Television – Receiver circuitry – Tuning
Reexamination Certificate
2002-01-03
2004-12-14
Hsia, Sherrie (Department: 2614)
Television
Receiver circuitry
Tuning
C348S725000
Reexamination Certificate
active
06831705
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a television tuner for tuning in a television radio wave by changing a tuning frequency on the basis of a reference frequency for each channel number, the tuning frequency that is tuned being set as the frequency of a channel number, when setting the channel number, and a television receiver having the television tuner.
2. Prior Art
FIG. 6
is a block diagram showing an exemplary configuration of the essence of the conventional television receiver. In this television receiver, an RF (Radio Frequency) signal received by an antenna
11
is tuned and amplified by an RF amplifier
12
that is a tuning circuit of an electronic tuner. The tuned and amplified RF signal is mixed with an oscillating signal from a local oscillator
14
phase locked by a PLL (Phase Lock Loop) circuit, not shown, by a mixer
13
, and then converted into an IF (Intermediate Frequency) signal. A tuner
15
is composed of the RF amplifier
12
, the local oscillator
14
and the mixer
13
.
The IF signal is amplified by an IF amplifier
16
, and band limited by a SAW (Surface Acoustic Wave) filter
17
, whereby the band-limited IF signal has its level detected by a detector
18
. The detected result of the level is passed to an AGC (Automatic Gain Control) circuit
19
, which then outputs a gain control signal on the basis of the detected result given. The RF amplifier
12
has its gain controlled in accordance with the gain control signal output from the AGC circuit. With this gain control, when a strong electric field signal is received, the tuner
15
itself is prevented from being overloaded and causing false modulation.
The IF signal has the color signals R, G, B, a horizontal synchronizing signal and a vertical synchronizing signal extracted in a video signal processing portion
20
, the extracted color signals R, G, B being input into a CRT
21
. In the CRT
21
, the color signals R, G, B are turned into the electron beams having respective intensities, and the horizontal scanning and the vertical scanning are performed by a drive circuit, not shown, based on the horizontal synchronizing signal and the vertical synchronizing signal.
The IF amplifier
16
, the SAW filter
17
, the detector
18
, the AGC circuit
19
and the video signal processing portion
20
are integrally formed on an IC
26
.
The RF amplifier
12
, the local oscillator
14
and the video signal processing portion
20
are operated under the control of a microcomputer
22
connected via a bus
27
. The microcomputer
22
has a ROM (Read Only Memory)
23
storing its operation program and the reference frequency of the television radio wave for each channel number, a RAM (Random Access Memory)
24
temporarily storing the data associated with the operation, and an E
2
PROM (Electrically Erasable ROM)
30
storing the channel set frequency for each channel number.
The microcomputer
22
is connected to an operation console
25
with the operation buttons, and is supplied with the detected result of the IF signal level detected by the detector
18
.
The frequency of television radio wave is allocated to each country or area by the CCIR (International Radio Committee) to avoid the interference, in which the frequency for each channel number is greatly different depending on the country or area.
In the apparatus manufacturing company for producing television receivers and video tape recorders, a channel plan that is a list of reference frequencies for the channel numbers is created for each destination with reference to a list of channel receiving frequencies for the destination as defined by the CCIR, and stored in the ROM for the microcomputer incorporated in the apparatus to be produced.
The user can make a channel setting operation simply in an automatic or manual channel preset mode, using this channel plan.
The maximum amount of drift from the center frequency (reference frequency) of each channel number is set up to make it possible to receive the broadcasting even in the case where the broadcasting frequency is off the reference frequency, or a newly opened broadcasting station broadcasts at a frequency off the reference frequency in the channel plan, whereby the broadcasting can be received within a set range. This range is referred to as a “cover range”, which is assigned to the plus or minus side from the center frequency of each channel number.
As above constituted, in the case where the channel is set up in an automatic channel preset mode, the television receiver is tuned to a television radio wave for each channel number by changing the tuning frequency of the RF amplifier
12
within the cover range around the center frequency that is the reference frequency of each channel number stored in the ROM
23
, and the tuning frequency that is tuned is set up as the frequency of the channel number successively and stored in the E
2
PROM
30
.
When the channel number is selected, the television radio wave at the frequency of each selected channel number that is set up and stored in the E
2
PROM
30
is received.
Also, in the case where the channel is set up in a manual channel preset mode, the television receiver is tuned to a television radio wave of the selected channel number by changing the tuning frequency of the RF amplifier
12
within the cover range around the center frequency that is the reference frequency of a selected channel number stored in the ROM
23
, and the tuning frequency that is tuned is setup as the frequency of the channel number successively and stored in the E
2
PROM
30
.
When the channel number is selected, the television radio wave at the frequency of each selected channel number that is set up and stored in the E
2
PROM
30
is received.
[Problems to be Solved]
In the conventional television receiver, in the case where the television radio wave of the channel number for a broadcasting station had extremely low power due to the reason that the broadcasting station was located at the remote site, a wide band RF amplifier (booster) was attached externally to amplify the television radio wave from the antenna and pass the amplified radio wave to the tuner. However, if the television radio wave for all the channel numbers is amplified by the booster, the television radio wave of the channel number at which the power of radio wave is not extremely low is too strong, giving rise to some input distortion. Therefore, there is a problem that the recipient must turn on or off the booster depending on whether the screen condition is excellent or not.
As a technique to solve this problem, a “television receiver” containing a radio frequency booster for wide band amplification without having to purchase the booster and attach it externally was disclosed in the Unexamined Japanese Patent Application Publication No. Sho61-206325.
SUMMARY OF THE INVENTION
This invention is achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a television tuner containing a wide band RF amplifier and not requiring to turn on or off the wide band RF amplifier for each channel, in which the excellent characteristics of image quality can be attained, irrespective of whether the television radio wave is weak or strong in the electric field.
Also, it is another object of the invention to provide a television receiver with the television tuner.
[Means for Solving the Problems]
According to a first aspect of the invention, there is provided a television tuner having a reference frequency for each channel number of television radio wave, which can be tuned to a television radio wave of a channel number by changing a tuning frequency of an RF amplifier on the basis of the reference frequency of the channel number, when setting the channel number, the tuning frequency that is tuned is set up as the frequency of the channel number, and the television radio wave of the set frequency is received as the television radio wave of the channel number, the television tuner characterized by comprising
Funai Electric Co. Ltd.
Hsia Sherrie
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