T13. On the other hand, transistors T14 and T
Since the conduction amount of 15 is the same, the difference between the emitter currents of the transistors T12 and T13 flows into the reference circuit 44 via the resistor R5. As a result, the audio signal and the reference signal are output as voltage from the point A.

Therefore, when the output level of the audio signal becomes high, the input from the AGC detection circuit 30 becomes high, and the difference between the potential at the point B or D and the potential at the point C or E becomes large. Therefore, the ratio of the current flowing through the transistors T6 and T7 becomes low, and the output level appearing at the point A decreases. On the other hand, when the output level of the audio signal decreases, the potential difference between the D point and the E point decreases, so that the output level appearing at the A point increases.

In operation, the L channel audio signal output from the input switching circuit 12a or the modulation / demodulation circuit 18 is
It is given to the switch 22a via the noise reduction circuit 14a and the amplifier 16a. Switch circuit 22a
In addition, a normal audio signal is directly applied to, and a signal in which the normal audio signal and the L channel audio signal are mixed is applied. The R channel audio signal is also applied to the switching circuit 22b in the same manner as described above, and the normal audio signal is also applied to the switching circuit 22b in the same manner as described above.
Given to. The audio signals output from the switching circuits 22a and 22b are then transferred to the AGC amplifiers 26a and 26b.
In b, the gain is controlled so that the output level becomes 0 dB _S or less.

Such AGC amplifiers 26a and 26
The audio signals amplified by b are respectively amplified by the amplifier 32.
The audio signals are supplied to a and 32c, and the respective audio signals are mixed and supplied to the amplifier 32b. Since the amplification degree of the amplifiers 32a to 32c is 5 dB, the maximum output voltage from these amplifiers 32a to 32c is 5 dB.
_{The S} audio signal is output as an L channel output, an RF audio output, and an R channel output, respectively. What should be noted is the maximum output voltage characteristic with respect to the power supply voltage of the amplifiers 32a to 32c shown in FIG. As you can see from Figure 3,
The maximum output voltage when the power supply voltage is 5V is 6 dB _S , but the maximum output voltage of the audio signal output from the amplifiers 32a to 32c is 5 dB _S as described above, so the amplifier circuit section 24a receives the 5 V power supply. There is no problem even if the voltage is supplied from 28.

In this way, the amplification levels of the AGC amplifiers 26a and 26b are adjusted according to the input level of the audio signal, so that the power supply voltage can be lowered to 5V and the chip size of the audio output integrated circuit 10 can be reduced. Can be downsized.
Referring to FIG. 4, an audio output integrated circuit 10 according to another embodiment.
Is the same as the audio output integrated circuit 10 shown in FIG. 1 except for the noise reduction circuits 14c and 14d and the amplifier circuit section 24b, and therefore only different points will be described.
A description of similar points will be omitted. Amplifier circuit section 24b
In, the audio signal output from the switching circuit 22a is amplified by the amplifier 32a and output as an L channel output. The audio signal output from the switching circuit 22b is amplified by the amplifier 32c and output as an R channel output. Further, the audio signals output from the switching circuits 22a and 22b are added by the adder 31, and the output from the adder is given to the AGC amplifier 26c. The amplification degree of the AGC amplifier 26c is the output of the AGC amplifier 26c.
The audio signal determined according to the detection signal obtained by the detection by the C detection circuit 30 and amplified according to this amplification degree is output as the RF audio output via the amplifier 32b. The AGC detection circuit 30 includes a capacitor C
And the resistor R is externally attached.

