JPH06153100A - Television tuner device - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent saturation of high frequency amplification when the reception electric field of adjacent channels is large, and to prevent adjacent channel interference due to this saturation. An adjacent channel tuning circuit 17 for extracting a signal component of an adjacent channel included in a video intermediate frequency signal,
A rectifying / smoothing circuit 18 that rectifies and smoothes the output signal of this circuit 17 and converts it into a direct current, and reduces the high frequency amplification gain by varying the AGC voltage for high frequency amplification when the output signal of this circuit 18 is above a predetermined value. And an AGC limiting circuit 19 that operates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner device such as an electronic tuning tuner used in video equipment such as a television receiver.

[0002]

2. Description of the Related Art Conventionally, a television tuner device of this kind having an electronic tuning tuner configuration used in a television receiver or the like is constructed as shown in FIG. The television tuner device 1 is provided with a VHF antenna input terminal 2 and a UHF antenna input terminal 3 for receiving VHF and UHF, and the VHF band input signal of the VHF antenna input terminal 2 is an FM signal or an intermediate frequency signal (hereinafter Intermediate frequency is I
Filter 4, VHF that removes unnecessary signals such as (F)
Is supplied to the VHF high-frequency amplifier circuit 6 via the input tuning circuit 5 for VHF.

The gain of the amplifier circuit 6 is controlled by an AGC voltage (tuner AGC voltage) for high frequency amplification at the AGC terminal 7, the received signal is amplified by a high frequency amplification gain according to the AGC voltage, and the amplified signal is double-tuned. VH via circuit 8
It is supplied to the mixing circuit 9 for F. This mixing circuit 9 is VHF
The local oscillation signal for VHF channel selection supplied from the local oscillation circuit 10 for VHF band, or the high frequency signal of the reception channel obtained by frequency-converting the high frequency signal of the reception channel of the VHF band or the reception signal of the UHF band described later is displayed at a predetermined frequency. Frequency conversion to IF signal.

Then, the video IF signal of the mixing circuit 9 is supplied from the IF output terminal 12 to the subsequent circuit via the IF tuning circuit 11 in the output stage. Also, UHF antenna input terminal 3
The received signal in the UHF band is supplied to the UHF high-frequency amplifier circuit 14 via the UHF input tuning circuit 13.

The amplifier circuit 14 is also connected to the AGC terminal 7
The gain is controlled by the AGC voltage, the received signal is amplified by the high frequency amplification gain according to the AGC voltage, and the amplified signal is supplied to the mixing circuit 15 for UHF. This mixing circuit 15
Converts a UHF band reception channel signal into a VHF band high frequency signal of a predetermined frequency by a UHF channel selection local oscillation signal supplied from the UHF local oscillation circuit 16.
This signal is supplied to the mixing circuit 9.

By the above operation, the high frequency signal of the selected channel (reception channel) in the VHF band and the UHF band is frequency-converted to obtain the video IF signal. In addition,
The oscillation frequency and the like of the local oscillator circuits 10 and 16 are changed by the tuning operation.

Further, an AG for high frequency amplification of the AGC terminal 7
The C voltage is formed by detecting the video signal by the AGC circuit provided in the video processing circuit in the subsequent stage of the tuner device 1. By the way, in a television receiver using this kind of television tuner device, when a channel having broadcasting on an adjacent channel is received, interference occurs when the received electric field of the adjacent channel is large (hereinafter referred to as adjacent channel interference).

As a measure for preventing this adjacent channel interference, conventionally, a channel trap that resonates with the signal component of the adjacent channel included in the video IF signal is provided in the IF tuning circuit of the tuner device, that is, the IF tuning circuit 11 of FIG. To provide. Then, the channel trap reduces the signal component of the adjacent channel included in the video IF signal,
Eliminate and prevent adjacent channel interference.

[0009]

However, only by providing a channel trap to prevent adjacent channel interference as in the prior art, particularly in a receiving state where the received electric field of the adjacent channel is large and the received electric field of the received channel is small. There is a problem that the high frequency amplification of the high frequency amplification circuits 5 and 14 is saturated with the signal of the adjacent channel, the adjacent channel is disturbed due to the saturation, and the image of the receiving channel cannot be obtained.

That is, in a receiving state in which the reception electric field of the adjacent channel is large and the reception electric field of the reception channel is small, since the signal component of the reception channel of the video IF signal is small, the AGC voltage of the AGC terminal 7 increases the high frequency amplification gain. To change.

