JP6200367B2 - Signal processing apparatus, CATV head end, and CATV system - Google Patents

Description

The present invention relates to a signal processing apparatus, CA, which performs predetermined processing on an input signal and retransmits the signal.
The present invention relates to a TV head end and a CATV system.

Conventionally, a signal processing device for receiving a radio frequency (RF) signal such as a broadcast signal and performing a predetermined process on the high frequency signal has been disclosed (for example, Patent Documents 1 to 4).

For example, in Patent Document 1, as a signal processing device used for a head end of a CATV system, a signal processing device (signal processor) for retransmitting an input broadcast signal
Is disclosed. In this signal processing apparatus, an input FM signal is converted into an intermediate frequency (IF) signal by a down converter, a signal (desired signal) corresponding to a desired wave is extracted from the intermediate frequency signal, and further converted into an FM signal by an up converter. It is reconverted and retransmitted.

Patent Documents 2 to 4 disclose techniques for removing multipath noise and improving sound quality.

JP 2000-40929 A JP 61-177824 A Japanese Patent Laid-Open No. 3-108818 Japanese Patent Laid-Open No. 4-134498

By the way, in response to improvements in performance of broadcast receiving devices and the like and requests from users, signal processing of signal processing apparatuses is required to have higher quality such as less noise.

The present invention has been made in view of the above, and an object thereof is to provide a signal processing device, a CATV head end, and a CATV system capable of performing signal processing with higher quality.

In order to solve the above-described problems and achieve the object, a signal processing apparatus according to the present invention supplies a down-converter that converts an input high-frequency signal into an intermediate frequency signal, and a local oscillation frequency signal to the down-converter. A local oscillation unit, an intermediate frequency processing unit having a bandpass filter that selectively transmits a predetermined band of the intermediate frequency signal, and A / D conversion that performs A / D conversion on the intermediate frequency signal transmitted through the bandpass filter A baseband converter that generates a baseband signal from the A / D converted intermediate frequency signal, a digital filter that performs digital signal processing that selectively transmits a predetermined band of the baseband signal, and the digital And a D / A converter that performs D / A conversion of the baseband signal transmitted through the filter into a high-frequency signal.

In the signal processing device according to the present invention as set forth in the invention described above, the down converter converts the input high-frequency signal into an intermediate frequency signal having a frequency equal to or higher than 1/2 of a lower limit value of a band of the high-frequency signal. Features.

In the signal processing device according to the present invention, in the above invention, the down converter converts the input high-frequency signal into an intermediate frequency signal having a frequency equal to or lower than a half of an upper limit value of a band of the high-frequency signal. Features.

In the signal processing device according to the present invention, in the above invention, the high-frequency signal is an FM signal, and the down-converter converts the input high-frequency signal into an intermediate frequency signal higher than 10.7 MHz. Features.

In the signal processing device according to the present invention, in the above invention, the high-frequency signal is a terrestrial digital signal, and the down-converter converts the input high-frequency signal into an intermediate frequency signal higher than 37.15 MHz. It is characterized by.

The signal processing apparatus according to the present invention is characterized in that, in the above-mentioned invention, an image rejection filter is provided in the down converter or a preceding stage of the down converter.

The signal processing apparatus according to the present invention is characterized in that in the above invention, the signal processing apparatus further comprises a multipath scancer that suppresses multipath noise included in the baseband signal that has passed through the digital filter and outputs the same to the D / A converter. To do.

The signal processing apparatus according to the present invention is the above-described invention, wherein the baseband conversion unit includes the A
/ D converted intermediate frequency signal is quadrature demodulated into I signal and Q signal, and the D / A conversion performs quadrature modulation processing using the I signal and Q signal to generate the high frequency signal It is characterized by.

In the signal processing apparatus according to the present invention, in the above invention, a branching unit that branches a part of the intermediate frequency signal, a detection unit that detects a level of the branched intermediate frequency signal, and a level of the detected intermediate frequency signal And an output adjusting unit that adjusts a gain for at least one of the high-frequency signal and the intermediate frequency signal to be constant.

