JPH03169178A - Video intermediate frequency circuit - Google Patents

Abstract

PURPOSE:To prevent sprious malfunction by providing a circuit to sufficiently attenuate the 1/2 component of a video intermediate frequency without attenuating a frequency near the video intermediate frequency between a tuner and a preamplifier. CONSTITUTION:Between a tuner 2 and an SAW(surface acoustic wave) filter preamplifier 4, a circuit 10 is provided to sufficiently attenuate the 1/2 IF component. Therefore, even when the 1/2 IF component appears at the IF output line of the tuner 2 by using the tuner 2 equipped with a wide band so as not to obtain a satisfactory sprious characteristic, the 1/2 IF component is almost not transmitted to the input of the preamplifier 4. Thus, a sprious noise components, which goes to an IF frequency component while being multiplied by the preamplifier 4, is largely reduced. Thus, the spurious malfunction caused by the 1/2 IF component is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video intermediate frequency circuit used in a television receiver.

2. Description of the Related Art In recent years, as the density of television signals has increased, there has been a demand for means for reducing malfunctions caused by spurious signals in video intermediate frequency circuits.

In particular, in television receivers such as LCD televisions that are strongly required to be miniaturized and use tuners that do not have sufficiently good spurious characteristics, suppression of spurious signals in intermediate frequency circuits is even more important. It is requested.

An example of a conventional video intermediate frequency circuit will be described below with reference to the drawings.

FIG. 7 is a block diagram showing the configuration of a conventional video intermediate frequency (hereinafter abbreviated as VIF) circuit. In Figure 7, 1
is an antenna, 2 is a tuner, 3 is an intermediate frequency output (hereinafter abbreviated as IF output) line of the tuner, 4 is a preamplifier provided before the surface acoustic wave filter (hereinafter abbreviated as SAW filter), 5 is a preamplifier output line, 6 is a SAW filter, 7 is a SAW filter output line, 8 is a VIFl4 product circuit (hereinafter abbreviated as VIP IC), and 9 is a VIP detection output line.

The operation of the conventional video intermediate frequency circuit configured as described above will be described below.

Television broadcast radio waves are received by an antenna 1, and channel selected and frequency converted by a tuner 2 to become an IF frequency signal. Preamplifier 4 and next stage SAW filter 6
is amplified to compensate for the loss, and the SAW filter 6 eliminates frequency components outside the reception channel band. After that, the SAW filter 6 output is V
Amplified and detected by IPIC8, VIP detection output line 9
The desired video signal can be obtained.

Problems to be Solved by the Invention However, in the above configuration, the IF of the tuner 2
When a frequency half of the IF frequency, that is, a 1/2 1F component appears on the output line 3, this 1/2
2 When the IF component is amplified by the Brian 4, a twice as high frequency component is generated. As a result, there is a problem in that an erroneous video signal based on the spurious signal is obtained on the detection output line 9.

In view of the above problems, the present invention provides a video intermediate frequency circuit that can suppress spurious malfunctions due to the 1/2 1F component in a television receiver using a tuner with insufficient spurious characteristics due to the strong demand for miniaturization. The purpose is to provide the following.

Means for Solving the Problems In order to solve the above problems, the video intermediate frequency circuit of the present invention has a circuit configuration in which a preamplifier is inserted between the tuner and the surface wave filter. A circuit is provided between the preamplifier and the preamplifier, which does not attenuate the vicinity of the video intermediate frequency, but sufficiently attenuates the 1/2 of the video intermediate frequency.

Effect: With the above configuration, the present invention provides a circuit that sufficiently attenuates this 1/2 1F component between the tuner and the preamplifier, even if the 1/2 IFtc component appears on the IF output line of the tuner. , almost no 1/2 IF component is transmitted to the input of the preamplifier, and therefore the erroneous VIF component that occurs when this 1/2 IFt component is multiplied by the preamplifier is greatly reduced, and the 1/2 IF component is greatly reduced.
Spurious malfunctions due to the F component are suppressed.

Embodiment Hereinafter, a video intermediate frequency circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a video intermediate frequency circuit in an embodiment of the present invention. In Figure 1, 1 is the antenna, 2 is the tuner, 3a is the IF output line of the tuner, 4 is the SAW filter preamplifier, 5 is the preamplifier output line, 6 is the SAW filter, 7 is the SAW filter output line, and 8 is the VIP IC. , 9 are VIP detection output lines. In the present invention, a circuit 10 is newly provided between the tuner 2 and the SAW filter ream 4 to sufficiently attenuate the 1/2 1F component. Note that 3b is an input line of the SAW Brian 4.

The operation of the video intermediate frequency circuit configured as described above will be described below with reference to FIGS. 1 to 5.

First, Fig. 2 is an IF tuning characteristic diagram of the tuner 2 on the tuner IF output line 3a, which shows that the 1/2 IF component is not sufficiently attenuated because the characteristic is designed to have a wide band characteristic. It shows.

