JPH0514615Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an RF modulator in which the modulated wave output can be arbitrarily selected between the PAL method (negative modulation method) and the SECAM method (positive modulation method).

(Prior art) For television receivers, PAL and PAL systems are used.
There is a SECAM method. For this reason, it is desirable that the modulated wave output of the RF modulator can be arbitrarily selected between the PAL system and the SECAM system.

FIG. 3 shows a circuit diagram of a main part of a first conventional example of an RF modulator that can select between the PAL system and the SECAM system.

In FIG. 3, a common contact c of a switch 1 having two contacts per circuit is connected to a power source 2, and contacts a and b are grounded through variable resistors 3 and 4, respectively. The sliding terminals 3a of these variable resistors 3, 4,
4a is connected to a bias voltage input terminal 7a of the video modulator 7 via diodes 5 and 6 in the forward direction, respectively.

Here, the video modulator 7 can obtain a modulated wave output in which a carrier wave input is subjected to amplitude modulation with a video signal. As shown in FIG. 4, the degree of modulation is 100% at a certain bias voltage E, a higher bias voltage results in negative modulation, and a lower bias voltage results in positive modulation.

Therefore, if the contact a of the switch 1 is set to the PAL system, the sliding terminal 3a of the variable resistor 3 is set to a bias voltage EP higher than the bias voltage E at a modulation degree of 100%. Also, connect contact b of switch 1.
When setting to the SECAM method, the sliding terminal 4a of the variable resistor 4 is set to a bias voltage ES lower than the bias voltage E at a modulation degree of 100%.

As a result, by appropriately switching the switch 1, an arbitrarily selected modulated wave output of the PAL system or the SECAM system can be obtained from the video modulator 7.

FIG. 5 is a circuit diagram of a main part of a second conventional example of an RF modulator that can select between the PAL system and the SECAM system. In FIG. 5, the same circuit elements as those in FIG. 3 are given the same reference numerals and redundant explanations will be omitted.

In Fig. 5, the differences from Fig. 3 are as follows.
Resistors 8 and 8 are connected to both ends of variable resistors 3 and 4, respectively.
9, 10, and 11 are provided, the bias voltage range that can be set by the sliding terminals 3a, 4a of the variable resistors 3, 4 is set by the resistors 8, 9, 10, 11 at both ends.
It is configured to restrict as appropriate.

(Problems to be Solved by the Invention) In the first conventional example shown in FIG. 3 above, the bias voltage EP of the PAL method and SECAM method is , ES can be set. Therefore, when setting the bias voltages EP and ES, set switch 1 to the PAL position on the device display to set the SECAM system bias voltage ES, and vice versa.
There was a problem in that it was easy to make an error in setting the bias voltage EP of the PAL system at the position of the SACAM system.

Therefore, in the second conventional example shown in FIG.
By resistors 8, 9, 10, 11, switch 1
In the PAL system position, the bias voltage EP is limited to a voltage range higher than the bias voltage E at 100% modulation using the sliding terminal 3a of the variable resistor 3, and in the SECAM system position, the variable resistor 3 The bias voltage ES is limited so that it can be set within a voltage range lower than the bias voltage E at the sliding terminal 4a of No. 4, which is improved so that setting errors will not occur during adjustment work. However, since the circuit configuration includes resistors 8, 9, 10, and 11, the number of components increases accordingly, resulting in an increase in price and another problem in that miniaturization is hindered.

The purpose of this invention was made in view of the above-mentioned circumstances, and was designed to prevent the bias voltage from being set incorrectly without increasing the number of parts.
Our goal is to provide an RF modulator.

(Means to be Solved by the Invention) In order to achieve this object, the RF modulator of the present invention is capable of adjusting the degree of modulation of the modulated wave output within the range of positive modulation and negative modulation by adjusting the bias voltage. In an RF modulator equipped with a video modulator, two variable resistors are connected in series between the power supply and ground, a switch is connected in parallel to one of the variable resistors, and one end of the variable resistor is connected to the switch. The sliding terminal of the other variable resistor is connected to the bias voltage input terminal of the video modulator.

(Function) Two variable resistors are interposed in series between the power supply and ground, a switch is connected in parallel to one of the variable resistors, and one end of this variable resistor is connected to a sliding terminal. Since the sliding terminal of the other variable resistor is connected to the bias voltage input terminal of the video modulator, closing or closing the switch will change the resistance value set by one variable resistor to an interposed or short circuit. The bias voltage generated at the sliding terminal of the other variable resistor is switched between high and low. The bias voltage level set when the switch is closed or opened cannot be reversed by adjusting the two variable resistors. SECAM
Appropriate bias voltages can be set for both methods.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of a main part of an embodiment of the RF modulator of the present invention. In FIG. 1, circuit elements that are the same as those in FIGS. 3 and 5 are given the same reference numerals, and redundant explanations will be omitted.