The signal processing apparatus according to the present invention is the signal processing apparatus according to the above invention, wherein a branching unit that branches a part of the baseband signal that has passed through the digital filter, and a calculation unit that calculates a level of the intermediate frequency signal from the branched baseband signal And an output adjustment unit that adjusts a gain for at least one of the high-frequency signal and the intermediate frequency signal to be constant based on the calculated level of the intermediate frequency signal.

The CATV head end according to the present invention includes a distribution unit that distributes a high-frequency signal, a plurality of signal processing devices according to the invention that perform signal processing on the high-frequency signal distributed by the distribution unit, and a signal by the signal processing device. A receiving device including a mixing unit that mixes the processed high-frequency signal, and a transmitting device that outputs the high-frequency signal output from the receiving device.

A CATV system according to the present invention includes a CATV head end according to the present invention, a signal transmission path for transmitting a high-frequency signal output from a transmission device of the CATV head end, and a transmission path for the signal transmission path. And a subscriber home device provided in the subscriber home for receiving the high frequency signal.

According to the present invention, it is possible to realize a signal processing apparatus, a CATV head end, and a CATV system that can perform signal processing with higher quality.

FIG. 1 is a diagram illustrating a configuration of a signal processing device according to the first embodiment. 2A and 2B are diagrams showing the frequency spectrum of the signal. FIG. 2A shows the case where the intermediate frequency Δf ₁ is set, and FIG. 2B shows the case where the intermediate frequency is set to Δf ₂ . FIG. 3 is a diagram illustrating a configuration of the signal processing device according to the second embodiment. FIG. 4 is a diagram illustrating a configuration of the signal processing device according to the first comparative example. FIG. 5 is a diagram illustrating the configuration of the signal processing device according to the second comparative example. FIG. 6 is a diagram illustrating a configuration example of a CATV head end and a CATV system using the signal processing device according to the first and second embodiments.

Hereinafter, a signal processing apparatus, a CATV head end, and a C according to the present invention will be described with reference to the drawings.
An embodiment of the ATV system will be described in detail. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding element.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a signal processing device according to Embodiment 1 of the present invention. A signal processing apparatus 100 shown in FIG. 1 is an FM broadcast multi-channel signal (here, simply referred to as an FM signal).
The frequency signal (desired high frequency signal, here called the desired FM signal) of the broadcasting station that wants to view is selected and retransmitted. Here, the frequency band of the FM signal is 76 MH
Let z be 90 MHz. Therefore, the frequency of the desired FM signal ranges from 76 MHz to 9
It is a value between 0 MHz and the frequency of the broadcasting station that wants to watch.

The signal processing apparatus 100 includes a signal input unit 1, a down converter 2, an IF processing unit 3 that is an intermediate frequency processing unit, an A / D conversion unit 4, an orthogonal demodulation unit 5 that is a baseband conversion unit, A digital filter 6, which is a digital filter, a multipath scancell 7, a quadrature modulation D / A conversion unit 8, and a signal output unit 9 are connected in this order. Furthermore, the signal processing apparatus 100 includes a detection unit 10 and a local oscillation unit 11 that supplies a local oscillation frequency signal to the down converter 2. The local oscillation unit 11 is configured using, for example, a PLL circuit.

The down converter 2 includes an image rejection filter 2a, an amplification unit 2b as an output adjustment unit, and a mixer 2c. The IF processing unit 3 includes an IF bandpass filter (BPF) 3a that is a first bandpass filter, an amplification unit 3b as an output adjustment unit, and a branching unit 3c.

The operation of the signal processing apparatus 100 will be described together with the operation of each component. Note that FIG.
FIG. 2B is a diagram illustrating an example of a frequency spectrum of a signal related to the operation of the signal processing apparatus 100. Hereinafter, description will be made with reference to FIG.

  First, an FM signal that is an analog signal and a broadband signal including a VHF band are input to the signal input unit 1 from the outside. The signal input unit 1 outputs the input signal to the down converter 2.

In the down converter 2, the image rejection filter 2a removes the VHF band component from the input FM signal and transmits it. The image rejection filter 2a can be configured with a known bandpass filter or the like.
The amplifying unit 2b amplifies the transmitted FM signal. The mixer 2c mixes the local oscillation frequency signal output from the local oscillation unit 11 and the amplified FM signal, and converts the mixed signal into an IF signal.

