JPH0648281U - RF modulator - Google Patents

Abstract

(57) [Abstract] [Object] An RF modulator suitable for a video tape recorder, in which adjustment is automated to reduce the cost of the circuit. An empty channel detection unit 6 generates a tuning control signal V _T by a tuning control signal generation unit 3 to variably control a tuning frequency of an external television tuner 9, and a detection unit 4
Detects that the external television tuner 9 is tuned to a predetermined channel on the basis of the tuning determination signal V _AFT from the external television tuner 9, and stores the detection result of the detection means 4 in the storage means 5 and An empty channel of the television signal is detected according to the detection result. The control unit 7 controls the video signal carrier Cp from the oscillating unit 1 to be adjusted to a predetermined frequency by generating the control signal Vc corresponding to the empty channel.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an RF modulator, and more particularly to an RF modulator suitable for a video tape recorder.

[0002]

[Prior art]

 In a video tape recorder, a channel selection circuit obtains an intermediate frequency signal from a high frequency signal coming into an antenna terminal and detects it to generate a video IF signal and an audio IF signal, and records these signals through an IF circuit. Feeding the circuit. Further, the baseband video signal and audio signal from the reproduction processing circuit are supplied to an RF modulator, modulated into a predetermined RF signal and output to a TV terminal.

In the conventional RF modulator, the video carrier frequency, the audio carrier frequency, etc. are adjusted according to the empty channels of the television signal at the destination of the video tape recorder, for example, the value of the variable capacitor of the resonance circuit is manually adjusted. It was done by doing. Some conventional RF modulators have a built-in test signal generation circuit, and the output of the test signal is turned on by a switch operation, and the above manual adjustment is performed while observing the screen on the television monitor.

[0004]

[Problems to be solved by the device]

 However, the above-described conventional RF modulator has a problem that it takes a long time for the adjustment process on the manufacturing line to manually adjust the frequency of the vacant channel. Further, there is a drawback that the cost is high because a circuit such as a test signal generation circuit is required.

An object of the present invention is to solve the above problems and provide an RF modulator that can easily perform automatic adjustment.

[0006]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention is configured as shown in the principle diagram of FIG.

That is, the oscillator 1 that oscillates and outputs the video signal carrier wave Cp having a predetermined frequency according to the control signal Vc from the outside, and the baseband video signal V that is input from the outside. _IN And a tuning control signal V for variably controlling the tuning frequency of the external television tuner 9 and the modulation section 2 for RF-modulating the signal based on the video signal carrier Cp from the oscillating section 1._TA tuning control signal generating means 3 for generating a signal and a tuning determination signal V according to the tuning state from the external television tuner 9._AFTIs supplied with the synchronization determination signal V_AFTThe tuning control signal V has a detection means 4 for detecting that the external television tuner 9 is tuned to a predetermined channel based on the above, and a storage means 5 for storing the detection result of the detection means 4._TThe empty channel detecting section 6 for detecting an empty channel of the television signal in accordance with the detection result of the detecting means 4 when the tuning frequency of the external television tuner 9 is changed, and the control signal corresponding to the empty channel. The control unit 7 is configured to generate Vc and control the video signal carrier Cp from the oscillating unit 1 to adjust it to a predetermined frequency.

[0008]

[Action]

According to the present invention having the above structure, the empty channel detecting section 6 generates the tuning control signal V _T by the tuning control signal generating means 3 to variably control the tuning frequency of the external television tuner 9, and the detecting means. 4 detects that the external television tuner 9 is tuned to a predetermined channel based on the tuning determination signal V _AFT from the external television tuner 9, and the storage means 5 stores the detection result of the detection means 4 and the detection means 4 The control section 7 operates to detect an empty channel of the television signal in accordance with the detection result, and the control section 7 generates a control signal Vc corresponding to the empty channel to set the video signal carrier wave Cp from the oscillating section 1 to a predetermined frequency. Acts to control to adjust.

[0009]

【Example】

 FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 2, reference numeral 11 is a microcomputer having a well-known configuration having a CPU, a RAM, a ROM and the like.

The high frequency signal from the antenna terminal 12 is input to the television tuner 9 via the RF amplifier 13 and the distributor 14, and is amplified by the RF amplifier 15 and output from the TV terminal 16 as a television signal. .

The television tuner 9 roughly includes antenna input circuits 41 and 42, RF amplifiers 43 and 44, mixers 45 and 46, local oscillators 47 and 48, an intermediate frequency amplifier 49, a detector 50, and an AFT. The circuit 20 and the PLL circuit 40 are configured as illustrated.

