JPS61200781A - Tuner circuit in television receiver - Google Patents

Abstract

PURPOSE:To simplify a circuit of switching between a lower vestigial sideband system and an upper vestigial sideband system by providing an input signal switching circuit of switching between the connection of a VHF high frequency amplifier circuit to the first VHF mixer and the connection of the second VHF mixer. CONSTITUTION:When the upper vestigial sideband signal is received, the input signal switching circuit 31 directly connects the VHF high frequency amplifier circuit 3 to the first VHF mixer 27 while the upper vestigial sideband signals are outputted directly. When the lower vestigial sideband signals are received, the circuit 31 eliminates the direct connection between the circuit 6 and the mixer 27 while the second VHF mixer 29 is connected through the circuit 31 to the mixer 27. As a result, after the mixer 29 has converted the lower vestigial sideband signals into the upper vestigial sideband signals, the lower sideband signals are outputted from the mixer 27 as the upper sideband signals as at the time of reception of the upper vestigial sideband signals, although the lower vestigial sideband signals are received for outputting to the mixer 27.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tuner circuit in a television receiver for the television reception system in France and other countries, and particularly to a tuner circuit for receiving a lower residual sidewave signal and an upper residual sidewave signal. Regarding technology for switching.

(Prior Art) Regarding television broadcasting systems, European countries other than France, Japan, and the United States use the upper residual sidewave system. On the other hand, in France, there is a lower residual sidewave system as shown in Figure 4 (A) and a lower residual sidewave system as shown in Figure 4 (B).
) is used in combination with the upper residual sidewave method as shown in ().

In the figure, pc is a video carrier wave and SC is an audio carrier wave. VHF A for lower residual sidewave system.

There are B, C, and CI channels, and the upper residual sidewave system includes VHF channels 1 to 6 and UHF channels.

In the case of this French television broadcast system, a processing circuit is essential, and a dedicated circuit design is required. be.

A conventional French television reception system of this type is shown in FIGS. 5 and 6. Figure 5 is a block diagram of a system switching circuit for the French television reception system, which is configured to switch systems using a PIF (picture intermediate frequency) circuit.
The figure is a frequency characteristic diagram of the PIF circuit.

In FIG. 5, 1 is a tuner circuit, and this tuner circuit 1 includes a UHF/VHF splitter 2, a UHF radio frequency (RF) amplifier circuit 3, a UHF mixer 4, a UHF local oscillation circuit 5, and a VHF high frequency amplifier circuit. 6, VHF mixer 7, V
It has an HF local oscillation circuit 8.

When you select UHF, UHF high frequency amplification circuit 3, UHF
Mixer 4 and UHF local oscillation circuit 5 are connected to the power supply, and at the same time, oscillation of VHF local oscillation circuit 8 is stopped, and VHF high frequency amplifier circuit 6 and VHF mixer 7 are grounded. On the other hand, from the output terminal of UHF mixer 4,
The signal U (IF) directly converted to the intermediate frequency is output to the VHF mixer 7.

Also, when VHF is selected, the UHF high frequency amplification circuit 3,
The UHF mixer 4 and the UHF local oscillation circuit 5 are disconnected from the power supply, and at the same time the VHF high frequency amplifier circuit 6 and the VH
The F mixer 7 is connected to the power supply, and the VHF local oscillation circuit 8 oscillates.

VHF high frequency amplifier circuit 6 and UHF high frequency amplifier circuit 3
Both amplify the video carrier wave pc and audio carrier wave SC signals in the same way.

The high frequency signal amplified by the VHF high frequency amplifier circuit 6 and the oscillation output signal from the VHF local oscillation circuit 8 are simultaneously input to the VHF mixer 7, and a predetermined intermediate frequency signal component is extracted and output to the next stage. VHF local oscillation circuit 8
outputs to the VHF mixer 7 a frequency signal that is a reference for extracting a determined intermediate frequency.

In the UHF mixer 4, the high frequency signal amplified by the UHF high frequency amplifier circuit 3 and the oscillation output signal from the UHF local oscillation circuit 5 are simultaneously input, a predetermined intermediate frequency signal component is extracted, and the next signal is output via the VHF mixer 7. output in stages. The UHF local oscillation circuit 5 outputs to the UHF mixer 4 a frequency signal that serves as a reference for extracting a predetermined intermediate frequency.

