Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
1998-11-18
2001-04-03
Peng, John K. (Department: 2714)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S737000, C455S188100
Reexamination Certificate
active
06211925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a intermediate-frequency signal processing device, which can be incorporated into television receivers, VTRs, or the like, for receiving FM broadcasts as well as television broadcasts.
2. Description of the Prior Art
Recent years have seen an increase in television receivers capable of receiving general FM broadcasts, such as portable color televisions, and liquid crystal televisions. Referring now to
FIG. 2
, there is illustrated a block diagram showing the structure of an example of a prior art video intermediate-frequency signal processing device which can be incorporated into such television receivers. In the figure, reference numeral
1
denotes an antenna for receiving broadcast waves, and
2
denotes a tuner which can select a desired broadcast wave from among the plurality of broadcast waves received via the antenna
1
, and which, when receiving television broadcast waves, can convert a selected television broadcast signal into an intermediate-frequency signal including a video modulated component and a sound modulated component, and, when receiving FM broadcast waves, can convert a selected FM broadcast signal into an intermediate-frequency signal having the same frequency as the sound intermediate-frequency component generated when receiving television broadcast waves. Furthermore, reference numeral
3
denotes a video intermediate-frequency surface acoustic filter, which is hereafter abbreviated as a VIF SAW filter, for extracting a video intermediate-frequency component of a certain frequency, for example 58.75 MHz, in the case where the television receiver is destined for Japan, from the output of the tuner
2
,
6
denotes a sound intermediate-frequency SAW filter, which is hereafter abbreviated as an SIF SAW filter, for extracting a sound intermediate-frequency component of a certain frequency, for example 54.25 MHz, in the case where the television receiver is destined for Japan, from the output of the tuner
2
, and
4
denotes a video intermediate-frequency signal processing IC for detecting or demodulating the output of the VIF SAW filter
3
. In addition, reference numeral
12
denotes a VIF amplifier for amplifying the output of the VIF SAW filter
3
,
13
denotes a video detector for demodulating the output of the VIF amplifier
12
,
14
denotes an intermediate-frequency automatic gain control circuit, which is hereafter abbreviated as an IF AGC circuit, for controlling the gain of the VIF amplifier
12
according to the output of the video detector
13
,
15
denotes an IF AGC filter terminal for connecting an IF AGC filter
16
, comprised of a capacitor, to the IF AGC circuit
14
,
31
denotes a switch which can be switched to a TV terminal so as to open both ends of IF AGC filter
16
when receiving television broadcast waves, and which can be switched to an FM terminal so as to close both ends of the IF AGC filter
16
when receiving FM broadcast waves, and
17
denotes an automatic phase control detector, which is hereafter abbreviated as an APC detector, for comparing the phase of an output signal from the VIF amplifier
12
and that of an output signal from a voltage-controlled oscillator or VCO
18
so as to furnish a signal indicating the phase difference between them to the VCO
18
and perform an automatic phase control operation on the VCO
18
. The VCO
18
furnishes a control voltage of a certain frequency, dependent on the output of the APC detector
17
, to both the video detector
13
and the APC detector
17
. In addition, reference numeral
19
denotes a VCO coil for setting the free-running frequency of the VCO
18
to 58.75 MHz. The VCO coil
19
includes an inductance component and a capacitance component. Reference numeral
20
denotes an APC filter terminal for connecting an APC filter
21
to the APC detector
17
. The APC filter
21
is comprised of a capacitor and a resistor. After the APC filter
21
filters the output of the APC detector
17
, the output of the APC detector
17
is applied as a control input to the VCO
18
.
Reference numeral
23
denotes a sound intermediate frequency detector for receiving both the output of the SIF SAW filter
6
and the output of the VCO
18
, and for an SIF detection,
24
denotes an FM detector for performing an FM detection on the output of the SIF detector
23
, and
25
denotes an FM detection coil terminal for connecting an FM detection coil
26
to the FM detector
24
. The FM detection coil
26
is connected between the FM detection coil terminal
25
and a ground potential, and includes an inductance component and a capacitance component. Furthermore, reference numeral
27
denotes an output terminal through which a detected sound (or voice) output from the FM detector
24
is furnished,
28
denotes a low-pass filter comprised of a resistor and a capacitor, for extracting low-frequency components from the detected sound output from the FM detector
24
, and
30
denotes a switch which can be switched to a TV terminal so as to disconnect the output of the low-pass filter
28
from the APC filter terminal
20
when receiving television broadcast waves, and which can be switched to an FM terminal so as to connect the output of the low-pass filter
28
to the APC filter terminal
20
when receiving FM broadcast waves.
Next, a description will be made as to the operation of the prior art video intermediate-frequency signal processing device. When receiving a television broadcast, the video detector
13
demodulates the video intermediate-frequency signal which has been amplified by the VIF amplifier
12
so that the video intermediate-frequency signal has a certain amplitude. The video detector
13
then furnishes the demodulated video signal by way of the output terminal
5
. Since the switch
31
does not short circuit the IF AGC filter
16
, the IF AGC circuit
14
produces an AGC voltage from the demodulated video output of the video detector
13
, and the IF AGC filter
16
then filters the AGC voltage from the IF AGC circuit
14
. The filtered AGC voltage is applied to the VIF amplifier
12
. Thus, the IF AGC loop is formed when receiving a television broadcast. The phase-locked loop or PLL comprised of the APC detector
17
, the APC filter
21
, and the VCO
18
generates a reference carrier wave used for demodulating the video intermediate-frequency signal from the VIF SAW filter. The reference carrier wave furnished by the VCO
18
has the same frequency as the VIF carrier wave, and is in phase with the VIF carrier wave.
For a sound signal in the received television broadcast wave, the SIF detector
23
performs a detection by multiplying the reference carrier wave from the VCO
18
by a sound intermediate-frequency signal extracted by the SIF SAW filter
6
(e.g. a sound signal at a frequency of 54.25 MHz in the case where the video intermediate-frequency signal processing device is destined for Japan), so as to convert the sound intermediate-frequency signal into an intermediate-frequency signal at a frequency of, for example, 4.5 MHz. After that, the FM detector
24
demodulates the intermediate-frequency signal to produce a sound signal and then furnishes it by way of the output terminal
27
. At that time, since the switch
30
is switched to the TV terminal, the demodulated sound signal filtered by the low-pass filter
28
does not reach the APC filter
21
.
On the other hand, when receiving an FM broadcast, the switch
31
is switched to the FM terminal and shorts circuits the IF AGC filter
16
. As a result, the gain of the VIF amplifier
12
is reduced to a minimum. Since the APC detector
17
does not output anything when the gain of the VIF amplifier
12
is set to its minimum, the VCO
18
oscillates freely while it is unaffected by the APC detector
17
. The other switch
30
is then switched to the FM terminal and the DC voltage that appears at the output terminal
27
therefore enters the low-pass filter
28
. The low-pass filter
28
then rejects a sound signal from th
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Peng John K.
Tran Trang U.
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