JP2005311964A - Television signal transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a television signal transmitter which can be shared even when either one of intermediate frequency signals of television systems different in system is inputted. <P>SOLUTION: The television signal transmitter is provided with frequency conversion circuits 25, 30 for converting an intermediate frequency signal of a television system into a frequency of a television signal of any channel. A first mixer 22, to which any one of intermediate frequency signal of a television system of a different scheme is inputted, and an AGC circuit 24 interposed between the first mixer 22 and the frequency conversion circuit 25, 30 are provided on a pre-stage of the frequency conversion circuits 25, 30. An intermediate frequency signal of a highest frequency is inputted to the AGC circuit 24 via the first mixer 22 without frequency conversion, and other intermediate frequency signals are inputted to the AGC circuit 24 after being converted into a frequency approximately equal to the intermediate frequency signal of the highest frequency by the first mixer 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a television signal transmitter used in a CATV (cable television) system or the like.

  A conventional television signal transmitter will be described with reference to FIG. The first intermediate frequency signal including the video signal and the audio signal is input to the first mixing circuit 3 through the attenuation circuit 2, and the first mixing circuit 3 oscillates from the first local oscillation circuit 4. By mixing with the signal, the frequency is converted into a second intermediate frequency signal of approximately 1.1 GHz. The first mixing circuit 3 and the first local oscillation circuit 4 constitute a first frequency conversion circuit 5. The attenuation circuit 2 is configured by a variable attenuation circuit.

  The second intermediate frequency signal from the first mixing circuit 3 passes through the bandpass filter 6 and is then amplified to a predetermined level by the second intermediate frequency amplification circuit 7 and input to the second mixing circuit 8. In the second mixing circuit 8, it is mixed with the oscillation signal from the second local oscillation circuit 9 and frequency-converted to a third intermediate frequency signal. The second mixing circuit 8 and the second local oscillation circuit 9 constitute a second frequency conversion circuit 10 that is a second-stage frequency conversion circuit.

  The third intermediate frequency signal is transmitted as a television signal to a subscriber of the CATV system via a cable (not shown), but the frequency differs for each program to be transmitted, and is approximately 50 MHz to 1 GHz. The oscillation frequency of the second local oscillation circuit 9 is set so as to match one of the frequencies of the respective channels set in between. The third intermediate frequency signal output from the second mixing circuit 8 is given a predetermined gain by the third intermediate frequency amplifier circuits 11 and 12, and then passes through the band pass filter 13 and the output amplifier circuit 14. In the mixing circuit (not shown), the third intermediate frequency signal (television signal) similarly derived from the other television transmission circuit is mixed and sent to a cable (not shown) ( For example, see Patent Document 1.)

Japanese Patent Laid-Open No. 10-304257 (FIG. 1)

  Here, the attenuation circuit 2 is supplied from a detection circuit (not shown) for detecting a part of the output signal so that an output signal having a constant level can be obtained regardless of the level of the first intermediate frequency signal inputted. The AGC circuit is configured such that the attenuation is controlled by the detection voltage.

  When the AGC circuit is provided, the first intermediate frequency input to the AGC circuit is detected in order to detect the first intermediate frequency signal through the trap circuit that attenuates the audio intermediate frequency band in order to eliminate the influence of the audio intermediate frequency signal. If the frequency of the signal differs depending on the television system, the AGC circuit cannot be shared. If the television system is different, it is necessary to provide an AGC circuit corresponding to the system, and the models cannot be unified. It was.

  It is an object of the present invention to provide a television signal transmitter that can be shared regardless of which intermediate frequency signal of a television system of a different system is input.

  In order to solve the above-described problem, a frequency conversion circuit that converts the frequency of an intermediate frequency signal of a television system into a television signal of any channel is provided. A first mixer to which any one of the intermediate frequency signals is input, and an AGC circuit interposed between the first mixer and the frequency conversion circuit are provided, and the intermediate frequency signal having the highest frequency is frequency converted. Without being input to the AGC circuit via the first mixer, and the other intermediate frequency signal is converted by the first mixer into a frequency substantially equal to the highest intermediate frequency signal by the first mixer. Input to the circuit.

  In addition, a PLL circuit for controlling an oscillation circuit for supplying a local oscillation signal provided in the frequency conversion circuit and a reference oscillation circuit for supplying a reference signal to the PLL circuit are provided, and other than the intermediate frequency signal having the highest frequency. The reference signal is supplied to the first mixer as it is or after being divided only when the intermediate frequency signal is frequency-converted by the first mixer.

  Further, the intermediate frequency signal input to the first mixer is either a Japanese or US NTSC intermediate frequency signal or a European PAL intermediate frequency signal, and the frequency of the reference signal is 20 MHz. When the US NTSC intermediate frequency signal is input to the first mixer, the reference signal is input to the first mixer without being divided, and the PAL intermediate frequency signal is input to the first mixer. When the signal is input to the first mixer, the reference signal is divided by two and input to the first mixer.

