JPH0435230A - Double heterodyne signal selection circuit device - Google Patents

Abstract

PURPOSE:To reduce the variable range of a local oscillating frequency by converting plural sets of intermediate frequency signal group of at least one channel each in a standby frequency band into an output signal of a single channel at a required frequency band again selectively. CONSTITUTION:A frequency division multiplex input signal is fed to a 1st frequency converter 1, in which frequency conversion is applied to the signal by using an oscillated output of a 1st local oscillator 2 whose frequency is variable and its converted output is provided with a pass band for one channel with different center frequencies respectively and the result is fed to band pass filters BPF 3A, 3B (two filters only shown). Then the filter output of the BPF 3A, 3B is fed to a 2nd frequency converter 4, in which the signal is frequency- converted again by using an oscillated output of a 2nd local oscillator 5 whose frequency is variable, the result is fed to a BPF 6 having a pass band by one channel at a desired frequency band and a desired signal is extracted as a selection output. Thus, the frequency variable width is made narrow and the local oscillator is easily realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is based on the first intermediate frequency band (BS-IF band) FM signal output from a satellite broadcasting receiver outdoor unit. Information signals are added to the service, and a single channel signal is heterodyne frequency converted according to the subscriber's request from a multi-channel information service signal group arranged in a service band with an extremely wide frequency range including the BS-+F band. The present invention relates to a heterodyne signal selection circuit device used in so-called demand access type CATV, etc., which selects and services subscribers based on the characteristics of the user, and in particular, it is possible to easily configure a local oscillator by reducing the variable range of local oscillation frequency required for heterodyne signal selection. This is how it was done.

(Summary of the Invention) The present invention provides information on multiple channels arranged in a service band of an extremely wide frequency range including the 1.3 GHz band, based on the BS-IP band whose frequency has been converted from the 12 GHz band to the 1.3 GHz band. When selecting a signal by heterodyne frequency conversion in demand access type CATV, etc., which selects a single channel signal from a group of service signals to serve a subscriber, the first variable frequency local oscillator is used to select a signal from multiple channels in the service band. For example, the signal is 1.8G)
(Once a plurality of band-pass filters are provided in a preliminary frequency band such as the Z-band and the signal is converted into a plurality of sets of intermediate signals each having at least one channel separated from each other, a second variable frequency local oscillator is used to Such multiple sets of intermediate signals are combined into one
．． By selectively reconverting a single channel BS-IP multiplied signal in the 3Gt (Z band), the variable range of the local oscillation frequency is reduced, making it possible to easily configure a local oscillator.

(Prior Art) Conventionally, in selecting a single channel signal from among multiple channel signals by this type of double heterodyne frequency conversion, the first
The frequency conversion output is filtered by a single bandpass filter to selectively extract a single channel signal, and the single channel signal is subjected to a second frequency conversion by a second local oscillator with a fixed frequency to obtain a desired frequency band. I was getting a single channel signal.

(Problem to be solved by the invention) However, in conventional heterodyne frequency conversion, even in the above-mentioned double heterodyne frequency conversion, the first step is to perform frequency conversion directly on signals of multiple channels arranged in a wide frequency range. Is it necessary to make the variable width of the oscillation frequency of the local oscillator the same frequency width as the signal band of multiple frequency-division multiplexed channels? Therefore, when the band of the signal to be selected is narrow, the number of arranged channels is small, or the frequency interval between signals is narrow, and
When the fractional band of the frequency variable range of the first local oscillator is small, the configuration of the frequency conversion circuit is easy even with the prior art. On the other hand, when the input signal has a wide band, it is necessary to set the first local oscillation frequency high in order to keep the ratio band of the oscillation frequency variable range to a small value. It is desirable to keep the frequency as low as possible. Furthermore, when the local oscillation frequency is made variable over a wide frequency band, it is generally not easy to ensure constant oscillation output power over the entire variable range. In addition, when frequency multiplication is performed to obtain the desired oscillation frequency,
Frequency components before multiplication or their harmonic components exist within the frequency variable range and cause interference during frequency conversion.
From a technical standpoint, there were some problems with conventional technology.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned conventional problems and reduce the variable width of the first local oscillation frequency to be much narrower than the frequency band of the signal to be selected. There are two types of circuits that provide a double heterodyne signal selection circuit arrangement.

That is, the double heterodyne signal selection circuit device of the present invention is a heterodyne signal selection circuit device that selectively converts a group of input signals of a plurality of channels sequentially arranged in a predetermined frequency band into a single channel output signal in a predetermined frequency band. , comprising a first variable frequency local oscillator, the input signal group of the plurality of channels in the predetermined frequency band is sequentially arranged in a preliminary frequency band different from the predetermined frequency band, each having at least l channels; While selectively converting once into a set of intermediate signals, the second
a variable frequency local oscillator for selectively reconverting the plurality of sets of intermediate signals each having at least l channels in the reserved frequency band into a single channel output signal in the desired frequency band. This is a characteristic feature.