This change in the AGC voltage increases the gain of the high frequency amplifier circuits 5 and 14, and at this time, not only the signal of the receiving channel but also the signal of the adjacent channel is amplified with a large gain, so that the signal of the adjacent channel becomes excessive. Then, the high-frequency amplifier circuits 5 and 14 are saturated, and so-called high-frequency amplification occurs.

[0012] Then, when the occurrence of high frequency amplification occurs,
In the video IF signal, the saturated adjacent channel signal component enters the band of the receiving channel to cause adjacent channel interference, and the image of the receiving channel cannot be obtained. An object of the present invention is to prevent saturation of high frequency amplification when the reception electric field of the adjacent channel is large, and to prevent adjacent channel interference due to this saturation.

[0013]

In order to achieve the above object, in the television tuner device of the present invention, the signal component of the adjacent channel included in the video IF signal obtained by frequency-converting the high frequency signal of the receiving channel is extracted. Adjacent channel tuning circuit, a rectifying and smoothing circuit that rectifies and smoothes the output signal of this tuning circuit and converts it to DC, and an AG for high frequency amplification when the output signal of this rectifying and smoothing circuit is above a predetermined value.
And an AGC limiting circuit for varying the C voltage to reduce the high frequency amplification gain.

[0014]

In the case of the television tuner device of the present invention configured as described above, the DC output signal of the rectifying / smoothing circuit obtained by rectifying and smoothing the output signal of the adjacent channel tuning circuit is the image I.
It changes according to the signal component of the adjacent channel included in the F signal. Then, when the signal component of the adjacent channel included in the video IF signal becomes larger than a predetermined value, the AGC voltage for high frequency amplification is changed by the AGC limiting circuit, and the high frequency amplification gain of the tube device is lowered.

Therefore, in a receiving state in which the reception electric field of the adjacent channel is large and the reception electric field of the reception channel is small, the saturation of the high frequency amplification based on the signal component of the adjacent channel does not occur, and the adjacent channel interference due to this saturation occurs. To be prevented.

[0016]

EXAMPLE One example will be described with reference to FIGS. 1, the same reference numerals as those in FIG. 3 indicate the same or corresponding ones, and the difference from FIG. 3 is that the tuner device 1 is supplied with the adjacent channel tuning circuit 17 to which the output signal of the IF tuning circuit 11 at the output stage is supplied. Rectifying and smoothing circuit 18 for rectifying and smoothing the output signal of this circuit 17, and this circuit 18
AGC limiting circuit 19 that switches according to the output signal of
Is added, and the AGC voltage for high frequency amplification of the AGC terminal 7 is supplied to the high frequency amplification circuits 6 and 14 through the resistor R1 for coupling.

The respective circuits 17, 18 and 19 are constructed as shown in FIG. 2, and the adjacent channel tuning circuit 17 is I
Capacitor C for coupling the video IF signal of the F tuning circuit 11
1 to the base of the transistor Q1 for tuning amplification.

At this time, in order to extract the signal component of, for example, the lower adjacent channel of the reception channel, the capacitor C2 and the coil L which resonate with the signal component of the lower adjacent channel between the collector of the transistor Q1 and the positive power supply terminal + B.
1 parallel resonance circuit is provided, and by the resonance of this circuit, the signal component of the lower adjacent channel included in the video IF signal is extracted and amplified, and this signal component is transmitted to the transistor Q1.
Is supplied to the rectifying / smoothing circuit 18 via the coupling capacitor C3. R2 of the tuning circuit 17
R3 and R4 are resistors for biasing the transistor Q1.

The rectifying / smoothing circuit 18 includes a diode D.
1, D2 and capacitor C4, rectifies and smoothes the input signal, converts it to DC, and outputs the DC output signal as AG.
It is supplied to the C limiting circuit 19. The limiting circuit 19 divides the output signal of the rectifying / smoothing circuit 18 by the variable resistor VR, and supplies the divided voltage signal of the sliding piece of the variable resistor VR to the base of the switching transistor Q2.

