JPH05153511A - Television receiver - Google Patents

Abstract

PURPOSE:To improve the reception performance of a television broadcast. CONSTITUTION:This television receiver composed of a tuner circuit and an intermediate frequency processing circuit is provided with a detection circuit 4 detecting the presence of an adjacent channel signal and a signal level as a DC voltage level based on an intermediate frequency signal conveted by a tuner circuit 2 and the tuner circuit 2 and the intermediate frequency signal processing circuit 3 are controlled in response to a DC voltage level detected by the detection circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiving device provided with a tuner circuit and an intermediate frequency signal processing circuit, and more particularly to a television receiving device for improving intermediate frequency signal processing for televisions and video.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an electrical configuration of a conventional television receiver, and FIG. 4 is a characteristic diagram of each part thereof. The television receiver 100 includes a tuner circuit 10
1 and an intermediate frequency signal processing circuit 108.

The tuner circuit 101 comprises an input circuit 103, a high frequency amplifier circuit 104, an interstage double tuning circuit 105, a frequency conversion circuit 106, and a local oscillation circuit 107. Further, the intermediate frequency signal processing circuit 108 includes a trap circuit 109, a bandpass filter (hereinafter referred to as SAW filter) 110 using a surface acoustic wave, an intermediate frequency amplification circuit 111, a detection circuit 112, an intermediate frequency AGC circuit (hereinafter, IF). -AGC circuit) 113 and high-frequency AGC circuit (hereinafter referred to as RF-AGC circuit) 114
It consists of.

The tuner circuit 101 includes a receiving antenna 102.
The high-frequency signal f1 of a desired channel is selected from the television signal received in step 1, and the selected signal is mixed with the local oscillation signal f2 generated by the local oscillation circuit 107 to be converted into the intermediate frequency signal f3 to obtain the intermediate frequency signal. The intermediate frequency signal f3 is output to the processing circuit 108, where a picture tube (not shown)
Amplify to the required size. At this time, the intermediate frequency signal f3 is greatly attenuated in the band outside the adjacent channel signal due to the selectivity characteristic determined by the frequency characteristic of the input circuit 103 of the tuner circuit 101 and the frequency characteristic of the high frequency amplifier circuit 104 including the interstage double tuning circuit 105.

However, since the frequency of the adjacent channel signal is input to the intermediate frequency signal processing circuit 108 as an intermediate frequency signal together with the desired channel signal, the trap circuit 109 and the S circuit are provided to prevent these signals from interfering with each other.
Adjacent channel signals of 40 to 40 using the AW filter 110
It was attenuated by 50 dB, and then intermediate frequency signal processing was performed.

[0006]

However, since the conventional intermediate frequency signal processing circuit does not detect the presence or absence of the adjacent channel signal and the signal level, almost no adjacent channel signal such as the current VHF band channel is detected. Even when there is no noise, the noise figure deteriorates due to the trap circuit itself, and the gain of the high-frequency amplifier circuit is set to a low value with a margin under certain conditions of the adjacent channel signal. There was a problem that (NF) could not be obtained.

The present invention has been made to solve the above problems, and its purpose is to make unnecessary circuits such as a trap circuit between channels unnecessary and to optimize the AGC level of a tuner circuit in a television. It is an object of the present invention to provide a television receiver having improved broadcast reception performance.

[0008]

By the way, the noise figure of the receiver (the value obtained by dividing the SN ratio at the output end of the receiver by the SN ratio at the input end) is NT, and the noise figure at each stage is N1, N.
2, ... Nn, and the gain of each stage is G1, G2, ... Gn, the noise figure NT of the receiver is expressed by Equation 1.

[0009]

[Equation 1]

It can be seen from Equation 1 that the larger the gain G1 is, the less affected the latter stage is. In view of this fact, the present invention is to provide an amplifier having a high gain. In order to solve the above problems, the television receiving apparatus according to the first aspect of the present invention is an intermediate circuit output from a tuner circuit. A detection circuit for detecting the presence or absence of the adjacent channel signal based on the frequency signal is newly provided, and it is determined whether or not the intermediate frequency signal processing circuit using the trap circuit is used according to the presence or absence of the adjacent channel signal.

In order to solve the above-mentioned problems, a television receiver according to a second aspect of the present invention is further provided with a detection circuit for detecting the signal level of the adjacent channel signal based on the intermediate frequency signal output from the tuner circuit. The gain of the high frequency amplifier circuit in the tuner circuit is controlled by the voltage according to the adjacent channel signal level.

[0012]

In the television receiving apparatus according to the present invention, the gain of the amplifier circuit is set high in advance, the presence or absence of the adjacent channel signal and the signal level are detected as the DC voltage level, and the high frequency amplification is performed according to the detected signal level. Controls the gain of the circuit and the intermediate frequency amplifier circuit.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a block diagram showing an electrical configuration of a television receiving apparatus according to a first embodiment of the present invention.

