JPS6348457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a high frequency input circuit for a composite radio device having a television receiver capable of receiving VHF/UHF broadcasts and an FM/AM radio receiver in the same housing.
The purpose is to configure it at low cost and with high performance.

Figure 1 shows a conventional example.
Signals received by the UHF/FM common rod antenna 1 or an external antenna (not shown) are transmitted through an external antenna jack 2. For example, if the input signal is a high frequency signal such as UHF, the signal is transmitted through a small capacitor 3. is added to the UHF tuner 4 of the television receiver 100.

Moreover, this received signal is passed through the capacitor 5,
It is added to the high frequency switching circuit formed by diodes 6 and 7. Here, when the power switch 8 is at the terminal TV position and the band conversion switch 9 of the television receiver is at the terminal V position, the voltage from the battery 10 is applied via the resistor 11 to the diode 6 and the resistor 12.
Diode 6 is turned on, and the high frequency signal passes from capacitor 5 to diode 6 and capacitor 13 to VHF tuner 1.
It is added to VRF, which is the input terminal of 4. On the other hand, when the band conversion switch 9 is at the terminal U position, no voltage is applied to the diode 6;
It is in the OFF state, and the input terminal of VHF tuner 14
No signal is transmitted to VRF. In this case, UHF
This is how Chuyuna 4 works.

When the power switch 8 is in the position of the terminal RAD10, current flows through the diode 7 and the resistor 12 via the inductance 15, and the diode 7 is turned on.
state. At this time, the signal from the antenna is applied to the RF input terminal of the radio receiver 200 via the capacitor 5 and diode 7.

The circuit shown in Figure 1 operates as described above, but since there is a junction capacitance between the electrodes of diodes 6 and 7 that perform high frequency switching operations, the signal received by the antenna is affected by these switching circuits during UHF reception. This causes attenuation of the UHF signal.
In order to prevent this UHF signal from attenuating, it is conceivable to use PIN diodes with small inter-electrode junction capacitance as these diodes 6 and 7.
In this case, expensive elements are required and it is not practical.

In addition, in order to sufficiently turn on this PIN diode, a sufficient switching current must flow. In equipment that uses a battery as a power source and operates at low voltage, a coil 15 is used to ensure that this switching current flows sufficiently.

As described above, in the conventional example, an expensive element must be used as the switching element, and the switching current also becomes large, which poses a big problem in low-voltage, low-power consumption equipment.

The present invention obviates the above drawbacks. An example of this will be explained below with reference to FIG.
Elements that are the same as those in the drawings will be described using the same numbers.

In Fig. 2, the difference from Fig. 1 is that an inductance 16 and a capacitor 1 are installed after the diode 7.
The point is that a low pass filter consisting of 7 is inserted. Other details are the same as in FIG. In this configuration, the signal from the antenna is passed through the small capacitor 3 only for UHF band signals.
It is added to the input terminal URF of the UHF tuner 4.

Here, when the power switch 8 is at the terminal TV position and the band conversion switch 9 is at the terminal V position, the power supply voltage from the battery 10 is added to the resistor 11, the diode 6, and the resistor 12, and the diode 6 is turned on.
state, the signal from the antenna passes through capacitor 5, diode 6, capacitor 13,
It is added to VRF, which is the input terminal of the VHF tuner 14. When the band changeover switch 9 is at the terminal U position, no current flows through the diode 6 and the diode 6 is in the FF state.

On the other hand, when the power switch 8 is in the position of the terminal RAD10, a current flows through the resistor 18, inductance 16, diode 7, and resistor 12, and the diode 7 is turned on, and the signal from the antenna passes through the capacitor 5, diode 7, and inductance 16. This is added to the RF input circuit of the radio receiver 200.

Here, a low-pass filter consisting of an inductance 16 and a capacitor 17 is inserted immediately after the diode 7, and due to the blocking effect of the inductance 16, even if the junction capacitance between the electrodes of the diode is slightly large, the UHF band applied to the UHF tuner 4 is Signal attenuation is improved.

Therefore, according to this configuration, a normal switching diode can be used without using an expensive element such as a PIN diode, and the switching current is also small, resulting in low power consumption. Also, regarding the connection lead wire from the television receiver 100 to the radio receiver 200, low pass filters 16, 1
7 is inserted, the signal band of the television receiver will not be affected even if a normal lead wire is used without using a coaxial cable. Note that a low-pass filter is usually inserted inside the input terminal of the VHF tuner 14 to block the UHF band and pass only the VHF band.
VHF tuners have no effect on signal attenuation in the UHF band. Furthermore, with this configuration, the inductance 15 can be replaced with the resistor 15.

As described above, according to the present invention, by inserting a low-pass filter immediately after the switching output circuit to the radio receiver, a normal switching diode can be used as a diode constituting the high frequency switching circuit. It requires only a small current, resulting in low power consumption, and is extremely effective when used in devices that operate at low voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional composite radio device, and FIG. 2 is a circuit diagram of a composite radio device according to an embodiment of the present invention. 1...VHF/UHF/FM common rod antenna,
2...External antenna jack, 3, 5, 13...
Capacitor, 4...UHF tuner, 6,7...
Switching diode, 8...Power switch,
9...TV band conversion switch, 10...Power supply, 11, 12, 18...Resistor, 14...VHF
Tuner, 16, 17... Inductance and capacitor forming the low-pass filter, 100...
Television receiver, 200...radio receiver.

Claims (1)

[Claims] 1 A television receiver and a radio receiver are included in one housing, and a received signal from an antenna shared by the television receiver and radio receiver is applied to the UHF tuner via a small capacitor. and transmits the received signal from the antenna through a high frequency switching circuit using a diode.
1. A composite radio device, which is connected to a high-frequency input circuit of a VHF tuner and a radio receiver, and a low-pass filter is inserted immediately after a switching output circuit to the radio receiver.