JPS5945708A - Electronic volume circuit - Google Patents

Abstract

PURPOSE:To obtain an electronic volume device excluding the effect of noise included in a control signal and avoiding the effect of temperature characteristcs, by feeding back a voltage formed with a constant current of a constant current circuit inserted to a level adjsting circuit to an amplifier for the control signal. CONSTITUTION:When a signal before level adjustment is given to an input terminal 2, a signal in response to an input signal is outputted at a differential amplifier 8, converted into a voltage at a current/voltage converting circuit 26 and given to an adjusting circuit 36. A control input is given to a terminal 58 to control a current of a transistor (TR)42. The synthesized value of a current to TRs 38, 40 is regulated with a current of the TR42. Further, a required current is taken from the collector of the TR54 so that the current in the TR54 is the same as that of the TR52 with the current mirror effect. The signal level is suppressed by this current regulating and a signal after level adjustment is generated at terminals 6 and 62. Since the current in the TR42 is converted into a voltage at a resistor 56 and fed back negatively to an amplifier 60, the temperature characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic volume circuit that electronically adjusts a signal level.

An electronic volume circuit is used to adjust a signal level in order to extract a signal at a constant level in a signal processing system. In conventional electronic volume circuits, an offset occurs in the current flowing from the input section, and it is difficult to adjust this offset externally.The volume characteristics fluctuate in response to temperature changes, causing changes in the signal level. However, there are also drawbacks such as noise contained in the control signal affecting the adjustment level. Furthermore, it was difficult to operate the conventional device at a low voltage of about 1.8V.

An object of the present invention is to provide an electronic volume circuit that avoids the influence of temperature characteristics and eliminates the influence of noise contained in control signals.

This Q light consists of a differential amplifier that generates a current according to the level of the input signal, a current-voltage conversion circuit that converts the output current of this differential amplifier into voltage, and a a level adjustment circuit that forms two currents with a current difference, combines these currents, and suppresses the input signal level in response to the difference; and a level adjustment circuit that is inserted into this level adjustment circuit to regulate the combined value of the two currents. The present invention is characterized in that it is composed of a constant current circuit, and an amplifier that provides a control input to the constant current circuit and receives the voltage generated by the constant current of the constant current circuit as feedback.

Embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of an electronic volume circuit according to the present invention. In the figure, a signal for level adjustment is applied to an input terminal 2, and this signal is input to a buffer circuit 4 via a resistor 3.

An output terminal 6 for taking out the level-adjusted signal is formed at the output section of the buffer circuit 4.

The signal that has passed through the buffer circuit 4 is input to a differential amplifier 8 that generates a current corresponding to the signal level. This differential amplifier 8bal transistor 1O112, 14, 1
6, 18, 2() and a constant current source 22.

In this differential amplifier 8, the output of the buffer circuit 4 is connected to the base of the transistor 12, and l
- A constant bias is applied to the base of the transistor 10 from the bias circuit 24. Transistor 14.1
6 constitutes a current mirror circuit, the output current of which is l.
The output current is regulated by the operation of the transistor I2, and the I-ransistor 18, 20 also constitutes a current mirror circuit, and its output current is regulated by the operation of the transistor I2.

The output current of each l-randisk 16.20 is supplied to a current-voltage conversion circuit 2G, and is converted into a constant voltage. That is, this current-voltage conversion circuit 26 is composed of diode-connected L-transistors 28, 30, and 32. That is, the collector of the L-transistor 28.30 is individually supplied with an output current from the I-transistor 16.20, and the emitters of each transistor 28.30 are connected in common, and the reference potential is applied via the transistor 32. It is connected to a point (GND) 34.

This corresponds to an input signal for voltage adjustment formed by the current-voltage conversion circuit 26, and this voltage is input to the level adjustment circuit 36. This level adjustment circuit 36 is composed of a voltage-current conversion circuit whose current value can be adjusted based on an external control input.

That is, this level adjustment circuit 36 includes transistors 38.4
0.42.44.46.48.50.52.54 and a resistor 56. Transistor 42 and resistor 5
6 constitutes a constant current circuit, and the control signal applied to the control input terminal 58 is connected to the base of the L-transistor 42 through the amplifier 6.
The voltage generated across the resistor 56 connected between the emitter of this transistor 42 and the reference potential point 34 is fed back to the input side of the amplifier 60.