The noise reduction circuit 14c is constructed as shown in FIG. Since the noise reduction circuit 14d has the same configuration as the noise reduction circuit 14c, duplicated description will be omitted. Either the audio signal from the input switching circuit 12a or the audio signal from the modulation / demodulation circuit 18 is transmitted via the switch 54 to the operational amplifier 5
The audio signal output from the CCA 58 or the output of the operational amplifier 56 is applied to the (−) input terminal of the operational amplifier 56 via the switch 55. Then, the audio signal output from the operational amplifier 56 is applied to the modulation / demodulation circuit 18 as an FM recording signal, and also applied to the NR emphasis circuit 60 and the weighting circuit 62. In the weighting circuit 62, the high frequency part of the input audio signal is weighted, and the weighted audio signal is rectified by the rectification circuit 64. The rectified signal is then converted into a current by the VI conversion circuit 66, and the converted current is supplied to the CCA 68 as the control current I ₂ or I ₂ ′ directly or through the limiter 68 having a maximum output current of 100 μA. Given. In the NR emphasis circuit 60, the high frequency part of the input audio signal is de-emphasized, and the de-emphasized audio signal is C.
Input to CA68. Then, the input control current I
₂ and I ₂ ′, the audio signal is amplified according to the amplification degree determined by I ₂ ′, and the output signal from the CCA 68 is switched by the switch 55
Is supplied to the terminal C3 and is output to the amplifier 16a. That is, the audio signal amplified based on the control current I ₂ is applied to the terminal C3, and the audio signal amplified based on the control current I ₂ ′ is output to the amplifier 16a.

The CCA 58 is constructed as shown in FIG. That is, the CCA 58 includes amplifying circuit units 60, 62 and 64, and the output signal from the NR emphasis circuit 60 is given to the amplifying circuit unit 60 to control currents I ₂ and I _2.
2 'is provided to each amplification circuit 66a and 66b. Then, the output signal from the amplifier circuit section 66a is given to the operational amplifier 56, and the output signal from the amplifier circuit section 66b is output to the amplifier 16a. Amplifier circuit section 60
Includes transistors T1 and T2, and transistor T
The emitters of 1 and T2 are grounded via constant current sources 62 and 64. The emitters of transistors T1 and T2 are also connected via resistor R1. The collectors of the transistors T1 and T2 are connected to the 5V power supply via the transistors T3 and T4, the base of the transistor T1 is grounded via the resistor R2 and the capacitor C1, and the transistor T2 is grounded via the capacitor C1. The audio signal from the NR emphasis circuit 60 is given to the base of the transistor T1.

The amplifier circuit section 66a includes transistors T5a and T6a, and the emitters of the transistors T5a and T6a are grounded via a constant current source 68a which outputs the same current as the control current I ₂ from the VI converter 66. It
Further, the collectors of the transistors T5a and T6a are connected to the 5V power supply through the transistors T7a and T8a, and the bases of the transistors T5a and T6a are connected to the collector of the transistor T1 and the base of the transistor T6b included in the amplifier circuit section 66b. The transistors T7a and T8a are respectively the transistors T
Current mirror circuit 70a between 9a and T10a
And 72a to form transistors T9a and T1.
The collector of 0a is connected to the collectors of transistors T11a and T12a forming the current mirror circuit 74a. The emitters of the transistors T9a and T10a are connected to the 5V power source, and the emitters of the transistors T11a and T12a are grounded. Further, the collector of the transistor T12a is connected to the base of the transistor T2 via the resistor R3a, and the audio signal is output from the collector of the transistor T12a to the operational amplifier 56.

The amplifier circuit section 66b is connected to the constant current source 68b.
The control current I from the limiter 68 ₂′ Is given,
From the collector of the transistor T12b to the amplifier 16a
Except that the audio signal is output by the amplifier circuit unit 66a.
Since it is the same, change a in the reference number to b.
A duplicate description of and is omitted. The CCA 58 is shown in FIG.
Noise reduction of the conventional audio output integrated circuit 1 shown in FIG.
The difference from the CCA 5d included in the circuit 5 is the amplification circuit.
This is the point where the road portion 66b is added.

Next, the amplification degree of the CCA 58 will be described. When the amplification degree of the amplifier circuit unit 60 is A1, this amplification degree A1 is expressed by the equation 1.

[0033]

## EQU1 ## A1 = r _e1 / (2r _e1 + R1) Here, r _e1 is the emitter resistance of the transistors T1 and T2, and this emitter resistance r _e1 is represented by the expression 2 when the emitter current is I _1. .

[0034]

[Number 2] _{r e1 = (1 / I 1} ) · (KT / q) Thus, the amplification degree A1 is represented by the number 3.

[0035]

## EQU3 ## A1 = KT / (2r _e1 + R1) I ₁ q When the amplification degree of the amplifier circuit section 66a is A2, this amplification degree A2 is expressed by the following equation 4.

