JPH0435228A - Double heterodyne signal selection circuit device - Google Patents

Abstract

PURPOSE:To improve the economy and to make the circuit small by providing plural frequency variable local oscillators whose frequency change width is equal to each other and whose frequency change band differs from each other and a single frequency fixed local oscillator to the circuit. CONSTITUTION:For example, a 40-channel frequency division multiplex FM signal is led to a distributer 1, in which the signal is divided into 8, eight division outputs are fed to, e.g., eight frequency conversion circuits comprising 1st local oscillators 2-1 - 2-8 of variable frequency and frequency converters 3-1 - 3-8 as 8BS channel for each other channel and the signals are once frequency-converted into 8-channel FM signals. Then the signal is led to a synthesizer 5 via eight band pass filters (BPF) 4-1 - 4-8, the 8-channel FM signal at a standby frequency band of the synthesis output is led to a frequency converter 7 in combination with the 2nd local oscillator 6 whose frequency is fixed and the 8-channel signals are frequency-converted into the BS-IF band altogether. Moreover, the result is extracted as the 8-channel frequency division multiplex BS-IF band FM signal via a BS-IF band BPF 8. Thus, excellent economy is attained by using a minimum number of circuit components.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is based on the frequency arrangement of the FM signal of the first intermediate frequency band (BS-IF band) output from the outdoor unit of a satellite broadcasting receiver. For so-called demant access type CATV, which supplies multiple channels of FM signals arranged in the service band including the IP band as a demant access type service for various information to a large number of indoor units of satellite broadcasting receivers according to their needs. The hub relates to a signal selection circuit device that selects a predetermined number of channels from a multi-channel signal by heterodyne frequency conversion, and in particular, it is possible to economically configure the circuit device by minimizing the number of circuit components required for signal selection. This is how it was done.

(Summary of the Invention) The present invention is a method for converting N-channel signals where M>N from M-channel signals in a service band including 1 and 3 GHz bands based on BS-IF multiplied signals frequency-converted from 12 GHz band to 1.3 GHz band. Demand access method CA by selecting a signal
When used for TV, N variable frequency local oscillators are used to convert M channel signals in the service band to, for example, 1.8 GH.
After converting to a group of N-channel intermediate signals selectively arranged in the Z-band at the same frequency interval as the BS channel every other channel, 1.3G is transmitted using a single fixed frequency local oscillator.
By reconverting the N-channel BS-IF signal in the Hz band, the number of local oscillators, BPFs, frequency converters, etc. required can be reduced.

(Prior Art) Regarding the signal selection circuit device of the type mentioned at the beginning, satellite broadcasting has reached the practical level and a considerable number of satellite broadcasting receivers have become widespread, and the need for CATV to service satellite broadcasting receivers has increased. Prior to this, there had been no demand for its realization, and therefore, prior art related to this type of circuit device was undeveloped.

In other words, in response to a request from a subscriber, the requested signal is selected from among the trunk CATV FM signals in which FM signals with the same specifications as satellite broadcasting are arranged at frequency intervals of every other channel, which is the same as satellite broadcasting. This demand access method selects only the FM signals of multiple channels, rearranges them in the BS-IP band at frequency intervals of every other channel, and supplies them to the subscriber CATV satellite broadcast receiver indoor unit. No prior art has been disclosed for configuring a so-called hub in a CATV system, that is, a signal selection circuit device having a switching function.

In the first place, in relation to the signal selection circuit device of the present invention, which aims to provide an economical configuration of a CATV system for various information services based on satellite broadcast reception services, first, a general configuration of a satellite broadcast receiver will be described. F with a frequency interval of 38.36 MHz and a channel bandwidth of 27 MHz in the 12 GHz band for satellite broadcasting.
Satellite broadcast waves with 8 channels of M signals arranged every other channel are received by a parabolic antenna and converted into 8 channels of first intermediate frequency FM signals with the same frequency arrangement in the 1.3 GHz band by a fixed frequency first local oscillator. The BS-IF signal of the outdoor unit output is multiplied by the coaxial cable and the indoor unit is guided by the variable frequency second local oscillator.
3GHz band 8 channels BS-IP double signal center frequency 4
The video signal is selectively converted into a second intermediate frequency FM signal of 0.02 MHz and subjected to FM detection, and the video signal obtained as the detection output is received by a monitor.

