JPH0898106A - Station selection circuit with automatic discrimination function for rf modulator output signal - Google Patents

Abstract

PURPOSE: To select a station and to automatically receive the output signal of an RF modulator when an inputted signal is the output signal of the RF modulator for receiving the output signal of the RF modulator by a television receiver and the reception device of VTR and the like. CONSTITUTION: When the signal inputted to a tuner 81 is the output of the RF modulator 9, whether the input signal of the tuner 81 is the output of the RF modulator 9 or not is judged by detecting AFT voltage in a control circuit 84 by using that the AFT voltage of an AFT circuit 83 is inverted at the three frequency points of a video carrier fp, a sound carrier fs and (2fp-fs) when the station-selecting frequency of the tuner 81 is changed. When the input signal is the output of the RF modulator 9 as the result of judgement, the tuner 81 is controlled by a station-selecting frequency control signal from the control circuit 84 and the output channel of the RF modulator 9 is automatically selected and received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuning circuit with an automatic discrimination function of an RF modulator output signal, and in particular, it detects a change in the AFT voltage, determines that the signal is from the RF modulator, and determines the receiving channel of the tuner. R that can be automatically set to the output channel of the RF modulator
The present invention relates to a tuning circuit with an automatic discrimination function of an F modulator output signal.

[0002]

2. Description of the Related Art An RF modulator is used to convert a reproduction signal of a video tape recorder (hereinafter referred to as VTR), a video signal such as an output of a video camera, and an audio signal into a broadcast frequency signal (hereinafter referred to as RF signal). To be done.

For example, a reproduced image of the VTR can be viewed by converting the reproduced signal of the VTR into an RF signal through an RF modulator and inputting it to the antenna terminal of the television receiver.

FIG. 7 shows a connection relationship between an electronic device 10 having a built-in RF modulator 11 and a television receiver 20. The electronic device 10 is a VTR, a CATV converter, or the like having a built-in RF modulator. Electronic device 10
The RF modulator 11 inside has an antenna input terminal 12 and R
An F output terminal 13 is provided, and an RF signal is input to the antenna input terminal 12 from the antenna 14 via the cable 15, and an R signal from the antenna 14 is input from the RF output terminal 13.
F signal or, for example, VTR section or C in the electronic device 10
RF converted from the video signal from the ATV converter section by RF
The signal is output and input to the antenna input terminal 21 of the television receiver 20.

As the RF modulator 11 in the electronic apparatus 10, there is a switch built-in type RF modulator as shown in FIG. 8A or a non-switch built-in type RF modulator as shown in FIG. 8B. .

The RF modulator 11 with a built-in switch shown in FIG. 8A has an antenna input terminal 12 and an RF output terminal 13 outside the housing 11A, and a switch 11B and an RF modulator 11C inside the housing 11A. are doing. Here, the switch 11B is configured to switch between the first and second two connection terminals a and b by the sliding portion connected to the common terminal c, and the antenna input terminal 12 and the first terminal of the switch 11B. a is connected, the second terminal b is connected to the output end of the RF modulator 11C, the common terminal c is connected to the RF output terminal 13, and the switch 11B is connected to the first terminal a, the antenna input The RF signal of the broadcast wave supplied to the terminal 12 is R
When the F output terminal 13 is passed through and the switch 11B is connected to the second terminal b, the RF signal from the RF modulator 11C is output to the RF output terminal 13.

The switchless RF modulator 11 shown in FIG. 8B has an antenna input terminal 12, an antenna output terminal 16 and an RF output terminal 13 outside the housing 11A, and an RF modulator 11C inside the housing 11A. have. Here, the antenna input terminal 12 and the antenna output terminal 16 are connected, the output end of the RF modulator 11C and the RF output terminal 13 are connected, and the RF signal of the broadcast wave supplied to the antenna input terminal 12 is output from the antenna. RF through terminal 16
The RF signal from the modulator 11C is output to the RF output terminal 13.