In FIG. 1, a power supply 2 connects two variable resistors 1
3 and 14 are connected in series to ground. A switch 11 is connected in parallel to one variable resistor 14 whose one end is grounded, and one end of this variable resistor 14 is connected to a sliding terminal 14a. Furthermore, the sliding terminal 13a of the other variable resistor 13, whose one end is connected to the power supply 2, is connected to the bias voltage input terminal 7a of the video modulator 7.

In this configuration, the switch 11 is first closed to short-circuit one variable resistor 14, and the sliding terminal 13a of the other variable resistor 13 is adjusted so that the SECAM
Set the bias voltage Es of the method. Next, when the switch 11 is opened, one variable resistor 14 is inserted, and depending on the resistance value, the other variable resistor 13 is connected.
The voltage generated at the sliding terminal 13a is equal to the bias voltage Es set as the bias voltage of the SECAM method.
Becomes higher. Therefore, the sliding terminal 14a of one variable resistor 14 is adjusted and the other variable resistor 13
The voltage generated at the sliding terminal 13a is set as the bias voltage EP of the PAL system. Here, switch 1
The bias voltage Es that can be set when 1 is closed and the bias voltage EP that can be set when 1 is open is ES≦EP,
SECAM only when the switch 11 is in the correct position.
The bias voltages ES and EP for both the PAL method and the PAL method can be appropriately set, and setting errors will not occur as in the conventional circuit shown in FIG.

FIG. 2 is a circuit diagram of a main part of another embodiment of the RF modulator of the present invention. In Figure 2, the first
Circuit elements and the like that are the same as those in the figures are given the same reference numerals and redundant explanations will be omitted.

In FIG. 2, the power supply 2 is connected to two variable resistors 2.
3 and 24 are successively interposed in series and grounded.
A switch 21 is connected in parallel to one variable resistor 23 whose one end is connected to the power source 2, and one end of this variable resistor 23 is connected to a sliding terminal 23a. Furthermore, the sliding terminal 24a of the other variable resistor 24, one end of which is grounded, is connected to the bias voltage input terminal 7a of the video modulator 7.

In this configuration, first, the switch 21 is closed to short-circuit one variable resistor 23, and the sliding terminal 24a of the other variable resistor 24 is adjusted to set the bias voltage EP for the PAL system. Next, when the switch 21 is opened, one variable resistor 23 is inserted, and the voltage generated at the sliding terminal 24a of the other variable resistor 24 due to its resistance value is the bias voltage EP set as the bias voltage of the PAL system. becomes lower. Therefore, the sliding terminal 23a of one variable resistor 23 is adjusted to set the voltage generated at the sliding terminal 24a of the other variable resistor 24 to the bias voltage ES of the SECAM system. Here, as in the embodiment shown in FIG. 1, the bias voltages ES and EP for both the SECAM system and the PAL system can be appropriately set only by setting the switch 21 in the correct position.

(Effect of the invention) As explained above, according to the RF modulator of the invention, only when the switch is in the correct position
The bias voltages for both the SECAM method and the PAL method can be set appropriately, and there are no setting errors during adjustment work, and the number of parts does not increase, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of an embodiment of the RF modulator of the present invention, and FIG. 2 is a circuit diagram of an RF modulator of the present invention.
It is a principal part circuit diagram of another example of a modulator,
Figure 3 shows that you can choose between PAL and SECAM methods.
FIG. 4 is a diagram showing the bias voltage versus modulation degree characteristics of the video modulator of the RF modulator, and FIG. 5 is a diagram showing the characteristics of the PAL system and the SECAM system. can choose
FIG. 2 is a circuit diagram of a main part of a second conventional example of an RF modulator. 1, 11, 21...Switch, 2...Power supply,
3, 4, 13, 14, 23, 24...variable resistor, 3a, 4a, 13a, 14a, 23a, 24
a...Sliding terminal, 7...Video modulator, 7a...Bias voltage input terminal.

Claims (1)

[Scope of utility model registration request] In an RF modulator equipped with a video modulator, the degree of modulation of the modulated wave output can be adjusted within the range of positive modulation and negative modulation by adjusting the bias voltage.
Connect two variable resistors in series between the power supply and ground, connect a switch in parallel to one variable resistor, connect one end of one variable resistor to the sliding terminal, and connect the other variable resistor to the sliding terminal. An RF modulator, characterized in that a sliding terminal of a resistor is connected to a bias voltage input terminal of the video modulator.