Here, as shown in FIG. 2A, the FM signal has a predetermined band BS, and the band BS
It is assumed that the lower limit value of f is f _L and the upper limit value is f _H. Reference S1 is a desired FM signal. The FM signal input to the signal processing apparatus 100 is a signal including the desired FM signal S1 and other FM signals included in the band BS, including the FM signals S2 and S3 that are adjacent in frequency to the desired FM signal S1.

Further, the local oscillation frequency signal SL1 is set to a frequency away from the desired FM signal S1 only intermediate frequency Delta] f _1. As a result, the mixer 2c mixes the local oscillation frequency signal SL1 and the desired FM signal S1, so that the desired FM signal S1 has a frequency equal to the intermediate frequency Δf ₁ and is referred to as a desired IF signal here. ) Converted to SIF1. IF
The signal includes a component obtained by converting a desired IF signal and another input FM signal.
The down converter 2 outputs the converted IF signal to the IF processing unit 3.

As shown in FIG. 2A, the signal input to the signal processing device 100 is an unnecessary wave with respect to the broadcast signal to be processed by the signal processing device 100 on the higher frequency side than the band BS of the FM signal. A VHF band exists as the unnecessary signal SU1.

Here, as shown in FIG. 2A, it is assumed that the frequency difference Δf _U between the unnecessary signal SU1 and the local oscillation frequency signal SL1 is set to be close to or equal to the intermediate frequency Δf ₁ . In such a frequency setting, when the unnecessary signal SU1 and the FM signal are input to the signal processing apparatus 100, the image signal of the unnecessary signal SU1 is output from the desired IF signal S at the output of the mixer 2c.
It occurs at a frequency close to or equal to IF1.
For example, the intermediate frequency Δf ₁ is 10.7 MHz, the frequency of the local oscillation frequency signal SL1 is 90.7 MHz with respect to 80 MHz of the FM signal, and the unnecessary signal SU1 is 10.7 MHz than the local oscillation frequency signal SL1. Only on the high frequency side (Δf _U = Δf ₁ = 10.7M
Hz), if present at 101.4 MHz, the desired IF with a frequency of 10.7 MHz
An image signal having the same frequency is generated for the signal SIF1.
Such an image signal causes interference and is difficult to remove in the subsequent stage of the down converter 2.

On the other hand, in the down converter 2, the image rejection filter 2a has a transmission band characteristic as indicated by the dotted line IR1 in FIG. 2A, and converts the input signal into a VHF band component. The unnecessary signal SU1 included is removed. Therefore, the generation of an image signal that causes interference in the subsequent mixer 2c is suppressed (in the example of FIG. 2A, the image signal is not shown because it has a sufficiently small level).

Next, the operation of the IF processing unit 3 will be described. In the IF processing unit 3, the IF bandpass filter 3 a is configured by a known bandpass filter having a transmission band as shown in FIG. 2A (see the line indicated by reference numeral BF 1 in FIG. 2A). A predetermined band including the desired IF signal SIF1 included in the IF signal output from the down converter 2 is selectively transmitted. The amplifying unit 3b amplifies the transmitted IF signal. The branching unit 3c outputs the amplified IF signal to the A / D conversion unit 4 and branches a part of the IF signal to output it to the detection unit 10 side.

Next, operations of the A / D converter 4, the quadrature demodulator 5, the digital filter 6, the multipath scan sera 7, and the quadrature modulation D / A converter 8 will be described.

The A / D conversion unit 4 performs A / D conversion on the IF signal output from the IF processing unit 3 to perform digital I
An F signal is output to the quadrature demodulator 5. The quadrature demodulator 5 performs a quadrature demodulation process on the digital IF signal to generate a digital baseband signal composed of an I signal and a Q signal. This digital baseband signal includes other signal band components including the signals S2 and S3 of the adjacent channels in addition to the baseband signal of the desired FM signal S1.

The digital filter 6 selectively transmits a predetermined band with respect to each of the I signal and the Q signal, removes other signal band components including the signal of the above-described adjacent channel, and outputs the desired FM signal 1.
The digital signal processing for extracting the baseband signal is performed. As such digital signal processing, for example, FIR (finite impulse response) filter processing can be used.

