JPH11112895A - Receiver - Google Patents

Abstract

(57) [Problem] To improve the image amplitude characteristics and the image S / N value at the time of a weak electric field. In a video / audio intermediate frequency demodulation unit, a matching resistor is formed between a video detection output unit and an audio signal trap circuit, and both ends of the matching resistor are provided from an RF-AGC circuit of a video / audio intermediate frequency IC. And a switching circuit 17 for switching the video frequency amplitude characteristic by the AGC voltage of the A / V converter. With this configuration, the video / audio intermediate frequency demodulation unit switches the video frequency amplitude characteristic by the AGC voltage from the RF-AGC circuit 11 to weaken it. An object of the present invention is to realize a receiving apparatus that improves an image S / N in an electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver effective for use in a terrestrial reception front end including a television receiver, a video tape recorder and the like.

[0002]

2. Description of the Related Art In recent years, a receiving apparatus has a tuner section and a video / audio demodulating section, and has an integrated structure.

[0003] A conventional receiving apparatus will be described below.
2. Description of the Related Art Conventionally, for example, a receiver described in U.S. Pat. No. 4,689,825 is known. FIG. 3 shows a conventional receiving apparatus. FIG. 3 is a block diagram showing a terrestrial tuner unit, a surface acoustic wave filter (hereinafter, referred to as a SAW filter), a video / audio intermediate frequency demodulation unit, and an audio signal trap unit of a conventional receiving apparatus.

In FIG. 3, reference numeral 1 denotes a terrestrial antenna.
It receives broadcast radio waves and transmits television signals to the tuner 3. Reference numeral 2 denotes an input terminal of the tuner 3, which is compatible with a television signal received by the antenna 1 in consideration of consistency. Reference numeral 3 denotes a tuner which selects a television signal supplied from the antenna 1 as a desired channel signal, eliminates interference, mixes a local oscillation frequency and a desired channel frequency with an internal mixer, and converts a desired intermediate frequency signal. It is something to take out. Reference numeral 4 denotes an RF-AGC terminal of the tuner 3. As a means for controlling the video / audio intermediate frequency demodulation unit 30 based on the gain level input to the video / audio intermediate frequency demodulation unit 30, the RF-AGC circuit in the IC converts the voltage to a voltage. The signal is converted and output, and the gain of the tuner 3 is controlled by the voltage.

[0005] Reference numeral 5 denotes an RF-AGC ripple filter and a capacitor for determining a transient response.
The AGC voltage depends on the level of the signal input to the IC. Since the input signal is a signal containing video information, the RF-AGC output voltage is affected by the video signal level, so an electrolytic capacitor is introduced. And smooth it. In addition, if the response of the RF-AGC is too slow, the control of the gain is greatly affected. Therefore, it is required to set a constant in consideration of the rising and falling characteristics of the voltage. 6 is a surface acoustic wave filter (hereinafter referred to as SAW
Input terminal for inputting a signal whose output impedance of the tuner 3 and impedance matching of the SAW filter 7 are matched. Reference numeral 7 determines the band characteristic and phase characteristic of the desired channel received by the SAW filter.

Reference numeral 8 denotes an RF-AGC voltage adjustment volume. Since the gain control range of the RF-AMP in the tuner 3 is limited, when the input level is a weak electric field, the gain control is performed by the IF-AMP in the video / audio intermediate frequency demodulation unit 30 to detect the video output signal after detection. This terminal operates so that the level becomes constant, and is a terminal for arbitrarily setting an operation input level in the RF-AMP. 9 and 10 are S
This is an input terminal for inputting the video intermediate frequency signal output from the AW filter 7 to the video / audio intermediate frequency signal demodulation unit 30 and is a balanced input. Reference numeral 11 denotes an RF-AGC circuit in the video / audio intermediate frequency demodulation unit 30, which performs voltage control by changing a sync chip level DC voltage after video input detection of the input intermediate frequency signal. It outputs a voltage.

