JP2545814Y2 - Amplifier circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an amplifier circuit used for an audio amplifier or the like.

[0002]

2. Description of the Related Art In a conventional audio amplifier, a variable resistor is arranged at an input stage or an output stage of an amplifier circuit for output adjustment, and audio output is adjusted by adjusting the variable resistor.

In a variable resistor, for example, in the case of a rotary type variable resistor, a change characteristic of an output / input voltage ratio (V1 / V0) with respect to a moving amount of an adjustment rotary shaft is indicated by a chain line in FIG. A B-curve characteristic that changes linearly in proportion to the change in the output / input voltage ratio while the movement amount is small, and the change in the output / input voltage ratio increases as the movement amount increases. A curve characteristics indicated by
Although not shown, a C-curve characteristic having a change opposite to the A-curve characteristic is provided, and is appropriately selected and used for the purpose.

On the other hand, in recent years, as audio equipment has been downsized, speaker systems have tended to be downsized. In general, the small loudspeaker system employed has a small speaker, and thus has insufficient low-frequency reproduction capability. Therefore, the low-frequency signal is electrically enhanced to compensate for the low-frequency reproduction. Particularly, in a three-dimensional (3D) speaker system, an audio device including a speaker system for low-frequency reproduction in addition to a set of speaker systems for full-band reproduction on the left and right is provided. In this apparatus, a dedicated amplifier is prepared to amplify a low-frequency signal supplied to a low-frequency reproduction speaker system. Further, an amplifier configured to select a function for amplifying the low-frequency signal in an amplification circuit for amplifying the entire band signal has been considered.

FIG. 8 shows an example thereof. In the figure, reference numeral 01 denotes a signal input terminal, and reference numeral 021 denotes a changeover switch. The input signal is selectively supplied to one of the variable resistors 031 and 032 by the switch 211. . Reference numeral 041 denotes a buffer amplifier circuit which receives the output of the variable resistor 031 as an input.
2 is a buffer amplifier circuit that receives the output of the variable resistor 032 as an input,
A low-pass filter 05 receives the output of the buffer amplifier circuit 041 as an input, and a switch 022 selects an input to the amplifier circuit 06, and operates in conjunction with the switch 21.

In this amplifier circuit, when the switches 021 and 022 are at the upper contacts in FIG. 8, the input signal is transmitted through the variable resistor 031, the buffer amplifier circuit 41, the low-pass filter 05, the switch 022, and the amplifier circuit 06. And supplied to the output terminal 07. In this case, since only the low-frequency signal selected by the low-pass filter 05 is supplied to the output terminal 07, low-frequency reproduction is achieved by connecting a low-frequency sound reproduction speaker system to the output terminal 07.

On the other hand, when the switches 021 and 022 are at the lower contacts in FIG.
32, a buffer amplifier circuit 042, a switch 022, and an amplifier circuit 06 to the output terminal 07. In this case, since the full band signal is supplied to the output terminal 07, the full band reproduction is achieved by connecting the full band reproduction speaker system to the output terminal 07.

As described above, in the amplifier of FIG. 8, the functions of the amplifier for full-band amplification and the amplifier for low-frequency amplification can be selected by the switch.

[0009]

In such an amplifier which can be used by switching between the full-band reproduction function and the low-band reproduction function, the volume adjustment at the time of full-band reproduction conforms to human hearing characteristics. Variable resistor 03 having curve characteristics
1 is used, and a variable resistor having a B-curve characteristic is used for volume adjustment at the time of low-frequency reproduction, which makes it easy to adjust the volume balance with the mid-high frequency amplifier at the time of reproduction. Therefore, as shown in FIG. 8, it is necessary to prepare independent variable resistors for the amplifier circuit at the time of low band reproduction and at the time of full band reproduction.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a B-curve variable resistor having one end connected to a signal input terminal and the other end connected to ground, and the variable resistor. A first switch for selectively inputting the output of the sliding piece directly or via a low-pass filter to the amplifier circuit, and a case where the output of the sliding piece is selected by the first switch so as to be directly input to the amplifier circuit. An amplifier circuit comprising a second switch for connecting a middle point of the resistance element of the variable resistor to ground via a resistor, wherein the intermediate point of the variable resistor is selectively connected to ground via a resistor. By using a single variable resistor, the pseudo A curve characteristic (at the time of full band reproduction function) and the B curve characteristic (at the time of low frequency reproduction function)
You can choose. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the embodiment shown in FIG. In FIG. 1, 1 is a signal input terminal, 3 is one end of a resistor connected to the input terminal 1, the other end is grounded, the middle point is connected to one end of a resistor 8, and the sliding piece is connected to the buffer amplifier circuit 4 input. This is a variable resistor having a B-curve characteristic. The other end of the resistor 8 is connected to the terminals a1 and a2 of the second switch 22.
2, terminal b1 is connected to ground,
Terminal b2 is not connected. When the terminal a1 and the terminal b2 are connected by the second switch 22, the resistor 8 is connected to the ground. The output of the buffer amplifier circuit 4 is connected to the terminal d1 of the first switch 21 and the low-pass filter 5, respectively, and the output of the low-pass filter 5 is connected to the terminal d of the first switch 21.
Connected to 2. The terminals c1 and c2 of the switch 21 are respectively connected to the inputs of the amplifier circuit 6, and the output of the amplifier circuit 6 is connected to the output terminal 7. As a result, when the terminals c1 and d1 are connected by the first switch 22, the output of the buffer amplifier circuit 4 is directly input to the amplifier circuit 6, and when the terminals c2 and d2 are connected by the first switch 22, the output of the buffer amplifier circuit 4 is output. Only the low-frequency signal selected via the low-pass filter 5 is input to the amplifier circuit 6.

