JPH0630355A - Afc circuit for bs tuner - Google Patents

Abstract

PURPOSE:To prevent the deterioration in reception performance at the time of selection of a MUSE signal channel. CONSTITUTION:The circuit is provided with a BS tuner 1 receiving a keyed AFC pulse AFCP in a High Vision broadcast and with a BSCPU2 receiving AFT voltages AFTV(+), AFTV(-) obtained by detecting a 2nd intermediate frequency signal outputted from the BS tuner 1, receiving channel selection data SD to select a channel and inputting a clock CLK based on the channel selection data SD and the AFT voltages AFTV(+), AFTV(-) to the BS tuner 1, and the BSCPU2 latches the channel selection data till the keyed AFC pulse AFCP is inputted to the BS tuner 1 in the case of MUSE signal channel selection to stop the AFC operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AFC circuit of a BS (satellite broadcast) tuner for receiving high-definition broadcast.

[0002]

2. Description of the Related Art In the conventional AFC (automatic frequency control) circuit system of a BS tuner for receiving high-definition broadcasting, as shown in FIG. 1, the MUSE signal channel is selected for about 1 second, that is, from the channel selection time t ₀ to the outside. The BS tuner operates as an average value AFC until the time t ₁ when a keyed AFC pulse is input from a device such as a MUSE decoder or MUSE / NTSC converter. Therefore, the local oscillation frequency of the BS tuner may change by 2MHz or more depending on the contents of the MUSE signal. Now, if the local oscillation frequency fluctuates to a higher direction and the reception performance begins to deteriorate, the local oscillation frequency f _H
If it exceeds, the second intermediate frequency of the BS tuner deviates from the center of the FM demodulation band, and thus the reception performance of high-definition broadcasting tends to deteriorate.

[0003]

As described above, when the MUSE signal channel is selected, if the reception performance is deteriorated, truncation noise of the video signal system, S / N, bit error of PCM audio data, etc. appear. . In view of such a problem, it is an object of the present invention to provide an AFC circuit for a BS tuner that does not deteriorate the reception performance when selecting a MUSE signal channel.

[0004]

The AFC circuit of a BS tuner according to the present invention is the AFC circuit of a BS tuner to which a keyed AFC pulse in high-definition broadcasting is input,
The AFT voltage obtained by detecting the intermediate frequency of the BS tuner is input, and the AFT voltage and the clock related to the tuning data that selects the channel are provided with a CPU that inputs the tuning data to the CPU. From the time of giving
During the period until the AFC pulse is input, the tuning data is retained and the AFC operation is stopped.
It is characterized in that it is configured to prevent deviation of the local oscillation frequency of the BS tuner.

[0005]

[Function] Immediately after selecting the MUSE signal channel, the CPU holds the tuning data and stops the AFC operation until the keyed AFC pulse is input to the BS tuner. The local tuning frequency of the BS tuner is controlled by the held tuning data, and the deviation of the local tuning frequency is reduced. When a keyed AFC pulse is input, the AFT voltage output by the BS tuner is monitored and the CPU operates the keyed AFC.

As a result, the local oscillation frequency of the BS tuner does not greatly shift immediately after the selection of the MUSE signal channel, and the reception performance of high-definition broadcasting does not deteriorate.

[0007]

The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 2 is a block diagram showing a main configuration of the AFC circuit of the BS tuner according to the present invention. To the BS tuner 1 to which the BS intermediate frequency BS-IF from an external device is input, a keyed AFC pulse AFCP output from a MUSE decoder or MUSE / NTSC converter which is an external device is input. For this BS tuner 1, for example, an IC with a product number CXA1401M is used. The AFT voltages AFTV (+) and AFTV (-) obtained by detecting the second intermediate frequency output from the BS tuner 1 are input to the BSCPU 2. BS
A clock CLK, which is PLL data output from the CPU 2, is input to a PLL circuit (not shown) that controls the second intermediate frequency of the BS tuner 1. The channel tuning signal transmitted by the remote control transmitter 3 is transmitted to the channel tuning CPU 4 and the channel tuning data SD output by the channel tuning CPU 4
Is input to BSCPU 2.