In the connection configuration of FIG. 7, when the television receiver 20 receives the output signal of the RF modulator 11, the user selects the receiving channel of the television receiver 20 by using the tuning operation means 30 such as a remote controller. Using R
By adjusting to the output channel of the F modulator 11 (the unused channel of TV broadcasting is used), the RF
The output signal of the modulator 11 can be received.

FIG. 9 shows the connection between the television receiver 20A with a CATV-dedicated input terminal and the CATV converter 10A. The CATV converter 10A has a converter section (including a BS tuner and the like) and an RF modulator (herein, for example, a switch built-in type RF modulator) 11 inside, and an antenna terminal 12 and R outside.
And an F output terminal 13. Television receiver 2
0A is a broadcast wave antenna input terminal 21 and CAT
A V-only input terminal 22 is provided so that mode switching between broadcast wave input and CATV input can be performed. CAT
The RF modulator 11 in the V converter 10A includes an input terminal 12 and an RF output terminal 13, and the input terminal 12
For example, a 1.3 GHz CATV signal from a BS converter or the like is input via a CATV cable 15, converted into a baseband signal by an internal converter unit (including a BS tuner, etc.), and then supplied to the RF modulator 11 to be supplied to the R modulator.
It is converted into an F signal. The RF output terminal 13 of the RF modulator 11 outputs an RF signal obtained by RF-converting the CATV baseband signal, and inputs the RF signal to the CATV-dedicated input terminal 22 of the television receiver 20A. An antenna cable 17 is connected to the antenna input terminal 21 of the television receiver 20A.

In the connection configuration of FIG. 9, the television receiver 20A has a CATV-dedicated input terminal 22 in addition to the antenna input terminal. In a mode for receiving a signal from the CATV-dedicated input terminal 22, the RF The output channel of the modulator 11 is selected and received.

FIG. 10 shows the connection relationship between the VTR 40 and the CATV converter 10A. The CATV converter 10A has a converter unit (including a BS tuner) inside.
And an RF modulator 11, and an external antenna input terminal 12 and RF output terminal 13. VTR40
Has a VTR circuit section and an RF modulator inside, and has an antenna input terminal 41 and an RF output terminal 42 outside. Antenna input terminal 1 in the CATV converter 10A
For example, a 1.3 GHz CATV signal from a BS converter or the like is input to 2 via a CATV cable 15, further converted into a baseband signal by an internal converter section, and then converted into an RF signal by an RF modulator 11. RF
An RF signal is output from the output terminal 13 and input to the antenna input terminal 41 of the VTR 40.

In FIG. 10, the user preliminarily sets the VT.
The signal input to the antenna input terminal 41 of R40 is CAT
The mode is set whether the RF signal from the V converter 10A is set (whether the CATV mode is set).
The number of channels of the output signal of the modulator 11 is set, and when these settings are made, the output channel of the RF modulator 11 can be forcibly selected and received.

In the connection of FIG. 7, when the television receiver 20 receives the output signal of the RF modulator 11, the user needs to match the reception channel of the television receiver 20 with the output channel of the RF modulator 11. is there. Especially in the electronic device 10,
In the case where the RF modulator 11 switches between a mode in which the broadcast wave signal from the antenna input terminal 12 is directly passed through and a mode in which the RF signal is output from the RF modulation unit (when the electronic device 10 is a VTR, a TV / It is necessary to change the receiving channel of the television receiver 20 according to each mode (video switching mode).

Also in the case of the CATV converter dedicated input terminal 22 as shown in the connection of FIG. 9, in the case of the system in which the RF modulator 11 switches between the through signal of the antenna input and the output of the RF modulator as described above, R in the RF modulator
Only the channel of the F-converted signal can be received by the television receiver 20A, and the antenna through output from the RF modulator 11 cannot be received by the television receiver 20A.

FIG. 11 shows a connection relationship between the CATV converter 10A and the VTR 40 when the external changeover switch 50 is used.

FIG. 11 shows an addition of an external changeover switch 50 consisting of two input terminals a and b and an output terminal c to which a sliding portion for switching the two input terminals is connected, to the connection relation of FIG. The output end of the cable 16 in FIG. 10 is connected to one input terminal a of the external changeover switch 50 in FIG. 11, the other input terminal b is connected to the external antenna via the cable 17, and the output terminal c is connected. It is connected to the antenna input terminal 41 of the VTR 40 via the cable 18. This allows the external changeover switch 50 to switch to the CATV
The output signal from the converter 10A and the broadcast wave signal from the external antenna can be switched and supplied to the antenna input terminal 41 of the VTR 40.

However, in the case of FIG.
Since the output channel of the converter 10A and the output channel of the external antenna are different, it is necessary to switch the reception mode (or channel setting) of the VTR 40 according to the switching of the external switch 50.

[0018]

As described above, when a receiver such as a television receiver or VTR receives an output signal from a device with a built-in RF modulator, it is necessary to match the receiving channel with the channel of the output signal of the RF modulator. There is. In addition, when a receiving device such as a television receiver or a VTR is provided with a CATV-dedicated input terminal for connecting a CATV converter with a built-in RF modulator,
In addition to the CATV input terminal, a receiving device such as a television receiver or a VTR needs an antenna input terminal for broadcast wave separately, and the input signal to the receiving device is switched from the RF modulator output of the CATV converter to the broadcast wave input. At that time, it was necessary to switch the channel setting and connection of the receiving device.

Therefore, in view of the above problems, the present invention automatically sets R when the signal input to the receiving device such as a television receiver or a VTR is the output signal of the RF modulator.
It is an object of the present invention to provide a channel selection circuit with an automatic discrimination function of an RF modulator output signal capable of selecting an output channel of an F modulator.

[0020]

A tuning circuit with an automatic discrimination function of an RF modulator output signal according to the present invention inputs an output signal from the RF modulator or a broadcast wave signal other than the RF modulator, and selects a channel corresponding to a broadcast channel. A tuner that changes the local oscillation frequency with a local frequency control signal to output an intermediate frequency signal of a predetermined frequency, and a change in the output frequency of this tuner is detected, and the deviation from the constant frequency of the intermediate frequency signal is used as the AFT voltage. While outputting a tuning frequency control signal to the AFT circuit for outputting and the tuner, the AFT voltage obtained in the AFT circuit has three frequencies with respect to changes in the input signal frequency selected by the tuner. It is to detect whether or not it is inverted at a point, and when it is detected to be inverted at three frequency points, the input signal is RF.
It is provided with a control means for judging the output signal of the modulator and controlling the tuner so that the output channel of the RF modulator is selected by the tuning frequency control signal.

[0021]

In the present invention, the AFT circuit is used to detect signals at three frequencies of the video carrier fp, the audio carrier fs, and the carrier of (2fp-fs) in the input signal. Using this detection result, the control means determines the input signal. As a result of the judgment, when the input signal is the output signal of the RF modulator, the tuner is controlled by the tuning frequency control signal from the control means to automatically select and receive the output channel of the RF modulator.

[0022]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a block diagram showing a tuning circuit with an automatic discrimination function of an RF modulator output signal according to an embodiment of the present invention. In FIG. 1, a CATV converter 2 has a converter section (including a BS tuner etc.) and an RF modulator 9 inside. have. The RF modulator 9 in the CATV converter 2 has an input terminal 2a and an RF output terminal 2b. For example, a 1.3 GHz CATV signal from a BS converter or the like (not shown) is input to the input terminal 2a via the CATV cable 1, and a converter unit is provided. Is converted into a baseband signal by the RF modulator 8, and is further RF-converted by the RF modulator 8.
It becomes an F signal and is supplied to the input end a of the external changeover switch 4 through the cable 3. The broadcast wave signal of the television is supplied from the antenna 5 to the input end b of the external switch 4 through the cable 6. The external changeover switch 4 can selectively change the two input ends a and b by a sliding portion connected to the output end c, and the output of the external changeover switch 5 is passed through a cable 7. And is supplied to the antenna input terminal 8a of the receiving device 8.