When the terminals c2 and d2 are connected by the first switch 21, the terminal a2 is connected by the second switch 22.
And b2 are connected, and the middle point of the variable resistor 3 (the middle point where the resistance value becomes 1/2 in the embodiment) floats with respect to the ground via the resistor 8. Therefore, the variable resistor 3
The B characteristic shows that the output / input voltage ratio changes linearly with respect to the amount of movement of the sliding piece. In this case, assuming that the input voltage is V0 and the output voltage is V1, V1 / V0 = kR / R = k (where k = change ratio of sliding piece 0 ≦ k ≦ 1, R is the resistance value of the resistor piece of the variable resistor) ), And has a B-curve characteristic indicated by an alternate long and short dash line in FIG. 6 which changes linearly. On the other hand, when the terminals c1 and d1 are connected by the first switch 21, the terminals a1 and b1 are connected by the second switch 22, and the middle point of the variable resistor 3 is connected to the ground via the resistor 8.

Here, 0 ≦ k ≦ 0.5 (in FIG. 1, when the sliding piece is located below the middle point), an equivalent circuit of the variable resistor is shown in FIG. Is selected to be 1/10 of the resistance value R of the variable resistor 3), and the output / input voltage ratio is represented by V1 / V0 = 2k / 7.

Further, 0.5 ≦ k ≦ 1 (when the sliding piece is located above the middle point in FIG. 1), an equivalent circuit of the variable resistor is shown in FIG. 8, and the output / input voltage ratio is V1 //. V0 =
It is represented by (12k-5) / 7. In other words, as shown by the dotted line in FIG. 6, in the region of 0 ≦ k ≦ 0.5, it changes linearly with a 2/7 gradient, and in the region of 0.5 ≦ k ≦ 1,
/ 7, the composite change characteristic changes with a gradient of
It acts as a variable resistor having a curve characteristic.

Therefore, the terminal c2 is set by the first switch 21.
When the terminals a2 and b2 are connected by the second switch 22, the input signal is the variable resistor 3, the buffer amplifier 4, the low-pass filter 5, the first switch 2
1. The low-frequency signal selected by the low-pass filter 5 is output to the output terminal 7 via the amplifier circuit 6. In this case, the output adjustment by the variable resistor 3 has a B curve characteristic.

The terminals c1 and d are set by the first switch 21.
1 are connected, and the terminals a1 and b1 are
Is connected, the input signal is output to the output terminal 7 via the variable resistor 3, the buffer amplifier circuit 4, the first switch 21, and the amplifier circuit 6 as a full-band signal. In this case, the output adjustment by the variable resistor 3 has a pseudo A-curve characteristic.

FIG. 2 shows an embodiment of the present invention actually used as a circuit. The variable resistor 3 has a B-curve characteristic of 100 kΩ, and the resistor 8 has a resistance of 10 kΩ.

When the terminals c2 and d2 are connected by the first switch 21 and the terminals a2 and b2 are connected by the second switch 22, the variable resistor 3 exhibits a B curve characteristic shown by a dashed line in FIG. The terminal c2 is set by the first switch 21.
And d2 are connected, and the terminals a2 and b2 are connected by the second switch 22, the variable resistor 3 exhibits a pseudo-A curve characteristic indicated by a dotted line in FIG.

[0019]

As described above, according to the present invention, in the amplifier circuit capable of selecting the full-band amplification function or the low-frequency amplification function, the output can be adjusted according to both functions by a single variable resistor. The cost can be reduced as compared with the example.

In the embodiment, the middle point of the resistor piece of the variable resistor is selectively connected to the ground. However, an arbitrary middle point of the resistor piece is connected to the ground according to required characteristics. May be.

[Brief description of the drawings]

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

FIG. 2 is a detailed circuit diagram of a main part of the embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram for explaining the operation of the embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram for explaining the operation of the embodiment of the present invention.

FIG. 5 is a characteristic diagram of a variable resistor.

FIG. 6 is a characteristic diagram of the variable resistor according to the present invention based on the equivalent circuits of FIGS. 4 and 5;

FIG. 7 is a graph showing measured characteristics of a variable resistor according to the present invention.

FIG. 8 is a circuit diagram of a conventional amplifier circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 21 1st switch 22 2nd switch 3 Variable resistor 4 Buffering amplifier circuit 5 Low-pass filter 6 Amplifier circuit 7 Output terminal 8 Resistance

Claims (1)

(57) [Scope of request for utility model registration] 1. A B-curve variable resistor having one end connected to a signal input terminal and the other end connected to ground, and an output of a sliding piece of the variable resistor directly or via a low-pass filter to an amplifier circuit. And a switch for selectively inputting to the switch, and when the output of the sliding piece is selected so as to be directly input to the amplifier circuit, the intermediate point of the resistance element of the variable resistor is grounded via a resistor. A second switch for connecting an intermediate point of the resistance element of the variable resistor to an open end when the output of the sliding piece is selected to be input to an amplifier circuit through a low-pass filter. Amplifier circuit.