JP2001185959A - Low-frequency amplifying circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve low-frequency characteristics by omitting coupling capacitance, to prevent pop noise from being generated, and to eliminate the adverse effect of variation in automobile battery voltage. SOLUTION: A source voltage supplied to a front-stage part and a driver circuit of a power amplifying integrated circuit is made to be a common source voltage supplied from a stabilized power source. Consequently, the DC bias voltage VA on the output side of the front-stage part and the DC bias voltage VB on the input side of the power amplifying integrated circuit have nearly the same potential. Consequently, the front-stage part and power amplifying integrated circuit can be connected directly to each other, low-frequency characteristics can be improved, and pop noise is prevented from being generated. The driver circuit of the power amplifying integrated circuit is supplied with the source voltage from the stabilized power source, so the adverse effect of variation in automobile battery voltage on the power amplifying integrated circuit can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated low-frequency amplifier circuit used for car audio such as a car stereo and for amplifying an audio signal.

[0002]

2. Description of the Related Art Conventionally, a low-frequency amplifier circuit of this type is constructed as shown in FIG. An audio signal output from the output terminal 11 of the former unit 1 configured by an electronic volume integrated circuit or the like is input to the input terminal 21 of the power amplification integrated circuit (power amplification unit) 2 via the coupling capacitor C,
After the power is amplified by the power amplification integrated circuit 2, the power is output from a speaker (not shown).

Normally, a power supply voltage Vcc1 (for example, 8 to 9 V) is supplied from a stabilized power supply to the former stage 1 and a power supply voltage Vcc2 (for example, 13.2 to 14) from an unshown vehicle battery is supplied to the power amplification integrated circuit 2. .4V) is supplied.

[0004]

In the low frequency amplifier circuit as described above, the DC bias voltage VA on the output side of the former stage 1 is used.
(Vcc1 / 2) and the DC bias voltage VB (Vcc2 / 2) on the input side of the power amplification integrated circuit 2 are different from the power supply voltage Vcc2 supplied to the power amplification integrated circuit 2 and the power supply voltage Vcc1 supplied to the preceding stage 1. As a result, they were not at the same potential.

As a result, a coupling capacitor C is required between the input stage of the power amplification integrated circuit 2 and the former stage 2, and this capacitance C deteriorates the low frequency characteristics and shortens the charging / discharging time. The necessity causes a problem that pop noise occurs when the power is turned on or off.

The power amplifier integrated circuit 2 operates on the power supply voltage Vcc2 supplied from the vehicle battery.
There are also problems such as an adverse effect due to a change in vehicle battery voltage (10 to 16 V) that occurs when an anti-lock brake is applied, that is, an output audio signal is distorted or an element having a high withstand voltage must be used. In particular, when the charger of the car comes off, the voltage instantaneously rises to about 50 V, so that a protection circuit and the like are required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to omit the coupling capacitance, improve the low frequency characteristics, and generate pop noise. It is an object of the present invention to provide a low frequency amplifying circuit which can prevent the occurrence of noise and can eliminate the adverse effect due to the fluctuation of the battery voltage of the vehicle.

[0008]

In order to achieve the above-mentioned object, a feature of the present invention is that an integrated front part,
A low-frequency amplifier circuit having an integrated power amplifier for inputting and amplifying the power of the output signal of the former stage, wherein a DC bias voltage on the output side of the former stage and a DC bias voltage on the input side of the power amplifier are provided. In other words, there is provided a bias adjusting means for setting the voltage to the same potential.

According to the first aspect of the present invention, since the DC bias voltage on the output side of the preceding stage and the DC bias voltage on the input side of the power amplifying unit have the same potential, the output side of the preceding stage and the DC bias voltage on the input side of the preceding stage are equal. The input side of the power amplifier is directly connected.

The bias adjusting means according to the second aspect of the present invention makes the power supply voltage for driving the pre-stage unit coincide with the power supply voltage for driving the driver circuit of the power amplification unit.

