JPS59122191A - Catv converter - Google Patents

Abstract

PURPOSE:To simplify a circuit constitution by providing a local oscillator generating a frequency corresponding respectively to plural channels and a filter in a converter converting a cable TV signal selectively to one of signals of plural adjacent channels. CONSTITUTION:An input signal is applied to a terminal 7 and passes through the filter 8, and the signal is mixed with a local oscillating signal from an oscillator 19 at a mixer 9 and an intermediate frequency signal is inputted to an intermediate frequency trap 37 via a filter 16, an amplifier 17 and a filter 18, and a disturbing signal such as an adjacent signal or the like is attenuated sufficiently at the trap and led to a mixer 19. The frequency of the local oscillating signal of an oscillator 20 is switched to select an output channel, the output of the mixer 19 passes through an output low pass filter 18 in the form to be selected to any channel of the desired 2-4 channels and is led to an output terminal 36. The characteristic of a filter 38 is designed not to pass through an undesirable disturbing signal but to pass through a selected full-channel output.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention simplifies the circuit configuration in a CAT converter, particularly in a CATV converter that selectively converts a cable television signal to, for example, a second, third, fourth channel, or channel. This invention relates to a CATV converter that is less susceptible to the effects of fluctuations in local oscillation frequencies.

The problems of the prior art will be outlined below. FIG. 1 shows a conceptual diagram when receiving a cable television signal and an airwave television signal, respectively.

A wired television signal is guided from a wired cable 1 via a tap 2 to a CATV converter 3, which performs frequency conversion to a selected one of a plurality of predetermined channels, and converts the frequency of the converted television signal to a selected one of a plurality of predetermined channels. A signal is supplied to a TV receiver 6 via a switch 5. Also, when receiving airwave television, antenna 4
The high frequency signal captured by T
The signal is guided to a V receiver, a channel is selected, and the signal is received.

Airwave television signals are used to skip one channel to avoid interference with adjacent channels, and CATV
The output channel of the converter 3 is set to an empty channel that is not used in the airwaves in order to avoid interference from reception medium waves during CATV reception. Needless to say, the sky channels differ depending on the region, and the above C
ATV converters are often designed to be able to selectively switch output channels, and when half-open, one of the second, third, and fourth channels can be selected.

FIG. 2 shows a conventional CA'TV converter with selectable output channels. The signal supplied to the received signal input terminal 7 passes through the input filter 8 and is mixed with the local oscillator signal from the first mixer 9 and the first oscillator 10 .

The local oscillator coil 11, the local oscillator varactor 12, the bypass capacitor 13, and the connecting resistor 14 are used to make the frequency of the first oscillator 10 variable, and apply a tuning voltage to the tuning voltage application terminal 15, for example, in a PLL synthesizer receiver. The desired CATV receive channel is then selected by applying a charge pump output voltage (not shown).

The intermediate frequency signal produced by the first mixer 9 is guided to the second mixer 19 through an intermediate frequency input filter 16, an intermediate frequency amplifier 17, and an intermediate frequency output filter 18. Then, it is mixed with the local oscillator signal from the second oscillator 20. Local coil 21. local varactor 22, bypass capacitor 23,
The connecting resistor 24 switches the frequency of the second oscillator 20, and by applying the voltage from the switching voltage supply device 25 to the local varactor 22 through the changeover switch 33, a desired output channel is selected.

The output channel and signal produced by the second mixer 19IC are transferred to one of the output filter 26 and output lap 29, the output filter 27 and output lap 30, and the output filter 28 and output lap 31 using a changeover switch 34.
．． 35 and output to the output terminal 3G. It should be noted that the output channel can be switched in one action using the switch f33, 34, 35id interlocking mechanism 32.

FIG. 3 shows an example of the pass characteristics of the output filter (26, 27, 28) and the output wrap (29, 30, 31), and P and S in the figure are the output channel images. A carrier signal and an audio carrier signal are shown, and S-
6 and P+6 represent the audio carrier signal and the video carrier signal of the adjacent channels.0 A conventional CATV converter is configured as described above and has an output channel for obtaining an output channel corresponding to the second channel. Direct filter notification and output rap 29, 3rd
It is equipped with independent circuit sections, such as an output filter 27 and an output lap 30 for obtaining an output channel corresponding to the fourth channel, and an output filter and an output lap 31 for obtaining an output channel corresponding to the fourth channel,
The configuration is relatively complicated, as it is necessary to switch the frequency in conjunction with the frequency switching of the second oscillator. For this reason, it is expensive and has the potential disadvantage that interference between each output filter or each output lap is likely to occur. Also, the output rap 29.30.31 is the second mixer 19.
Since the second oscillator 200 is inserted at a later stage, if the frequency of the second oscillator 200 fluctuates, a gap occurs between the trap frequency and the interference signal, which tends to cause beat interference. Furthermore, since there is no trap circuit before the second mixer 19, there is a problem in that interference with adjacent signals is likely to occur in the second mixer. Furthermore, the changeover switches 34 and 35 are for switching high-frequency signals, and they have the problem of deteriorating signal transmission characteristics and being susceptible to leakage as interference signals.

