Television – Receiver circuitry – Tuning
Reexamination Certificate
1999-12-20
2003-02-18
Kostak, Victor R. (Department: 2611)
Television
Receiver circuitry
Tuning
C348S707000, C725S151000
Reexamination Certificate
active
06522367
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a CATV (cable television) tuner apparatus which receives a voice signal delivered on a CATV channel.
(2) Description of the Related Art
A CATV system is usually configured by using a coaxial cable to carry a CATV signal from central equipment. For example,
FIG. 3
shows a configuration of the CATV system of this type.
In the CATV system of
FIG. 3
, central equipment
20
and a plurality of bidirectional trunk amplifiers
10
through
19
are linked together by a coaxial cable having a relatively large diameter. This trunk cable runs through the CATV system distributing the CATV signal to each neighborhood. Each of the trunk amplifiers
10
-
19
includes feeder lines that branch off the trunk typically use a smaller diameter cable to carry the signal into the neighborhoods passing each subscriber's home. In
FIG. 3
, “A” denotes a subscriber connected to the trunk amplifier
19
, “B” denotes another subscriber connected to the trunk amplifier
13
, and “C” denotes another subscriber connected to the trunk amplifier
16
.
CATV signals from the central equipment
20
are usually distributed on the trunk cable at a certain level per channel. It is necessary that the signal level delivered to the home is higher than the desired lowest level per channel. In order to maintain the signal level, the trunk amplifiers
10
-
19
are spaced along the lines at certain distances that are less than a permissible maximum distance.
The trunk amplifiers
10
-
19
serve to branch the CATV signal transmitted by the central equipment
20
downstream to subscribers and to deliver it to the individual subscribers. Further, the trunk amplifiers
10
-
19
serve to insert the subscriber information into the signal delivered upstream to the central equipment
20
. Hence, the two-way communications between the subscribers and the central equipment
20
are carried out with the CATV system.
In the CATV system of
FIG. 3
, video information is delivered from the central equipment
20
to the trunk amplifiers
10
,
14
,
17
,
18
and
19
on the trunk cable along the downstream path, in this order. For example, the. trunk amplifier
19
branches the video signal from the central equipment
20
and supplies it to the subscriber A connected to the trunk amplifier
19
. Further, the trunk amplifier
19
inserts subscriber information from the subscriber A into the signal that is delivered upstream to the central equipment
20
in the opposite direction.
FIG. 2
shows a CATV tuner apparatus according to the related art. Specifically, the CATV tuner apparatus of
FIG. 2
is applicable to an input module of a CATV tuner. The CATV tuner is located at each subscriber's home and connected through a coaxial cable to one of the plurality of trunk amplifiers within the CATV system of FIG.
3
.
As shown in
FIG. 2
, the CATV tuner apparatus according to the related art includes a tracking filter
1
, a band-pass filter (BPF)
2
, an automatic gain control (AGC)
3
, an amplifier (AMP)
4
, a band-pass filter (BPF)
5
, a frequency synthesizer (FS)
6
, and a local oscillator (OSC)
7
. In
FIG. 2
, reference numeral
8
denotes an input module of a CATV tuner located at each subscriber's home. The local oscillator
7
generates a predetermined oscillation frequency which is supplied to the frequency synthesizer
6
.
In the CATV tuner apparatus of
FIG. 2
, the tracking filter
1
serves to perform, through a filtering process, a channel selection in which a specific one of multiple CATV channels delivered on the coaxial cable is selected, based on an input signal Vin (for example, a video signal) received at an input terminal of the apparatus. The band-pass filter
2
eliminates the out-of-band noise components from the received signal from the tracking filter
1
and passes only the in-band signal components through the band-pass filter
2
.
In the CATV tuner apparatus of
FIG. 2
, the automatic gain control
3
detects the level of the signal received from the band-pass filter
2
, and either increases or decreases the amplitude of the signal before passing the signal to the amplifier
4
. Each of the tracking filter
1
, the band-pass filter
2
and the automatic gain control
3
will attenuate the level of the received input signal Vin. The amplifier
4
amplifies the level of the signal received from the automatic gain control
3
. The band-pass filter
5
eliminates the out-of-band noise components from the received signal from the amplifier
4
and passes only the in-band signal components through the band-pass filter
5
. The frequency synthesizer
6
produces an intermediate-frequency (IF) signal through a multiplication (or a division) of a frequency of the signal, received from the band-pass filter
5
, by the oscillation frequency supplied by the local oscillator
7
. In the CATV tuner apparatus of
FIG. 2
, the IF signal output by the frequency synthesizer
6
is supplied to the output terminal.
Referring back to
FIG. 3
, in the above-described CATV system, when the CATV signal is delivered from the central equipment
20
to the CATV tuner apparatus (or the subscriber's home) via some of the trunk amplifiers
10
-
19
, or vice versa, the signal level delivered to the CATV tuner apparatus is maintained at an appropriate level by the bidirectional trunk amplifiers. For example, in a case of the signal transmission between the central equipment
20
and the subscriber A, the signal level delivered to the CATV tuner apparatus (connected to the trunk amplifier
19
) is maintained at the appropriate level by the transit trunk amplifiers
10
,
14
,
17
,
18
and
19
. In a case of the signal transmission between the central equipment
20
and the subscriber B, the signal level delivered to the CATV tuner apparatus (connected to the trunk amplifier
13
) is maintained at the appropriate level by the transit trunk amplifiers
10
,
11
,
12
and
13
.
However, in a case of the transmission of a voice signal between the subscriber A and the subscriber B over the CATV system of
FIG. 3
, the signal level delivered to the CATV tuner apparatus is not properly maintained at the appropriate level. The signal transmission from the subscriber A to the trunk amplifier
10
in the upstream direction may be performed such that the signal level delivered to the trunk amplifier
10
is properly maintained by the transit trunk amplifiers. However, the subsequent transmission of the same signal from the trunk amplifier
10
to the subscriber B has to be performed in the downstream direction, and the signal level delivered to the subscriber B is not properly maintained by the transit trunk amplifiers. In the above case, the signal level delivered to the CATV tuner apparatus on the receiver side becomes too low.
In the case of the voice signal transmission between the subscribers over the CATV system, such as that shown in
FIG. 3
, the following problems will arise with the CATV tuner apparatus of
FIG. 2
because the level of the input signal Vin received at the input terminal is quite low.
1. The level of the received input signal is significantly low, and the tracking filter
1
, the BPF
2
and the AGC
3
of the CATV tuner apparatus of
FIG. 2
act to attenuate the level of the received signal and add a certain noise to the received input signal. The carrier-to-noise ratio (CNR) of the received signal will deteriorate considerably. In a case of the reception of an analog voice signal, the quality of the reproduced signal deteriorates. In a case of the reception of a digital voice signal, the bit error rate of the received signal is raised.
2. In a case of the reception of a digital audio signal from another node over the CATV system, the bit error rate of the received signal will be significantly raised. It is difficult that the CATV tuner apparatus of
FIG. 2
produces a high quality signal from the received signal.
3. When the voice signal is received by using one of a large number of CATV channels (for example,
Ogino Toshikazu
Shibano Hayato
Yamasaki Masashige
Kostak Victor R.
Mitsumi Electric Co. Ltd.
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