JPS6033013B2 - UHF/VHF receiver - Google Patents

Description

[Detailed Description of the Invention] The present invention is a so-called up converter (frequency conversion circuit).
When receiving UHF and VH on TV receivers with
This is to eliminate the difference in sensitivity when receiving F.

When each VHF/UHF tuner is configured as an electronic tuning type using a variable capacitance element, in the VHF tuner, it is not possible to cover the entire frequency band of the low channel and high channel by changing the capacitance of one variable capacitance element. Therefore, the inductance value that determines the tuning frequency is normally switched between the low channel and the high channel in cooperation with the variable capacitance element, which requires a switching diode and a switching signal forming circuit for band switching. Become.

On the other hand, since UHF tuners handle high frequencies, the frequency change rate itself is lower than that of VHF tuners, and it is not possible to cover the entire frequency band by changing the capacitance of a single variable capacitance element. Since there is no need to switch the inductance value as described above, there is no need for a switching diode or the like for switching, which has the advantage of simplifying the circuit configuration. Therefore, recently, it has been considered to replace the VHF tuner with a UHF tuner.

To do this, when receiving a VHF signal, the frequency of the VHF signal is first converted into a UHF signal, and this converted signal is supplied to a UHF tuner in the same way as the UHF signal, so that the desired VHF signal can be transmitted. Just configure it. With this configuration, it is possible to receive VHF signals without using a VHF tuner, so it is possible to avoid problems that would otherwise occur when using an electronic tuning system. Such a frequency conversion circuit is generally called an up-converter, and a tuner system including the up-converter is schematically shown in FIG.

In the figure, IU is a UHF antenna, IV is a VHF antenna, and the UHF signal SU is sent to the UHF antenna via the signal switching circuit 2.
Tuner 1 for F is supplied by Kawako. As is well known, the tuner 10 has a high frequency amplifier 11, a local oscillation circuit 12, and a mixing circuit 13, and the output of the mixing circuit I3 is supplied to the intermediate frequency circuit 15, where an intermediate frequency signal of 58.78M is extracted and amplified. Ru.

The VHF signal Sv is supplied to the above-mentioned up converter 20 and converted into the desired UHF signals S and F, and then
One tuner is supplied via the conversion circuit 2. Up converter 20', local oscillation circuit 22, mixing circuit 23,
It is composed of a filter 24 and an amplifier 25, and the voltage to be received is
All HF signals Sv are UHF signals S with constant frequencies f, F.
, F. This example is for an upper sideband upconverter, so the frequency of the VHF signal Sv is reduced to f
v, the oscillation frequency of the local oscillation circuit 22 is f. When V, only the converted outputs (mixed outputs) S and F of the sum frequency component (fv+fov) are extracted by the filter 24 at the subsequent stage. UH
FIG. 2 shows the frequency band relationship between the F signal SU and the frequency-converted UHF signal SIF.

In Japan, the frequency band of UHF signal SU is 470-7.
Since the frequency is up to 70 MHz, an 890M ratio is selected in this example as the frequencies f and F of the UHF signals S and F after frequency conversion. By the way, in the above-mentioned circuit, generally both the mixing circuit 23 and the filter 24 have an attenuation amount of about -&, and the amplifier 25 has a gain of lidB.

Roughly speaking, the switching circuit 2 has an attenuation of -ldB, the high frequency amplifier 11 has a gain of 1 B, the mixing circuit 13 has a gain of 1 B, and the intermediate frequency circuit 15 has a gain of 1 B. Therefore, in the circuit described above, the total gain from antenna IV to intermediate frequency circuit 15 during VHF reception is 3B, whereas UH
The total gain from the antenna IU to the intermediate frequency circuit 15 during F reception is 33.

In other words, the base gain is larger when receiving VHF,
This causes a difference in sensitivity. However, considering the radio wave conditions of television in general, UHF radio waves are weaker, and the reality is that UHF reception requires a gain greater than that required for VHF reception.

Conventionally, therefore, a fixed attenuator has been installed between the amplifier 25 and the switching circuit 2, or AGC has been applied to the high frequency amplifier 11, but in either case, although this can be done by correcting the sensitivity, the noise figure deteriorates. There were problems such as deterioration of selection characteristics. In view of these points, the present invention is designed to eliminate sensitivity differences with a simple configuration without affecting the characteristics of the circuit. An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 3, 31 is a power supply terminal to which an operating voltage is supplied, and the operating voltage from this terminal 31 is supplied to the UHF tuner 10 and the intermediate frequency circuit 15, and the VHF side of the switch circuit 32. It is supplied to the up converter 20 through the contact v, and further the V of the switch circuit 32 is
Voltages from the HF side contact v and the UHF side contact u are respectively supplied to the switching circuit 2, and the switching circuit 2 is switched.

In this circuit, the voltage obtained at the VHF side contact v of the switch circuit 32 is supplied to the intermediate frequency circuit 15, and the gain of the intermediate frequency circuit 15 is controlled to be lowered, for example. Therefore, according to this circuit, the gain of the intermediate frequency circuit 15 becomes 1 when receiving VHF, for example,
During UHF reception, 1 remains B, so the overall gain is always 3 degrees higher, eliminating the sensitivity difference.

In this way, the difference in sensitivity between VHF reception and UHF reception is eliminated, but according to the present invention, the gain of the intermediate frequency circuit at the subsequent stage is controlled, so that the noise figure and selection characteristics are not affected. It is possible to obtain good characteristics without any problems.

Furthermore, FIGS. 4 and 5 show specific circuit examples of the intermediate frequency circuit 15 suitable for application to the present invention.

First, FIG. 4 shows a case where the forward AGC characteristic of an intermediate frequency amplifier is utilized.

In the figure, the base of the amplifying transistor Q is normally biased by resistors R, , R2, and has a gain as shown in FIG. 6 due to the collector current 1 determined by this potential. When a voltage is supplied to the gain control terminal GC, the base potential of the transistor Q increases, the collector current becomes large, and the gain decreases. Further, FIG. 5 shows a case where a variable attenuator is provided at the output end of the intermediate frequency circuit.

In the figure, the signal from the output transformer T is normally connected to the resistor R
4~R? The level is determined by When the voltage is supplied to the gain control terminal G, the diode D is turned on, the resistor R7 is shorted, and the level of the output signal is lowered. Thus, by using these circuits,
The gain of the intermediate frequency circuit can be lowered during VHF reception.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining an up-converter type receiver, FIG. 3 is a configuration diagram of an example of the present invention, and FIGS. 4 to 6 are diagrams for explaining the same. 2 is a switching circuit, 10 is a UHF tuner, 15 is an intermediate frequency circuit, 20 is an up converter, 31 is a power terminal,
32 is a switch circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 A broadcast signal in the VHF band is supplied to a frequency conversion circuit having a predetermined gain to convert the frequency to the UHF band, and this
In a UHF/VHF receiver that receives a signal whose frequency has been converted to the HF band and a broadcast signal in the UHF band by supplying it to an intermediate frequency amplifier circuit through a receiving circuit in the UHF band, the above-mentioned receiving circuit is used when receiving UHF. When receiving VHF, the operating voltage is supplied to the frequency conversion circuit and the receiving circuit, and a part of the operating voltage supplied to the frequency conversion circuit is used to control the gain of the intermediate frequency amplification circuit. A UHF/VHF receiver configured to supply power to a terminal and correct the gain of the frequency conversion circuit.