A feature of the invention according to claim 3 is that a power supply voltage for driving the pre-stage and a power supply voltage for driving the driver circuit of the power amplifier are supplied from a common stabilized power supply.

According to a fourth aspect of the present invention, the bias adjusting means sends a reference voltage generated from a constant voltage source for generating a DC bias voltage of the preceding stage to the power amplifier, and the power amplifier receives power. A DC bias voltage on the input side of the driver circuit is generated from the reference voltage thus obtained, and the DC bias voltage on the output side of the preceding stage and the DC bias voltage on the input side of the power amplifier are set to the same potential.

The low-frequency amplifier circuit according to the invention of claim 5 is used in car audio.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the low-frequency amplifier circuit of the present invention. It has a pre-stage unit 1 composed of an electronic volume integrated circuit and the like, and a power amplification integrated circuit (power amplification unit) 2 for power-amplifying an audio signal input from the pre-stage unit 1, and has an output terminal 11 of the pre-stage unit 1 and a power amplification unit. The input terminal 21 of the integrated circuit 2 is directly connected.

The power amplifying integrated circuit 2 is composed of a power amplifying circuit comprising a driver circuit 22 and a push-pull circuit of transistors T1 and T2. Vcc1 is supplied from a stabilized power supply (not shown) to the former stage 1, The power supply voltage Vcc1 is supplied to the driver circuit 22 of the amplification integrated circuit 2 via the power supply terminal 23, and the power supply voltage Vcc2 from the vehicle battery (not shown) is supplied to the power amplification circuit of the power amplification integrated circuit 2. ing.

Next, the operation of this embodiment will be described. An audio signal output from the output terminal 11 of the former section 1 composed of an electronic volume integrated circuit or the like is input to an input terminal 21 and is power-amplified by the power amplification integrated circuit 2 and then to a speaker (not shown). Output from

Here, the DC bias voltage VA on the output side of the pre-stage unit 1 becomes Vcc1 / 2, and the DC bias voltage VB on the input side of the power amplification integrated circuit 2, ie, the driver circuit 2
2, the input DC bias voltage VB also becomes Vcc1 / 2, so that the DC bias voltage VA on the output side of the pre-stage unit 1 and the DC bias voltage VB on the input side of the power amplification integrated circuit 2 are VA =
The potential becomes the same at VB.

As a result, since there is no DC potential difference between the output terminal 11 of the former stage 1 and the input terminal 21 of the power amplifier integrated circuit 2, the output terminal 11 of the former stage 1 and the input terminal of the power amplifier integrated circuit 2 The terminal 21 is directly connected without any coupling capacitance.

According to the present embodiment, since the output side of the pre-stage unit 1 and the input side of the power amplifier integrated circuit 2 are directly connected and the coupling capacitance is omitted, the low-frequency characteristics can be improved and the power supply can be improved. It is possible to prevent pop noise from being generated at the time of ON or OFF.

The driver circuit 2 of the power amplifier integrated circuit 2
Since the power supply voltage Vcc1 is supplied from the stabilized power supply to the driver circuit 2, the driver circuit 22 does not receive the fluctuation of the battery power supply voltage, so that the power amplification integrated circuit 2 as a whole is less likely to receive the fluctuation of the battery power supply voltage, and Problems such as distortion of the audio signal can be eliminated.

Further, as for the driver circuit 22 of the power amplification integrated circuit 2, an element having a low withstand voltage can be used, and a protection circuit for protecting the element from an instantaneous high voltage can be eliminated.

FIG. 2 is a circuit diagram showing the configuration of a second embodiment of the low-frequency amplifier circuit according to the present invention. However, the same parts as those in the first embodiment shown in FIG.

The low-frequency amplifier circuit of the present embodiment is supplied with a reference voltage for generating a DC bias voltage on the input side of the driver circuit 22 of the power amplifier integrated circuit 2 from the front stage 1. The driver circuit 22 of the power amplification integrated circuit 2 is configured to receive the power supply voltage Vcc2 supplied from the vehicle battery power supply.