Therefore, in the CATV mainline system that performs broadband transmission with the satellite broadcast receiver indoor unit as the service target, in addition to the BSIF signals of every other 8 channels obtained as the output of the satellite broadcast receiver outdoor unit, the BS-
In the service band including the IP band, FM signals with the same specifications as the B5-4F signal and representing various other information are arranged every other channel to prepare, for example, a 4o channel FM signal and respond to subscriber requests. 8 channels of FM signals selected from 40 channels in the service band are arranged every other channel in the BS-IP band and sent out.

Now, let the number of channels of the mainline CATV transmission FM signal be M, and let the FM signal carrier frequencies of the lowest and highest channels in the service band be f and fM, respectively.
Frequency interval of every other channel of satellite broadcasting is 38.36MH
If z is Δf, then L is counted from the lowest frequency channel.
The FM signal carrier frequency fL of the th channel is (
1) Equation becomes.

f,,・f, + (L-])・△f In addition, the 8-channel FM signal carrier frequency f B5- is arranged every other channel as described above in the BS-IF band of 1.0 to 1.3 GHz. 1eh+fI]5-3ch
+ −−−−−−+ fBs-ISch is the following (2)
The formula becomes

fBS-1eh　　　　　　f　　　”26・Δf.

fas-3ch = f + 27・△f and (
2) □ fB5-. 5eh= f-+ 33・Δ layer 22, f
' is the frequency that the carrier wave frequency f1 can take in the channel in the lowest frequency region in which FM signals with a bandwidth of 27 MHz are arranged, and is 52.12 MHz. Note that the carrier frequency of the FM signal with a bandwidth of 27 MHz is f
- = 13.76M, which is 38.36MHz lower than 52.12MHz, which is the frequency interval of every other channel of satellite broadcasting.
Hz is excluded because it is impractical to use it as a carrier wave frequency that carries an FM signal with a bandwidth of 27 MHz. In addition,
The carrier frequency f of the lowest channel can be generalized by setting K to be a positive integer and can be expressed by the above equation (3).

f, = f−+ K・△f(3) (Invention or problem to be solved) From the M channel signals having such a frequency relationship, N channel signals where M>N are arbitrarily selected and placed in a predetermined frequency band. As for the configuration of a circuit device that rearranges the signals at predetermined frequency intervals of every other channel, the following five configurations can be considered based on conventionally well-known and commonly used circuit technology.

■ As shown in Fig. 3, M bandpass filters (BPF) 4-1 to 4-M each have a center frequency f, which is a frequency division multiplexed FM signal of an arbitrary frequency band.
are supplied in parallel to M channel FM signals, and these M channel FM signals are sent to FM demodulators 28-1 to 28-.
M baseband signals demodulated by supplying them to MXN
N
N-channel BS-IP band FM in which N baseband signals are extracted and frequency division multiplexed by supplying these N baseband signals to N FM modulators 30-1 to 30-N.
Take out the signal.

A signal selection circuit device having such a configuration requires an extremely large number of circuit elements and is therefore not economically practical.

■ As shown in Fig. 4, a frequency division multiplexed high frequency signal in an arbitrary frequency band is supplied in parallel to M BPFs 4-1 to 4-M having center frequencies f and -fM, respectively.
The high-frequency signals of the M channels are separated into high-frequency signals of the channels, and the high-frequency signals of the M channels are supplied to the high-frequency switch 31 having MXN cross points to extract the high-frequency signals of the N channels. 1 to 2-N and frequency converters 3-1 to 3-N, and frequency-division multiplexed N-channel BS-IP band doubled signals are extracted.

