JPS59202069A - Level meter circuit - Google Patents

Abstract

PURPOSE:To simplify the constitution of a level meter circuit, by holding a part of the circuit of the amplifier provided to a signal system in common. CONSTITUTION:Signal voltage inputted from a terminal is taken out from a terminal 60 while amplified by a differential amplifier 2. A constant current is supplied to said amplifier 2 from a constant current source 32 through a first current reversal circuit 4 and also taken out to the side of LED 8 by the circuit 4. In addition, the output current of the amplifier 2 is taken out to the side of LED 8 while synthetically outputted through second - fourth current reversal circuits 2, 42, 54 and LED 8 is driven by the circuit 1, 2. The driving current thereof corresponds to a current change component with the change of input voltage and level change of a predetermined value or more is displayed by LED 8 in such a state that a part of the circuit of the amplifier provided to a signal system is held in common and the constitution of a level meter circuit becomes simple.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a level making circuit that displays a signal level.

Conventionally, when displaying the signal strength level or recording signal level in radio receivers, tape recorders, etc., a drive circuit for the display element is configured separately from the signal system circuit, which has the disadvantage of complicating the circuit configuration. was there.

An object of the present invention is to provide a level meter circuit which drives a display element in conjunction with a signal system amplifier circuit and whose configuration is simplified.

The present invention includes an amplifier that amplifies a signal to be level-displayed, a first current inversion circuit that takes out the output of this amplifier, and a second current inversion circuit that detects a constant current that provides an operating current to the differential amplifier.
and a display element to which an operating current is applied by combining the output currents of the first and second current inverting circuits.

Hereinafter, the present invention will be described in detail with reference to 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 constructed in relation to an amplification system that amplifies the signal to be level-displayed, and a differential amplifier 2 is installed at the front stage thereof, and
By combining the respective output currents of the first current inverting circuit 4 that determines the operating current of the differential amplifier 2 and the second current inverting circuit 6 that extracts the output of the differential amplifier 2, a display element,
For example, it is configured to drive a light emitting diode 8. That is, the differential amplifier 2 is composed of transistors 10 and 12 whose emitters are connected in common, and an input terminal 16 to which an input signal is applied via a resistor 14 is formed at the base of the transistor 10, and a bias input terminal is formed at the base of the transistor 10. A constant DC bias is set from the 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,
A resistor 24 is connected between the base of the transistor 12 and the output point.
is connected to the base, and a constant DC bias is set to the base via the resistor 28 from the bias input terminal 26.

Further, between the emitter of the transistor 10.12 and the reference potential line grounded via the reference potential point terminal 30, a constant current is passed from a constant current source 32 to the differential amplifier 2, and the constant current is A first current reversing circuit 4 is installed to take out the light on the light emitting diode 8 side. That is, the power terminal 34
A constant current source 32 is connected between a power supply line to which a drive voltage Vcc is applied from the source and a reference potential line, and a transistor 3 configured as a diode with a common collector.
6 is connected, and the bases of transistors 38 and 40 are connected to the base and collector of this transistor 36. Transistor 38 is connected between the emitter of transistor 10.12 and the reference potential line with its emitter on the reference potential line side, and has an emitter area larger than that of transistor 36 such that the operating current is twice the current flowing through transistor 40. It is set to twice the size of that of .

Also, the output of the differential amplifier 2 is
taken out from the collector side of each transistor 10.12
Second and third current inversion circuits 6.42 are installed between the collector and the power supply line. Each transistor 1
Transistors 44 and 46 serving as diodes with the bases and collectors of each current inverting circuit 6 and 42 connected in common are connected between the collectors of the transistors 44 and the power supply line. 48.50 bases are connected in common, and 1
- The base and collector of the transistor 46 are connected to the base of the transistor 52. transistor 48.5
0.52 emitters are commonly connected to the power supply line, and a fourth current inversion circuit 54 is installed between the collector of the transistor 52.48 and the reference potential line. That is, transistors 56 and 58 are individually connected between the collectors of transistors 52 and 48 and the reference potential line.
The base and collector of the l-transistor 56 and the base of the transistor 58 are commonly connected. The second, third, and fourth current inverting circuits 6, 42, and 54 constitute an output circuit that combines and takes out the output current of the differential amplifier 2, and the collector of the transistor 48, 58 has an output terminal 60. is formed, and an amplified output can be taken out from this output terminal 60.