Reference numeral 12 denotes an equalizer correction circuit that corrects a high frequency amplitude characteristic by applying feedback to an input video signal. Reference numeral 13 denotes a detector which multiplies the intermediate frequency signal and a signal arbitrarily transmitted by the same phase to perform video detection. 14 is a voltage controlled oscillator (hereinafter, referred to as
In this case, the transmission frequency required for detection by the detector 13 is controlled by a voltage, and a loop is formed to make the frequency constant. Reference numeral 15 denotes a VCO tuning circuit.
The oscillation frequency controlled in step 4 is tuned by LC. Reference numeral 16 denotes a matching resistor for attenuating a high-frequency part in order to remove noise of a video signal from the detector 13,
It determines the attenuation and frequency amplitude characteristics of the audio signal trap unit 18. Reference numeral 18 denotes an audio signal trap section for attenuating a slight audio signal contained in the video signal input via the matching resistor 16 at 5.5 [MHz] and 6.0.
This attenuates audio signals of [MHz] and 6.5 [MHz] to desired values, and generally uses a ceramic trap or the like.

Reference numeral 19 denotes a video signal output terminal after passing through the equalizer correction circuit 12. Reference numeral 22 denotes an input terminal of an audio intermediate frequency signal of the video / audio intermediate frequency demodulation unit 30;
The audio intermediate frequency carrier within the audio intermediate frequency band selected by the AW filter 7 is input. 2
Reference numeral 3 denotes an AM / FM detector, which performs FM detection and SEC at PAL.
At the time of AM, it is an audio signal processing circuit that performs AM detection and extracts an audio signal, and details are omitted. Reference numeral 24 denotes an audio signal output terminal for extracting a signal detected by the PLL in the audio signal processing circuit 23. Reference numeral 30 denotes a video / audio intermediate frequency demodulation unit, and reference numeral 37 denotes a power supply voltage input terminal, for example, 5 V is used.

The operation of the conventional receiving apparatus configured as described above will be described below.

A broadcast signal input from an antenna 1 is received by a tuner 3. A desired channel frequency is selected, interference is eliminated, the local oscillation frequency is mixed with the desired channel frequency, and an intermediate frequency signal is extracted. The broadcast signal received by the tuner 3 is input to the SAW filter 7 to eliminate adjacent video and audio. SAW filter 7
Outputs a video / audio intermediate frequency signal, the video intermediate frequency signal is input from input terminals 9 and 10 to a video / audio intermediate frequency demodulation unit 30, and the audio signal intermediate frequency signal is input from an input terminal 22.

The video intermediate frequency signal is gain-controlled by the IF-AMP 50 and input to the detector 13. The detector 13 performs video detection by multiplying the video intermediate frequency signal from the IF-AMP 50 and the signal oscillated by the VCO 14 by the same phase. The output signal of the detector 13 is input to the matching resistor 16 and attenuates a high frequency portion to remove noise in the signal. The output signal of the matching resistor 16 is input to the audio signal trap section 18 and attenuates the audio signal slightly contained in the video intermediate frequency signal by designating a predetermined frequency. The output signal of the audio signal trap section 18 is input to the equalizer correction circuit 12 and corrects the high frequency portion of the video signal attenuated by the matching resistor 16. The output signal of the equalizer correction circuit 12 is output from the video signal output terminal 19, while the audio intermediate frequency signal output from the SAW filter 7 is input to the AM / FM detection unit 23, and performs FM detection at the time of PAL. At the time of SECAM, AM detection is performed. The audio intermediate frequency signal output from the AM / FM detector 23 is output from an audio signal output terminal 24.

[0012]

However, in the above-described conventional configuration, the image amplitude characteristic and the image S /
Since the means for improving the N value is not configured, there is a problem that the image amplitude characteristics and the image S / N value at the time of a weak electric field are not improved.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide a receiving apparatus that switches an image frequency amplitude characteristic in a certain appropriate electric field by an AGC voltage from a circuit to improve an image amplitude characteristic and an image S / N value in a weak electric field.

[0014]

In order to achieve this object, a receiving apparatus according to the present invention comprises a tuner for receiving a broadcast signal input from an antenna, and a surface for eliminating adjacent video and audio in the broadcast signal received by the tuner. A receiving device comprising an elastic wave filter and a video / audio intermediate frequency demodulator for demodulating an intermediate frequency band of a video / audio signal output from a surface acoustic wave filter, wherein a video output from the video / audio intermediate frequency demodulator is provided. It is provided with a matching resistor for attenuating the high-frequency portion of the signal and a switching circuit for switching the resistance value of the matching resistor under the control of the video / audio intermediate frequency demodulator to vary the amount of attenuation.

