JPH0711543B2 - Level meter circuit - Google Patents

Description

The present invention relates to a level meter circuit for displaying a signal level.

Conventionally, when displaying a signal strength level or a recording signal level in a radio receiver, a tape recorder, or the like, a drive circuit for a display element is configured separately from the signal system circuit, which makes the circuit configuration complicated. was there.

Therefore, an object of the present invention is to provide a level meter circuit having a simplified circuit configuration by also using a signal system amplifier circuit for driving a display element.

That is, as illustrated in FIG. 1, the level meter circuit of the present invention comprises first and second transistors (10, 12) having a common emitter, and a constant bias is applied to the base of the first transistor. Input signal with voltage, the second
A differential amplifier (2) to which an output signal is fed back from the output side through a feedback circuit (22) together with the bias voltage to the base of the transistor, and a constant current source (3) that generates a constant current.
2), a third transistor (36) whose base and collector are connected to this constant current source to receive a constant current, and a fourth and fifth transistor (38, 40) connected to the base collector of this third transistor. The first and second transistors are connected by connecting bases and drawing a constant current from the emitter side of the first and second transistors to the fourth transistor in response to the constant current flowing in the third transistor. A first current reversing circuit (4) for supplying an operating current to the second transistor and drawing a constant current into the fifth transistor;
The base and collector of a sixth transistor (44) are connected in common to the collector side of the first transistor of the differential amplifier, and the seventh and eighth transistors (48, 48) are connected to the base and collector of the sixth transistor. 50) is connected to the base, and the first and second transistors are connected through the seventh and eighth transistors.
The individual currents flowing in the transistor side, the current is flown into the feedback circuit side through the seventh transistor, and the eighth transistor is connected in series to the fifth transistor, and the fifth transistor is connected in series. A second current is supplied to the side according to the current flowing through the first transistor, and an output current composed of a difference current between this current and a constant current drawn into the fifth transistor is generated separately from the output signal. Of the current inverting circuit (6) and the collector side of the second transistor of the differential amplifier, and the base and collector of the ninth transistor (46) are connected to the base and collector of the ninth transistor. The base of the transistor (52) is connected, and the current flowing to the side of the second transistor is collected by the tenth transistor. To third current inversion circuit (42)
And the base and collector of the eleventh transistor (56) are connected to the collector side of the tenth transistor of the third current inverting circuit, and the twelfth transistor (58) is connected to the base and collector of the eleventh transistor. ) Connect the base,
The output signal is generated by drawing the current extracted through the third current inversion circuit from the seventh transistor and the feedback circuit side of the second current inversion circuit to the twelfth transistor side. A fourth current reversing circuit (54); and a light emitting diode (8) connected in parallel to the fifth transistor, supplied with the output current to emit light, and representing the level of the input signal. Characterize.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the level meter circuit of the present invention. In the figure, this level meter circuit is configured in relation to an amplification system for amplifying a signal to be level-displayed, and a differential amplifier 2 is installed in the preceding stage, and
A display element is obtained by combining the output currents of the first current inverting circuit 4 for determining the operating current of the differential amplifier 2 and the second current inverting circuit 6 for extracting the output of the differential amplifier 2.
For example, it is configured to drive the light emitting diode 8. That is, the differential amplifier 2 is composed of first and second transistors 10 and 12 whose emitters are commonly connected, and an input terminal 16 to which an input signal is given via a resistor 14 is formed at the base of the transistor 10. At the same time, a constant DC bias is set from the bias input terminal 18 via the resistor 20. On the other hand, a feedback circuit 22 is formed between the base of the transistor 12 and the output point. That is, the resistor 24 is connected between the base of the transistor 12 and the output point, and a constant DC bias is set to the base from the bias input terminal 26 via the resistor 28.

Also, the emitters of the transistors 10 and 12 and the reference potential terminal
A first current inverting circuit 4 is provided between the constant current source 32 and the differential amplifier 2 between the reference potential line grounded via 30 and the constant current source 32. is set up. That is, the drive voltage from the power supply terminal 34
A third transistor 36, which is configured as a diode with the constant current source 32 having a common base and collector in common, is connected between the power supply line to which Vcc is applied and the reference potential line, and the base and collector of this transistor 36 are connected. The bases of the fourth and fifth transistors 38 and 40 are connected to. The transistor 38 is connected between the emitters of the transistors 10 and 12 and the reference potential line with the emitter on the reference potential line side, and the emitter area is set to that of the transistor 36 so that the operating current is twice the current flowing through the transistor 40. It is set twice as large as that.

The output of the differential amplifier 2 is taken out from the collector side of each of the transistors 10 and 12, and the second and third current inverting circuits 6 and 42 are installed between the collectors of the transistors 10 and 12 and the power supply line. Has been done. Between the collectors of the transistors 10 and 12 and the power supply line, the sixth and ninth transistors 44 and 46 as diodes having the bases and collectors of the current inversion circuits 6 and 42 connected in common are connected, respectively.
The bases of the seventh and eighth transistors 48 and 50 are commonly connected to the base and collector of the transistor 44, and
The base and collector of the transistor 46 are connected to the base of the tenth transistor 52. Transistors 48, 5
The emitters of 0 and 52 are commonly connected to a power supply line, and a fourth current inverting circuit 54 is provided between the collectors of the transistors 52 and 48 and the reference potential line. That is, between the collector reference potential lines of the transistors 52 and 48,
And the twelfth transistors 56 and 58 are individually connected, and the base and collector of the transistor 56 and the base of the transistor 58 are commonly connected. The second, third and fourth current inversion circuits 6, 42 and 54 constitute an output circuit which synthesizes and takes out the output current of the differential amplifier 2, and the transistor 48,
An output terminal 60 is formed on the collector of 58, and this output terminal is
Amplified output can be taken from 60.

The transistor 40 of the first current inverting circuit 4 and the transistor 50 of the second current inverting circuit 6 are connected in series between the power supply line and the reference potential line,
An output terminal 62 is formed on the collectors of 40 and 50, and a light emitting diode 8 as a display element is connected between the output terminal 62 and the reference potential terminal 30 with the reference potential side as the cathode. That is, the driving circuit for driving the light emitting diode 8 is the first circuit for setting the operating current of the differential amplifier 2.
The current reversing circuit 4 and the second current reversing circuit 6 for taking out the output of the differential amplifier 2 are constituted by the transistors 40 and 50 which are the constituent elements thereof. It is configured to drive by flowing a difference current of flowing currents.

The operation will be described based on the above configuration. After the signal voltage applied to the input terminal 16 is amplified by the differential amplifier 2,
It can be taken out from the output terminal 60. In this amplification operation, the input signal voltage applied to the input terminal 16 is V _IN , the change is ΔV _IN , and the current flowing through the transistor 10 is I _IN .
_1, I ₂ the current flowing through the transistor 12, the current flowing through the transistor 38 which is a composite current I _3, the output current of the constant current source 32 for providing the current I ₃ When I _4, the collector of the transistor 48 A current I ₀₁ flows through the transistor 5
A current I ₀₂ flows through 8. In this case, if the current flowing through the transistor 50 is I ₀₃ and the current flowing through the transistor 40 given by the constant current source 32 is I ₀₄ , the drive current I _L flowing through the light emitting diode 8 is I _L = I ₀₃ −I ₀₄ ... (1), and in the formula (1), current I ₀₃ is the _{I 03 = 1 1 = I 3} /2 = I 4 ··· (2), the current I ₀₄ is I ₀₄ = I ₄ And ΔI by ΔV _IN
By the increment ΔI ₁ of ₁ , the formula (1) becomes I _L = (ΔI ₁ + I ₁ ) −I ₀₄ = ΔI ₁ (3) That is, the drive current I flowing through the light emitting diode 8
_L becomes a value corresponding to the input signal voltage, and the light emission amount of the light emitting diode 8 follows the change of the input signal voltage.

As described above, in this level meter circuit, a part of the amplifiers installed in the signal system is made common, and the amplification relationship of the current is detected to obtain the drive current without installing a special circuit. Since the change in the drive current corresponds to the input signal voltage, the light emitting current of the light emitting diode 8 depends on the input signal level. In particular, since the light emitting state of the light emitting diode 8 is linked to the amplified output of the amplifier 2, it is possible to prevent the occurrence of a signal level display error due to the installation of another circuit.

FIG. 2 shows another embodiment of the present invention, in which a resistor 64 as a current limiting element for suppressing an output current is inserted on the emitter side of the transistor 50. By adjusting the ratio of the currents flowing through the transistors 40 and 50 with the resistor 64, the value of the drive current flowing through the light emitting diode 8 can be freely set. For example, the light emitting state of the light emitting diode 8 is low when the input signal level is low. It is sometimes possible to obtain a light emitting state in which the light emission state is changed in response to the level change, and when a certain level is exceeded, the light emission state is set to a certain state.

In the above-described embodiment, the case where the light emitting diode is used as the display element has been described as an example, but the same effect can be expected when the display element uses a light emitting element other than the indicator or the light emitting diode.

As described above, according to the present invention, the signal-system amplifier circuit is also used as the display-output circuit, and the output current corresponding to the input signal level is extracted separately from the output signal according to the input signal to emit light. Since the input signal level is displayed by emitting light to the diode and emitting light from the light emitting diode, the display accuracy of the signal level can be improved,
Moreover, since it is not necessary to separately configure the signal system circuit and the display system circuit, the circuit configuration can be simplified and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a level meter circuit of the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the present invention. 2 ... Differential amplifier 4 ... First current inverting circuit 6 ... Second current inverting circuit 8 ... Light emitting diode 10 ... First transistor 12 ... Second transistor 22 ... Feedback circuit 32 ... ... constant current source 36 ... third transistor 38 ... fourth transistor 40 ... fifth transistor 42 ... third current reversing circuit 44 ... sixth transistor 46 ... ninth transistor 48 ... 7th transistor 50 8th transistor 52 10th transistor 54 4th current reversing circuit 56 11th transistor 58 12th transistor

Claims (1)

[Claims] 1. A first and second transistor having a common emitter, wherein an input signal is supplied to a base of the first transistor together with a constant bias voltage, and an output unit is supplied to the base of the second transistor together with the bias voltage. Differential amplifier to which an output signal is fed back from a side through a feedback circuit, a constant current source for generating a constant current, a third transistor having a base / collector connected to the constant current source and receiving a constant current, and a third transistor The bases of the fourth and fifth transistors are connected to the bases and collectors of the first transistor, and the first and second transistors are connected to the fourth transistor according to the constant current flowing in the third transistor.
A first current reversing circuit that draws a constant current from the emitter side of the transistor to supply an operating current to the first and second transistors and draws a constant current to the fifth transistor; Connect the base and collector of the sixth transistor in common to the collector side of the first transistor,
The bases and collectors of the sixth transistor are connected to the bases of the seventh and eighth transistors, and the currents flowing to the first transistor side through the seventh and eighth transistors are individually taken out to obtain the seventh transistor. The current is caused to flow into the feedback circuit side through a transistor, the eighth transistor is connected in series to the fifth transistor, and the first transistor is connected to the fifth transistor side.
A second current reversing circuit for injecting a current corresponding to the current flowing through the transistor and generating an output current composed of a difference current between this current and a constant current drawn into the fifth transistor separately from the output signal. Connecting the base and collector of the ninth transistor to the collector side of the second transistor of the differential amplifier, and connecting the base of the tenth transistor to the base and collector of the ninth transistor, A third current inversion circuit for extracting the current flowing to the transistor side by the tenth transistor, and a base / collector of an eleventh transistor are connected to the collector side of the tenth transistor of the third current inversion circuit. , To the base-collector of this 11th transistor
The bases of 12 transistors are connected, and the current drawn through the third current inverting circuit is drawn from the side of the seventh transistor and the feedback circuit of the second current inverting circuit to the side of the twelfth transistor. By
A fourth current reversing circuit for generating the output signal; and a light emitting diode connected in parallel to the fifth transistor to supply the output current and emit light to indicate the level of the input signal. Level meter circuit characterized by.