The receiving device 8 is, for example, a television receiver or a VTR. The receiver 8 includes a tuner 81, an intermediate frequency amplifier circuit 82, an AFT circuit 83, and a control circuit 8
4 is equipped. The tuner 81 has an antenna input terminal 8
The RF signal from a is input, the local oscillation frequency is changed according to the tuning frequency control signal from the control circuit 84 corresponding to the desired broadcast channel, and an intermediate frequency signal of a predetermined frequency is output. The intermediate frequency amplification circuit 82 amplifies the intermediate frequency signal from the tuner 81 and supplies the intermediate frequency signal to the video detection unit in the next stage, and also supplies it to the AFT circuit 83. AFT circuit 83
Detects a change in the frequency of the intermediate frequency signal from the intermediate frequency amplifier circuit 82 and outputs the deviation of the frequency of the intermediate frequency signal from the constant frequency to the control circuit 84 as an AFT voltage.
The control circuit 84 outputs a tuning frequency control signal to the tuner 81, while the level of the AFT voltage obtained by the AFT circuit 83 changes with respect to a change in the input signal frequency selected by the tuner 81. Then, it is detected whether or not the signal is inverted at three frequency points, and when it is detected that the signal is inverted at three frequency points, it is determined that the input signal is the output signal of the RF modulator 9, and the tuning frequency control signal The tuner 81 is controlled so that the reception channel is automatically set as the output channel of the RF modulator 9.
A microcomputer is used as the control circuit 84.

FIG. 2 is a block diagram showing the configuration of the RF modulator 9 shown in FIG. In FIG. 2, input terminals 91,
A video signal and an audio signal, which have been converted into baseband signals by the converter unit of the CATV converter 2, are input to 93. The video signal is modulated by the video modulator 92, the video carrier of frequency fp is output, the audio signal is modulated by the audio modulator 94, and the second audio carrier of frequency fs-fp (where fs is the first audio carrier frequency). Is output). Then, the frequency is calculated by the adder 95 and the frequency fp,
Three carrier waves of fs and 2fp-fs are output from the output terminal 96 as RF signals.

Next, the operation of FIG. 1 will be described with reference to FIGS. The spectrum of the output signal of the RF modulator 9 is normally fp, fs, 2fp-f as shown in FIG.
It exists at three frequencies of s. This is because the structure of the RF modulator 9 is as shown in FIG. 2 and generally three filters are output because a filter for attenuating the frequency 2fp-fs is not inserted. is there.

As the AFT circuit 83, one that changes to a high level (High) and a low level (Low) before and after the above three carrier frequencies is used. Therefore, AF
In the T circuit 83, when the tuner 81 receives the output signal of the RF modulator 9, the AFT voltage characteristic with respect to the change of the tuning frequency is 3 points A as shown in FIG.
-Reverse with B, C-D, and E-F.

On the other hand, the spectrum of the broadcast wave exists at two frequencies fp and fs as shown in FIG. The AFT voltage characteristic with respect to the change in the tuning frequency when the broadcast wave signal is input to the antenna input terminal 8a is inverted at two points AB and CD as shown in FIG.

Therefore, the AF for each frequency of the input signal
When the T voltage is measured and the AFT voltage is inverted at three points as shown in FIG. 4, the control circuit 8 indicates that the output is the RF modulator.
Make a judgment in 4.

According to the result of this judgment, when the input signal is the RF modulator output, the control circuit 84 causes the tuner 81 to operate.
To automatically select and receive the output channel of the RF modulator (for example, two channels of empty channels).