According to this configuration, in the video / audio intermediate frequency demodulation unit, the video frequency amplitude characteristics are switched by the AGC voltage from the RF-AGC circuit to improve the video amplitude characteristics and the video S / N value in a weak electric field. A device is obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claims 1 and 2 of the present invention is directed to a tuner for receiving a broadcast signal input from an antenna, and a surface acoustic wave for eliminating adjacent video and audio in the broadcast signal received by the tuner. A filter, and a receiving device including a video and audio intermediate frequency demodulation unit that demodulates an intermediate frequency band of the video and audio signal output from the surface acoustic wave filter, and a video signal output from the video and audio intermediate frequency demodulation unit. A matching resistor for attenuating the high frequency part,
A switching circuit that switches the resistance value of the matching resistor under control of the video / audio intermediate frequency demodulation unit and varies the attenuation amount. This configuration improves the video amplitude characteristics and the video S / N value at the time of a weak electric field. It has the effect of doing.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a block diagram of a receiving apparatus according to the present embodiment. In FIG. 1, reference numeral 1 denotes an antenna which receives a broadcast wave and transmits a television signal or the like to a tuner 3. Reference numeral 2 denotes an input terminal of the tuner 3, which is compatible with a television signal received by the antenna 1 in consideration of consistency. Reference numeral 3 denotes a tuner which selects a television signal supplied from the antenna 1 as a desired channel signal, performs interference elimination, mixes a local oscillation frequency and a desired channel frequency with a mixer, and extracts a desired intermediate frequency signal. Things. 4 is RF-AGC
As a means for controlling the video / audio intermediate frequency demodulation unit 30 at the terminal based on the gain level input to the video / audio intermediate frequency demodulation unit 30, the voltage is converted into a voltage by an RF-AGC circuit 11 described later and output. The gain of the tuner 3 is controlled by the voltage.

Reference numeral 5 denotes an RF-AGC ripple filter and a capacitor for determining a transient response.
The AGC voltage depends on the level of the signal input to the IC. Since the input signal is a signal containing video information, the RF-AGC output voltage is affected by the video signal level, so an electrolytic capacitor is introduced. And smooth it. In addition, if the response of the RF-AGC is too slow, the control of the gain is greatly affected. Therefore, it is required to set a constant in consideration of the rising and falling characteristics of the voltage. Reference numeral 6 denotes an input terminal of the SAW filter 7, to which a signal whose output impedance of the tuner 3 is matched with impedance of the SAW filter 7 is input. Reference numeral 7 determines the band characteristic and phase characteristic of the desired channel received by the SAW filter.

Reference numeral 8 denotes an RF-AGC voltage adjustment volume. Since the gain control range of the RF-AMP in the tuner 3 is limited, when the input level is a weak electric field, the gain control is performed by the IF-AMP in the video / audio intermediate frequency demodulation unit 30 to detect the video output signal after detection. This terminal operates so that the level becomes constant, and is a terminal for arbitrarily setting an operation input level in the RF-AMP. 9 and 10 are S
This is an input terminal for inputting the video intermediate frequency signal output from the AW filter 7 to the video / audio intermediate frequency signal demodulation unit 30 and is a balanced input.

Reference numeral 11 denotes an RF-AGC circuit in the video / audio intermediate frequency demodulation unit 30, which performs voltage control based on a change in a DC voltage at a sync chip level after video detection of the input intermediate frequency signal. A voltage is output by peak AGC. Numeral 12 denotes an equalizer correction circuit which corrects a high frequency amplitude characteristic by applying feedback to an input video signal. Reference numeral 13 denotes a detector which multiplies the intermediate frequency signal and a signal arbitrarily transmitted by the same phase to perform video detection. 14 is a VCO,
The detector 13 controls the transmission frequency required for detection by voltage, and forms a loop to make the frequency constant.

Reference numeral 15 denotes a VCO tuning circuit which tunes the oscillation frequency controlled by the VCO 14 by LC. 16 is a matching resistor of the trap for the audio signal,
The noise is removed by attenuating the high frequency portion of the video signal from the detection unit 13. It also determines the attenuation and frequency amplitude characteristics of the audio signal trap circuit 18.