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

First, an example of the configuration and the mode of operation of the double heterodyne signal selection circuit device of the present invention are shown in FIGS.
In contrast, the configuration and operation of the conventional device are shown in FIGS. 2(al), (b), and (C).

In the configuration example of the double heterodyne signal selection circuit device according to the present invention shown in FIG. For simplicity, only two bandpass filters (BPFs) 3A and 3 are shown, each having a passband width of one channel with a different center frequency.
B is supplied in parallel. Then each BPF 3A and 3
The filtered outputs of B are both supplied to the second frequency converter 4, and the frequency is converted again by the oscillation output of the second local oscillator 5, which can vary the frequency or switch the frequency.
A bandpass filter with a passband for each channel (
BPF) 6 and take out the desired signal as a selected output.

An aspect of the first frequency conversion in such double heterodyne signal selection is shown in FIG. 1(b), and an aspect of the second frequency conversion is shown in FIG. 1(C). That is, the lowest frequency f of the first local oscillator 2 whose frequency is variable for the frequency division multiplexed input signal 7 over a wide frequency band. 1n oscillation output 9 and highest frequency f. , a first frequency conversion is performed using the two oscillation outputs 10 to obtain a converted output 8B with a center frequency f and a converted output 8A with a center frequency fA, respectively. Then, the first frequency conversion outputs 8A and 8B are subjected to a second frequency conversion using the oscillation output 12 of the lower frequency fL and the oscillation output 13 of the higher frequency f of the second local oscillator 5 of variable frequency or frequency switching. In the example shown in the figure, the second section described below, which shows a conventional mode of signal selection of this type, is used.
As is clear from the comparison with Fig. (bL (C)), the converted output 11 of the center frequency f. It has gained.

On the other hand, for ease of comparison, in the conventional double heterodyne signal selection circuit device shown in FIG. 2(a) constructed under the same conditions as the signal selection circuit device of the present invention shown in FIG. The division multiplexed input signal is supplied to the first frequency converter 1, where frequency conversion is performed using the oscillation output of the first local oscillator 2 with variable frequency, and the converted output is passed through a bandpass filter (with a passband width for one channel). B.P.
F) Supply to 3A. Then, the filtered output of the BPF 3A is supplied to the second frequency converter 4, and the frequency is converted again using the oscillation output of the second local oscillator 5 with a fixed frequency, thereby creating a bandpass having a passband for one channel in the desired frequency band.・Supply to filter (BPF) 6 and take out the desired signal as a selected output.

The first step in such conventional double heterodyne signal selection is
An aspect of frequency conversion is shown in FIG. 2(b), and an aspect of the second frequency conversion is shown in FIG. 2 fc). That is, the lowest frequency fm+ shown in FIG. 1 tb+ of the frequency variable first local oscillator 2 is applied to the frequency division multiplexed input signal 7 over a wide frequency band.

A first frequency conversion is performed using the oscillation output 9 with a much lower minimum frequency f', 1° and the oscillation output 10 with the maximum frequency fm&X shown in FIG.
A conversion output of 8 A is obtained by the oscillation output of 10. Then, a fixed frequency second signal is applied to the first frequency conversion output 8A.
A second frequency conversion is performed using the oscillation output 12 of the frequency fL of the local oscillator 5 to obtain the center frequency f. The converted output 11 is obtained as a selected output signal of a desired frequency band.

Therefore, in the conventional double heterodi signal selection circuit device, as shown in FIG. 2(b), the frequency variable width f, . However, in the double heterodyne signal selection circuit device according to the present invention, the first frequency band corresponding to the lower half of the frequency band of the input signal is smaller than or equal to the bandwidth. The frequency conversion pressure is applied to the BPF 3B with the higher passband center frequency fB, and the first frequency conversion output corresponding to the higher half band is the lower passband center frequency f,
As shown in FIG. 1(b), the frequency variable width f of the first local oscillator 2 is controlled by the BPF 3A. 6.
-fゎ7 should be approximately half the frequency bandwidth of the input signal 7. Furthermore, the second local oscillator 5 has a lower frequency f.

If the oscillator is a frequency variable oscillator that actually requires only the neighboring regions of the higher frequency fH, the frequency variable width may be approximately half the input signal bandwidth.