FIG. 4 shows the configuration of an embodiment of the present invention.

Reference numerals 7 to 25, 33, and 36 in the figure correspond to those in FIG. 2, 37 represents an intermediate frequency trap created in the present invention, and 38 represents an output low-pass filter also created in the present invention. .

An input signal is supplied to the received signal input terminal 7, and 1. desired C
Until the ATV receive channel is selected and routed to the intermediate amplifier 17, it may be considered to be exactly the same as in FIG. In the case shown in FIG. 4, the intermediate frequency output filter 18
Subsequently, an intermediate frequency trap 37 is provided, and the output from the amplifier 17 is guided to the second mixer 19 after sufficiently attenuating interfering signals such as adjacent signals. Second
The frequency of the oscillator 2o is switched to select the output channel as in the case shown in FIG.
The output of is selected as one of the desired second, third, or fourth channels and is passed through an output low-pass filter 38.
is led to the output terminal 36 through the. The output low-pass filter has a pass characteristic as shown in FIG. 5, for example, and passes the output from the second mixer 19. However, the characteristics of the filter 8 are not limited to those shown in FIG. 5, and may be any characteristics that allow the output from the second mixer 19 to pass and prevent undesired interference signals from passing as much as possible. , or may be a band pass filter. In the case shown in FIG. 4, when selecting, for example, the third channel as the output channel, it is sufficient to set the switch 33 to the roaring signal. Then 2nd mixer 1
9, the CA converted to the frequency of the third channel
The TV television signal is passed through the output low pass filter 38.
-\ and is led to the output terminal 36.

According to the CATV converter of the present invention, which is configured as described above, the configuration is simple and inexpensive, as can be seen by comparing Figure 2 with Figure WJ4, and on the other hand,
Since the trap circuit is inserted before the second mixer, adjacent interference is less likely to occur in the second mixer.

Furthermore, even if the frequency of the second oscillator drifts, the trapping performance of the preceding trap circuit is not affected, nor is it undesirably attenuated by the output low-pass filter. Therefore, the influence of such frequency drift is caused by the TV connected to the output terminal 36.
This will be absorbed by an AFC circuit (not shown) built into the receiver. Furthermore, since the switch only switches the DC voltage, the problems associated with FIG. 2 (--described) do not occur.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of the case where a cable television signal and an airwave television signal are received respectively, Fig. 271 is an example of the conventional configuration of the CATV converter shown in Fig. 1, and Figs. FIG. 4 shows an example of the frequency pass characteristics of the output filter and the output lap, which constitutes an embodiment of the present invention, and FIG. 5 shows an example of the frequency characteristics of the output low pass filter shown in FIG. 4. There is. In the figure, 9 is the first mixer, 10 is the first oscillator, and 16 is □
An intermediate frequency input filter, 17 an intermediate frequency amplifier, 18 an intermediate frequency output filter, 19 a second mixer, and 20 a violet 2
An oscillator, 37 an intermediate frequency trap, and 38 an output low-pass filter. Patent applicant: Alpenu Electric Co., Ltd. Representative Patent Attorney Mori 1) Hiroshi (3 others) -48'

Claims (2)

[Claims] (1) In a converter that selectively frequency-converts a cable television signal into one of the television signals of a plurality of adjacent channels and inputs it to a television receiver, there is a connection between the frequency conversion circuit stage and the output end. The frequency conversion circuit stage includes a filter whose pass band is all the bandwidths of the plurality of adjacent channels, and the frequency conversion circuit stage is an oscillation frequency switching means for oscillating a different frequency corresponding to each of the plurality of adjacent channels. A CATV converter characterized in that it is equipped with a local oscillator. (2) The frequency conversion circuit stage includes a first mixer circuit and a second mixer circuit, and the frequency conversion circuit stage includes a first mixer circuit between the first mixer circuit and the second mixer circuit. Claim (1) characterized by comprising a bandpass filter that passes only the band of a specific channel obtained by the method, and a trap circuit that removes signals of other channels adjacent to the specific channel. CATV converter described.