A switching circuit 17 is connected in parallel with the matching resistor 16 and switches the video frequency amplitude characteristic.
The internal switch is turned on / off by the RF-AGC voltage from the AGC circuit 11. When the AGC voltage value of the video signal is equal to or more than a predetermined value, the RF-AGC circuit 11 determines that the electric field is weak, and when the AGC voltage value is equal to or less than the predetermined value, it determines that the electric field is normal. The switching circuit 17
According to the control signal from the RF-AGC circuit 11, the internal switch of the switching circuit 17 is turned off during the normal electric field, and the video signal is input only to the matching resistor 16. When a weak electric field is applied, the internal switch is turned on, and a video signal is input in parallel with the impedance matching resistor 35 and the matching resistor 16 shown in FIG.

Reference numeral 18 denotes an audio signal trap circuit.
[MHz], 6.0 [MHz], and 6.5 [MHz] are attenuated to desired values, and generally a ceramic trap circuit or the like is used. Reference numeral 19 denotes a video signal output terminal after passing through the equalizer correction circuit 12. 20
Is an input terminal of the switching circuit 17 and is connected in circuit with one of the matching resistors 16. Reference numeral 21 denotes an output terminal of the switching circuit 17, which is connected in circuit with the other one of the matching resistors 16 and serves as an input terminal of the audio signal trap circuit 18. Reference numeral 22 denotes an input terminal of an audio intermediate frequency signal of the video / audio intermediate frequency demodulation unit 30 to which an audio intermediate frequency carrier in the audio intermediate frequency band selected by the SAW filter 7 is input.

Reference numeral 23 denotes an AM / FM detection unit.
In the case of M detection and SECAM, it is an audio signal processing circuit that performs AM detection and extracts an audio signal, and details are omitted. Reference numeral 24 denotes an audio signal output terminal for extracting a signal detected by the PLL in the audio signal processing circuit 23. 25 is an input terminal for controlling the video frequency amplitude characteristic switching circuit 17. A signal from the RF-AGC circuit 11 is input to this input terminal.
The video frequency amplitude characteristic is switched by the GC voltage. Reference numeral 30 denotes a video / audio intermediate frequency demodulation unit, and reference numeral 37 denotes a power supply voltage input terminal, for example, 5 V is used.

FIG. 2 is a circuit diagram of a switching circuit of the receiving apparatus according to the present embodiment. In FIG. 2, reference numeral 17 denotes a switching circuit for switching video frequency amplitude characteristics, and RF-AG
The switching operation is performed using the C voltage. A switching circuit 17 is formed independently of the matching resistor 16 of the audio signal trap circuit to switch the video frequency amplitude characteristics. Reference numeral 20 denotes a video signal output terminal for outputting an audio signal and a video signal detected by the detector. Reference numeral 21 denotes an output terminal of the switching circuit 17, which is connected in circuit with the other one of the matching resistors 16 and serves as an input terminal of the audio signal trap circuit 18. Reference numeral 16 denotes a matching resistor of the audio signal trap, which determines the attenuation and frequency amplitude characteristics of the audio signal trap.

25 is a video frequency amplitude characteristic switching circuit 1
7 is an input terminal for performing the control of FIG. RF-
The video frequency amplitude characteristics are switched by the AGC voltage from the AGC circuit 11. 32 and 33 are DC
For the switching circuit
The operation is performed so as not to be affected by the C fluctuation. Reference numeral 34 denotes a first transistor for switching the matching resistor 16, which controls a parallel operation with the matching resistor 16 by turning on or off the transistor 34. Numeral 35 denotes an impedance matching resistor, which is connected in parallel through this resistor.

Reference numeral 36 denotes a pull-up resistor for switching the first transistor 34. Reference numeral 37 denotes a power supply terminal of the switching circuit 17 to which a voltage of, for example, 5 V is supplied. 38 is a ground resistance at the time of switching,
When the transistor 39 is on, an impedance is provided between the transistor 39 and the ground to prevent the signal level from deteriorating. Reference numerals 39 and 41 denote second and third transistors for switching, which are operated by the RF-AGC voltage. When the third transistor 41 is turned on, the second transistor 39 is turned off.
When the transistor 41 is off, the second transistor 39 is on. Reference numerals 42 and 43 denote voltage dividing resistors.
Is determined. Reference numeral 44 denotes a resistor for supplying power to the second and third transistors 39 and 41. Reference numeral 40 denotes a capacitor for removing a ripple for stably operating the second transistor 39.

The operation of the receiving apparatus of the present embodiment configured as described above will be described below.