[0036]

## EQU4 ## A2 = R3a / r _e2 where r _e2 is the emitter resistance of the transistors T5a and T6a, and this emitter resistance r _e2 is expressed by the _expression 5.

[0037]

Equation 5] _{r e2 = (1 / I 2} ) · (KT / q) Thus, the amplification degree A2 is expressed by the number 6, tables in amplification degree A3 number 7 combined from the amplifier circuit 60 and 66a which To be done.

[0038]

[Equation 6] A2 = (I ₂ q / KT) · R3a

[0039]

A3 = A1 × A2 = R3aI ₂ / (2r _e1 + R1) I ₁ On the other hand, the amplification degree A obtained by combining the amplification circuit units 60 and 66b
3'is represented by the equation 8.

[0040]

A3 ′ = A1 × A2 ′ = R3bI ₂ ′ / (2r _e1 + R1) I _{1 From} Equations 7 and 8, it is understood that the amplification degree of the CCA 58 can be adjusted by the control currents I ₂ and I ₂ ′. Where I ₁ = 100 μA, R1 = 10 kΩ and R3a =
Amplification A3 for control current I ₂ when 12 kΩ
Is represented as in FIG. As the characteristics with respect to the control current I ₂ amplification degree A3 ', 100 microns to the control current I ₂
Since the limiter is applied at A, it reaches a peak when the amplification level rises to 0 dB.

The noise reduction circuit 14c shown in FIG.
Switches 54 and 55 included in the terminal C1
And (C3) to output the audio signal output from the input switching circuit 12a as an audio output and record it on a tape (not shown), the (+) of the operational amplifier 56.
When an audio signal containing a plurality of frequencies is applied to the input terminal as shown in FIG.
The signal shown in (B) is output. The audio signal in which the high frequency band is raised as compared to the low frequency band is supplied to the modulation / demodulation circuit 18 and the NR emphasis circuit 60 and the weighting circuit 62. Then, in the NR emphasis circuit 60, de-emphasis is applied to high frequencies as shown in FIG.
The output signal from is provided to CCA 58. On the other hand, in the weighting circuit 62, high frequency is weighted as shown in FIG. 9 (A), and the control current I ₂ is output from the VI conversion circuit 66 based on the audio signal weighted in this way. Rutotomoni control current control limiter 68 with respect to I ₂ has been applied current I ₂ 'is CC
Given to A58. Therefore, the CCA 58 outputs a signal as shown in FIG. 9B amplified based on the control current I ₂ to the operational amplifier 56, and
An audio signal as shown in FIG. 9C amplified based on the control current I ₂ 'is output to the amplifier 16a.

When reproducing the audio signal recorded on the tape as shown in FIG. 8B, the switches 54 and 55 are used.
Are connected to terminals C2 and C4, respectively, and the output signal from the modulation / demodulation circuit 18 is directly output from the operational amplifier 56. Then, hiss noise generated during reproduction is reduced by the NR emphasis circuit 60, and the noise-reduced audio signal is amplified by the CCA 58 based on the control current I ₂ ′ and output to the amplifier 16a.

FIG. 10 shows the FM recording signal characteristics for the audio signals applied to the input switching circuits 12a and 12b and the L channel and R channel output characteristics for the inputs to the input switching circuits 12a and 12b. Straight line a in FIG.
Is the FM recording signal characteristic, and it can be seen that the signal is compressed to 1/2 of the input signal. Further, the straight line b represents the characteristics of the L channel and R channel output signals. The FM recording signal is expanded by the CCA 58 in the region where the input signal is negative, and has the same slope as the FM recording signal in the region where the input signal is positive. You can see that the signal is being output. This is because when the input signal becomes 0 dB, the VI conversion circuit 6
Limiter is applied to the output signal from 6 and CCA58
This is because the extension of the amplification degree is stopped when the amplification degree becomes 0 dB. As can be seen from this characteristic, the maximum output voltage is 10 dB (2 dB _S ). On the other hand, the maximum output voltage characteristic with respect to the working voltage of the amplifiers 32a and 32c is shown in FIG.
The maximum output voltage for a power supply voltage of 5 V is 5.5 dB _S. Therefore, the amplifier circuit section 24b
There is no problem even if a voltage is supplied from the 5V power source 28.