Next, the signal selection circuit device of the present invention configured as described above is used as a so-called hub for selectively distributing information service signals for, for example, 4o channels provided in the trunk CATV to the subscriber CATV. 4 according to the wishes of the person
Demand access type optical CAT that selectively sends channel information service signals to subscriber CATV
An example of the schematic configuration of the V system is schematically shown in FIG. In the illustrated schematic configuration, the FM in the CATV head end 14
A frequency division multiplexing information service signal for 40 channels similar to that shown in FIG. 1 or FIG. The modulated light wave is sent out via the trunk CATV optical fiber 17, reconverted into a service band signal group by the trunk photoelectric converter 18 in the hub, and supplied in parallel to subscriber hubs 19-1 to 19-M. . For example, in the subscriber hub 19-1, the signal group of the service band is
51ch, B5-5ch, B5-9ch, B5-
Divider lO1 frequency conversion circuits 20-1 to 20-4 configured in the same manner as shown in the second diagram so as to be rearranged to 13ch.
, selectively converted into a frequency division multiplexed BSIF band signal of a desired channel by a signal selection circuit including a combiner 13, and sequentially passed through an electro-optical converter 21 and an optical demultiplexer 22 for transmitting downlink video signals at the hub. The modulated light wave is transmitted to the subscriber system C.
It is transmitted through the ATV optical fiber 25-1, and at the receiving terminal subscriber device 26-1, the incoming modulated light wave is transmitted through the optical demultiplexer 27 and then sent to the subscriber downlink video signal photoelectric converter 28. BS-IF band double signal reconversion and distributor 29
4 satellite reception indoor units 30-1 to 30-3
0-4 in parallel.

Note that a request for desired channel selection from a subscriber viewing each indoor unit is sent to the request encoder 3.
1, the uplink channel request signal electro-optical converter 32 converts it into a modulated light wave, and the uplink request signal photoelectric converter 23 in the subscriber hub 19-1 converts it into a code signal via the optical fiber 25-1. The request decoder 24 converts the FM signal into a control signal to control the first frequency conversion circuits 20-1 to 20-4, respectively, and transmits the requested FM signal of the desired channel to the subscriber device 2.
6-1.

Also, in other subscriber hubs 19-2 to 19-M and subscriber devices 26-2 to 26-M, each independently
Reception is performed in exactly the same manner as described above.

In addition, in the above explanation, 4 in the service band
0 channel signal to any desired channel signal to BS-
As described above, the signal selection circuit device of the present invention is not limited to this example, but as long as the input signal is frequency division multiplexed at equal intervals,
Of course, both can be processed in exactly the same way.

(Effects of the Invention) As is clear from the above description, according to the present invention, when selecting one channel signal from frequency division multiplexed signals arranged in a predetermined frequency band at equal intervals, by double heterodyne frequency conversion. The frequency variable width of the local oscillator used can be made much narrower than in the past, making it easier to configure the local oscillator, and also relaxing the frequency characteristics required of the frequency converter. It is also economically advantageous.

If the number of band-pass filters that filter and extract the first frequency conversion output is increased, the frequency variable width of the first local oscillator can be inversely narrowed, but the frequency variable width of the second local oscillator can be widened accordingly. As a result, the effect will fade. For example, if the number of bandpass filters arranged in parallel is 4,
Compared to the example shown in FIG. 1 fb), the frequency variable width of the first local oscillator can be further halved, or the frequency variable width of the second local oscillator can be increased by l5 times. This adverse effect is because the sum of the oscillation frequency widths of the first local oscillator and the second local oscillator matches the frequency bandwidth of the input signal.

Therefore, the optimum B that can maximize the effects of the present invention
There will be a number of parallel PFs.

[Brief explanation of drawings]

FIG. 1 (ai and (b)), fcJ are block diagrams and spectrum diagrams respectively showing a configuration example and operational aspects of the signal selection circuit device of the present invention; FIGS. 2 (a), (b), (C) 3 is a block diagram and a spectrum diagram respectively showing a configuration example and operation mode of a conventional signal selection circuit device, and FIG. 3 is a block diagram showing a schematic configuration of a demand access type CATV system.・Frequency converter 2.5...Local oscillator 3A, 3B...Bant pass ・14...CATV head end 15...FM signal generator 16, 21.32...Electronic converter 17, 25...・Optical fibers 18, 23, 28...Photoelectric converter 19...Subscriber hub 20...Frequency conversion circuit 22...Optical demultiplexer 24...Request decoder 26...Subscriber device 27...Optical demultiplexer 30...Satellite broadcast reception indoor unit 31...Request encoder filter (BPF) (b) Fig. 1

Claims (1)

[Claims] 1. In a heterodyne signal selection circuit device that selectively converts a group of input signals of a plurality of channels sequentially arranged in a predetermined frequency band into a single-channel output signal in a predetermined frequency band, the first frequency a variable local oscillator, converting the input signal group of the plurality of channels in the predetermined frequency band into a plurality of intermediate signal groups each having at least one channel each sequentially arranged in a preliminary frequency band different from the predetermined frequency band; A second variable frequency local oscillator is provided to sequentially and selectively convert the plurality of sets of intermediate signals each having at least one channel in the reserved frequency band into a single channel output signal in the desired frequency band. A double heterodyne signal selection circuit device characterized in that the double heterodyne signal selection circuit device is configured to selectively reconvert the signal.