JPS622801Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electronic volume circuit for adjusting volume, and more particularly, to an electronic volume circuit whose purpose is to improve attenuation by removing residual signals that become harsh when the volume is minimized.

Conventionally, variable resistors have been used in volume adjustment circuits, but they have the disadvantage of generating sliding noise due to the sliding parts of the variable resistors, so a differential amplifier is used to adjust the volume. A so-called electronic volume circuit was considered. However, compared to using a variable resistor to adjust the volume, it has the disadvantage that it does not provide sufficient attenuation, and when the attenuation of the electronic volume circuit is minimized, approximately
It has the disadvantage that a signal component of approximately 70 dB is derived as an output, causing a sense of indecision.

The present invention was devised in view of the above-mentioned problems, and provides a circuit that improves attenuation by removing residual signals when the volume of an electronic volume circuit is minimized, and also provides an electronic volume suitable for semiconductor integrated circuits. To provide the circuit.

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a diagram showing an outline of an electronic volume circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing the embodiment.

In FIG. 1, reference numeral 1 denotes a double balanced differential amplifier which is the basic circuit of an electronic volume circuit; 2 denotes a signal input circuit consisting of two differential amplifiers 2a and 2b; 3 denotes a signal switching circuit which controls the signal input circuit 2 according to the voltage level of a variable DC power supply 4; and OUT denotes the output terminal of the electronic volume circuit, from which an output is obtained via a load resistor 23.

The differential amplifier 2a constituting the signal input circuit 2 is
A signal source 21 and a DC bias source 22 are connected in series, and the signal voltage and DC voltage are supplied to the double-balanced differential amplifier 1, and the other differential amplifier 2b supplies a DC potential equivalent to that of the DC bias source 22. A DC bias source 5 is connected. These differential amplifiers 2a and 2b are selected by a signal from a signal switching circuit 3.

The operation of the electronic volume circuit according to the present invention will be explained below. Normally, a signal source 21 is supplied to the input stage of the double-balanced differential amplifier 1 through the differential amplifier 2a, and is derived from the output terminal OUT via a load resistor 23 as an audio signal. At this time, the differential amplifier 2b is in a cutoff state. On the other hand, in order to attenuate the output of the electronic volume circuit, the voltage of the variable DC power supply 4 is gradually reduced to minimize the audio signal. The voltage level of the variable DC power supply 4 at this time is detected by the signal switching circuit 3 consisting of a comparator circuit or the like. This detection signal interrupts the function of the differential amplifier 2a. The signal component supplied via the differential amplifier 2a is cut off, and the differential amplifier 2b is operated at the same time.
A DC component equivalent to a DC bias source 22 with a signal component superimposed thereon is supplied to the input stage of the double-balanced differential amplifier 1 through the differential amplifier 2b. In this way, the supply of only the signal component is substantially cut off, thereby improving the amount of attenuation of the electronic volume circuit.

FIG. 2 shows an electronic volume circuit including a specific embodiment of this signal input circuit 2. In FIG. This will be explained below.

In FIG. 2, differential amplifiers 2a and 2b constituting the signal input circuit 2 include a pair of transistors 7 and 8, a current source transistor 9, and a pair of transistors 10 and 1.
1 and a current source transistor 12. Each differential amplifier is supplied with current from a current source transistor 6 consisting of a multi-collector. Base of transistor 7 on the signal input side of differential amplifier 2a
A DC bias source 22 and a signal source 21 are connected in series to _B2 , and a signal component superimposed on the DC component is applied to the differential amplifier 2a. On the other hand, the base of the transistor 10 on the signal input side of the differential amplifier 2b
A DC bias source 5 is connected to _B1 . Transistors 7 and 1 on the input side of differential amplifiers 2a and 2b
The collectors of transistors 8 and 11 on the output side are connected in common, and the collectors of transistors 8 and 11 on the output side are connected in common. Furthermore, the collectors of the transistors 8 and 11 on the output side are connected to the base of the current source transistor 13, and the emitters of the transistors 8 and 11 are connected to the base of the current source transistor 13.
are commonly connected to the connection point A of the commonly connected bases. Each differential amplifier 2a, 2b is
Together with the current source transistor 13, it forms a voltage follower circuit. Note that 20 is an emitter resistor, and the DC bias sources 5 and 22 have the same DC potential.

In this way, since the differential amplifiers 2a and 2b form a voltage follower circuit, the base _B1 of the transistor 10 and the base of the transistor 7
The potential of B ₂ becomes equal to the potential of the connection point A between the bases of transistors 8 and 11 and the emitter of current source transistor 13. Utilizing this, the differential amplifier 2 is controlled by the detection signal from the signal switching circuit 3.
By operating the differential amplifier 2b at the same time as the function of the differential amplifier 2b is stopped, it is possible to maintain a direct current potential equal to the point A, so that the effect is substantially equivalent to that of removing only the signal component.

In addition, only the signal component can be effectively blocked without producing noise such as popping sounds that are often caused by blocking the signal component. In this way, since the signal component is completely blocked, an electronic volume circuit with excellent damping effect can be obtained as a result.

As mentioned above, the electronic volume circuit of the present invention is characterized in that the current source transistor 13 of the signal input stage of the double-balanced differential amplifier forms two voltage follower circuits together with the differential amplifiers 2a and 2b. are doing. The first voltage follower circuit superimposes a signal component on the DC component, and the second voltage follower circuit supplies the DC component to each double-balanced differential amplifier. These voltage follower circuits are selectively supplied with a signal component superimposed on a DC component or a DC component based on a signal from a signal switching circuit. In this way, by forming a double-balanced differential amplifier and two voltage follower circuits as a semiconductor integrated circuit,
An electronic volume circuit with excellent characteristics can be obtained. Furthermore, circuits such as the electronic volume circuit shown in Figure 2, which use a resistive load in the output stage of a double-balanced differential amplifier to obtain the output, are susceptible to the output being affected by a signal source mixed into the power supply. This is an effective circuit, and is also effective for amplifiers with resistive loads on other output stages.

As described above, the electronic volume circuit according to the present invention improves the amount of attenuation and also solves various problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an outline of a voltage follower circuit according to the present invention, and FIG. 2 is an embodiment thereof. DESCRIPTION OF SYMBOLS 1... Double balanced differential amplifier, 2... Signal input circuit, 3... Signal switching circuit, 4... Variable DC power supply, 5, 22... DC bias source, 6... Current source transistor, 7, 8, 10, 11, 14-17
...transistor, 9,12,13...current source transistor, OUT...output terminal, 21...signal source, 23...load resistor, 2a, 2b...differential amplifier.

Claims (1)

[Scope of utility model registration request] In an electronic volume circuit including a double balanced differential amplifier, a circuit detects the voltage level of a variable DC power supply that controls the output of the electronic volume circuit, and a circuit that superimposes a signal component on a DC bias source to The first voltage supplied to the input stage of the balanced differential amplifier
comprising a follower circuit and a second voltage follower circuit that supplies a DC potential equal to the potential of the DC bias source to the input stage of the double-balanced differential amplifier, so that the voltage level of the variable DC power source is minimized. An electronic volume circuit characterized in that a first voltage follower circuit is interrupted and a second voltage follower circuit is activated by an electric potential.