In this way, the noise reduction circuit 14c
C according to the output level from the operational amplifier 56 included in
Since the amplification degree of the CA 58 is adjusted, the power supply voltage can be lowered to 5 V, and the chip size of the audio output integrated circuit can be reduced. However, in the audio output integrated circuit 10 shown in FIG. 4, the (+) input terminal of the operational amplifier 56 included in the noise reduction circuit 14c is connected to the (+) input terminal of FIG.
Input a single frequency signal as shown in
Therefore, there is a problem that the level is lowered in the high frequency range of the audio signal output from the amplifier 16a. That is, when a single frequency signal as shown in FIG. 12A is input to the (+) input terminal of the operational amplifier 56, the operational amplifier 56 outputs a signal as shown in FIG.
This is given to the NR emphasis circuit 60 and the weighting circuit 62. As a result, the NR emphasis circuit 60 outputs a signal as shown in FIG. 12 (C), and the weighting circuit 62 outputs a signal as shown in FIG. 13 (A). As the control current of CCA58,
The output signal from the weighting circuit 62 is rectified to V-
Given the current I ₂ 'multiplied by the limiter current I ₂ and the current I ₂ and I conversion. Then, the signal shown in FIG. 13B obtained by amplifying the output signal from the NR emphasis circuit 60 based on the control current I ₂ is (−) of the operational amplifier 56.
FIG. 13 (C) in which the output from the NR emphasis circuit 60 is amplified based on the control current I ₂ ′ given to the input terminal.
The audio signal shown in is output to the amplifier 16a.
As can be seen from the signal shown in FIG.
Regarding the audio signal for a, the effect of the weighting circuit 62 cannot be obtained in the high frequency region due to the limiter 68,
The output level will drop. FIG. 14 shows an audio output integrated circuit 10 for solving such a problem.

Referring to FIG. 14, an audio output integrated circuit 10 of another embodiment is similar to FIG. 2 except for the amplifier circuit section 24c.
Since the configuration is similar to that of the conventional audio output integrated circuit 10 shown in FIG. 0, only different points will be described, and description of the same points will be omitted. The audio signal output from the switching circuit 22a is applied to the (+) input terminal of the operational amplifier 76a, and C is applied to the (-) input terminal of the operational amplifier 76a.
The audio signal output from CA 78a is given. The audio signal output from the operational amplifier 76a is CCA78a.
In addition, the signal given to the rectifying circuit 80a and rectified by the rectifying circuit 80a is converted into a current by the VI converting circuit 82a. Then, the VI conversion circuit 82a
The current output from the CCA 78 is the control current I ₃ .
a, which determines the amplification of CCA 78a. The audio signal output from the operational amplifier 76a is also input to the CCA 84a and amplified to a predetermined level by the control current I ₃ ′ obtained by limiting the control current I ₃ output from the V-I conversion circuit 82a by the limiter 86a. To be done. The audio signal output from the CCA 84a is further amplified by the amplifier 88a and then output as an L channel output. The processing from when the audio signal output from the switching circuit 22b is input to the (+) input terminal of the operational amplifier 76b to when it is amplified by the amplifier 88b and output as the R channel output is performed by the operational amplifier 76a described above.
Since it is the same as the processing from the input to the output to the output as the L channel, duplicate description will be omitted by changing the reference number from a to b.

The audio signal output from the CCA 84a and the audio signal output from the CCA 84b are also added by the adder 90, and the AGC amplifier 92 adds the AGC detection circuit 9 to each other.
Amplification is performed based on the detection signal from 4. And AG
The audio signal output from the C amplifier 92 is supplied to the AGC detection circuit 94, amplified by the amplifier 88c, and output as an RF audio output.

The structure of the CCA 78a is shown in FIG. Note that CCA78b, 84a and 84b are also CCA78a.
Is constructed in the same way as. However, CCA 84a and 84
For b, the constant current source 68a is supplied with the current I ₃ ′ output from the limiters 86a and 86b. Figure 15
CCA 78a is referred to as amplifier circuit section 96 and 98.
However, each of the amplifier circuit sections 96 and 98 includes
The amplifier circuit units 60 and 66a shown in FIG. 6 have the same configuration, and the characteristics of the amplification degree A4 with respect to the current I ₃ are the same as those in FIG. 7, and therefore the same reference numerals are given and detailed description thereof is omitted. By the way, the amplification degree A4 of CCA78a and 78b
Is represented by Equation 9, and the amplification degree A of CCA 84a and 84b is
4'is represented by the expression 10.