Next, the case where the receiving device 8 is a VTR will be described in detail.

Before the channel selection operation, the control circuit 84 performs carrier wave detection on a channel in which the output signal of the RF modulator 9 may exist. For example, the following (1 ) ~ There is a method like (3).

(1) Generally, the channel that is widely used as the output channel of the RF modulator is used. For example, carrier detection is performed on channel 3 or 4 in North America and channel 1 or 2 in Japan.

(2) The presence / absence of signals is detected for all channels, and carrier waves are detected in the channels determined to have signals.

(3) Carrier wave detection is performed for all channels.

The carrier wave is detected at three points of fp (video carrier wave frequency), fs (audio carrier wave frequency) and 2fp-fs. For example, in the case of 3 US channels, fp
= 61.25 MHz, fs = 65.75 MHz, 2 fp
Carrier wave detection is performed at three points of -fs = 56.75 MHz. If there is a carrier at each point, the AFT voltage is inverted from high level to low level. Therefore, the control circuit 84
Sets the reception frequency to a frequency before and after each frequency of the above three carrier waves and detects a change in the AFT voltage. When the AFT voltage is inverted before and after the three frequencies, such as between A-B, between C-D, and between E-F in FIG. 4, it is determined that the input signal of the VTR 8 is the output signal of the RF modulator 9. .

The carrier wave detection method is, for example, as follows.
There are methods like (1) to (3).

(1) AFT operation during normal channel selection is performed to search for a video carrier. The AFT voltage is inverted at two points before and after the image carrier frequency fp. Next, the sound carrier frequency fs
The reception frequency is set at two points before and after, and the AFT voltage is detected. When there is a voice carrier, the AFT voltage is inverted at two points before and after fs. The AFT voltage is similarly detected at two points before and after 2fp-fs. If the AFT voltages are inverted, it is determined that the carrier wave exists.

(2) A video carrier is searched in the same manner as (1).
Next, a frequency at which the AFT voltage is inverted is searched for near the audio carrier frequency fs, and if there is a reversal point, the difference between the frequency and the video carrier frequency fp is fs-fp (for example, 4.5 MHz in the case of the NTSC system). If it is close, it is determined to be a voice carrier. Similarly for 2fp-fs, the frequency at which the AFT voltage is inverted is searched for near the carrier frequency 2fp-fs, and if there is a point at which it is inverted, if the difference between that frequency and the video carrier frequency fp is near fs-fp. , 2fp-fs.

(3) The AFT voltage is detected by changing the tuning frequency from the higher frequency to the lower frequency (or from the lower frequency to the higher frequency), and the carrier wave is detected at three points (when the carrier wave exists). If the AFT voltage changes in the same direction as),
When the frequency intervals at the three locations are close to fs-fp, it is determined that the signals are output signals from the RF modulator.

If the signal input to the antenna input terminal 8a of the VTR 8 is the output of the RF modulator 9, f
Carrier waves are detected at three points of p, fs, and 2fp-fs, and in the case of a broadcast wave signal or the like, 3 of fp, fs, and 2fp-fs.
No carrier detected at point.

In the control circuit circuit 84, the input signal is RF
When it is determined that the output is from the modulator, the output channel of the RF modulator is preferentially selected and received instead of the channel originally requested to be selected.

For example, when the reserved recording is executed, the RF modulator output is input to the antenna input terminal,
If channels other than the output channel of the RF modulator are reserved, the RF modulator output can be recorded without recording the channel with no signal.

Further, when the reserved recording is performed by the G code, conventionally when the CATV converter is connected, the CA is previously set.
The user had to set the use of the TV converter and the output channel of the CATV converter, but the RF modulator output can be automatically received without making these settings. In particular, the output of the CATV converter and the broadcast wave signal are switched by a switch to change the VTR.
In the case of inputting to, it was necessary to switch the setting of the use or non-use of the CATV converter in accordance with the switching of the two hot water signals, but in the present embodiment, the channel selection according to the input signal is performed. In the case of the output signal of the CATV converter, that is, the RF modulator, the output channel of the RF modulator can be automatically selected and received.

