JPS5926662Y2 - FM receiver tuning display device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tuning display device for an FM receiver using light emitting elements such as light emitting diodes.

In FM receivers, in order to know the optimal tuning state, a tuning display meter has traditionally been used, in which the pointer indicates the zero point in the optimal tuning state, and when the tuning deviates, the needle swings to the + side or one side. has been used.

However, such a tuning display meter has a large shape and is susceptible to impact, so it is not suitable for miniaturization and diversification of receivers.

Therefore, recently, devices have been developed that use multiple light emitting diodes and allow the state of tuning to be determined by the number of light emitting diodes lit or the lighting position of the light emitting diodes. Electronic tuning display devices that light up light emitting diodes have come to be widely used.

This type of electronic tuning display device generally uses a voltage comparator, and one input terminal of the voltage comparator is applied with the DC output voltage from the FM detection circuit, and the other input terminal is applied with a predetermined voltage. Since the reference voltage must be applied externally,
Fluctuations and accuracy of this reference voltage affect the determination of the tuned state, and adjustment for this is also required.

In view of this, the present invention provides a tuning display device for an FM receiver that is not affected by variations in the characteristics of ICs constituting the FM detection circuit, and is configured so that the voltage comparator operates without bias adjustment. An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

In Figure 1, 1 is an FM intermediate frequency amplification circuit, 2 is an FM
The detection circuit is, for example, a quadrature detection circuit, and the FM intermediate frequency amplification circuit 1 and the FM detection circuit 2 are IC3 (LA 12
30 etc.).

4 is the first voltage comparator (operational amplifier), and the first input terminal (10 input terminal) I is connected to the FM detection circuit 2 via the resistor R1.
is connected to the output terminal A of the constant DC voltage [the reference side voltage of the tuning meter output, that is, the voltage shown by EA (approximately 5 V) in Figure 2 A], and the second input terminal (-input terminal) The variable DC voltage of the FM detection circuit 2 (the variable side voltage of the tuning meter output, i.e. EB in Figure 2 A)
It is connected to the output terminal B of the voltage indicated by .

Resistors R1 and R2 are bias resistances of the first voltage comparator 4;
R3 is a feedback resistor, and the gain of the first voltage comparator 4 is determined by R3/R2. Ea)
occurs.

5 is a second voltage comparator (operational amplifier), the first input terminal (10 input terminal) 1' is connected to the constant DC voltage output terminal A of the FM detection circuit 2 via a resistor R4, and the second input terminal (-input terminal) 2' is connected to the output terminal a of the first voltage comparator 4 via a resistor R5.

The resistor R4 is a bias resistor on the first input terminal (10 input terminal) 1' side of the second voltage comparator 5, and R6 is a feedback resistor.

By setting R5=R6, the gain of the second voltage comparator 5 becomes 1, and it operates as a simple phase inverter (the output voltage waveform of the second voltage comparator 5 is Eb in FIG. ).

LEDl and LED2 are first and second light emitting diodes connected in parallel between the respective output terminals a and l of the first and second voltage comparators 4 and 5 via a resistor R7.

Qo is a transistor for driving a light emitting diode, LED3 is a third light emitting diode connected between the emitter of the transistor and ground 6, R1□ is a current limiting resistor connected between the collector of transistor Q1 and power supply B, R8
゜Ro is between the power supply element B and the base of the transistor Q1,
RIO are bias resistors connected between the base of transistor Q1 and ground 6, respectively; D1. D2 has an anode connected to a connection point C between resistors R8 and R9, and a cathode connected to each output terminal a of the first and second voltage comparators 4 and 5.

diode connected to b, Q2 is a muting output inversion transistor with a grounded emitter whose collector is connected to the base of transistor Q1, R13 is a resistor connected between the base of transistor Q2 and ground 6, R□2
is a resistor whose one end is connected to the base of the transistor Q2, and the other end of the resistor receives a control signal related to the magnitude of the received input signal, for example, a control signal from the muting signal output terminal M provided in the IC3 as shown in FIG. A muting signal with a waveform as shown in is applied.

The operation of the thus configured FM receiver tuning display device will now be described.