  According to the first aspect of the present invention, the first stage to which any one of the intermediate frequency signals of the television systems having different systems is input before the frequency conversion circuit, and between the first mixer and the frequency conversion circuit. An intermediate frequency signal having the highest frequency is input to the AGC circuit via the first mixer without frequency conversion, and the other intermediate frequency signals are frequency-converted by the first mixer. Is converted to a frequency substantially equal to the highest intermediate frequency signal and inputted to the AGC circuit, so that a television signal transmitter that can be shared regardless of which intermediate frequency signal of a different television system is inputted can be configured. .

  According to the invention of claim 2, the PLL circuit for controlling the oscillation circuit for supplying the local oscillation signal provided in the frequency conversion circuit and the reference oscillation circuit for supplying the reference signal to the PLL circuit are provided, and the frequency is the highest. Since the reference signal is supplied to the first mixer as it is or after being divided only when the intermediate frequency signal other than the high intermediate frequency signal is frequency-converted by the first mixer, it is necessary to provide an oscillation circuit dedicated to the first mixer. Therefore, the entire configuration can be simplified.

  According to the invention of claim 3, the intermediate frequency signal input to the first mixer is either a Japanese or US NTSC intermediate frequency signal or a European PAL intermediate frequency signal, and the reference signal When the intermediate frequency signal of the US NTSC system is input to the first mixer, the reference signal is input to the first mixer without being divided, and the PAL intermediate frequency signal is input to the first mixer. Since the reference signal is frequency-divided to 1/2 and input to the first mixer, the transmitter of the above-described three-system television system can be configured simply by adding a general-purpose frequency divider.

  The television signal transmitter of the present invention will be described with reference to FIG. Any one of the intermediate frequency signals of the television systems having different systems is input to the intermediate frequency amplifier circuit 21. Representative television systems with different systems include, for example, the American NTSC system (video intermediate frequency: fp = 45.75 MHz, audio intermediate frequency: fs = 41.25 MHz), Japanese NTSC system (video intermediate frequency). : Fp = 58.75 MHz, audio intermediate frequency: fs = 54.25 MHz), German PAL system (video intermediate frequency: 38.9 MHz, audio intermediate frequency fs = 33.4 MHz).

  These intermediate frequency signals are input to the first mixer 22 via the intermediate frequency amplifier circuit 21. The first mixer 22 functions as a frequency converter when a local oscillation signal is input, and functions as a simple amplifier circuit or a buffer amplifier circuit when a local oscillation signal is not input. In the present invention, when a Japanese NTSC intermediate frequency signal having the highest frequency is input, a local oscillation signal is not input to the first mixer 22. Accordingly, an intermediate frequency signal that is not frequency-converted is output from the first mixer 22.

  When an intermediate frequency signal having a low frequency is input, the local oscillation signal is converted to a frequency approximately equal to that of the high frequency intermediate frequency signal (that is, the Japanese NTSC system intermediate frequency signal). The intermediate frequency signal output from the first mixer 22 is defined as a first intermediate frequency signal. The frequency of the first intermediate frequency signal is, for example, 10 MHz higher in the US NTSC system (fp = 51.25 MHz, fs = 55.75 MHz), and 20 MHz higher in the German PAL direction (fp = 53.4 MHz, fs = 58). .9 MHz).

  The first intermediate frequency signal is input to the AGC circuit (automatic gain control circuit) 24 through the band pass filter 23. The bandpass filter 23 has a pass band of approximately 50 to 60 MHz so that all of the converted first intermediate frequency signal passes through. The AGC circuit 24 is controlled by itself so that its output level becomes constant with respect to the level fluctuation of the first intermediate frequency signal on the input side, and the variable attenuation circuit 24a, the branch circuit 24b, and the trap circuit 24c. And a detection circuit 24d. The variable attenuation circuit 24a is configured by a PIN diode (not shown).

  Part of the first intermediate frequency signal output from the variable attenuation circuit 24a is branched by the branch circuit 24b, and the branch signal is input to the trap circuit 24c. The trap circuit 24c is for eliminating the influence of the audio intermediate frequency signal included in the branch signal, and is set to have a characteristic of attenuating the band of 51.25 MHz to 54.25 MHz. After the voice intermediate frequency signal is removed by the trap circuit 24c, it is detected by the detection circuit 24d. The PIN diode is controlled so that the detection voltage is fed back to the variable attenuation circuit 24a and the output level becomes constant.