FIG. 3 is a frequency characteristic diagram of the circuit 10 newly provided in the present invention for sufficiently attenuating the 1/2 rF component. Same figure (
a) is a frequency characteristic diagram of circuit 1o in the case of a trap circuit,
FIG. 2B is a frequency characteristic diagram when a high-pass filter is used as the circuit 10. Figure 3(a). (
As can be understood from b), this circuit 10 is set to have frequency characteristics such that the IF component is hardly attenuated and the 1/2 IF component is sufficiently attenuated.

FIG. 4 shows the frequency characteristics from the tuner IF tuning stage to the SAW preamplifier input line 3b, and FIG. 4(a) shows the frequency characteristics when a trap is used as the circuit 10.
The figure (b) shows the case when a high-pass filter is used.

FIG. 5 is a diagram for explaining the improvement effect of the present invention.

Consider an S combination in which 1/2 IFtc occurs at the level A in Figure 5 on the IF output line 3a of tuner 2. If there is no 1/2 RL" ML path 10 in the conventional example, the preamplifier An IF component with a large level, B in FIG. Since the component is attenuated to C in FIG. 5, only the IF component at a small level D in FIG. 5 appears on the preamplifier output line 5.

As described above, according to this embodiment, in a video intermediate frequency circuit that has a circuit configuration in which a preamplifier is inserted between a tuner and a surface wave filter, the area around the video intermediate frequency is attenuated between the tuner and the preamplifier. By providing a circuit that sufficiently attenuates the 1/2 component of the video intermediate frequency, the tuner can be used with a wide band characteristic that does not provide good spurious characteristics.
Even if an IF component appears on the tuner's IF output line, this 1/2 1F
Since a circuit is provided to sufficiently attenuate the preamplifier, almost no 1/2 IF component is transmitted to the human power of the preamplifier, and therefore spurious noise components that are multiplied by the preamplifier and become IF frequency components are greatly reduced. /2
Spurious malfunctions due to 1F power will be suppressed.

Specific examples of the present invention will be described below with reference to the drawings.

FIG. 6 is a circuit diagram showing a specific example from a tuner to a VIF circuit in a CCIR television receiver.

FIG. 6(a) shows a case where a trap is used as the 1/2 IF attenuation circuit. 68μH coil and 1
A 19 MHz series resonant circuit is constructed with a 00 pF capacitor.

FIGS. 6(b) and 6(C) show the case where a high pulse filter is used as the 1/2 1F attenuation circuit. In the same figure (b), the input coupling capacitor of the preamplifier (100pF) and the bias resistor of the amplifier (15K
Ω//5.6KΩ> and the preamplifier input impedance constitute a high-pass filter. Also, the same figure (C
), the emitter bypass capacitor of the preamplifier is set to 1
The preamplifier gain is set to 80 pF, and a high-pass filter is configured by giving frequency characteristics to the gain of the preamplifier.

Effects of the Invention According to the present invention, between the tuner and the surface wave filter,
In a video intermediate frequency circuit having a circuit configuration in which a preamplifier is inserted, a circuit is provided between the tuner and the preamplifier that does not attenuate the vicinity of the video intermediate frequency, but sufficiently attenuates the power of 1/2 of the video intermediate frequency. By providing a tuner with broadband characteristics, even if the spurious characteristics are not good and a 1/2 1F component appears on the tuner's IF output line, this 1/2 1F component can be connected between the tuner and the preamplifier. 2 Since a circuit is provided to sufficiently attenuate the IF component, almost no 1/2 1F component is transmitted to the input of the preamplifier, and therefore, it is not multiplied by the preamplifier to become an IFtc component.
Spurious malfunctions due to IF components are suppressed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a video intermediate frequency circuit in an embodiment of the present invention, FIG. 2 is a tuner IF tuning characteristic diagram in the tuner IF output line, and FIG. 2 A frequency characteristic diagram of the circuit 10 that sufficiently attenuates the 1F component, FIG. 4 is a frequency characteristic diagram of the signal in the SAW preamplifier input line, FIG. 5 is an explanatory diagram for explaining the improvement effect of the present invention, and FIG. 6 is a circuit diagram showing a specific example of a CCIR type television receiver,
FIG. 7 is a block diagram showing the configuration of a conventional video intermediate frequency circuit. 1...Antenna, 2...Tuner, 4
...Preamplifier, 6 ...SAW filter, 8 ...VIFIC.

Claims (1)

[Claims] A video intermediate frequency circuit having a circuit configuration in which a preamplifier is inserted between a tuner and a surface acoustic wave filter, the video intermediate frequency circuit having a circuit configuration in which a preamplifier is inserted between the tuner and the preamplifier, the video intermediate frequency region is not attenuated, and the video intermediate frequency region is not attenuated. A video intermediate frequency circuit, characterized in that it is provided with a circuit that sufficiently attenuates a frequency component of 1/2.