The television receiver 1 includes a tuner circuit 2, an intermediate frequency signal processing circuit 3, a detection circuit 4, and a switching circuit 5. The tuner circuit 2 includes an input circuit 6, a high frequency amplifier circuit 7, an interstage double tuning circuit 8, a frequency conversion circuit 9, and a local oscillation circuit 10.

After the television high frequency signal received by the antenna 11 is matched with the input impedance by the input circuit 6 and unnecessary unnecessary signals are eliminated, the high frequency amplifier circuit 7 is provided.
And a desired channel signal is selected by the interstage double tuning circuit 8.
Amplify to improve noise figure (NF). Further, in the frequency conversion circuit 9, the desired channel signal amplified by the high frequency amplification circuit 7 and the local oscillation signal generated by the local oscillation circuit 10 are mixed and converted into an intermediate frequency signal.

The intermediate frequency signal processing circuit 3 comprises a trap circuit 12, a preamplifier 13, a SAW filter 14, an intermediate frequency amplification circuit 15 and a detection circuit 16. The intermediate frequency signal input from the tuner circuit 2 is transferred to the trap circuit 1
60.25MHz component (in case of domestic channel) is attenuated by 2 and amplified by preamplifier 13 and SAW filter 1
After determining the band characteristic in 4, the intermediate frequency amplifier circuit 15 amplifies the band characteristic. The amplified intermediate frequency signal is detected by the detection circuit 16, and the detected output is taken out as a television signal.

The detection circuit 4 includes a bandpass filter (BPF) 1
7, envelope detector 18, low-pass filter (LPF) 19,
And a detection circuit 20. The BPF 17 takes out the signal of the intermediate frequency component of the predetermined bandwidth with the center frequency of 60.25 MHz, the envelope detector 18 rectifies it by the diode, and further the LPF 19 attenuates the high frequency component remaining in the detection output. Only the intermediate frequency component is output to the detection circuit 20.

The detection circuit 20 has a collector connected to a load resistor 21.
And npn transistor Q1 and npn transistor Q2 whose emitters are connected to each other are connected to the power source via LPF 19 and resistor 23, and the emitter is connected to resistor 2
The base and collector of the pnp transistor Q3 connected to the power supply via 4 are connected to the collector of the transistor Q1 and the switching circuit 5 described later, respectively. Here, 25, 26, and 27 respectively show resistance.

In the detection circuit 20, the signal from the LPF 19 is applied as an input signal to the base of the transistor Q1, and the power supply voltage Vcc is applied to the base of the transistor Q3 via the resistor 21. The current amplified by the differential circuit of the transistors Q1 and Q2 is
Added to the base of 3. Therefore, the collector voltage of the transistor Q3 becomes the ground potential (L level) when the transistor Q1 is off,
When 1 is ON, the power supply voltage Vcc (H level) divided by the resistors 24 and 25 is supplied to the switching circuit 5.

The switching circuit 5 has a trap circuit 12 of the intermediate frequency signal processing circuit 3 according to the detection output of the detection circuit 20.
It is configured to selectively select either one of the circuits using or not using. Specifically, the trap circuit 12 is not used when the detection output is at the L level, and the trap circuit 1 is used when the detection output is at the H level.
2 is used as the circuit, and the trap circuit 12 is always used as the circuit.

The television receiver thus constructed converts the television signal into an intermediate frequency signal by the tuner circuit 2 and outputs it to the detection circuit 4 and the switching circuit 5. At this time, if there is no adjacent channel signal in the intermediate frequency signal input to the detection circuit 4, the signal output from the detection circuit 20 becomes L level, so the trap circuit 12
Switch to a circuit that does not use. By making this unnecessary circuit (trap circuit 12) through, the trap circuit 12
The noise figure (N
It is possible to prevent the deterioration of F).

FIG. 2 is a block diagram showing the electrical construction of a television receiving apparatus according to the second embodiment of the present invention. The same parts are designated by the same reference numerals. Television receiver 1
Includes a tuner circuit 2, an intermediate frequency signal processing circuit 3, and a detection circuit 40.

The tuner circuit 2 has the same configuration as that of the first embodiment except that the gain of the high frequency amplifier circuit 7 is controlled, and the description thereof will be omitted.

The intermediate frequency signal processing circuit 3 has an IF / AGC circuit 28 and an RF / AGC circuit in addition to the configuration of the first embodiment which comprises a trap circuit 12, a preamplifier 13, a SAW filter 14, an intermediate frequency amplification circuit 15 and a detection circuit 16. Circuit 2
9 was provided.

The intermediate frequency signal processing circuit 3 uses the television signal detected by the detection circuit 16 to generate a voltage according to the strength of the input radio wave, and the high frequency amplifier circuit 7 and the intermediate frequency signal according to the voltage. The gain of the amplifier circuit 15 is controlled. That is, when the input radio wave is strong, the gains of the high frequency amplification circuit 7 and the intermediate frequency amplification circuit 15 are decreased, and when the input radio wave is weak, the gains are increased so that the gain is changed and the sensitivity is changed when the channel is switched. I try to prevent it.