The multipath scan cell 7 suppresses multipath noise contained in the I signal and the Q signal transmitted through the digital filter 6 and outputs the result to the quadrature modulation D / A converter 8. As the multi-pass scan cera 7, for example, a known multi-pass scan cera that performs the processing described in Patent Document 2 to suppress multi-path noise can be used.

The quadrature modulation D / A conversion unit 8 performs the I signal and Q in which multipath noise is suppressed in this way.
The signal is subjected to orthogonal modulation processing on the carrier wave to generate a desired FM signal S1. This hope FM
The signal S1 is output from the signal output unit 9 to the outside of the signal processing apparatus 100. Here, the signal is reconverted into the same desired FM signal S1 as originally received, but may be reconverted into an FM signal of another frequency or a high frequency signal other than the FM signal.

The detector 10 detects the level of the IF signal that is branched and input, and outputs a control signal for constant gain control (AGC) for the amplifier 2 b of the down converter 2 and the amplifier 3 b of the IF processor 3. And output to each of the amplifying units 2b and 3b. The gains of the amplifying units 2b and 3b are set based on the control value. Here, the control value is a control value calculated so that the gains of the FM signal input to the mixer 2c and the IF signal output from the IF processing unit 3 are constant. As a result, AGC is realized for the FM signal input to the mixer 2 c and the IF signal output from the IF processing unit 3. The amplifying units 2b and 3b may be configured to adjust the output of the amplifier to set the gain, or include an amplifier and an attenuator. The gain may be set.

In the signal processing device 100 configured as described above, the desired signal (desired IF signal SIF1 or its baseband signal) is subjected to two-stage filter processing of the IF bandpass filter 3a and the digital filter 6. As a result, the transmission band characteristics required for the IF bandpass filter 3a (more specifically, characteristics such as the transmission bandwidth and attenuation gradient (roll-off)) are alleviated. That is, the IF signal adjacent to the desired IF signal SIF1 may pass through the IF bandpass filter 3a to some extent. Therefore, as the IF bandpass filter 3a, for example, a filter composed of a simple RLC circuit and having good in-band delay characteristics can be used. Also, as the digital filter 6, there can be used, for example, an FIR filter process that has a flat characteristic without in-band delay. As a result, the desired FM signal S1 output from the signal processing apparatus 100 is less susceptible to distortion degradation of the audio signal when received by the FM receiver.

Thus, while the transmission band characteristics of the IF bandpass filter 3a may be relaxed, the signal processing apparatus 100 uses the entire level of the IF signal output from the IF bandpass filter 3a for AGC control. In order to perform this AGC control with a desired accuracy, the adjacent I
It is preferable to set the transmission band characteristic of the IF bandpass filter 3a so that the F signal is cut.

In the signal processing apparatus 100, the down converter 2 performs frequency conversion using the local oscillation frequency signal SL only in one stage, and the quadrature modulation D / A conversion unit 8 directly generates an FM signal from the quadrature baseband signal. ing. Thereby, the phase noise included in the desired FM signal S1 that is finally output is reduced. As a result, the S / N characteristic of the audio signal is improved.