In this level adjustment circuit 36, a transistor 44 and a transistor 46 connected to the collector of a transistor 38 form a current mirror circuit, and a transistor 48 and a transistor 50 connected to a collector of a transistor 40 form a current mirror circuit. It consists of Further, the transistors 52 and 54 constitute a current mirror circuit, and the collector of the transistor 50 is connected to the collector of the transistor 52, and the collector of the transistor 46 is connected to the collector of one transistor 54. An output terminal 62 is formed at the collector of these L-transistors 46 and 54, and this output terminal 62 is directly connected to the input section of the buffer circuit 4. Note that a driving DC voltage Vcc is applied to the power supply terminal 66.

The operation based on the above configuration will be explained with reference to the operation waveforms shown in FIG. In FIG. 2, A is the level-adjusted signal waveform applied to the input terminal 2, B and C are the level-adjusted signal waveforms generated at the output terminal 6.62, and D is the control signal level applied to the control input terminal 58. It shows.

That is, when a level adjustment signal shown in FIG. 2 is applied to the input terminal 2, the differential amplifier 8 outputs a current corresponding to the input signal from the transistors 16 and 20, and this output Current is current voltage conversion times 1? δ26 and is converted into a voltage corresponding to the input signal. The voltage generated by the current/voltage conversion circuit 2G is individually applied to the bases of the 1-range disks 38 and 40 of the level adjustment circuit 36.

On the other hand, when the control input shown in FIG. 2 (1) is applied to the control input terminal 58, this control input becomes the base input of the F-landestor 42 via the amplifier 60, and the collector current of the transistor 42 is level controlled. Controlled by input. The voltage generated across the resistor 56 by the current flowing through the transistor 42 is negatively fed back to the input side of the amplifier 60, and this feedback system controls the current flowing through the transistor 42, thereby avoiding the influence of temperature characteristics. There is.

The current flowing through transistors 38, 40 varies depending on their respective base inputs, but the combined value of the currents flowing through both is regulated by the current in transistor 42 based on the level control input. The current flowing through the transistor 38 flows from the l-transistor 44 to the transistor 46 due to the current mirror effect, and similarly, the current flowing through the I-transistor 40 flows from the l-transistor 48 to the current transistor 46.
The mirror 9JJ signal flows to the 1-transistor 50.

In this case, since the current flowing through the 1-transistor 50 flows through the 1-transistor 52, this current regulates the current flowing through the transistor 54 due to the Karen 1-Miller effect.

That is, the current of the 1-transistor 54 functions to draw the necessary current from the collector side of the transistor 54 so that it becomes the same as the current of the transistor 52 due to the current mirror effect.

Here, the current flowing through the transistor 38 is I3, the current flowing through the transistor 40 is 12, and each current 11, I2
The size relationship of 1. <12, transistor 48.
The current flowing through the transistor 50 is I2, and the current flowing through the transistor 38 is I2, and the current drawn by the transistor 54 is I2.
-I+) will be supplied. In this case, the current flowing through the output terminal 62 is I,=12, and as shown in FIG.
As shown in Figure 2, the increase in control input level is shown.

Since the output terminal 62 receives a signal to be adjusted from the input terminal 2, the signal level is suppressed by this current draw, and as a result, the signal level is adjusted, and the output terminal 6 , 62 are shown in Fig. 2B and C.
As shown in FIG. 2E°Ia), offset 1- occurs, but this offset 1- can be effectively suppressed by installing the buffer circuit 4. That is, if the current gain of the buffer circuit 4 is a and its output current is Ib, then Ia=I
Since the ratio is b/a, the occurrence of offset 1. is suppressed.

Further, such a circuit can be configured as a low-voltage driven IC, and can be driven at a low voltage of about 1.8V, for example.

As explained above, according to the present invention, it is possible to avoid the influence of temperature characteristics, and also to eliminate the influence of noise included in the control signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the electronic volume circuit of the present invention, and FIG. 2 is an explanatory diagram showing its operating waveforms. 8... Differential amplifier, 26... Current-voltage conversion circuit, 3
6...Level adjustment circuit, 42...l~Lansistor as a constant current circuit, 60...%i increaser.

Claims (1)

[Claims] A differential amplifier that generates a current according to the level of an input signal, a current-voltage conversion circuit that converts the output current of this differential amplifier into a voltage, and a current difference that corresponds to the output voltage of this current-voltage conversion circuit. a level adjustment circuit that forms two currents having a current value, synthesizes these currents, and suppresses the input signal level according to the difference; and a level adjustment circuit that is inserted into this level 8 frequency adjustment circuit and regulates the combined value of the two currents. constant current circuit,
An electronic volume circuit characterized in that it comprises an amplifier that provides a control input to the constant current circuit and receives a feedback voltage formed by the constant current of the constant current circuit.