[0048]

## EQU9 ## A4 = R3aI ₃ / (2r _e1 + R1) I ₁

[0049]

## EQU10 ## A4 '= R3aI₃′ / (2r_e1+ R1) I₁ In operation, from the switching circuit 22a to the operational amplifier 76a
A voice as shown in FIG. 16A for the (+) input terminal
When a signal is input, the operational amplifier 76a outputs the signal shown in FIG.
An audio signal whose level is suppressed is output as shown in (B).
To be done. The output of this operational amplifier 76a is a rectifier circuit.
The signal rectified by 80a and the rectified signal is the VI conversion circuit 8
Control current I at 2a₃Is converted to. Then converted
Control current I ₃Is limited by the limiter 86a,
Control current I output from the limiter 86a₃By '
The amplification degree of the CCA 84a is determined. From operational amplifier 76a
The output audio signal is CCA84 according to this amplification degree.
sound from CCA 84a amplified by a.
A voice signal is output. And the output of CCA84a is
It is further amplified by the output 88a and output as L channel output.
To be done. On the other hand, the switching circuit 22a to the operational amplifier 76a
The single frequency shown in FIG. 17A for the (+) input terminal
When a signal is input, the operational amplifier 76a outputs the signal shown in FIG.
The signal shown in (B) is output, and further, from the CCA 84a.
Outputs the signal shown in FIG.

FIG. 18 shows L channel and R channel output characteristics with respect to inputs to the (+) input terminals of the operational amplifiers 76a and 76b. It can be seen that the straight line a is the output signal characteristic of the operational amplifier 76a and is compressed to 1/2 of the input signal. A straight line b represents the output signal characteristics of the amplifiers 88a and 88b, and the output signals of the operational amplifiers 76a and 76b are C when the input signal is negative.
Although expanded by the CAs 84a and 84b, it can be seen that the output signals of the operational amplifiers 76a and 76b are output as they are in the region where the input signal is positive. This is because the output signals from the V-I conversion circuits 82a and 82b are limited when the input signal becomes 0 dB, and the CCA8
This is because the extension of the amplification level stops when the amplification levels of 4a and 84b reach 0 dB.

FIG. 19 shows the maximum output voltage characteristic with respect to the working voltage of the amplifiers 88a and 88b. As can be seen from FIG. 19, the maximum output voltage for the power supply voltage of 5V is +
It becomes 5.5 dB _S. On the other hand, as can be seen from FIG.
Since the maximum output voltage of the amplifiers 88a and 88b is 2 dB _S , there is no problem even if the voltage from the 5V power supply 28 is supplied to the amplifier circuit section 24c.

Thus, the operational amplifiers 76a and 76 are
CCA 84a and 84b depending on the output level from b
Since the amplification degree is adjusted, the power supply voltage can be lowered to 5 V, and the chip size of the audio output integrated circuit can be reduced. Further, since the waiting circuit and the NR emphasis circuit are not provided in the next stage of the operational amplifiers 76a and 76b, as can be seen from FIG. 17C,
The level does not drop in the high frequency part of the single frequency signal. Further, since the audio signal is processed in the subsequent stage of the switching circuits 22a and 22b, the above-described processing can be performed on the normal audio signal input from the terminal 94.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a part of the embodiment shown in FIG.

FIG. 3 is a graph showing a maximum output voltage characteristic with respect to an amplifier use voltage.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing a part of the embodiment shown in FIG. 4;

FIG. 6 is a circuit diagram showing another part of the embodiment shown in FIG. 4;

FIG. 7 is a graph showing a part of the operation of the embodiment in FIG. 4;

8A is a graph showing the (+) terminal input of the operational amplifier, FIG. 8B is a graph showing the operational amplifier output, and FIG. 8C is a waveform diagram showing the output of the NR emphasis circuit.

9A is a waveform diagram showing the output of the weighting circuit, and FIGS. 9B and 9C are waveform diagrams showing the output of CCA.

FIG. 10 is a graph showing a part of the operation of FIG. 4 embodiment.