Further, the RF / AGC circuit 29 controls so that the gain of the high frequency amplifier circuit 7 is lowered when the output voltage of the detection circuit 20 described later is lowered.

The detection circuit 40 includes BPFs 17a, 17b,
It is composed of envelope detectors 18a and 18b, LPFs 19a and 19b, and a detection circuit 20. That is, intermediate frequency components having a predetermined bandwidth are extracted with respect to the two center frequencies (54.25 MHz and 60.25 MHz), and the envelope detector 18a, the LPF 19a, and the envelope detector 1 are respectively extracted.
It outputs to the detection circuit 20 via 8b and LPF19b.

The detection circuit 20 in this embodiment includes a variable resistor 30 connected to a connection point of collectors connected to each other.
Npn transistor Q4 and npn transistor Q5 connected to the power supply via the
Is connected to the outputs of the LPFs 19a and 19b, the emitters are connected to the emitters of the transistors Q4 and Q5, and the collectors are connected to the power supply via the resistor 31 to the base of the npn transistor Q6. To do. Where 32, 33, 3
Reference numerals 4 and 35 represent resistances.

The detection circuit 20 includes transistors Q4 and Q4.
LPF1 as an input signal is connected to each base of Q5.
Signals from 9a and 19b are added to the base of the transistor Q6 and the power supply voltage Vcc divided by the resistors 31 and 32 is applied.
Has been added. When at least one of the transistors Q4 and Q5 is turned on, a collector current flows, and a collector voltage according to the voltage division ratio determined by the variable resistor 30 and the resistors 33 and / or 34 is output. Therefore, the power supply voltage Vcc is supplied to the RF / AGC circuit 29 when both the transistors Q4 and Q5 are off, and otherwise the voltage at the level according to the voltage division ratio is RF.
It is supplied to the AGC circuit 29.

The television receiver thus constructed converts the television signal into the intermediate frequency signal by the tuner circuit 2 and outputs it to the detection circuit 40 and the intermediate frequency signal processing circuit 3. At this time, if there is an adjacent channel signal in the intermediate frequency signal input to the detection circuit 40, the voltage level output from the detection circuit 20 decreases, and accordingly, the RF / AGC circuit 29 lowers the AGC voltage level and increases the high frequency. The gain of the amplifier circuit 7 is optimized.

[0031]

The television receiver according to the present invention is
Since the presence or absence of the adjacent channel signal and the signal level are detected as a DC voltage level and the high frequency amplifier circuit and the intermediate frequency amplifier circuit are controlled and amplified in accordance with the detected signal, the trap circuit, which is an unnecessary circuit, can be made through. Thus, the AGC level of the high frequency amplifier circuit can be optimized, and when there is no adjacent channel signal, the image quality is improved and the reception performance of television broadcasting is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a television receiving apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of a television receiver according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing an electrical configuration of a conventional television receiving device.

FIG. 4 is a characteristic diagram of each part of a conventional television receiving device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Television receiving device, 2 ... Tuner circuit, 3 ... Intermediate frequency signal processing circuit, 4,40 ... Detection circuit, 5 ... Switching circuit, 6 ... Input circuit, 7 ... High frequency amplification circuit, 8 ... Interstage double tuning circuit , 9 ... Frequency conversion circuit, 10 ... Local oscillation circuit, 1
1 ... Antenna, 12 ... Trap circuit, 13 ... Preamplifier, 14 ... SAW filter, 15 ... Intermediate frequency amplification circuit,
16 ... Detection circuit, 17, 17a, 17b ... Bandpass filter (BPF), 18, 18a, 18b ... Envelope detector, 1
9, 19a, 19b ... Low-pass filter (LPF), 20 ...
Detection circuit 21-27, 30-35 ... Resistance, 28 ... Intermediate frequency AGC circuit (IF / AGC circuit), 29 ... High frequency A
GC circuit (RF / AGC circuit), Q1 to Q6 ... Transistors.

Claims (2)

[Claims] 1. A television receiver including a tuner circuit and an intermediate frequency signal processing circuit, wherein the intermediate frequency signal processing circuit detects the presence or absence of an adjacent channel signal based on the intermediate frequency signal output from the tuner circuit. A television receiver characterized in that a circuit is newly provided, and whether or not the circuit is an intermediate frequency signal processing circuit using a trap circuit is determined according to the presence or absence of an adjacent channel signal. 2. In a television receiver including a tuner circuit and an intermediate frequency signal processing circuit, the intermediate frequency signal processing circuit detects a signal level of an adjacent channel signal based on the intermediate frequency signal output from the tuner circuit. A television receiver characterized in that a detection circuit is newly provided to control the gain of a high frequency amplifier circuit in a tuner circuit with a voltage according to an adjacent channel signal level.