JP3253512B2 - Electronic volume 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 electronic volume circuit for adjusting the level of an input signal in accordance with the level of a control signal. The present invention relates to an electronic volume circuit whose level can be adjusted by tone.

[0002]

2. Description of the Related Art In recent audio equipment and video equipment, a plurality of I
C is provided in the device, and control of the IC is often performed by a digital signal from a microcomputer in the device. A D / A (digital / analog) converter is disposed inside or outside the IC. There is an electronic volume as an object of digital signal control from such a microcomputer. The electronic volume adjusts the level of an input signal according to the level of a control signal.

FIG. 2 shows such an electronic volume. The audio input signal is level-adjusted by the GCA (2) applied from the input terminal (1) and changing the gain.
The signal whose level has been adjusted by the GCA (2) is led to an output terminal (3). The gain of the GCA (2) is controlled by a digital signal from the microcomputer (4).
A digital signal from the microcomputer (4) is output in a serial format, and is converted into a parallel format by a converter (5). The digital signal in the parallel format is converted into an analog signal by the D / A converter (6). The converted analog signal is applied to a variable reference voltage source (7) whose reference voltage changes according to the control signal. Then, the level of the control signal generated from the control circuit (8) changes according to the change of the reference voltage of the variable reference voltage source (7), and the gain of the GCA (2) changes.

The reference voltage value of the variable reference voltage source (7) and GC
The relationship between the gains of A (2) is shown by the solid line in FIG. Decreasing the reference voltage value of the variable reference voltage source (7) increases the attenuation. In FIG. 3, -100 dB assumes that the level of the audio signal is zero. The step-like waveform described along the solid line in FIG. 3 indicates a step of the digital signal of the D / A converter (6). Normally, a 5-bit control signal is applied to the D / A converter (6), and there are 32 steps.

Therefore, according to the circuit of FIG. 2, the electronic volume can be controlled by digital signal control from the microcomputer.

[0006]

However, the circuit of FIG. 2 has a problem that the sound signal cannot be attenuated in a natural tone. In the circuit of FIG.
You have to control in just 32 steps over a wide range up to B. Therefore, when the sound level is greatly attenuated, the change is clearly understood.
Steps in the range of the attenuation rate of about B or more cannot be sufficiently secured. Then, there is a problem that when the listener lowers the volume of the audio device from a high volume, the volume suddenly drops, giving a sense of incongruity.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a variable reference voltage source whose reference voltage changes according to the control amount of an electronic volume, and one end of the variable reference voltage source at one end. A current generating circuit including a resistor to which a voltage is applied, a transistor having an emitter connected to the other end of the resistor and a constant voltage applied to a base, and a differential amplifier operating according to an output current of the current generating circuit. A GCA for adjusting the level of an input signal according to an output signal of the differential amplifier, and detecting that a voltage of the variable reference voltage source has reached a predetermined value, and detecting the differential amplifier according to the detected output signal. And a switching control circuit for forcibly switching the state of the output signal.

[0008]

FIG. 1 shows an electronic volume circuit according to the present invention. (9) is a resistor to which the voltage of a variable reference voltage source (7) is applied at one end, and (10) is an emitter having the emitter. A transistor (11) connected to the other end of the resistor (9) and having a constant voltage applied to its base, and a constant current source (12) (1)
3) a resistor (9) including a current mirror circuit (14);
A current generating circuit that generates a current i equal to the current i flowing through the current generating circuit, (15) a differential amplifier that operates according to the output current of the current generating circuit (10), and (16) a differential amplifier (15)
The GCA for adjusting the level of the input signal from the signal source (17) in accordance with the output signal of the variable reference voltage source (17) detects that the voltage of the variable reference voltage source (7) has fallen below a predetermined value, and The state of the output signals at the output terminals (19) and (20) of the differential amplifier (15) is forced to "L" in accordance with the output signal.
This is a switching transistor for switching to a level.

In FIG. 1, the same circuit elements as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The relationship between the reference voltage value of the variable reference voltage source (7) and the gain of the GCA (16) is shown by the solid line in FIG. Decreasing the reference voltage value of the variable reference voltage source (7) increases the attenuation. As shown in FIG. 4, the operation of the circuit of FIG. 1 differs at the voltage VA. That is, when the voltage is equal to or higher than the voltage VA, a normal attenuation curve is drawn, and the voltage V
A and below are muted. The voltage VA is -5
It is set around 0 dB. Usually, about -50 dB is the limit that a listener can hear. Therefore, the level below this level is not controlled stepwise, but is muted suddenly. Thereby, from about -50 dB to 0
Since all 32 steps can be used in the dB range, the steps in that range (large volume) become finer, and the audibility of the entire electronic volume becomes natural.

Specifically, when the voltage of the variable reference voltage source (7) becomes equal to or lower than VA, the switching transistor (18) turns on, and the voltage of the output terminal (19) of the differential amplifier (15) becomes "L". This is performed by muting the GCA (16). First, the case where the voltage of the variable reference voltage source (7) is equal to or higher than the predetermined value VA will be described. In this case, the switching transistor (18) is off. Now, assuming that the voltage of the variable reference voltage source (7) is equal to the voltage of the constant voltage source (21), no current flows through the resistor (9). It is assumed that the rising voltages of the transistor (11) and the transistor (26) are equal.