Next, the case where the receiving device 8 is a television receiver and the RF modulator 9 is built in the VTR will be described. Also in the case of a television receiver, the above is the same as in the case where the above-mentioned receiving device 8 is a VTR until the determination as to whether or not the input signal is the RF modulator output.

In the case of a television receiver, RF of VTR
When receiving the modulator output, the RF modulator output and the broadcast wave signal are switched depending on the mode of the VTR (TV / VTR switching mode).
It was necessary to switch the reception channel of the television receiver in accordance with the mode of (1), but in the present embodiment, when the input signal is switched (the result of no-signal detection in the channel that has been received until then is no signal). When the input signal is the RF modulator output, it is determined whether or not the input signal is the RF modulator output, and the channel selection channel is automatically switched when the input signal is switched between the RF modulator output and the broadcast wave signal. You can

In FIG. 1, the CATV converter 2
The baseband signal such as a relay line output may be directly input to the RF modulator of the RF modulator 9 without passing through the antenna input terminal thereof.

Further, in FIG. 1, reference numeral 2 indicates a CATV converter, but the present invention is not limited to the CATV converter, and a device (for example, VT) having a built-in RF modulator.
R) is sufficient.

[0048]

As described above, according to the present invention, an input signal of a receiving device such as a television receiver or a VTR is an RF signal.
When it is the output of the modulator, it is possible to determine that the input signal is the RF modulator output and automatically select and receive the RF modulator output channel.
This ensures that when receiving the RF modulator output,
The user does not need to switch the receiving channel or set the output channel of the RF modulator in advance, and thus it is possible to provide a tuning circuit having excellent operability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a tuning circuit with an automatic discrimination function of an RF modulator output signal according to an embodiment of the present invention.

FIG. 2 is a block diagram of an RF modulator.

FIG. 3 is a spectrum diagram of an RF modulator output.

FIG. 4 is a diagram showing a change in AFT voltage when an RF modulator output is received.

FIG. 5 is a spectrum diagram of broadcast waves.

FIG. 6 is a diagram showing a change in AFT voltage when a broadcast wave is received.

FIG. 7 is a perspective view showing a connection relationship between a device with a built-in RF modulator and a television receiver.

FIG. 8 is a perspective view showing an RF modulator.

FIG. 9 is a perspective view showing a connection relationship between a television receiver with a CATV-dedicated input terminal and a CATV converter.

FIG. 10 is a perspective view showing a connection relationship between a VTR and a CATV converter.

FIG. 11 is a perspective view showing a connection relationship between a CATV converter and a VTR when an external changeover switch is used.

[Explanation of symbols]

 2 ... CATV converter 4 ... Changeover switch 5 ... Antenna 8 ... Receiver 8a ... Antenna input terminal 9 ... RF modulator 81 ... Tuner 83 ... AFT circuit 84 ... Control circuit

Claims (1)

[Claims] 1. An output signal from an RF modulator or another broadcast wave signal is input, and a local oscillation frequency is changed by a tuning frequency control signal corresponding to a broadcast channel,
A tuner that outputs an intermediate frequency signal of a predetermined frequency, an AFT circuit that detects a change in the output frequency of the tuner and outputs a deviation from the constant frequency of the intermediate frequency signal as an AFT voltage, and a tuner that is tuned to the tuner. While outputting the frequency control signal, it detects whether or not the AFT voltage obtained in the AFT circuit is inverted at three frequency points with respect to the change of the input signal frequency selected by the tuner. hand,
When the inversion at three frequency points is detected, the input signal is determined to be the output signal of the RF modulator, and the tuner is controlled so that the output channel of the RF modulator is selected by the tuning frequency control signal. A tuning circuit with an automatic discrimination function of an RF modulator output signal, comprising: