JPS5928089B2 - Meter drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a meter drive circuit for displaying the input of two types of signals with one meter, and particularly to an input display meter (signal meter) for an AM-FM receiver. It is best used as a

Background Art and its Problems In a receiver capable of receiving both AM waves and FM waves, one meter may be used as an input display meter (signal meter) for each.

Generally, a limiter is used in a signal meter drive circuit in an AM receiver to prevent the meter from being blown out due to excessive input that cannot be removed by AGC.

On the other hand, in a signal meter drive circuit in an FM receiver, the meter input is taken out from the IF stage, and the IF stage has the FM transmitter characteristic.

Therefore, not only is there no need for a limiter in the meter drive circuit itself, but on the other hand, if a limiter is installed, the meter swing will be constant for signals above a certain level, so it will not be necessary to use a limiter when receiving FM. It will no longer show the appropriate tuning points.

Conventionally, a changeover switch 1 was provided as shown in FIG. 1 to switch between AM reception and FM reception, thereby preventing the diode 2 as a limiter from affecting the FM reception.

Further, in consideration of the cost of the changeover switch 1 itself and the installation cost, a circuit is known in which the changeover switch is not used, as shown in FIG. 2.

When such a circuit receives FM, only a lower voltage can be supplied to the meter 3 than when receiving AM so that the diode 2 as a limiter does not operate.
Therefore, the original full scale of the meter 30 cannot be used effectively.

OBJECTS OF THE INVENTION The present invention provides a meter drive circuit that solves the above-mentioned problems.

Summary of the Invention The present invention comprises a first amplifier (9 in the embodiment, hereinafter the same numbers in parentheses) to which a first detection signal (for example, an AM detection signal) is supplied; A load resistor 30 connected to the output side, a Mitsuter circuit 33 connected in parallel to this load resistor 30, and a second detection signal (for example, an FM detection signal).
The emitter follower circuit 1 has a second amplifier 11 supplied with
By supplying the output signal of the second amplifier 11 to the meter 3 via the amplifier 9 and directly supplying the output signal of the second amplifier 11 to the meter 3, the first and second detected signals are selectively displayed by the meter 3. This is a meter drive circuit characterized in that:

With this configuration, two types of detected signals can be selectively displayed with one meter without influencing each other (and without using a changeover switch).

Embodiment In FIG. 3, a signal for indicating an input level in an AM receiver is taken out from an intermediate frequency amplification circuit 5 and detected by a detection circuit 6.

The detected signal is smoothed by a capacitor 7 and supplied to the base of the transistor 200 via a balanced resistor 8.

The transistor 20 and the transistor 21 constitute the differential amplifier 9, and the emitters of the transistors 20 and 21 are connected to each other, and the transistors 20 and 21 are connected to a 10B power source via a resistor 24.

The collector of the transistor 20 is grounded, and the collector of the transistor 21 is connected to a resistor 30 as a load of the differential amplifier 9.
and a Zener diode 33.

Resistor 25.26 connected to the base of transistor 210
is a resistor for bias setting.

The voltage developed across resistor 30 is supplied to the base of transistor 19.

The Zener diode 33 is used as a limiter to limit this voltage when it exceeds a predetermined value.

Note that instead of the Zener diode 330, for example, a circuit in which two diodes are connected in series may be used.

The transistor 19 constitutes an emitter follower circuit, and a load circuit 10 consisting of variable resistors 31, 32 and a meter 3 is connected to its emitter, and a 10B power source is directly connected to its collector.

On the other hand, a signal for displaying the input level in the FM receiver is taken out from the intermediate frequency amplification circuit 12 and subjected to envelope detection in the detection circuit 13.

Since the intermediate frequency amplification circuit 12 in the FM receiver is sufficiently biased, an excessive signal is not applied to the detection circuit 13.

The signal detected by the detection circuit 13 is transferred to the capacitor 1
4 and then supplied to the base of transistor 23 via balance resistor 15.

This transistor 23 constitutes the differential amplifier 11 together with the transistor 22, and the emitters of the transistors 22 and 23 are connected to each other, and the transistors 22 and 23 are connected to a 10B power source via a resistor 29.

The collector of the transistor 23 is grounded, and the collector of the transistor 22 is grounded via the load circuit 10 as a load of the differential amplifier 11.

Resistor 27.2B connected to the base of transistor 22
is a resistor for bias setting.

Next, the operation of the configuration described above will be explained.

First, during FM reception, a signal amplified by the differential amplifier 11 is supplied to the meter 3.

At this time, since the load circuit 10 is connected as a collector load of the transistor 22, this load is driven with a constant current.

Therefore, the voltage applied to the meter 3 is determined by the current division ratio between the meter 3 and the variable resistor 32, regardless of the value of the variable resistor 31.

During this FM reception, the diode characteristic between the base and emitter of transistor 19 exhibits a reverse characteristic with respect to the collector output of transistor 22, so transistor 2
The Zener diode 31 does not act on the collector output of No.2.

On the other hand, during AM reception, a signal amplified by the differential amplifier 9 is supplied to the resistor 30 and the Zener diode 33.

Zener diode 33 limits the voltage across resistor 30 to the Zener voltage when it exceeds a predetermined value.

Therefore, even if an excessive signal that cannot be removed by the AGC is supplied, it is limited by the Zener diode 33, so that the excessive signal will not be supplied to the meter 3 and cause the meter 3 to swing out.

The voltage developed across resistor 30 is applied to the base of transistor 190 forming an emitter follower circuit.

Since the load circuit 10 is connected as an emitter load of this transistor 19, it is driven at a constant voltage.

In this case, the voltage applied to the meter 3 is the variable resistor 31, 32
It is determined by the partial pressure ratio of meter 3.

Since the variable resistor 32 adjusts the voltage applied to the meter 3 during FM reception as described above, it is preferable to adjust the voltage applied to the meter 3 by adjusting the variable resistor 31 during AM reception.

If the variable resistor 31 is insufficient for adjustment, the voltage applied to the meter 3 may be adjusted by changing the resistance value of the resistor 30 and changing the emitter potential of the transistor 19.

Effects of the Invention It is possible to selectively display two types of detected signals without influencing each other and without using a changeover switch (and without using a changeover switch).

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing a conventionally known meter driving circuit, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. In addition, in the symbols used in the drawings, 3 is a meter;
6 and 13 are detection circuits, 9 and 11 are differential amplifiers, 30 is a resistor, 33 is a Zener diode, and 19 is a transistor.

Claims (1)

[Claims] 1 A first amplifier to which the first detection signal is supplied, a load resistor connected to the output side of the first amplifier, a Mitzter circuit connected in parallel to the load resistor, and a first amplifier connected to the output side of the first amplifier. a second amplifier to which the detection signal of No. 2 is supplied; and the voltage of the load resistor of the first amplifier is supplied to the meter via an emitter follower circuit, and the voltage of the second amplifier is supplied with the second amplifier. By supplying the output signal of directly to the meter, the first
and a meter drive circuit, characterized in that the magnitude of the second detected signal is selectively displayed by the meter.