Then, the current of the constant current source (12) flows through the transistor (11) and further flows through the current mirror circuit (14). Since the current of the constant current source (12) and the current of the constant current source (13) are set to be equal, the terminal (2
No current flows in 2). If no current flows through the terminal (22), the same voltage is applied to the bases of the transistors (23) and (24) constituting the differential amplifier (15) from the reference voltage source (25). Transistor (23) (2
If the base voltages of 4) are equal, the output terminals (19) and (2)
The level of the output signal of 0) is also equal. Output terminal (1
9) If the levels of the output signals of (20) are equal, GCA
The gain of (16) is an intermediate value. Therefore, the signal source (1
The level of the input signal from 7) is amplified with an intermediate gain and obtained at the output terminal (3).

When the voltage of the variable reference voltage source (7) is increased from this state, a current i flows from the resistor (9) to the constant current source (12). Then, the emitter current of the transistor (11) decreases by the current i, and the current mirror circuit (1)
The current i of the terminal (27) of 4) also decreases. as a result,
A current i flows from the reference voltage source (25) to the constant current source (13) via the terminal (22), and the base voltage of the transistor (23) decreases. When the base voltage of the transistor (23) decreases, the level of the output signal at the output terminal (19) increases, and the level of the output signal at the output terminal (20) decreases. Then, the gain of the GCA (16) increases, and the level of the input signal from the signal source (17) is amplified with a high gain and obtained at the output terminal (3).

At this time, the gain of the GCA (16) is -50.
Since 31 steps can be used in the range from about dB to 0 dB, the range (large volume)
Step becomes finer, and the audibility of the whole electronic volume becomes natural. Next, a case where the voltage of the variable reference voltage source (7) is equal to or lower than the predetermined value VA will be described. In this case, the switching transistor (18) turns on. When the switching transistor (18) is turned on, the level of the output signal at the output terminal (19) drops to "L" level. Then, the gain of GCA (16) becomes -100.
dB, that is, the mute state, the level of the input signal from the signal source (17) is muted, and no signal appears at the output terminal (3).

Therefore, according to the circuit of FIG. 1, the level of the audio signal can be adjusted in a natural tone in accordance with the analog control signal after the D / A conversion. FIG. 5 shows a specific circuit example of the GCA (16) of FIG. In FIG. 5, the same reference numerals are given to the same circuit elements as those in FIG. 1, and the description will be omitted. FIG.
In the circuit of (1), the DC voltage of the output terminal (3) is
9) Regardless of the level of the output signal of (20), it is always constant, and only the level of the AC signal from the signal source (17) changes. The level of the AC signal is determined by the transistor (28)
Is determined by the shunt ratio of the collector current. The shunt ratio changes depending on the current flowing through the transistors (30) and (31) of the differential amplifier (29). If the level of the output signal of the output terminal (19) is high and all the collector current of the transistor (28) flows through the transistor (31), the gain becomes 1. Conversely, if the level of the output signal at the output terminal (19) is low and all the collector current of the transistor (28) flows through the transistor (30), the gain becomes zero.

Therefore, according to the circuit shown in FIG. 5, the output signal at the output terminal (19) can be muted by lowering the level of the output signal.

[0016]

As described above, according to the present invention, it is possible to provide an electronic volume circuit capable of adjusting the level of an input signal according to the level of a control signal. In particular, according to the present invention, it is possible to provide an electronic volume circuit capable of adjusting the level of an audio signal in a natural tone in accordance with an analog control signal after D / A conversion.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electronic volume circuit according to the present invention.

FIG. 2 is a circuit diagram showing a conventional electronic volume circuit.

FIG. 3 is a characteristic diagram for explaining a conventional characteristic.

FIG. 4 is a characteristic diagram for explaining characteristics of the present invention.

FIG. 5 is a circuit diagram showing a specific circuit example of the GCA (16) of the present invention.

[Description of References] (7) Variable reference voltage source (9) Resistance (10) Current generation circuit (15) Differential amplifier (16) GCA (18) Switching transistor

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03G 1/00-3/18

Claims (3)

(57) [Claims] A variable reference voltage source whose reference voltage changes in accordance with a control amount of an electronic volume; a resistor having one end to which the voltage of the variable reference voltage source is applied; and an emitter connected to the other end of the resistor. A current generating circuit including a transistor to which a constant voltage is applied to a base; a differential amplifier that operates according to an output current of the current generating circuit; and adjusting a level of an input signal according to an output signal of the differential amplifier A switching control circuit that detects that the voltage of the variable reference voltage source has reached a predetermined value and forcibly switches the state of the output signal of the differential amplifier in accordance with the detected output signal. Electronic volume circuit featuring. 2. A variable reference voltage source whose reference voltage changes in accordance with a control amount of an electronic volume, a resistor to which one end of the variable reference voltage source is applied, and an emitter connected to the other end of the resistor. A current generating circuit including a first transistor to which a constant voltage is applied to a base; a differential amplifier operating according to an output current of the current generating circuit; and a level of an input signal according to an output signal of the differential amplifier A GCA to be adjusted; and a second transistor having an emitter to which the voltage of the variable reference voltage source is applied, a base to which a reference voltage is applied, and a collector connected to the output side of the differential amplifier. And a switching control circuit for detecting that the output signal of the differential amplifier has reached a predetermined value, and forcibly switching the state of the output signal of the differential amplifier in accordance with the detected output signal. Beam circuit. 3. A variable reference voltage source whose reference voltage changes in accordance with an analog control signal after D / A conversion; a resistor to which one end of the variable reference voltage source is applied; A current generation circuit including a transistor connected to an end and having a base applied with a constant voltage; a differential amplifier that operates according to an output current of the current generation circuit; and an input signal corresponding to an output signal of the differential amplifier. A switching control circuit for detecting that the voltage of the variable reference voltage source has reached a predetermined value and forcibly switching the state of the output signal of the differential amplifier in accordance with the detected output signal; An electronic volume circuit comprising: