Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
2000-04-13
2004-01-27
Lee, Michael H. (Department: 2614)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S737000, C348S725000, C455S188100
Reexamination Certificate
active
06683656
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image intermediate-frequency processing apparatus which makes it possible to receive an FM broadcast in a television or a VTR.
BACKGROUND OF THE INVENTION
In recent years, portable televisions such as liquid crystal televisions, color televisions attached with VTRs or the like have become very popular. There have also come in the market television receivers capable of receiving ordinary FM broadcast as well as television broadcast.
FIG. 3
is a block diagram that shows a schematic configuration of a prior-art image intermediate-frequency processing apparatus that is built into such a television receiver.
The image intermediate-frequency processing apparatus shown in
FIG. 3
can broadly be divided into three sections, i.e. a tuner section, an intermediate-frequency filtering section and an image intermediate-frequency processing section. As shown in
FIG. 3
, the tuner section is structured by an antenna
1
that receives broadcasting waves, and a tuner
2
that selects a desired broadcasting wave from the waves received by the antenna
1
. The tuner
2
also converts the selected television broadcasting signal into an intermediate frequency signal including an image i.e., video modulation component and a voice i.e., audio modulation component when receiving a television broadcast. Further, in order to make it possible to receive FM broadcast as well a television broadcast, during reception of FM broadcast, the tuner
2
converts the selected FM broadcasting signal into intermediate-frequency signal of the same frequency as that of a voice intermediate-frequency component received during the reception of a television broadcast. The tuner
2
then outputs this converted intermediate-frequency signal.
The intermediate-frequency filtering section includes an image intermediate-frequency SAW filter
3
(hereinafter to be referred to as VIF-SAW filter) which extracts an image intermediate-frequency signal of 58.75 MHz (in the case of Japan) from the output of the tuner
2
, and a voice intermediate-frequency SAW filter
4
(hereinafter to be referred to as SIF-SAW filter) which extracts a voice intermediate-frequency signal of 54.25 MHz (in the case of Japan) from the output of the tuner
2
.
The image intermediate-frequency processing section can be further divided into an image signal processing section and a voice signal processing section. The image signal processing section includes a VIF amplifier
5
(hereinafter to be referred to as VIF-AMP) which amplifies the output of the VIF-SAW filter
3
, an image detector
6
which detects the output of the VIF-AMP
5
, an IF automatic gain control circuit
7
(hereinafter to be referred to as IF-AGC circuit) which controls the gain in the VIF-AMP
5
according to the output of the image detector
6
, an IF-AGC filter
8
made up of a capacitor, an automatic phase detector
11
(hereinafter to be referred to as APC detector) which compares phase of the output signal of the VIF-AMP
5
with phase of an output signal of a voltage control oscillator (hereinafter to be referred to as VCO)
12
, outputs a signal that represents a phase difference between these two phases to the VCO
12
, and carries out automatic phase control to the VCO
12
, and an APC filter
14
.
The APC filter
14
is generally structured by a capacitor and a resistor. An IF-AGC filter terminal
9
is a terminal that connects the IF-AGC filter
8
to an output of the IF-AGC circuit
7
. An APC filter terminal
13
is a terminal that connects the APC filter
14
to an output of the APC detector
11
.
The voice signal processing section is structured by an SIF detector
16
that receives the outputs of the SIF-SAW filter
4
and VCO
12
, carries out SIF detection and obtains a signal of 4.5 MHz that is an inter-carrier, and an FM detector
17
(hereafter to be refereed to as FM-DET) which FM-detects the output of the SIF detector
16
and converts the detected wave into a voice signal. The voice signal is output from a voice signal output terminal
18
.
Further, there are provided a switch
10
that is changed over to a TV terminal side so as to open both sides of the IF-AGC filter
8
at the time of receiving a television broadcast and that is changed over to an FM terminal side so as to short-circuit both sides of the IF-AGC filter
8
at the time of receiving an FM broadcast, and a switch
15
that is changed over to the TV terminal side so as to supply the output of the APC detector
11
to the VCO
12
at the time of receiving a television broadcast and that is changed over to the FM terminal side so as to oscillate the VCO
12
in the free running oscillation frequency at the time of receiving an FM broadcast. Further, for the image intermediate-frequency processing apparatus to function as a color television receiver, although not shown here, there are provided a color signal processing section and a luminance signal processing section, etc., in addition to the above-described structure, in the image intermediate-frequency processing section.
The operation of the prior-art image intermediate-frequency processing apparatus will be explained next. The case of receiving a television broadcast is explained first. In this case the switch
10
and the switch
15
are changed over to the TV terminal side. When the antenna
1
receives a signal sent from a broadcasting station, the received broadcasting signal is mixed with a local oscillation output corresponding to a desired channel selected by the tuner
2
, and is input into the filtering section (VIF-SAW
3
and IF-SAW
4
).
The VIF-SAW
3
takes out only the image intermediate-frequency signal from the signal obtained from the tuner
2
, and inputs this image intermediate-frequency signal into the VIF-AMP
5
at the next stage. The VIF-AMP
5
amplifies the image intermediate-frequency signal obtained from the VIF-SAW
3
to a constant level. The image intermediate-frequency signal output from the VIF-SAW
3
is detected and demodulated by the image detector
6
. The demodulated image signal is output from an image signal output terminal
19
. In this case, as the switch
10
is in the status of not short-circuiting either end of the IF-AGC filter
8
, the IF-AGC circuit
7
can input into the VIF-AMP
5
an AGC voltage generated based on the image-detected output of the image detector
6
.
The AGC voltage obtained from the IF-AGC circuit
7
is smoothed by the IF-AGC filter
8
. The smoothed AGC voltage is input into the VIF-AMP
5
. As explained above, when receiving a television broadcast, a negative feedback loop is formed by the VIF-AMP
5
, the image detector
6
, the IF-AGC circuit
7
, and the IF-AGC filter
8
.
A reference carrier to be input into the image detector
6
for detecting an image is generated by a phase-locked loop (hereinafter to be referred to as a PLL) formed by the APC detector
11
, the APC filter
14
and the VCO
12
that are closed by the switch
15
. In other words, a reference carrier of which phase is aligned with the phase of the carrier of the VIF signal by the VCO
12
, is input into the image detector
6
.
Thus, when receiving a television broadcast, the VIF-AMP
5
can maintain the amplification operation at a constant level, by changing over the switch
10
and the switch
15
to the TV terminal side respectively. Resultantly, it is possible to obtain a desired image signal corresponding to a selected channel, from the image signal output terminal
19
.
Regarding a voice signal of the television broadcast, at first, the SIF-SAW
4
takes out only the voice intermediate-frequency signal (54.25 MHz in the case of Japan) from the signal obtained by the tuner
2
. This voice intermediate-frequency signal is then input into the SIF detector
16
. The SIF detector
16
multiplies the voice intermediate-frequency signal obtained from the SIF-SAW filter
4
by a reference carrier obtained from the VCO
12
, thereby to carry out the wave detection. Further, this voice intermediate-frequency signal is converted into the FM s
Lee Michael H.
Leydig , Voit & Mayer, Ltd.
Tran Trang U.
LandOfFree
Video intermediate frequency processing apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video intermediate frequency processing apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video intermediate frequency processing apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3267026