9 is a SAW filter using a surface acoustic wave element (SAW) for determining the frequency characteristics of the PIF circuit, 10 is a PIF amplifier circuit, 11 is a PIF detection circuit, and 12 is an AGC
(automatic gain control m) circuit, and 13 is an AFT (automatic fine adjustment) circuit.

The output of the VHF mixer 7 is input to a SAW filter 9 and also to an SIF (sound intermediate frequency) circuit.

The SAW filter 9 is a type of IF filter, removes unnecessary signal components such as low-order harmonics of intermediate frequencies, and extracts only necessary video signals.

The AGC circuit 12 creates an AGC voltage based on the output of the PIF video detection circuit 11, and applies this to the PIF amplifier circuit 10.
By inputting , the gain is automatically held constant.

The AFT circuit 13 inputs the DC voltage obtained by the PIF detection circuit 11 to the VHF local oscillation circuit 8 and the UHF local oscillation circuit 5, and automatically maintains their oscillation frequencies at a constant value.

14 is a tuning transformer Tll'T2 with different resonance frequencies;
15 is a detection tuning circuit 14 consisting of a detection tuning circuit 14;
and a detection tuning frequency switching circuit including an operation switching switch 16 for both tuning transformers T, , and 'rz. The detection tuning frequency switching circuit 15 is for switching to a tuning frequency corresponding to each broadcasting system based on a system switching signal SI generated in response to the lower residual sidewave signal DS and the upper residual sidewave signal US. be.

17 is a tuning transformer Tx having different resonance frequencies;

A tuning circuit for AFT detection consisting of T4; 18, a tuning circuit for AFT detection 17 and both tuning transformers T;

This is an AFT circuit operating frequency switching circuit including an operation switching switch 19 of T4, and this AFT circuit operating frequency switching circuit 18 performs switching to an operating frequency corresponding to each broadcast system based on a system switching signal S1.

20 is an AFT voltage polarity switching circuit having an inverting circuit 21, a non-inverting circuit 22, and a changeover switch 23 therefor. The AFT voltage polarity switching circuit 20 switches the polarity of the output voltage of the AFT circuit 13 to a polarity corresponding to each broadcasting system based on the system switching signal S1, and outputs it to the VHF local oscillation circuit 8 and the UHF local oscillation circuit 5.

The feature of this system switching circuit for the French television reception system is that the SAW filter 9 is configured to be used for both the lower residual sidewave system and the upper residual sidewave system.

The received signal is converted into a PIF signal by a tuner circuit 1, and the output of this tuner circuit 1 is an upper residual sidewave signal U.
The video intermediate frequency and the color subcarrier intermediate frequency are designed to be exactly opposite in the case of S and the case of the lower residual sidewave signal DS-.

Therefore, by making the frequency characteristics of the SAW filter 9 which determines the frequency characteristics of the PIF circuit symmetrical as shown in FIG. 6, the operating points for each signal are determined as shown in the following table.

Table Operating Frequency of SAW Filter In this table, P is the frequency of the video carrier pc, S is the frequency of the audio carrier SC, C0 is the frequency of the color subcarrier, Adj-
3 is the frequency of the audio carrier wave of the adjacent channel.

Since the video carrier wave pc input to the PIF detection circuit 11 and the AFT circuit 13 is of two types, point a and point b in FIG. 6, depending on the reception method, the detection tuning frequency switching circuit 15
An AFT circuit operating frequency switching circuit 18 is provided.

Furthermore, since the change characteristics of the operating voltage of the AFT circuit 13 with respect to the frequency required in both types are opposite, the AFT voltage polarity switching circuit 20 is provided.

Then, a system switching signal S1 corresponding to the received signal (receiving method) is output, and the detection tuning frequency switching circuit 15
By switching the output signals of the AFT circuit operating frequency switching circuit 18 and the AFT voltage polarity switching circuit 20, reception of both types is made relatively easy.

However, the conventional example having such a configuration has the following problems.