Therefore, the front stage 1 has a reference voltage output terminal 15 for outputting a reference voltage generated from the internal constant voltage source 14 to the outside, and a reference for receiving the reference voltage output from the reference voltage output terminal 15. The voltage input terminal 24 is provided on the power amplification integrated circuit 2.

Next, the operation of this embodiment will be described.
The constant voltage source 14 in the former stage 1 generates a reference voltage with the DC bias voltage on the output side of the buffer amplifier 13 as VA.
This reference voltage is applied to the bias resistor 25 through the terminals 15 and 24, thereby generating a DC bias voltage VB having the same potential as the DC bias voltage VA on the input side of the driver circuit 22.

For this reason, the DC bias voltage VA on the output side of the pre-stage unit 1 and the DC bias voltage VB on the input side of the power amplification integrated circuit 2 have the same potential, so that the pre-stage unit 1 and the power amplification integrated circuit 2 are connected. Since direct connection can be made without a capacitor, low frequency characteristics can be improved, and pop noise can be prevented.

[0027]

As described in detail above, claim 1
According to the low-frequency amplifier circuits of 2, 4, and 5, the coupling capacitance can be omitted, the low-frequency characteristics can be improved, and the generation of pop noise can be prevented.

According to the low frequency amplifying circuit of the third aspect, in addition to the above-mentioned effects, it is possible to eliminate the adverse effect on the power amplifying integrated circuit due to the fluctuation of the battery voltage of the vehicle, that is, to eliminate the distortion of the output audio signal, Eliminate the use of high element
A protection circuit for protecting the element from momentary high voltage can be eliminated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a low-frequency amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a second embodiment of the low frequency amplifier circuit of the present invention.

FIG. 3 is a circuit diagram showing a configuration example of a conventional low-frequency amplifier circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Front stage 2 Power amplification integrated circuit (power amplification part) 11 Output terminal 12 Electronic volume circuit 13 Buffer amplifier 14 Constant voltage source 15 Reference voltage output terminal 21 Input terminal 22 Driver circuit 23 Power supply terminal 24 Reference voltage input terminal 25 Bias resistance T1 , T2 transistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J090 AA02 AA41 CA21 CA48 CA49 CA61 CA93 CN04 FA10 HA02 HA25 HA26 HA29 KA03 KA11 KA12 MA22 SA05 SA07 TA01 5J091 AA02 AA41 CA21 CA48 CA49 CA61 CA93 FA10 HA02 HA25 HA26 HA29 KA12 KA11 KA11 SA05 SA07 TA01 5J092 AA02 AA41 CA21 CA48 CA49 CA61 CA93 FA10 HA02 HA25 HA26 HA29 KA03 KA11 KA12 MA22 SA05 SA07 TA01 VL08

Claims (5)

[Claims] 1. A low-frequency amplifier circuit comprising: an integrated front-stage unit; and an integrated power amplifier unit for inputting an output signal of the front-stage unit and amplifying the power of the output signal. A low-frequency amplifier circuit, comprising: bias adjusting means for setting a bias voltage and a DC bias voltage on the input side of the power amplifier to the same potential. 2. The low-frequency amplifier circuit according to claim 1, wherein said bias adjustment unit matches a power supply voltage for driving said pre-stage unit with a power supply voltage for driving a driver circuit of said power amplification unit. . 3. The low-frequency amplifier circuit according to claim 2, wherein a power supply voltage for driving said pre-stage and a power supply voltage for driving a driver circuit of said power amplifier are supplied from a common stabilized power supply. . 4. The power adjustment section sends a reference voltage generated from a constant voltage source for generating a DC bias voltage of the preceding stage to the power amplification section, and the power amplification section receives the received reference voltage. And generating a DC bias voltage on the input side of the driver circuit from the DC bias voltage on the input side of the power amplification section and the DC bias voltage on the input side of the power amplification section. A low frequency amplifier circuit as described. 5. The low-frequency amplifier circuit according to claim 1, wherein said low-frequency amplifier circuit is used in car audio.