A signal selection circuit device having such a configuration also requires an extremely large number of circuit elements and large-scale high-frequency switches, and is therefore not economically practical.

3) In order to select a signal by frequency conversion of a sinkle heterodyne without using a large-scale switch as described above, as shown in FIG. N frequency conversion circuits consisting of -1 to 2-N and frequency converters 3-1 to 3N, and N BS [F-band BPFs 4-1 to 4-N, which are supplied in parallel and frequency-division multiplexed. BS-
Extract IP band double signal.

In the signal selection circuit device having such a configuration, the oscillation frequency of the local oscillators 2-1 to 2-N is selected to be higher than or lower than the carrier frequency of the BS-IP band. For the carrier frequency fL, F
M high frequency signal to F of B5-1 channel (fBS, .h)
The case of frequency conversion to an M signal will be described.

First, if the local oscillation frequency is selected lower than fBS-1ch, the local oscillation frequency or l fBs-1ch-f
As well as becoming L, ft-(fBs-1ch-fL)
-fBs-1chThe carrier wave frequency ft holds true.
The FM high frequency signal of the L first channel with , - is also f
The frequency can be converted to a Bs-1eh FM signal, and from equations (1) to (3) above, the FM signal of the L'th channel, which has the relationship shown in equation (4) above, can be calculated. This will cause interference to the fBs-lch FM signal which is the converted output.

L' ・54-L-2K (4) For example, when FM signals are arranged down to the lowest frequency region and = 0, the carrier wave frequency of the L-18th channel is fi8 70
If we select the local oscillation frequency of 345.24MHz to select 4.24MHz, then L'・36th channel carrier frequency f36=]394.72M! (The FM signal of Z is simultaneously frequency-converted to TBS-1ch, causing interference. Therefore, this circuit configuration is BSIF
Application is limited only to CATV systems in which FM signals are arranged in a frequency band lower than the frequency band. Furthermore, increasing the value of K reduces the number of selectable FM signal channels.

On the other hand, when the local oscillation frequency is selected higher than fBs-1eh, the local oscillation frequency is l fBs-1eb+f
At the same time, 2 (fBs-+, h+bl b
The FM high-frequency signal of the L'-th channel having the carrier frequency f, - for which the relationship of --fas-+eb holds, can also be frequency-converted to the FM signal of fBS-1ch, and as in the case described above, interference interference can be caused. will occur. For example, K
=O, then L=carrier frequency L of the first channel
-1101.60M to select 52,12MHz
If we choose a local oscillation frequency of Hz, L” = 30th channel carrier frequency f3. = 1164.56MH
The FM signal of z is simultaneously converted to a frequency of 1038.64MHz, fBs-1ch = 1049.48MH
Since it is not more than 10.84 MHz L away from Z, interference occurs as described above.

Therefore, the signal selection circuit device with such a configuration also has a BS-
This method cannot be applied to mainline CATV that arranges FM signals in frequency bands higher than the IF band.

Furthermore, when converting the frequency of an FM signal and transmitting it to the BS-IP band, it is generally necessary to isolate the high frequency input end and the conversion output end of the frequency conversion circuit, or to
Considering that it is insufficient to obtain a good co-channel interference protection ratio in the
The number of channels of the M signal will be limited to 26.

■ As mentioned above, F that can be transmitted on trunk CATV
As a signal selection circuit device that repeats frequency conversion twice without limiting the number of M signal channels,
As shown in FIG. 6, the frequency division multiplexed signal in an arbitrary frequency band is guided to the frequency converter 7, and the subsequent
- fL > 2 for the highest center frequency f at M
The oscillation output of the first local oscillator 6 with a fixed frequency f, fM, is subjected to frequency conversion to a high frequency band that is not affected by interference, and the converted output signal is transmitted to M BPFs 4-1 to 4.
- M channel high frequency signals are separated into M channel high frequency signals, and these M channel high frequency signals are guided to a high frequency switch having MXN cross points via M BPFs 4-1 to 4-M, each having a different center frequency. , selects and extracts desired N-channel high frequency signals, and outputs variable frequency local oscillators 2-1 to 2-N and frequency converter 3-, respectively.
The signals are supplied to N frequency conversion circuits consisting of 1 to 3-N, each converted into N-channel high frequency signals arranged in the BS-IP band, and then passed through the BPF 32 of the BS-IP band to be frequency-divided into the BS-IP band. extract high frequency signals.