The emitter of the transistor Q2 is grounded and the collector is connected to the high-frequency amplifier circuits 6 and 14 through the resistor R5 for coupling, and the output of the rectifying / smoothing circuit 18 is increased by the increase of the signal component of the lower adjacent channel. When the signal becomes equal to or higher than a predetermined value and the divided voltage becomes equal to or higher than the ON voltage between the base and the emitter, the signal is inverted from OFF to ON. At this time, the AGC for high frequency amplification is supplied from the AGC terminal 7 to the high frequency amplification circuits 6 and 14 through the resistor R1.
The voltage is divided by the resistors R1 and R5 and is reduced, and the gain of the high frequency amplifier circuits 6 and 14 is reduced by this reduction.
It is reduced from the gain of the AGC voltage supplied to.

Therefore, in the receiving state in which the reception electric field of the lower adjacent channel of the reception channel is large and the reception electric field of the reception channel is small, the AGC voltage of the AGC terminal 7 increases so as to increase the signal component of the reception channel. However, this voltage is not lowered when the transistor Q2 is turned on, and the high frequency amplification gain does not become excessive, and the saturation of both the amplification circuits 6 and 14 based on the signal of the lower adjacent channel is prevented.

Therefore, the occurrence of high frequency amplification is prevented, adjacent channel interference does not occur in the video IF signal of the IF output terminal 12, and the image of the receiving channel based on the video IF signal can be obtained.

Note that the image I
Although the level of the F signal decreases, an IF-AGC circuit is usually provided in the video processing circuit in the subsequent stage of the tuner device 1, and the high frequency amplification AGC of the tuner device 1 operates in a place where the received electric field strength is large, and the IF-AGC circuit operates. Since the AGC operates in a small or medium area of the received electric field strength, the IF-AGC raises the level to a normal level without causing any inconvenience.

The variable resistor VR is provided in consideration of variations in the characteristics of the high frequency amplifier circuits 6 and 14 between tuner devices, and is adjusted and set at the time of shipping. by the way,
In the above embodiment, the signal component of the lower adjacent channel is extracted by the adjacent channel tuning circuit 17, but the capacitor C
2, the signal component of the upper adjacent channel may be extracted by changing the constant of the coil L1, and two sets of tuning circuits of the transistor Q1, the capacitor C2 and the coil L1 may be provided to extract the signal component of the adjacent channel on both sides. May be.

Further, a Schmitt trigger circuit is provided between the rectifying / smoothing circuit 18 and the AGC limiting circuit 19, and when the signal component of the adjacent channel fluctuates in the vicinity of the switching threshold level of the transistor Q2, the variable resistance VR is changed. By providing hysteresis to the voltage change of the voltage-divided signal due to sliding and preventing the careless repetition of switching of the transistor Q2, the operation is stabilized and the performance is further improved.

[0026]

Since the present invention is configured as described above, it has the following effects. The adjacent channel signal contained in the video intermediate frequency signal of the output stage is extracted by the adjacent channel tuning circuit 17, and this circuit 1
The output signal of No. 7 is rectified and smoothed by the rectifying / smoothing circuit 18 and converted into DC, so that the output signal of the rectifying / smoothing circuit 18 changes according to the signal component of the adjacent channel.

When the signal component of the adjacent channel contained in the video intermediate frequency signal becomes larger than a predetermined value, the AGC limiting circuit 19 in the subsequent stage of the rectifying / smoothing circuit 18 changes the AGC voltage for high frequency amplification, and the tuner device of the tuner device. The high frequency amplification gain is reduced. Therefore, when the reception electric field of the adjacent channel is large and the reception electric field of the reception channel is small, the saturation of the high frequency amplification based on the signal component of the adjacent channel does not occur and the occurrence of the adjacent channel interference due to this saturation is prevented. can do.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a television tuner device of the present invention.

FIG. 2 is a detailed connection diagram of each part of FIG.

FIG. 3 is a block diagram of a conventional device.

[Explanation of symbols]

 17 Adjacent channel tuning circuit 18 Rectification smoothing circuit 19 AGC limiting circuit

Claims (1)

[Claims] 1. An adjacent channel tuning circuit for extracting a signal component of an adjacent channel included in an image intermediate frequency signal of an output stage obtained by frequency-converting a high frequency signal of a receiving channel, and rectifying and smoothing an output signal of the tuning circuit. And a rectifying / smoothing circuit for converting into a direct current, and an AGC limiting circuit for varying the AGC voltage for high-frequency amplification to reduce the high-frequency amplification gain when the output signal of the rectifying / smoothing circuit is a predetermined value or more. TV tuner device.