Next, the operation of the AFC circuit of the BS tuner at the time of channel selection will be described with reference to FIG. 3 showing the operation contents of the BS tuner 1 and the BSCPU 2. When you operate the remote control transmitter 3 and select the MUSE signal channel,
Channel tuning CPU 4 inputs tuning data SD to BSCPU 2, and clock CLK related to tuning data SD is input to a PLL circuit (not shown) of BS tuner 1. Thereby, the local oscillation frequency of the BS tuner 1 is controlled. BS tuner 1
Performs AFT detection on the second intermediate frequency. AFT detected A
The FT voltages AFTV (+) and AFTV (-) have AFTV (+) of "0" and AF when the local oscillation frequency is lower than the second intermediate frequency.
When TV (−) becomes “1”, when it is high, AFTV (+) becomes “1” and AFTV (−) becomes “0”. When the second intermediate frequency is equal to the local oscillation frequency, AFTV (+), AFTV
Both (-) become "1". This AFT voltage AFTV (+),
BSCPU 2 takes in AFTV (-). This AFT voltage AFTV
Control the clock CLK based on (+), AFTV (-),
The local oscillation frequency is controlled so as to correct the deviation of the second intermediate frequency based on the tuning data SD.

From the operation of inputting the clock CLK to the PLL circuit (not shown) of the BS tuner 1 as described above,
The intermediate frequency shift is corrected based on the tuning data SD, and a series of operations until controlling the local oscillation frequency of the BS tuner is repeated to converge the local oscillation frequency. This series of operations is similarly performed when the channel of the MUSE signal is selected, and immediately after the channel is selected, that is, as shown in FIG.
Keyed AFC for approximately 1 second from the time t ₀ when the signal channel is selected
Since pulse AFCP is not input, AFT in BS tuner 1
The circuit operates the average value AFC based on the held tuning data. At this time, the local oscillation frequency may shift by several MHz depending on the contents of the MUSE signal. Therefore, the AFC operation is stopped until the keyed AFC pulse is input. That is BSCPU
The AFT voltages AFTV (+) and AFTV (-) fetched in 2 are ignored and the tuning data of the MUSE signal channel tuning is held by the tuning program.

Next time t when the keyed AFC pulse is input
_{In 1} , the keyed AFC operation is performed to suppress the deviation of the local oscillation frequency immediately after channel selection. As a result, it is possible to prevent the reception performance of high-definition broadcasting from being deteriorated when the channel is selected, and to always improve the reception state of high-definition broadcasting. In the present embodiment, the reception performance is prevented from being deteriorated by the channel selection software, but the keyed AF is performed from the channel selection time t ₀ by the hardware.
The same effect can be obtained by muting the AFT circuit in the BS tuner ₁ until the time t ₁ when the C pulse AFCP is input.

[0011]

As described above in detail, according to the present invention, the MU
It is possible to suppress the local oscillation frequency shift when the SE signal channel is selected and prevent the reception performance from deteriorating. Therefore, it has an excellent effect of being able to provide the AFC circuit of the BS tuner that can always receive the high-definition broadcast in a good condition.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of operation contents in an AFC circuit of a conventional BS tuner.

FIG. 2 is a block diagram showing a main configuration of an AFC circuit of a BS tuner according to the present invention.

FIG. 3 is an explanatory diagram of AFC operation contents when selecting a MUSE signal channel.

[Explanation of symbols]

 1 BS tuner 2 BSCPU 3 Remote control transmitter 4 Channel tuning CPU

Claims (1)

[Claims] 1. An AFC circuit of a BS tuner to which a keyed AFC pulse is input in high-definition broadcasting, an AFT voltage obtained by detecting the intermediate frequency of the BS tuner is input, and the AFT voltage and channel are selected. CPU that inputs the clock related to station data to the BS tuner
During the period from when the tuning data is given to the CPU until the keyed AFC pulse is input, the tuning data is retained and the AFC operation is stopped, and the local oscillation of the BS tuner at the time of channel tuning is performed. BS tuner AFC circuit characterized by being configured to prevent frequency shift.