Television – Synchronization – Phase locking regenerated subcarrier to color burst
Reexamination Certificate
2000-10-10
2004-06-22
Lee, Michael H. (Department: 2614)
Television
Synchronization
Phase locking regenerated subcarrier to color burst
C348S507000
Reexamination Certificate
active
06753924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillation signal processing apparatus, and more particularly, to an oscillation signal processing apparatus which obtains a tuner reference signal and a subcarrier by oscillating one quartz oscillator included in a television apparatus, a television apparatus using the oscillation signal processing apparatus, and an oscillation signal processing control method.
2. Description of the Prior Art
FIG. 6
is a block diagram showing the arrangement of principal elements of a conventional television apparatus having a circuit to oscillate one quartz oscillator to oscillate a tuner reference signal and a subcarrier to demodulate color difference signal. In
FIG. 6
, a tuner
1
is connected to a SAW filter
2
and a PLL circuit
5
. A television broadcast signal is received via an antenna, and based on the received signal, an intermediate frequency signal is outputted. The tuner
1
, having a so-called PLL tuning mechanism, obtains a desired local oscillation frequency with the output signal from the PLL circuit
5
as a reference.
The intermediate frequency signal outputted from the tuner
1
is inputted via the SAW filter
2
and a VIF circuit
3
into a signal processing circuit. Through correction by the SAW filter
2
then a predetermined amplification by the VIF circuit
3
, the signal is inputted into a signal processing circuit
4
. The signal processing circuit
4
detects an input video intermediate frequency signal and outputs RGB signals. Upon signal detection, a subcarrier to demodulate a color difference signal from a carrier chrominance signal is obtained from the PLL circuit
5
connected to the signal processing circuit
4
. The signal processing circuit
4
also outputs a color burst signal as a reference signal for oscillation of the subcarrier to the PLL circuit
5
.
The PLL circuit
5
is connected to a quartz oscillator
6
, and feed-back controls an oscillation signal from the quartz oscillator
6
with the input color burst signal as a reference signal. As a result, an oscillation signal synchronized with the color burst signal is outputted, and the oscillation signal is used as a reference signal for the subcarrier inputted into the signal processing circuit
4
and for the tuner
1
. That is, to obtain the reference signal in the tuner and the subcarrier in signal detection, any oscillation mechanism is necessary. In the oscillation signal processing apparatus of the conventional art, the common quartz oscillator
6
is used for obtaining both oscillation signals.
On the other hand, Japanese Published Unexamined Utility Model Registration No. Hei 3-53050 discloses a technique to obtain a subcarrier by inputting a color burst signal, based on a video intermediate frequency signal generated via a tuner and a VIF circuit, into a PLL circuit having an APC (Automatic Phase Control) filter and VCO (Voltage Controlled Oscillator). The time constant of the APC filter is variable. In this construction, the response speed of the PLL circuit is changed by changing the time constant of the APC filter in a just-tuning period and in a non-just-tuning period, thus preventing occurrence of tuning noise.
The conventional oscillation signal processing apparatuses have the following problems.
That is, in the former conventional art, the tuner
1
and the signal processing circuit
4
can be driven by only one quartz oscillator
6
, however, in the PLL circuit
5
, in a case where noise is inputted or an input signal is unstable, the phase, level and the like of the oscillation signal become unstable. The instability of oscillation signal from the PLL circuit
5
causes instability of the intermediate frequency signal outputted from the tuner
1
, and further causes instability in the signal inputted into the PLL circuit
5
, thus causing tuning error and tuning shift.
Further, in the technique disclosed in Japanese Published Unexamined Utility Model Registration No. Hei 3-53050, although the PLL circuit can be controlled in accordance with the operation state of the tuner, there is no solution for the problem of instability in tuning operation in use of construction as in the former art to drive the tuner and the signal processing circuit by one quartz oscillator.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems, and has its object to provide an oscillation signal processing apparatus capable of stable tuning operation while obtaining a tuner reference signal and a subcarrier by oscillating one quartz oscillator, a television apparatus using the oscillation signal processing apparatus, and an oscillation signal processing control method.
The above object is attained by providing an oscillation signal processing apparatus for oscillating a subcarrier to demodulate a color difference signal from a carrier chrominance signal, comprising: PLL oscillation unit that performs predetermined oscillation synchronized with a color burst signal by a predetermined PLL and outputting an oscillation output as the subcarrier; external output unit that outputs the oscillation output from the PLL oscillation unit as a reference signal for an external tuner; and PLL oscillation control unit that controls the PLL oscillation unit to stop a phase comparison operation upon start of tuning operation by the external tuner, so as to stabilize the reference signal from the external output unit.
In the present invention having the above construction, the oscillation signal processing apparatus oscillates a subcarrier to demodulate a color difference signal from a carrier chrominance signal. For this purpose, the PLL oscillation unit performs predetermined oscillation synchronized with the color burst signal by a predetermined PLL, and outputs the oscillation signal as the subcarrier. When the PLL oscillation unit outputs the oscillation signal, the external output unit outputs the oscillation output from the PLL oscillation unit as the reference signal for the external tuner. The PLL oscillation control unit controls the PLL oscillation unit upon start of tuning operation by the external tuner to stop the phase comparison operation, to stabilize the reference signal outputted from the external output unit.
That is, the oscillation signal from the PLL oscillation unit is used as the reference signal for the tuner and as the subcarrier for demodulation of color difference signal. The tuner selects only a necessary signal from a received television broadcast signal and high-frequency amplifies the selected signal, converts signal into an intermediate frequency signal and outputs the signal, in accordance with various methods. For example, in a frequency synthesizer method, phase detection is made between a signal frequency-converted from a reference signal via a fixed frequency divider, and a signal frequency-converted from an oscillation signal oscillated from a local oscillator via a variable frequency divider for frequency division in correspondence with a user's desired channel.
The frequency of the local oscillator is changed by a tuner PLL circuit which feed-back controls the local oscillator by using the result of phase detection, there by a desired local oscillation signal is obtained. Then, the local oscillation signal corresponding to the desired channel is mixed with a signal high-frequency amplified from a signal received via an antenna, into a 58.75 MHz intermediate frequency signal. Note that in the present invention, as the reference signal is the PLL oscillation signal outputted from the external output unit, if the phase and/or level of the reference signal is unstable, the reference for the tuner PLL becomes unstable, which causes instability in the output from the local oscillator, as a result, causing tuning error or tuning shift.
Accordingly, in the present invention, the output from the external output unit upon start of tuning operation is stabilized. For this purpose, the PLL oscillation unit does not perform the phase comparison operati
Suzuki Hirotsugu
Yamamoto Kazuhiko
Crowell & Moring LLP
Funai Electric Co. Ltd.
Lee Michael H.
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