The signal selection circuit device having such a configuration also has the following features as described above.
Its construction requires a large number of circuit elements and large-scale high-frequency switches, making it economically impractical.

■ As shown in FIG. 7, a high frequency signal obtained by frequency division multiplexing M channels having carrier frequencies f and -fM respectively is transmitted to N first local oscillators 2-, each having a variable frequency range L+ft to L+ft. 1 to 2-N are connected in parallel to N frequency converters 3-1 to 3 to N, respectively, to perform frequency conversion (up-conversion) to a high frequency band free from interference, and to convert each local oscillation into a high frequency band free from interference. By changing the frequency appropriately, the high frequency signal of the desired N channels is transmitted through N BPFs, all of which have the same center frequency f7.
N frequency converters 34-1 to 34-N, each of which is a combination of N second local oscillators 33-1 to 33-N, each having a fixed frequency, via 4-1 to 4-N, respectively;
frequency conversion (down conversion) is performed, and the converted output high frequency signal is passed through the BS-IP band BPF 32,
It is extracted as a frequency division multiplexed BS-IF band N channel high frequency signal.

In the signal selection circuit device having such a configuration, the frequency variable range and variable bandwidth of the first local oscillators 2-1 to 2-N used are the same, and the center frequency f of the BPFs 41 to 4-N is also the same as the highest channel. The carrier wave frequency fM is selected in the same frequency band free from interference,
The change bandwidth of the first local oscillation frequency is also the same f, ten f,
It is set to ~f,,,↑f7, and furthermore, BS-IF
a second frequency converter to each different frequency of the band;
The local oscillation frequencies are sequentially set to frequencies that differ by an integer multiple of the inter-channel frequency interval Δf for the desired N channels. Therefore, unlike the above-mentioned configuration, only N BPFs are required, which is economically advantageous in that large-scale high-frequency switches are not used.On the other hand, 2N local oscillators and 2N It is economically impractical because it requires a frequency converter.

(Means for Solving the Problems) An object of the present invention is to solve the problems in the prior art described above, and to minimize the number of circuit elements used when used for selecting transmission signals in a demand access type CATV system. It is an object of the present invention to provide a signal selection circuit device having a small structure and excellent economical efficiency.

In other words, the signal selection circuit device of the present invention can select the minimum number of high-frequency signals that can be sent to the trunk CATV system without using large-scale switches or placing any restrictions on the channel selection of high-frequency signals that can be sent to the trunk CATV system. It uses a local oscillator, a frequency converter, and a frequency filter (BPF) to enable the selection and rearrangement of signal channels.It is a group of input signals of multiple channels arranged at predetermined frequency intervals in a predetermined frequency band. in the predetermined frequency band into a group of output signals of a predetermined plurality of channels smaller than the plurality of channels rearranged at the predetermined frequency intervals, the frequency change widths being equal to each other, and frequency change regions or mutually The predetermined plurality of channels are provided with the predetermined plurality of different frequency variable local oscillators, and the input signal group of the plurality of channels in the predetermined frequency band is arranged at the predetermined frequency interval in a preliminary frequency band different from the predetermined frequency band. a single frequency fixed local oscillator, and arranges the intermediate signal group of the predetermined plurality of channels in the predetermined frequency band at the predetermined frequency interval in the predetermined frequency band. The present invention is characterized in that the output signal group of the predetermined plurality of channels is converted again.