First and second light emitting diodes LED1. The LED 2 is applied with the voltage difference between the respective output terminals a, l) of the first and second voltage comparators 4 and 5, that is, the voltage difference between the voltages shown in FIG.

Therefore, as the tuning operation is performed from the lower frequency to the higher frequency, that is, from left to right in Figure 2, the potential difference between output terminals a and b during no signal is OV, but the output gradually increases. The voltage Eb at the terminal A changes in one direction with respect to the voltage EA, and the voltage Ea at the output terminal a changes in one direction with the voltage EA as a reference, so that a potential difference is generated between the output terminals a and l).

In this case, voltage Eb at output terminal A>voltage E at output terminal a
Since the potential relationship is a, the first light emitting diode LED1 is in the forward direction, and the second light emitting diode LED is in the forward direction.
2 is in the opposite direction.

If the tuning operation continues and the potential difference between the output terminals a and b exceeds a predetermined voltage (approximately 2V), the first light emitting diode LE
D1 turns ON and lights up (region 2L1 in FIG. 2).

At this time, a reverse voltage is applied to the second light emitting diode LED2, but when the voltage across both ends of the first light emitting diode LED1 becomes 2■ or more, it turns ON, so the output terminal a
, l) will not further increase from 2■, and the voltage between
A reverse withstand voltage of 3■ or more is never applied to the light emitting diode LED2.

If the tuning operation is continued and the frequency is further moved from left to right in Fig. 2, as it approaches the zero point of the S card characteristic, that is, the center fC (tuning center point) of the target frequency, the output terminals a, l) The potential difference between them gradually decreases, and when the synchronization is complete, the potential difference between the output terminals a and l) becomes zero again, and the first light emitting diode LED is turned off and goes out.

If the frequency is further shifted to the right, ``contrary to the above, the voltage Ea of the output terminal a changes in the sub-direction with respect to the voltage EA, and the voltage Eb of the output terminal A changes in one direction with the voltage EA as the reference. However, since the voltage Ea of the output terminal a is greater than the voltage Eb of the output terminal A, the second light emitting diode LED1 is in the forward direction, the first light emitting diode LED1 is in the reverse direction, and the second light emitting diode LED2 is turned on. and lights up.

(Region 2L2 in Figure 2).

Note that the resistor R7 is connected to the light emitting diode LED1. This is a resistor that limits the current flowing through LED2, and is set appropriately depending on the type of light emitting diode.

Next, a third light emitting diode LED3 for displaying the center frequency
The operation of this will be explained.

Connection point C is connected to diode D1. Since it is connected to each output terminal a, l) of the first and second voltage comparators 4 and 5 via D2, the potential of the connection point C changes as the potential of each of the output terminals a and b changes. changes as shown in Figure 3A.

Furthermore, a muting signal that becomes zero potential near the tuning center point fc is applied to the four base points of the transistor Q2, as shown in the opening of FIG.

Therefore, the potential at the base point e of the transistor Q1 becomes as shown by the solid line in FIG.

That is, when the voltage of the muting signal is zero near the tuning center point fc, the change in voltage at the output terminals a, l appears as it is at the base of the transistor Q1, and the voltage at point e reaches a predetermined level (approximately 2.6 V). ), the third light emitting diode LED3 lights up (region L3 in FIG. 3).

Now, if we consider the case where there is no transistor Q2, in this case the voltage waveform appearing at the base of transistor Q1 will be like the broken line in Figure 3, and even in the no signal state, transistor Q1 will be ON, and the third light emitting diode will be turned on. LED3 lights up.

Therefore, in the present invention, a muting output inverting transistor Q2 is provided, and when there is no signal, the potential of the base of the transistor Q1 is forcibly brought to zero by the muting signal, and the third light emitting diode LED3 is turned off.

The above is an explanation of the operation of the tuned display device of the present invention.

By the way, the first to third light emitting diodes LED1 to LED
The relationship between the lighting area and frequency of No. 3 is as shown in FIG.

That is, on the circuit, the first and second light emitting diodes LED1. L
0N-OFF of ED2 and third light emitting diode LED
3 ON-OFF operate completely separately.