The broadcast signal input from the antenna 1 is received by the tuner 3. A desired channel frequency is selected, interference is eliminated, the local oscillation frequency is mixed with the desired channel frequency, and an intermediate frequency signal is extracted. The broadcast signal received by the tuner 3 is input to the SAW filter 7 to eliminate adjacent video and audio. SAW filter 7
Outputs a video / audio intermediate frequency signal, the video intermediate frequency signal is input from input terminals 9 and 10 to a video / audio intermediate frequency demodulation unit 30, and the audio signal intermediate frequency signal is input from an input terminal 22.

The video intermediate frequency signal is gain-controlled by the IF-AMP 50 and input to the detector 13. The detector 13 performs video detection by multiplying the video intermediate frequency signal from the IF-AMP 50 and the signal oscillated by the VCO 14 by the same phase. The output signal of the detector 13 is input to the matching resistor 16 and attenuates a high frequency portion to remove noise in the signal.

Here, a switching circuit 17 is connected in parallel with the matching resistor 16, and the internal switch is turned on / off under the control of the RF-AGC circuit 11. R
When the AGC voltage value of the video signal is equal to or more than a predetermined value, the F-AGC circuit 11 determines that the electric field is weak, and when the AGC voltage value of the video signal is equal to or less than the predetermined value, it determines that the electric field is normal.
In the switching circuit 17, the internal switch of the switching circuit 17 is turned off during the normal electric field, and the video signal is input only to the matching resistor 16 in response to the control signal from the RF-AGC circuit 11. When a weak electric field is applied, the internal switch is turned on, and a video signal is input in parallel with the impedance matching resistor 35 and the matching resistor 16 shown in FIG.

The output signal of the matching resistor 16 is input to the audio signal trap section 18 and attenuates the audio signal slightly contained in the video intermediate frequency signal by designating a predetermined frequency. The output signal of the audio signal trap section 18 is input to the equalizer correction circuit 12 and corrects the high frequency portion of the video signal attenuated by the matching resistor 16. The output signal of the equalizer correction circuit 12 is output from the video signal output terminal 19, while the audio intermediate frequency signal is output from the AM / FM detector 2.
3 for FM detection at PAL and AM detection at SECAM. The audio intermediate frequency signal output from the AM / FM detector 23 is output from an audio signal output terminal 24.

As described above, according to the present embodiment, in the video / audio intermediate frequency demodulation unit 30, the matching resistor 16 is formed between the detection unit 13 and the audio signal trap unit 18, and is arranged in parallel with the matching resistor 16. , Video / audio intermediate frequency demodulation unit 30
By configuring the switching circuit 17 for switching the video frequency amplitude characteristics by the AGC voltage from the RF-AGC circuit 11, the video amplitude characteristics and the video S / N value at the time of a weak electric field can be improved.

[0034]

As described above, according to the present invention, since the image amplitude characteristic can be changed symmetrically around the chroma band, the image amplitude characteristic under a weak electric field can be obtained without attenuating only the high band of the chroma band. , The color characteristics are faithfully reproduced, the Y / C delay and resolution are improved, and the video S / N value is greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a receiving apparatus according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a switching circuit in the receiving device according to the embodiment;

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 3 Tuner 7 SAW filter 11 RF-AGC circuit 16 Matching resistor 17 Switching circuit 30 Video / audio intermediate frequency demodulation unit

Claims (2)

[Claims] 1. A tuner for receiving a broadcast signal input from an antenna, a surface acoustic wave filter for eliminating adjacent video and audio in a broadcast signal received by the tuner, and a video and audio signal output from the surface acoustic wave filter A video / audio intermediate frequency demodulation unit for demodulating an intermediate frequency band of the audio / video intermediate frequency demodulation unit, wherein a matching resistor for attenuating a high frequency portion of a video signal output from the video / audio intermediate frequency demodulation unit; A receiving circuit comprising: a switching circuit that switches a resistance value of the matching resistor under control of a frequency demodulation unit to vary an attenuation amount. 2. Receiving a broadcast signal input from an antenna, eliminating adjacent video and audio in the received broadcast signal,
By demodulating the intermediate frequency band of the video / audio signal, attenuating the high frequency part of the demodulated video signal, and varying the amount of attenuation by switching the resistance value, the video amplitude characteristics and the The receiving device according to claim 1, wherein the image S / N value is improved.