The PLL circuit 40 is connected to the microcomputer 11 via the I ² C bus 10 together with the PLL circuit 70 of the RF modulator 17 described later. The microcomputer 11 receives a serial clock and serial data (control signal Vc and tuning control signal V _T ) according to an input signal (tuning determination signal V _AFT ) from an AFT circuit and a key input device 18 described later. To generate.

The I ² C bus 10 is composed of a data line D and a clock line CK, through which the serial clock and serial data from the microcomputer 11 are transferred to both PLL circuits. Is controlled on the basis of the following to generate the modulated voltages V _TT and V _TR .

In the television tuner 9, the local oscillators 47 and 48 oscillate at a frequency corresponding to the tuning voltage V _TT , and these oscillation outputs and a signal obtained by increasing the RF signal from the antenna terminal 19 are mixers. By mixing in 45 and 46, a desired intermediate frequency signal is taken out, amplified by an intermediate frequency amplifier 49, and then detected by a detector 50 to output a video IF signal V _I and a sound IF signal A _I. It

Therefore, the tuning adjustment is automatically controlled according to the input signal from the key input device 18 based on the program of the microcomputer 11 described above. Also, adjustments such as band switching are automatically controlled in the same manner.

Further, the AFT circuit 20 has a reference oscillator (not shown) inside, and a horizontal synchronization signal is extracted from the output signal of the intermediate frequency amplifier 49 and the tuning determination signal V _{AFT obtained} by comparing with the phase of the reference oscillator is compared with the reference signal. Output to the computer 11. This tuning determination signal V _AFT is a signal whose voltage value changes according to the tuning state of the television tuner 9, and 0 V is output when tuning is performed.

On the other hand, the RF modulator 17 is roughly composed of the microcomputer 11, the PLL circuit 70, the UHF oscillator 71, the audio oscillator 72, the audio modulator 73, the mixer 74, and the video amplifier circuit 75. , The PLL circuit 70 and the UHF oscillator 71 constitute the above-mentioned oscillating unit (1), and the audio oscillator 72, the audio modulator 73, the mixer 74 and the video amplifying circuit 75 constitute the above-mentioned modulating unit (2). Are configured.

Further, the microcomputer 11 constitutes an empty channel detection section (6) having the tuning control signal generation means (3), the detection means (4) and the storage means (3) and the control section (7). ing.

For the part of the RF modulator 17 other than the microcomputer 11, specifically, a one-chip modulator IC (model name T DA8720) manufactured by Philips having a PLL frequency synthesizer is used, and a UHF oscillator 71 is used. It can be configured by adding an external resonance circuit (not shown), a voice oscillator 72, and the like. For this external resonance circuit, a general tank circuit composed of a capacitor and an inductance may be used. Note that other ICs or individual circuits may be used as long as they have the same structure as the modulator IC (TDA8720) described above.

The baseband audio signal A _IN from the reproduction processing circuit of the video tape recorder (not shown) is amplitude-modulated by the audio modulator 73 based on the audio signal carrier from the audio oscillator 72 and output to the mixer 74. . The similar baseband video signal V _IN is DC clamped and gain-controlled by the video amplifier circuit 75 and output to the mixer 74.

On the other hand, the PLL circuit 70 is controlled by the serial clock and the serial data from the microcomputer 11 via the I ² C bus 10 as described above, and has a desired tuning voltage according to the input from the key input device 18. The _VHF is generated, and the UHF oscillator 71 oscillates at a frequency corresponding to the tuning voltage V _TR and outputs the video signal carrier Pc to the mixer 74.

Therefore, based on the program of the microcomputer 11, the video carrier frequency Pc is automatically adjusted to the video carrier frequency according to the empty channel of the television signal of the shipping destination of the video tape recorder without manually adjusting the video signal carrier wave Pc. Can be adjusted to.

Here, an example of automatic adjustment of the image carrier frequency by the microcomputer 11 will be described with reference to the flowchart of FIG.

That is, in step S31 (hereinafter step S is referred to as S), the tuning control signal V _T is varied to continuously increase the tuning frequency of the television tuner 9, for example.

Subsequently, while the tuning frequency of the television tuner 9 is rising, the tuning determination signal V _AFT is changed to zero in S32, that is, the television tuner 9 is _switched to any channel. Judge whether or not they are synchronized.