That is, as many as three switching circuits 15.18°20 are required to switch between the lower residual sidewave method and the upper residual sidewave method. This not only complicates the circuit configuration and requires a specialized chassis design, but also increases costs.
It is inevitable that this method will be at a disadvantage compared to other countries' methods in terms of product development time.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to make it possible to share the downstream circuit of the lower residual sidewave system and the upper residual far side tuner circuit. shall be.

(Structure of the Invention) In order to achieve the above object, the present invention has the following structure.

That is, the tuner circuit in the television receiver of the present invention includes a VHF high-frequency amplification circuit, a first VHF mixer at a subsequent stage of the VHF high-frequency amplification circuit, a first VHF local oscillation circuit for the first VHF mixer, and the VHF high-frequency amplification circuit. A second VHF mixer is provided at the next stage of the circuit and converts the lower residual sidewave signal into the upper residual sidewave signal, and this second VHF mixer
The device includes a second VHF local oscillation circuit for the HF mixer, and an input signal switching circuit for switching between the connection of the VHF high frequency amplifier circuit and the second VHF mixer to the first vHF mixer.

The effects of this configuration are as follows.

(i) When the upper residual sidewave signal is received, the input signal switching circuit directly outputs the VHF high frequency amplifier circuit as it is.

(ii) When the lower residual sidewave signal is received, the input signal switching circuit switches the VHF high frequency amplifier circuit and the first VHF
The direct connection with the mixer is disconnected, and the second V
An HF mixer is connected to the first VHF mixer via an input signal switching circuit.

As a result, the second VHF mixer converts the lower residual sidewave signal into an upper residual sidewave signal and then outputs it to the first VHF mixer. is output as an upper residual sidewave signal in the same way as when receiving the upper residual sidewave signal.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings. FIG. 1 is a block diagram of a system switching circuit for a French television reception system including a tuner circuit in a television receiver according to an embodiment of the present invention.

In FIG. 1, the same reference numerals as those shown in FIG. 5 according to the conventional example refer to the same parts as the parts 9 indicated by the reference numerals in this embodiment as well.

Further, unless otherwise specified, the present embodiment and the conventional example have the same configuration regarding the connection relationship.

The configuration of this embodiment differs from the conventional example as follows.

The first VHF mixer 27 is the VHF mixer 7 in the conventional example.
The first VHF local oscillation circuit 28 is similar to the VHF local oscillation circuit 8 in the conventional example.

29 is a second VHF mixer connected to the next stage of the VHF high frequency amplification circuit 6 and converts the lower residual sidewave signal DS into the upper residual sidewave signal US; 30 is the second VHF mixer 29;
This is a second VHF local oscillation circuit for the second VHF local oscillation circuit. 31 is the first
This is an input signal switching circuit that switches between direct connection of the VHF high frequency amplification circuit 6 to the VHF mixer 27 and connection between the second VHF mixer 29 and the VHF high frequency amplification circuit 6.

Conventional detection tuning frequency switching circuit 15, AFT
There is no wave number switching circuit 18 and AFT voltage polarity switching circuit 20.

Instead, the PIF detection circuit 11 includes a normal tuning circuit 3.
2 is connected to the AFT circuit 13, and a normal tuning circuit 3 is connected to the AFT circuit 13.
3 is connected.

That is, the PIF circuit after the tuner circuit 1' has exactly the same circuit configuration as that used in other countries.

Although the tuner circuit 1' is different from tuner circuits for other countries, the tuner circuit in the system switching circuit of the French television reception system has traditionally been dedicated due to the reception band, etc. In this sense, it is not particularly disadvantageous.

The rest of the configuration is the same as the conventional example, so the explanation will be omitted.

Next, the operation of this embodiment will be explained based on FIGS. 2 and 3. FIG. 2 is an explanatory diagram of the operation of converting a lower residual sidewave signal into an upper residual sidewave signal, and FIG. 3 is a frequency characteristic diagram of the PIF circuit.

(2) When the upper residual sidewave signal USI is received, the VHF high frequency amplifier circuit 6 is directly connected to the first VHF mixer 27, and the upper residual sidewave signal US is output as it is.

■ When the lower residual sidewave signal DS+ is received, the input signal switching circuit 31 is switched to the Y side, disconnecting the direct connection between the VHF high frequency amplifier circuit 6 and the first VHF mixer 27, and switching the input signal switching circuit 31 to the Y side. 2nd VH via 31
The F mixer 29 is connected to the first VHF mixer 27.

As shown in FIG. 2, the second VHF mixer 29 has a second voltage
An oscillation signal having a higher frequency ft than the lower residual sidewave signal DSI is input from the HF local oscillation circuit 30.

As a result, in the second VHF mixer 29, the frequency P of the video carrier wave pc of the lower residual sidewave signal DSI is converted to a frequency P2 higher than the frequency f2 by (f, -P). Further, the frequency S of the audio carrier wave SC is converted to a frequency SO higher than the frequency f2 by (f, -5). That is, the lower residual pea! +1+1&ezvqrs u
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+w red m is done.

The filter of the second VHF mixer 29 passes only the upper residual sidewave signal US, so this upper residual sidewave signal U
Sl is output to the first VHF mixer 27.

In this way, even though the lower residual sidewave signal DSI is received, the output from the first VHF mixer 27 is the upper residual sidewave signal USI, which is the same as when the upper residual sidewave signal is received.
and is output to the SAW filter 9 and the S''IF circuit.

In the case of the French Television broadcasting system, the VHF low channels (A, B, CCt) are conveniently in the lower residual sidewave system, and the other channels are in the upper residual sidewave system, so the tuner circuit It is possible to generate a control signal to the input signal switching circuit 31 in conjunction with the band switching voltage 1'. With this configuration, there is no need to supply a control signal to the input signal switching circuit 31 from the outside, and in this respect, further simplification of the circuit configuration can be achieved.

Regarding the SIF circuit, in the case of the French television reception system, because it uses AM modulation, it cannot be shared with those for other countries, but frequency switching is not required, as is the case with video signal processing. In this sense as well, the circuit configuration can be simplified.

In the above embodiment, the DC voltage from the AFT circuit 13 is input to the first VHF local oscillation circuit 28 and the UHF local oscillation circuit 5, but instead of this,
The DC voltage may be configured to be input to the second VHF local oscillation circuit 30 and the UHF local oscillation circuit 5.

(Effects of the Invention) As described above, according to the present invention, the following effects are exhibited.

(a) When the lower residual sidewave signal is received, the second VH
The configuration is such that the F mixer converts the lower residual sidewave signal into an upper residual sidewave signal and then outputs it to the first VHF mixer, so it is difficult to switch between the lower residual sidewave method and the upper residual sidewave method. By simplifying the circuit for this purpose and sharing the circuit at the stage after the tuner circuit, the PIF circuit at the stage after the tuner circuit can have the same configuration as the circuit configuration for other countries.

[Brief explanation of the drawing]

1 to 3 relate to embodiments of the present invention; FIG. 1 is a block diagram of a system switching circuit for the French television reception system including a tuner circuit in a television receiver;
Figure 2 is an explanatory diagram of the operation of converting the lower residual sidewave signal to the upper residual sidewave signal, Figure 3 is a frequency characteristic diagram of the PIF circuit, Figures 4 and 5 relate to the conventional example, and Figure 4 (A) is a frequency characteristic diagram of the lower residual sidewave system in France, and (B) is a frequency characteristic diagram of the upper residual sidewave system in France.
The figure is a block diagram of a mode switching circuit for the French television reception system, which is configured to switch modes using a PIF (picture intermediate frequency) circuit, and FIG. 6 is a frequency characteristic diagram of the PIF circuit. In the figure, 1' is the tuner circuit, 6 is the VHF high first V
HF local oscillation circuit, 29 a second VHF mixer, 30 a second VHF local oscillation circuit, 31 an input signal switching circuit, DS
, is the lower residual sidewave signal, and DSt is the upper residual sidewave signal.

Claims (1)

[Claims] (1) A VHF high frequency amplification circuit, a first VHF mixer at the subsequent stage of this VHF high frequency amplification circuit, a first VHF local oscillation circuit for this first VHF mixer, and a lower residual side wave located at the next stage of the VHF high frequency amplification circuit. a second VHF mixer for converting a signal into an upper residual sidewave signal; a second VHF local oscillation circuit for the second VHF mixer; and an input for switching between connection of the VHF high frequency amplification circuit and connection of the second VHF mixer for the first VHF mixer. A tuner circuit in a television receiver equipped with a signal switching circuit.