Therefore, when the third light emitting diode LED3 is ON, the first and second light emitting diodes LED1 and LED2 are not necessarily OFF.
It doesn't necessarily mean it will be F.

(However, depending on how the constants of each circuit are set, it is also possible to set the first and second light emitting diodes LED1 and LED2 to be OFF whenever the third light emitting diode LED3 is ON).

In this embodiment, as shown in Fig. 4, when the tuning operation is performed from the left to the right (from the lower intermediate frequency to the higher intermediate frequency), first the first light emitting diode LED □ turns on and lights up. However, before the first light emitting diode LED1 is turned off and turned off, the third light emitting diode LED3 is turned on and turned on.

Next, the first light emitting diode LED1 is turned off and turned off, and before the third light emitting diode LED3 is turned off, the second light emitting diode LED2 is turned on and turned on.

After that, the light emitting diode LED3 of the hair 3 turns off,
Finally, the second light emitting diode LED2 is turned off and goes out.

Therefore, in the region L3, the first and third light emitting diodes LED1. LED3 or second and third light emitting diode L
ED2. The LEDs 3 are lit at the same time, and only the third light emitting diode LED 3 is lit in the region L4.

Therefore, the optimum tuning point is in the region L4, and the three light emitting diodes LED1. LED2. By using the LED 3, it is possible to obtain an effect substantially equivalent to a 5-point display.

In addition, each light emitting diode LED1. LED2. The lighting width of the LED 3 can be varied by the feedback resistor R3 of the first voltage comparator 4.

Furthermore, in the example of the present invention, an example was explained in which a quadrature detection type detection circuit was used as the FM detection circuit, but the present invention is not limited to such an embodiment. A detection circuit may also be used.

As described above, the FM receiver tuning display device according to the present invention has the following features:
The reference voltage given to the voltage comparator is not given from an external external circuit like in the past, but instead uses a constant DC voltage generated from a stable FM detection circuit. (a) FM detection circuit It is not affected by variations in the characteristics of the ICs that constitute it.

(b) At the time of design, it is only necessary to determine the constants of each circuit element once, and there is no need to adjust the bias of the voltage comparator, etc.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the main part of an FM receiver using a tuning display device according to the present invention, Fig. 2 shows the voltage waveforms at each point in Fig. A diagram showing the lighting area of the light emitting diode, Figure 3 A9 and C are diagrams showing the voltage waveform at each point in Figure 1, and Figure 4 is a diagram showing the lighting area of the first, second and third light emitting diodes. It is. 2...FM detection circuit, 3,4...Voltage comparator, LED3...Light emitting diode, R3,
R6... Feedback resistor, Qo... Transistor for driving light emitting diode.

Claims (5)

[Scope of utility model registration request] (1) An FM detection circuit that generates a constant DC voltage at a first output terminal and a variable DC voltage that changes around the constant DC voltage at a second output terminal in response to tuning deviation from the tuning center point. an FM receiver comprising: a first voltage comparator to which the constant DC voltage is applied to a first input terminal and the variable DC voltage to a second input terminal; a second voltage comparator to which a constant DC voltage is applied and to which the output voltage of the first voltage comparator is applied to a second input terminal; means for operating the first voltage comparator as an amplifier; means for operating the voltage comparator as a phase inverter; a light emitting element driving element controlled by the outputs of the first and second voltage comparators and a signal related to the magnitude of the received input signal; and the light emitting element. 1. A tuning display device for an FM receiver, comprising a light emitting element connected to the output side of a driving element, the light emitting element being turned on only in an optimal tuning state near the tuning center point. (2) The F according to claim 1 of the utility model registration claim, wherein the FM detection circuit is a quadrature detection circuit.
M receiver tuning display device. (3) A utility model registration claim characterized in that the means for operating the first voltage comparator as an amplifier and the means for operating the second voltage comparator as a phase inverter each include a feedback resistor. A tuning display device for an FM receiver according to scope 1. (4) The tuning display device for an FM receiver according to claim 1, wherein the signal related to the magnitude of the received input signal is a muting signal. (5) The tuning display device for an FM receiver according to claim 1, wherein the light emitting element is a light emitting diode, and the light emitting element driving element is a transistor for driving the light emitting diode.