(Function) Therefore, in the signal selection circuit device of the present invention, excellent economic efficiency can be achieved by using a minimum number of circuit elements when selecting a transmission signal channel in a mainline CATV such as for receiving satellite broadcasting. I can do it.

(Example) The present invention will be described in detail below with reference to the drawings.

The signal selection circuit device of the present invention is used as a main line CAT for broadcasting satellite reception.
For the sake of simplicity, an example of the configuration when used for V is a 40-channel FM signal that is frequency division multiplexed in the BS-IP band as the output of a satellite broadcast receiving outdoor unit, and an 8-channel FM signal that corresponds to the subscriber's wishes. FIG. 1 shows the case of selective conversion to .

In the signal selection circuit device of the present invention having the configuration shown in the figure,
40 channels of BS-IF band FM signal frequency arrangement,
The first intermediate frequency band or BS-IF of the satellite broadcast receiver
52.12MHz to 1548.16M based on the band
Hz frequency band with the same frequency spacing as satellite broadcasting, 40 channels (M=40) of frequency division multiplexed FM signals based on this frequency arrangement are guided to the distributor 1 and divided into 8, each with a variable 8 divided outputs are distributed to 8 frequency conversion circuits consisting of first frequency local oscillators 2-1 to 2-8 and frequency converters 3-1 to 3-8.
1.3GHz band BS-IP
8, arranged at the same frequency intervals as satellite broadcasting, in a spare frequency band appropriately set, for example, the 1.8 GHz band.
Once the frequency is converted to the FM signal of the channel, each BS
Eight bandpass filters (BPFs) 4-1 to 4-4 each have a center frequency fA-f for extracting the frequency-converted output signal for each channel and a respective BS channel signal, and have the same passband width. 8 to the synthesizer 5, and the synthesized output, for example, 1
．． Eight channels of FM signals arranged at the same frequency intervals as satellite broadcasting in a reserved frequency band such as the 8 GHz band are guided to a frequency converter 7 combined with a second local oscillator 6 with a fixed frequency, and the eight channels are combined. Frequency conversion to BS-IF band,
It is extracted as an 8-channel frequency division multiplexed BS-IP band FM signal through a BS-IP band band pass filter (BPF) 8 having an 8-channel passband characteristic for removing spurious components other than the B51F band.

The oscillation frequency ranges of the first local oscillators 2-1 to 2-8 and the second local oscillator 6 for B5-1ch-BS-15ch are shown in Table 1. The center frequencies of 1 to 4-8 are shown in Table 2.

Table 1 Table 2 Next, the signal selection circuit device of the present invention configured as described above is used as a so-called hub, and information service signals of 4 channels are selected from among the 40 channels in trunk CATV according to the wishes of the subscriber. FIG. 2 schematically shows an example of a schematic configuration of a demand access type optical CATV system that selects and transmits the selected information to the subscriber CATV. In the schematic configuration shown in the figure, 40 channels of frequency division multiplexed FM signals similar to those shown in FIG. The carrier light wave is intensity-modulated, the modulated light wave is sent out via the trunk CATV optical fiber 12, and is reconverted into an FM signal group by the trunk photoelectric converter 13 in the hub, and then sent to the subscriber hubs 14-1 to 14. −M in parallel. For example, in the subscriber hub 14-1, the FM signal group is divided into a distributor 1 and a first frequency conversion circuit 14A-1 configured in the same manner as shown in the first diagram so as to select four desired channels for simplicity. ~14A-4, a synthesizer 5, and a second frequency conversion circuit I5 selectively converts the signal into a frequency division multiplexed BS-IF band FM signal of four desired channels, and performs electro-optical conversion for transmitting downstream video signals at the hub. The modulated light waves obtained through the optical demultiplexer 16 and the optical demultiplexer 17 are sent out through the subscriber system CATV optical fiber 20, and the received modulated light waves are transmitted to the subscriber equipment 21-1 of the receiving terminal. It is reconverted into a BS-IP band FM signal by a photoelectric converter 23 for downlink video signals for subscribers via an optical demultiplexer 22, and then sent to four satellite broadcast receiving indoor units 25-1 via a distributor 24.
~25~4 in parallel.