The process of S32 is continued until the television tuner 9 tunes to any channel, and when it is determined that the channel has been tuned to any channel (Yes), the frequency of the tuned channel CH1 is continued at S33. Is stored in the RAM as f1.

Further, while the tuning frequency of the television tuner 9 is rising, the tuning determination signal V _AFT is changed to zero in S34, that is, the television tuner 9 is one of the channels next to CH1. It is judged whether or not it is synchronized with.

The process of S34 is continued until the television tuner 9 tunes to any channel, and if it is determined that the channel has tuned to any channel (Yes), then at S35, the channel is tuned next to this CH1. The frequency of channel CH2 is stored in RAM as f2.

Then, in step S36, the frequency f1 of CH1 and the frequency f2 of CH2 are read from the RAM and compared with each other, and it is determined whether or not they are apart from each other by a predetermined value ΔF stored in advance and stored in the RAM. To do. ΔF is set appropriately according to the frequency of each channel of the defined television signal, and if f2-f1> ΔF, one empty channel is defined between CH1 and CH2. Is always set to an existing value.

Therefore, when the predetermined value ΔF or more is separated in the process of S36 (Yes), the values of the frequencies f1 and f2 and the television set in the standard and stored in the RAM in advance are stored in S37. The frequency f3 of the vacant channel between CH1 and CH2 is detected from the channel allocation of the signal and stored in the RAM.

Subsequently, the process proceeds to the output frequency control process of S38, and the control is performed via the PLL circuit 70 as described above so that the frequency of the image signal carrier Pc from the UHF oscillation circuit 71 becomes f3.

In the process of S36, when the distance is not more than the predetermined value ΔF (No), the value of the frequency f1 is replaced with the value of f2 in S39, and the value of the frequency f1 is cancelled. The process returns to the above process and is executed.

As described above, according to the present embodiment, various adjustments of the tuning circuit 4 and the RF modulator 7 can be automatically performed based on the program of the microcomputer 11 without manual operation. Therefore, for example, the adjustment process on the production line of video tape recorders can be completed in a short time.Since the test signal generation circuit is not required, the circuit configuration can be simplified and the design can be facilitated and the product cost can be reduced. it can. In particular, the frequency of the video signal carrier is automatically adjusted by detecting a vacant channel from the tuning judgment signal V _AFT from the external television tuner, so that the optimum channel can be selected according to the channel allocation of the shipping destination and the receiving conditions. It is also possible to set.

The frequency of the sound carrier signal of the RF modulator 7 may be controlled by the microcomputer 11 and adjusted.

[0035]

[Effect of device]

 As described above, according to the present invention, the adjustment of the video signal carrier of the RF modulator is automatically performed without detecting the empty channel of the television signal on the basis of the tuning determination signal from the external television tuner, without manual operation. Therefore, the adjustment process on the production line of a video tape recorder can be completed in a short time, and the circuit configuration can be simplified to facilitate the design and reduce the cost of the product. In addition, there is a feature that the optimum channel can be set according to the channel allocation of the shipping destination and the receiving conditions.

[Brief description of drawings]

FIG. 1 is a principle view of the present invention.

FIG. 2 is a block diagram of an embodiment of the present invention.

FIG. 3 is a flowchart of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 oscillating unit 2 modulating unit 3 tuning control signal generating unit 4 detecting unit 5 storing unit 6 empty channel detecting unit 7 control unit 9 television tuner 11 microcomputer 20 AFT circuit 40, 70 PLL circuit 71 UHF oscillator S31, ... S39 step

Claims (1)

[Scope of utility model registration request] 1. An oscillating section for oscillating and outputting a video signal carrier having a predetermined frequency according to a control signal from the outside, and a baseband video signal input from the outside based on the video signal carrier from the oscillating section. And a tuning control signal generating means for generating a tuning control signal for variably controlling the tuning frequency of the external television tuner, and a tuning determination signal corresponding to the tuning state from the external television tuner. The external television tuner has detection means for detecting that the external television tuner has tuned to a predetermined channel based on the synchronization determination signal, and storage means for storing a detection result of the detection means. An empty channel for detecting an empty channel of a television signal in accordance with the detection result of the detecting means when the tuning frequency of the tuner is changed. A channel detecting unit, RF modulator to generate the control signal corresponding to the air-out channel formed by a control unit for controlling to adjust the video signal carrier from the oscillation part to a predetermined frequency.