The transistor 40 of the first current inversion circuit 4 and the transistor 50 of the second current inversion circuit 6 are connected in series between the power supply line and the reference potential line, and the collectors of the transistors 40 and 50 have output terminals. 62 is formed, and a light emitting diode 8 as a display element is connected between the output terminal 62 and the reference potential point terminal 30 with the reference potential side as a cathode. That is, the drive circuit for driving the light emitting diode 8 includes a first current inversion circuit 4 for setting the operating current of the differential amplifier 2 and a second current inversion circuit for taking out the output of the differential amplifier 2. The light emitting diode 8 is configured to be driven by passing a current difference between the currents flowing between the transistors 40 and 50 into the light emitting diode 8.

The operation will be explained based on the above configuration. Input terminal 16
After the signal voltage given to 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
N, its change is ΔVIN, the current flowing through transistor 10 is I1, the current flowing through transistor 12 is 12,
The current flowing through the transistor 38, which is the combined current, is 1
3. If the output current of the constant current source 32 that supplies this current I3 is I4, a current I01 flows through the collector of the transistor 48, and a current +02 flows through the transistor 58. In this case, the current flowing through the transistor 50 is
3. Transistor 40 provided by constant current source 32
If the current flowing through the LED is ro4, the driving type /JrLIL flowing through the light emitting diode 8 is IL=IQ3 [04... (1), and the formula (
In 1), the current 103 is 103''I+ = I 3 / 2 = I 4 ... (2)
, the current I04 is l04=14, and ΔVI
Due to the increase ΔI in the current 11 due to N, equation (1) becomes: IL=(ΔI++1+) ro4 =Δ■1 (3). That is,
The drive current 11- flowing through the light emitting diode 1'8 has a value corresponding to the input signal voltage, and the amount of light emitted from the light emitting diode 8 follows the change in the input signal voltage.

In this way, in this level making circuit, a part of the circuit of the amplifier installed in the signal system is shared, and the drive current is obtained by detecting the increase/decrease relationship of the 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 corresponds to 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 display errors in signal levels caused by installing another circuit.

FIG. 2 shows another embodiment of the present invention, in which a resistor 64 is inserted on the emitter side of the transistor 50 as a current limiting element to suppress the output current. By adjusting the ratio of the current flowing through the transistors 40 and 50 using the resistor 64, the value of the drive current flowing through the light emitting diode 8 can be freely set. At times, it is possible to obtain a light emitting state in which the light is changed in response to a change in the level, and when the light exceeds a certain level, the light emitting state remains constant.

Although the above embodiments have been described using a light emitting diode as a display element, similar effects can be expected even if an indicator or a light emitting element other than a light emitting diode is used as the display element.

As explained above, according to the present invention, it is possible to simplify the circuit by sharing a part of the circuit of the amplifier installed in the signal system, and to faithfully display the signal level of the signal system. By sharing the circuit, the circuit configuration can be simplified and the configuration can be made at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a level making circuit according to the invention, and FIG. 2 is a circuit diagram showing another embodiment of the invention. 2... Differential amplifier, 4... First current inversion circuit, 6
. . . second current inversion circuit, 8 . . . a light emitting diode as a display element.

Claims (1)

[Claims] an amplifier that amplifies a signal to be level-displayed; a first current inversion circuit that takes out the output of the amplifier; a second current inversion circuit that detects a constant current that provides an operating current to the differential amplifier; and a display element to which an operating current is given by combining the output currents of the second current inverting circuit.