Note that a request for desired channel selection from a subscriber viewing each indoor unit is sent to the request encoder 2.
6, the uplink channel request signal electro-optical converter 27 converts it into a modulated light wave, and the uplink request signal photoelectric converter 18 in the subscriber hub 14-1 regenerates it into a code signal via the optical fiber 20. The request decoder 19 converts the signal into a control signal to control each of the first frequency conversion circuits 14A-1 to 14A-4, and transmits the requested FM signal of the desired channel to the subscriber device 2.
Send to 1-1.

Also, the other subscriber hubs 14-2 to 14-M and subscriber devices 21-2 to 21-M perform the same reception as described above.

(Effects of the Invention) As is clear from the above explanation, the present invention provides CA
The configuration of the signal conversion circuit device used in the TV hub requires only a minimum number of circuit elements such as local oscillators, frequency converters, band pass filters, etc., and this type of circuit device can be configured simply. Regardless of the number of FM signal channels sent to mainline CATV, a miniaturized hub is constructed with one more circuit elements such as local oscillators, frequency converters, and bandpass filters than the number of channels transmitted to subscribers. I can do it.

Furthermore, in the demand access type CATV system, since the hub and the subscriber equipment are connected one-to-one, the signal selection circuit device of the present invention may be required in the same number as the subscriber equipment, or a fixed frequency The two local oscillators can be used in common for each subscriber unit, allowing further miniaturization of the hub.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a configuration example of a signal selection circuit according to the present invention, FIG. 2 is a block diagram showing a schematic configuration of a demand access type CATV system, and FIG. 3 is a block diagram showing a configuration example of a conventional signal selection circuit. 4 is a block diagram showing another configuration example of the conventional signal selection circuit; FIG. 5 is a block diagram showing still another configuration example of the conventional signal selection circuit; FIG. FIG. 7 is a block diagram showing still another example of the structure of the conventional signal selection circuit. FIG. 7 is a block diagram showing still another example of the structure of the conventional signal selection circuit. 1.24...Distributor 2,6...Synthesizer 3,
7.34...Frequency converter 4, 8.32...Band pass filter (BPF) 5.
...Synthesizer 9...CATV head end 10...FM signal generator 11.16.27...
・Light-light converter 12, 20...Optical fiber 13.1
8.23...Photoelectric converter 14...Subscriber hub 14A, 15...Frequency conversion circuit 17...Optical demultiplexer 19...Request decoder 21...Subscriber device 22...・Optical demultiplexer 25
...Satellite broadcast reception indoor unit 26...Request encoder 28...FM demodulator 29.31...Switch 30...FM modulator Claw ゛ fight 1 Fig. 4 A to 1 lucky number EKE01 (-6 digits) '1 base' A P1 5th chart J true bottom iso f1 figure 7

Claims (1)

[Claims] 1. A group of output signals of a plurality of predetermined channels smaller than the plurality of channels obtained by rearranging a group of input signals of a plurality of channels arranged in a predetermined frequency band at predetermined frequency intervals in the predetermined frequency band at the predetermined frequency intervals. The signal selection circuit device selectively converts the input signals of the plurality of channels in the predetermined frequency band, comprising the predetermined plurality of variable frequency local oscillators having equal frequency change widths and different frequency change regions, the input signal of the plurality of channels in the predetermined frequency band group into a group of intermediate signals of the predetermined plurality of channels arranged at predetermined frequency intervals in a reserve frequency band different from the predetermined frequency band, and a single frequency fixed local oscillator is provided, Double heterodyne signal selection characterized in that the intermediate signal group of the predetermined plurality of channels in a frequency band is reconverted into the output signal group of the predetermined plurality of channels arranged at the predetermined frequency interval in the predetermined frequency band. circuit device.