JP2001177429A - Electronic tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electronic tuner that can automatically select its circuit component in a way of being able to properly tune a television radio wave depending on its electric field strength. SOLUTION: The electronic tuner incorporates a low noise amplifier 32 when the electric field strength of a received television radio wave is weak or automatically closes a switch circuit 20 that short-circuits the low noise amplifier 32 in terms of high frequencies when the electric field strength of a received television radio wave is strong. Thus, the electronic tuner that can automatically select its circuit component in a way of being able to properly tune a television radio wave depending on its electric field strength by means of setting data in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuner used for a television receiver.

[0002]

2. Description of the Related Art A conventional electronic tuner will be described below.

As shown in FIG. 4, a conventional electronic tuner includes an input terminal 1, a low-noise amplifier 2 connected to the input terminal 1, and an input circuit 3 connected to an output of the low-noise amplifier 2. A high-frequency (hereinafter referred to as RF) amplifier circuit 4 connected to the output of the input circuit 3;
, An inter-stage circuit 5 connected to the output of the inter-stage circuit 5, an intermediate frequency amplifier circuit 7 connected to the output of the inter-stage circuit 5, Output terminal 8 connected to the output of intermediate frequency amplifier 7
A data terminal 9 to which tuning data is input from outside;
The PLL circuit 10 was connected to the data terminal 9, and the local oscillation circuit 11 was connected between the PLL circuit 10 and the other input of the mixing circuit 6.

In the thus configured electronic tuner, the local oscillation circuit 11 is controlled by inputting tuning data from the data terminal 9, and the frequency of the local oscillation circuit 11 and the input from the input terminal 1 are input. The selected television signal is mixed with the received television wave, and the output is output from the output terminal 8.

Here, there is a problem that when a television signal is strong due to the strength of a television signal input to the input terminal 1, the signal is excessively amplified by the low noise amplifier circuit 2 to cause distortion.

Therefore, as shown in FIG. 5, a series connection of a mechanical switch 13 and a resistor 14 is provided between the input of the low noise amplifier 12 and the ground, as shown in FIG.
When the input electric field is strong, the switch 13 is closed to lower the electric field level. By doing so, distortion in a strong electric field was reduced.

[0007]

SUMMARY OF THE INVENTION However, PLL
Each time a channel is selected by the circuit 10, the switch 13 must be manually turned on (hereinafter, referred to as ON) or turned off (hereinafter, referred to as OFF) in accordance with the electric field level, which is very troublesome.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an electronic tuner that can automatically switch according to the electric field intensity.

[0009]

In order to achieve this object, an electronic tuner according to the present invention has a weak electric field strength between an input and an output of a low noise amplifier circuit in accordance with the electric field strength of a television wave. If you insert a low noise amplifier,
When the electric field strength is strong, a switch circuit for short-circuiting both ends of the low-noise amplifier at a high frequency is provided, and the switch circuit is automatically switched according to preset data.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to an input terminal to which a television wave is input, a low-noise amplifier connected to the input terminal, and an output of the low-noise amplifier. A mixing circuit supplied to one input, an intermediate frequency amplifier circuit to which the output of the mixing circuit is connected, an output terminal to which the output of the intermediate frequency amplifier circuit is connected,
A data terminal to which data is externally input, a PLL circuit connected to the data terminal, and a local oscillation circuit connected between the PLL circuit and the other input of the mixing circuit; Between the input and output of the amplifier circuit,
According to the electric field strength of the input television wave,
When the electric field strength is weak, a low noise amplifier is inserted, and when the electric field strength is strong, a switch circuit for short-circuiting both ends of the low noise amplifier in high frequency is provided, and the switch is set according to preset data. An electronic tuner that automatically switches circuits. By setting data in advance as described above, switching can be automatically performed in accordance with the intensity of a television wave.

Further, since the control is performed to insert or short-circuit the low-noise amplifier, distortion can be reduced without attenuating the signal.

According to a second aspect of the present invention, there is provided the electronic tuner according to the first aspect, wherein information as to whether or not a low noise amplifier is inserted is stored in one of band information data of the PLL circuit. It is not necessary to separately provide a memory for inserting or short-circuiting a low noise amplifier.

Further, since data can be set by sharing the data terminal of the PLL circuit, there is no need to provide a separate terminal for connecting the set side and the electronic tuner.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an electronic tuner of the present invention. In FIG. 1, the electronic tuner of the present invention
An input terminal 1 to which a television wave is input, a low noise amplifier circuit 21 connected to the input terminal 1, an input circuit 3 connected to the output of the low noise amplifier circuit 21, and an output of the input circuit 3 And an RF amplifier circuit 4 connected to
An interstage circuit 5 connected to the output of the F amplifier circuit 4 and a mixing circuit 6 connected to the output of the interstage circuit 5 to one input;
An intermediate frequency amplifying circuit 7 connected to the output of the mixing circuit 6, an output terminal 8 connected to the output of the intermediate frequency amplifying circuit 7, and a data terminal 9 to which tuning data is input from the outside. It comprises a PLL circuit 22 to which the data terminal 9 is connected, and a local oscillation circuit 11 connected between the PLL circuit 22 and the other input of the mixing circuit 6.

In the electronic tuner configured as described above, the tuning data is inputted from the data terminal 9 to control the local oscillation circuit 11, and the frequency of the local oscillation circuit 11 and the input to the input terminal 1 are inputted. The selected signal is mixed with the selected television wave and the selected channel is output, and the output is output from the output terminal 8.

A low-noise amplifier 32 is inserted between the input and the output of the low-noise amplifying circuit 21 according to the electric field strength of the input television wave when the electric field strength is weak. When the electric field strength is strong,
A switch circuit 20 for short-circuiting both ends of the low-noise amplifier 32 at a high frequency is provided. The switch circuit 20 is automatically switched every time a channel is selected, based on preset data.

FIG. 2 is a detailed circuit diagram of the low noise amplifier circuit 21. In FIG. 2, reference numeral 23 denotes a low noise amplifier circuit 21.
And 24 is an output point of the low noise amplifier circuit 21. The input point 23 is connected to a high-pass filter 25. The output is connected to a first connection point 27 via a DC cut capacitor 26. This first connection point 2
A switching diode 29 is connected between 7 and the second connection point 28. A DC cut capacitor 31 and a low noise amplifier 32 are connected between the second connection point 28 and the third connection point 30, and a switching diode 33 and a DC power supply are connected between the third connection point 30 and the output point 24. A cutting capacitor 34 is connected in series. Second connection point 28
, The bias resistor 35 is connected to the PLL terminal 37. Further, a bias resistor 45 is inserted between the second connection point 28 and the ground. From the third connection point 30, a high-frequency choke coil 38 is connected to the PLL terminal 37. This PLL terminal 37 is connected to the band data output of the PLL circuit 22. Further, the first connection point 27 and the fourth connection point (the switching diode 33 and the capacitor 3
4), a switching diode 40 is connected between the first connection point 27 and the fifth connection point 42, and between the fifth connection point 42 and the fourth connection point 36. Is connected to a switching diode 41. The connection point 42 is connected to a power supply line 44 via a bias resistor 43. The bias resistor 46 is inserted between the first connection point 27 and the ground. The resistor 47 is connected to the fourth connection point 3
6 and ground.

Next, a description will be given of the operation. 5 V is supplied to the power supply line 44, and about 2.5.
The bias resistors 43, 46 and 47 are set so as to be 5V. At this time, the PLL terminal 37 is switched between 0V and 5V. When the voltage of the PLL terminal 37 is 5 V, the switching diode 29 and the switching diode 33 are short-circuited, and the switching diode 40 and the switching diode 41 are opened. Therefore, in this case, the input point 23
Are amplified by the low-noise amplifier 32 and output to the output point 24. When the PLL terminal 37 is at 0 V, the switching diode 29 and the switching diode 33 are opened, and the switching diode 4
0 and the switching diode 41 are short-circuited. Therefore, in this case, the high-frequency signal input to the input point 23 passes through the switching diode 40 and the switching diode 41 and is output to the output point 24.

Since the configuration is as described above, in particular, P
When the LL terminal 37 is set to 0 V and is not allowed to pass through the low-noise amplifier 32, the input high-frequency signal passes through the switching diode 40 and the switching diode 41, so that the high-frequency signal is not attenuated as in the related art.
Distortion can be minimized. Therefore, in the low noise amplifier circuit 21, by setting the PLL terminal 37 to 0V or 5V, the low noise amplifier 32 is connected to the switching diode 40.
And the switching diode 41 can select whether to short-circuit or open in high frequency.

FIG. 3 is a diagram showing a PLL tuning data format. Here, 50 stores address data. A program divider 51 stores frequency data for channel selection. 52 is a charge pump test bit, and 53 is an input / output (I / O) port control bit. Here, among the I / O port control bits 53, 54 is a channel selection port of the VHF low channel, 55 is a channel selection port of the VHF high channel, and 56 is a channel selection port of UHF. 57 was used as a port for selecting ON / OFF of the low noise amplifier 32. Setting 1 to this port 57 turns on the low-noise amplifier 32, and setting to 0 turns off the low-noise amplifier 32. Therefore, by setting this bit first, the low noise amplifier 3 is automatically set in accordance with the electric field strength of the received television wave.
2 can be turned ON / OFF.

[0022]

As described above, according to the present invention, a low-noise amplifier is inserted according to the electric field strength of an input television wave when the electric field strength is weak, and the electric field strength of the television wave is increased. Is strong, a switch circuit that short-circuits both ends of the low-noise amplifier at high frequency can be provided, and the switch circuit can be automatically switched according to preset data. It can be switched automatically according to the electric field strength of the radio wave. In addition, since this low-noise amplifier is inserted or short-circuited, the signal is not attenuated and distortion can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic tuner according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a low-noise amplifier circuit of the electronic tuner.

FIG. 3 is a diagram showing a PLL data format of the electronic tuner.

FIG. 4 is a block diagram of a conventional electronic tuner.

FIG. 5 is a circuit diagram of a low-noise amplifier circuit of the electronic tuner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 6 Mixing circuit 7 Intermediate frequency amplification circuit 8 Output terminal 9 Data terminal 11 Local oscillation circuit 20 Switch circuit 21 Low noise amplification circuit 22 PLL circuit 32 Low noise amplifier

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K020 AA02 DD21 EE00 EE01 EE04 GG01 HH12 KK04 KK09 5K061 AA03 AA11 BB07 CC00 CC08 CC11 CC14 CC16 CC23 CC45 JJ04 JJ24 5K062 AA06 AB05 AB12 AD00 AD04 AD05 AG01 BC03 BE04

Claims (2)

[Claims] An input terminal to which a television wave is input, a low-noise amplifier circuit connected to the input terminal, a mixing circuit in which an output of the low-noise amplifier circuit is supplied to one input, An intermediate frequency amplifying circuit to which the output of the circuit is connected, an output terminal to which the output of the intermediate frequency amplifying circuit is connected, a data terminal to which data is input from outside,
A PLL circuit connected to the data terminal;
A local oscillation circuit connected between the circuit and the other input of the mixing circuit, and between an input and an output of the low-noise amplifier circuit according to an electric field strength of the input television wave. When the electric field strength is weak, a low-noise amplifier is inserted, and when the electric field strength is strong, a switch circuit that short-circuits both ends of the low-noise amplifier at high frequency is provided. An electronic tuner that automatically switches the switch circuit. 2. The electronic tuner according to claim 1, wherein information as to whether or not a low noise amplifier is inserted is stored in one of band information data of the PLL circuit.