FIG. 11 is a graph showing a part of the operation of the example in FIG. 4;

12A is a graph showing an (+) terminal input of an operational amplifier, FIG. 12B is a graph showing an operational amplifier output, and FIG. 12C is a waveform diagram showing an output of an NR emphasis circuit.

FIG. 13A is a waveform diagram showing the output of the weighting circuit, and FIGS. 13B and 13C are waveform diagrams showing the output of the CCA.

FIG. 14 is a block diagram showing another embodiment of the present invention.

FIG. 15 is a circuit diagram showing part of the embodiment shown in FIG. 14;

16A is a waveform diagram showing an operational amplifier (+) terminal input, FIG. 16B is a waveform diagram showing an operational amplifier output, and FIG. 16C is a waveform diagram showing a CCA output.

17 (A) is a waveform diagram showing an operational amplifier (+) terminal input, FIG. 17 (B) is a waveform diagram showing an operational amplifier output, and FIG. 17 (C) is a waveform diagram showing a CCA output.

FIG. 18 is a graph showing a part of the operation of the example in FIG. 14;

FIG. 19 is a graph showing a part of the operation of the embodiment in FIG.

FIG. 20 is a block diagram showing a conventional technique.

FIG. 21 is a block diagram showing a part of the conventional technique.

FIG. 22 is a graph showing a part of the operation of the conventional technique.

23A is a waveform diagram showing an operational amplifier (+) terminal input, FIG. 23B is a waveform diagram showing an operational amplifier output, and FIG. 23C is a waveform diagram showing an NR emphasis output.

FIG. 24A is a waveform diagram showing the output of the weighting circuit, and FIG. 24B is a waveform diagram showing the CCA output.

25A is a waveform diagram showing an operational amplifier (+) terminal input, FIG. 25B is a waveform diagram showing an operational amplifier output, and FIG. 25C is a waveform diagram showing an NR emphasis output.

FIG. 26 (A) is a waveform diagram showing the output of the weighting circuit, and FIG. 26 (B) is a waveform diagram showing the CCA output.

27A is a graph showing characteristics of a noise reduction circuit during recording, and FIG. 27B is a graph showing characteristics of a noise reduction circuit during reproduction.

FIG. 28 is a graph showing a maximum output voltage characteristic with respect to an amplifier use voltage.

[Explanation of symbols]

10 ... Voice output integrated circuits 26a, 26b, 26c,
92 ... AGC amplifier 30, 94 ... AGC detection circuit 60 ... NR emphasis circuit 62 ... Waiting circuit 68, 86a, 86b ... Limiter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H03G 7/04 9067-5J 11/00 B 9067-5J

Claims (4)

[Claims] 1. An audio output integrated circuit for amplifying an audio signal and outputting it as an audio line output, wherein an amplification degree is adjusted according to an output level of the audio line output. Integrated circuit. 2. An audio output integrated circuit for outputting an audio signal from which noise is removed by a noise removing means as an audio line output, wherein the noise removing means outputs a high frequency component of a recorded audio signal whose high frequency band is raised. De-emphasis means for suppressing, signal generating means for generating a control signal based on the recorded audio signal, limiter for limiting a level of the control signal above a predetermined level, and audio signal in which a high frequency component is suppressed by the de-emphasis means. An audio output integrated circuit comprising: an amplifying means for amplifying the signal according to a control signal whose level is limited by the limiter. 3. A suppressing means for suppressing the level of a voice signal from which noise has been removed by a noise removing means according to a control signal, and a signal generating means for generating the control signal based on the voice signal suppressed by the suppressing means. A limiter for limiting a level of the control signal equal to or higher than a predetermined level, and an amplifying means for amplifying an audio signal of which level is suppressed by the suppressing means according to the control signal of which level is restricted by the limiter. An integrated circuit for audio output that outputs the amplified audio signal as an audio line output. 4. The signal generating means, weighting means for weighting high frequency components of the recorded audio signal, rectifying means for rectifying the audio signal weighted by the weighting means, and the signal rectified by the rectifying means. 3. The limiter limits the current, and the amplifying unit amplifies the audio signal in which the high frequency component is suppressed according to the current limited by the limiter. Alternatively, the integrated circuit for audio output according to the item 3.