  The first intermediate frequency signal output from the AGC circuit 24 is input to the second mixer 25, mixed with the local oscillation signal supplied from the first oscillation circuit 26, and a second intermediate frequency of approximately 1.1 GHz. Converted to a signal. The second mixer 25 and the first oscillation circuit 26 constitute a frequency conversion circuit. Note that the oscillation frequency of the first oscillation circuit 26 is controlled by the first PLL circuit 27. Further, a reference signal for phase comparison is supplied from the reference oscillation circuit 28 to the first PLL circuit 27.

  The second intermediate frequency signal is input to the third mixer 30 through the band pass filter 29 and mixed with the local oscillation signal supplied from the second oscillation circuit 31 to be used for the television signal (America) of any channel. In this case, the signal is converted into a television channel signal between about 50 MHz and 1000 MHz. The third mixer 30 and the second oscillation circuit 31 constitute a frequency conversion circuit. The oscillation frequency of the second oscillation circuit 31 is controlled by the second PLL circuit 32. Further, the reference signal for phase comparison is supplied from the reference oscillation circuit 28 to the second PLL circuit 32.

  The television signal output from the second mixer 30 is input to the output filter 33. The output filter 33 is formed by connecting a plurality of band pass filters having a band passing through a plurality of channels in parallel, and one of the band pass filters is selected according to the frequency of the output television signal. Is done. Then, it is sent to a cable (not shown) via the output amplifier circuit 34.

  The frequency of the reference signal output from the reference oscillation circuit 28 is, for example, 20 MHz. This reference signal is also used for the local oscillation signal of the first mixer 22. That is, when an American NTSC intermediate frequency signal is input to the first mixer 22, the reference signal is divided by ½ by the frequency divider 35, and the 10 MHz local oscillation signal is supplied to the first mixer 22. input. When a PAL intermediate frequency signal is input, a 20 MHz reference signal is supplied as it is as a local oscillation signal without frequency division. When a Japanese NTSC intermediate frequency signal is input, the local oscillation signal is not supplied. These local oscillation signals are switched by the switching means 36.

  Since a recent frequency divider can obtain a division ratio below the decimal point, if the frequency division ratio of the frequency divider 35 is 13/20, a 13 MHz local oscillation signal can be supplied to the first mixer. Since the US NTSC intermediate frequency signal can be converted to the same frequency as the Japanese intermediate frequency signal, the trap circuit 24c can be easily designed. In addition, the passband of the bandpass filter 23 can be narrowed. However, even if there is a difference of about 2 to 3 MHz in the audio intermediate frequency in the first intermediate frequency signal due to the difference in the system, this can be sufficiently attenuated by the trap circuit 24c.

  As described above, even if the intermediate frequency signal input to the first mixer 22 differs depending on the system, the frequency of the local oscillation signal supplied thereto is changed to make the output frequency almost the same (that is, the same) This trap signal 24b can be used in a system with a different system if it is converted so that any audio intermediate frequency signal can be attenuated).

It is a circuit diagram which shows the structure of the television signal transmitter of this invention. It is a circuit diagram which shows the structure of the conventional television signal transmitter.

Explanation of symbols

21: Intermediate frequency amplifier circuit 22: First mixer 23: Band pass filter 24: AGC circuit 24a: Variable attenuation circuit 24b: Branch circuit 24c: Trap circuit 24d: Detection circuit 25: Second mixer 26: First oscillation Circuit 27: First PLL circuit 28: Reference oscillation circuit 29: Band pass filter 30: Third mixer 31: Second oscillation circuit 32: Second PLL circuit 33: Output filter 34: Output amplifier circuit 35: Minute Circulator 36: Switching means

Claims (3)

A frequency conversion circuit that converts the frequency of the intermediate frequency signal of the television system into a television signal of any channel is provided, and any one of the intermediate frequency signals of the television system having a different system is input to the preceding stage of the frequency conversion circuit. And a first AGC circuit interposed between the first mixer and the frequency conversion circuit, and the first mixer without frequency conversion of an intermediate frequency signal having the highest frequency. The other intermediate frequency signal is converted into a frequency substantially equal to the highest intermediate frequency signal by the first mixer and input to the AGC circuit. TV signal transmitter. A PLL circuit for controlling an oscillation circuit for supplying a local oscillation signal provided in the frequency conversion circuit and a reference oscillation circuit for supplying a reference signal to the PLL circuit are provided, and an intermediate frequency other than the highest intermediate frequency signal is provided. The television signal transmitter according to claim 1, wherein the reference signal is supplied to the first mixer as it is or after being divided only when the signal is frequency-converted by the first mixer. The intermediate frequency signal input to the first mixer is either a Japanese or US NTSC intermediate frequency signal or a European PAL intermediate frequency signal, and the reference signal has a frequency of 20 MHz. When the intermediate frequency signal of the NTSC system is input to the first mixer, the reference signal is input to the first mixer without being divided, and the intermediate frequency signal of the PAL system is input to the first mixer. 3. The television signal transmitter according to claim 2, wherein the reference signal is frequency-divided by half and input to the first mixer.

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