Further, the frequency (intermediate frequency) of the desired IF signal can be an arbitrary frequency, but in order to reduce the influence of the image signal, instead of the frequency arrangement as shown in FIG. As shown in FIG. 2 (b), a generally used intermediate frequency (FIG. 2 (a)
In this case, it is preferable to use a frequency higher than 10.7 MHz.
For example, the frequency of the desired IF signal SIF2 is set higher by α than the desired IF signal SIF1,
The intermediate frequency Δf ₂ = Δf ₁ + α. Then, the frequency of the local oscillation frequency signal SL2 is set to a higher frequency side by α than the conventional local oscillation frequency signal SL1. As a result, the frequency difference between the local oscillation frequency signal SL2 and the unnecessary signal SU1 is reduced to Δf _U −α, and as a result, the frequency of the image signal SIM1 of the unnecessary signal SU1 is also reduced to Δf _U −α. The frequency difference between the frequency of SIM1 and the frequency of desired IF signal SIF2 increases. Therefore, the influence of the image signal SIM1 on the desired IF signal SIF2 can be further reduced.
Further, when there is an unnecessary signal SU2 on the frequency side higher by Δf _U + α than the local oscillation frequency signal SL2, Δf _U is a frequency that is the same as or close to Δf ₁ , so that the desired IF signal SIF2
An image signal is generated at the same frequency. Therefore, an image rejection filter 2a having a transmission band characteristic that can remove the unnecessary signal SU2 is used.
Thus, by setting the intermediate frequency as high as Δf ₁ to Δf ₂ = Δf ₁ + α, as shown in FIG. 2B, the transmission band characteristic IR2 of the image rejection filter 2a.
Since the unnecessary signal SU1 only needs to be removed to some extent, the transmission band characteristic IR1 in the case of FIG. 2A can be relaxed, which is preferable.
It is also preferable that the upper limit of the frequency of the desired IF signal is set appropriately. For example, F
In the case of the M signal, in order to ensure a sufficient frequency difference with respect to the band BS of the FM signal, it is preferable to set the frequency to be somewhat lower than the band BS of the FM signal.

In this way, the image rejection filter 2a removes the unnecessary signal SU2 to suppress the generation of the image signal SIM1, and the IF bandpass filter 3a provided in the IF processing unit 3 by setting the intermediate frequency higher as described above. Since the frequency of the signal to be removed can be separated from the frequency of the desired signal (desired IF signal SIF2), the transmission band characteristic indicated by BF2 in FIG. 2B of the IF bandpass filter 3a is relaxed.
In order to sufficiently obtain the above effects, the frequency of the desired IF signal SIF2 (intermediate frequency Δ
f ₂ ) is, for example, not less than 1/2 of the lower limit value f _L of the band BS of the high-frequency signal and 1/2 of the upper limit value f _H
When the following frequency, that is, when the high frequency signal is an FM signal, it is more preferable to set the frequency Δf ₂ of the desired IF signal SIF2 to a frequency of 38 MHz to 45 MHz.

Further, since the signal processing apparatus 100 includes the A / D conversion unit 4 and the quadrature modulation D / A conversion unit 8, a multipath scancella 7 by digital processing is provided between them to reduce multipath noise. Therefore, the signal quality can be further improved.
As described above, according to the signal processing apparatus of the first embodiment, high-quality signal processing of high-frequency signals can be performed.

(Comparative form 1)
Here, Comparative Examples 1 and 2 as objects to be compared with the signal processing apparatus 100 according to Embodiment 1 of the present invention will be described. FIG. 4 is a diagram illustrating a configuration of the signal processing device according to the first comparative example.
Similar to the signal processing apparatus 100, the signal processing apparatus 1000 shown in FIG.
The M signal is selectively processed and retransmitted.

The signal processing apparatus 1000 includes a signal input unit 1, a down converter 20, an IF processing unit 30, an up converter 40, a detection unit 10, and a local oscillation unit 11.

The down-converter 20 includes a wideband bandpass filter 20a that selectively transmits the frequency band of the FM signal, an amplification unit 2b, and two mixers 2c. The IF processing unit 30 includes an IF bandpass filter 30a, a branching unit 3c, and a limiter 30d. The up-converter 40 includes two mixers 2c.

Next, the operation of the signal processing apparatus 1000 will be described together with the operation of each component.
First, when a signal including an FM signal is input from the outside to the signal input unit 1, the signal input unit 1 outputs the input signal to the down converter 20.

In the down converter 20, the bandpass filter 20a transmits the FM signal. The amplifying unit 2b amplifies the transmitted FM signal. The two mixers 2 c mix the local oscillation frequency signal output from the local oscillating unit 11 and the amplified FM signal, convert the mixed signal into an IF signal, and output the IF signal to the IF processing unit 30. As described above, the down converter 20 performs conversion from the FM signal to the IF signal in two stages in order to remove unnecessary waves such as an image signal. Note that the frequency (intermediate frequency) of the IF signal is set to 10.7 MHz that is normally used for the FM signal.

In the IF processing unit 30, a steep ceramic filter or SAW filter is usually used for the IF bandpass filter 30a to remove adjacent signals and secure out-of-band attenuation, and the 10.7 MHz input from the down converter 20 is used. The IF signal is selectively transmitted. Branch 3
c outputs the IF signal that has passed through the IF bandpass filter 30a to the limiter 30d and branches a part of the IF signal to output it to the detection unit 10 side. Furthermore, the limiter 30d stabilizes the level of the amplified IF signal and outputs it to the up-converter 40.

In the up-converter 40, the two mixers 2c mix the local oscillation frequency signal output from the local oscillation unit 11 and the IF signal, and reconvert them into FM signals. As described above, the up-converter 40 performs conversion from the IF signal to the FM signal in two stages for removing spurious and the like. The reconverted FM signal is output from the signal output unit 9 to the outside of the signal processing apparatus.

The detection unit 10 detects the level of the IF signal that is branched and input, calculates a control value for the amplification unit 2b of the down converter 20, and outputs the control value to the amplification unit 2b. The amplification unit 2b
A gain is set based on the control value. Thus, constant gain control (AGC) is realized for the FM signal input to the mixer 2c.

In this signal processing apparatus 1000, since the frequency conversion using the local oscillation frequency signal is performed in four stages, the phase noise generated in the local oscillation unit 11 is mixed into the FM signal for each frequency conversion. As a result, the S / N characteristic of the audio signal tends to deteriorate. In addition, since 10.7 MHz is selected as the intermediate frequency, and a steep ceramic filter or SAW filter is used correspondingly, the in-band delay characteristics are likely to deteriorate, and the FM signal is received by the receiver. Distortion degradation of the audio signal is likely to occur.

(Comparative form 2)
Next, FIG. 5 is a diagram illustrating a configuration of the signal processing device according to the second comparative example. A signal processing device 2000 shown in FIG. 5 replaces the IF processing unit 30 of the signal processing device 1000 shown in FIG. 4 with an IF processing unit 30A, and is externally connected by cable connection between the IF processing unit 30A and the up-converter 40. The multi-pass canceling device 50 is added.

The IF processing unit 30A has a configuration in which the limiter 30d of the IF processing unit 30 is deleted and an amplification unit is added between the IF bandpass filter 30a and the branching unit 3c. The multipath cancel device 50 includes an A / D conversion unit 50a, a multipath scan cell 50b, and a D / A conversion unit 50.
c.

The operation of the signal processing device 2000 is basically the same as that of the signal processing device 1000, but differs in the following points. That is, the multipath cancel device 50 receives the IF signal output from the IF processing unit 30, and the A / D conversion unit 50a performs A / D conversion to a digital IF signal and outputs the digital IF signal to the multipath scan cell 50b. The multipath scan cell 50b suppresses the multipath noise included in the input digital IF signal and outputs it to the D / A converter 50c. The D / A conversion unit 50 c D / A converts the digital IF signal in which multipath noise is suppressed into an IF signal, and outputs the IF signal to the up-converter 40. If the limiter is used in the IF processing unit 30A as in the first comparative example, information on multipath noise is lost. Therefore, in the IF processing unit 30A in the second comparative example, the detection unit 10 AGC with an amplifier is performed.

In the signal processing device 2000, as in the signal processing device 1000, the S / N characteristic of the audio signal due to phase noise and the distortion of the audio signal due to the deterioration of the in-band delay characteristic are likely to occur. Further, the A / D conversion unit 50a and the D
Since the / A conversion unit 50c must be provided, the cost increases.

Compared to the first and second comparative embodiments as described above, the signal processing device 10 according to the first embodiment of the present invention.
At 0, the signal quality such as the S / N characteristic of the audio signal and the distortion characteristic of the audio signal are improved. In addition, since the number of local oscillators can be reduced, the configuration is simplified. Moreover, since it is not necessary to use an expensive SAW filter or the like, a low-cost configuration can be achieved.

(Embodiment 2)
FIG. 3 is a diagram showing the configuration of the signal processing apparatus according to Embodiment 2 of the present invention. The signal processing device 200 shown in FIG. 3 is configured by replacing the IF processing unit 3 with the IF processing unit 3A in the configuration of the signal processing device 100 shown in FIG. 1 and adding a branching unit 12, a calculation unit 13, and a control unit 14. Have

The IF processing unit 3A has a configuration in which the branching unit 3c is deleted from the IF processing unit 3.
The branching unit 12 is provided at the subsequent stage of the digital filter 6, and outputs a part of the I signal and the Q signal that have passed through the digital filter 6 to the arithmetic unit 13.

When the branched I signal and Q signal are input, the calculation unit 13 calculates the level of the IF signal output from the IF processing unit 3A, and provides information on the calculated level to the control unit 1
4 is output. The control unit 14 calculates a control value for constant gain control (AGC) for the amplifying unit 2b of the down converter 2 and the amplifying unit 3b of the IF processing unit 3A from the input IF signal level information, and the amplifying unit Output to 2b and 3b respectively. The gains of the amplifying units 2b and 3b are set based on the control value. Here, the control value is a control value calculated so that the gains of the FM signal input to the mixer 2c and the IF signal output from the IF processing unit 3A are constant. As a result, AGC is realized for the FM signal input to the mixer 2c and the IF signal output from the IF processing unit 3A. The amplifying units 2b and 3b may be configured to adjust the output of the amplifier to set the gain, or include an amplifier and an attenuator, and adjust the attenuation amount by the attenuator while keeping the output of the amplifier constant. The gain may be set.

Here, by using the I signal and the Q signal that have passed through the digital filter 6 for calculation, the level of the desired IF signal included in the IF signal output from the IF processing unit 3A can be obtained more accurately. As a result, the accuracy of AGC with respect to the desired IF signal or the desired FM signal becomes higher.

Hereinafter, usage examples of the signal processing apparatus according to the first or second embodiment will be described.
FIG. 6 shows a CATV headend using the signal processing apparatus of the first or second embodiment,
This is a configuration example of a CATV system configured using the head end.

As shown in FIG. 6, the CATV system A includes an antenna C that receives FM signals, a CATV head end B of a CATV station that processes the FM signals transmitted from the antenna C, and C
A signal transmission path I for transmitting the FM signal sent from the ATV head end B, and a signal transmission path I
And a subscriber home device K provided in the subscriber home J that receives the FM signal transmitted.

The CATV head end B is a distributor E that distributes the FM signal transmitted from the antenna C through the amplifier F, and a plurality of FM signals distributed from the distributor E, The signal processing apparatus 100 (200) according to the first or second embodiment and a mixing unit that is a mixing unit that mixes each desired FM signal that has been signal-processed by each signal processing apparatus 100 (200) and outputs the result as a high-quality FM signal. FM receiver D provided with device G, and transmitter H that mixes the FM signal output from FM receiver D and another CATV signal, amplifies and outputs (sends).

According to such a CATV system A, the signal processing apparatus 100 of the first or second embodiment is used.
The high-quality FM signal generated by (200) can be provided to the subscriber's home J.

In the above embodiment, AGC is performed on both the FM signal and the IF signal, but AGC may be performed on either the FM signal or the IF signal.

In the above embodiment, the intermediate frequency is ½ of the lower limit value f _L of the band BS of the FM signal.
Although is set to 1/2 or less of the frequency of the upper limit value f _H, the upper limit value of the intermediate frequency, in accordance with the transmission band characteristic of the IF bandpass filter 3a to be used may be appropriately finely adjusted . For example, in the transmission band characteristic of the IF bandpass filter 3a, if the high-frequency roll-off is smaller than the low-frequency roll-off, the upper limit value of the intermediate frequency may be increased accordingly.

In the above embodiment, the input broadcast signal is an FM signal, but may be another broadcast signal such as satellite broadcast or terrestrial digital broadcast. The range of the intermediate frequency is set as appropriate according to the upper limit value and the lower limit value of the band of the input broadcast signal.
For example, when the high-frequency signal is not an FM signal but a terrestrial digital broadcast signal, generally used is 37.15 MHz, and the frequency (intermediate frequency) of the desired IF signal is higher than 37.15 MHz. It is preferable to set to.

Moreover, although the noise canceller is provided in the above embodiment, a configuration in which the noise canceller is deleted may be employed as the signal processing device according to the embodiment of the present invention. Also,
An image rejection filter that is externally attached to the front stage of the down converter of the signal processing device may be used.

Further, the signal processing apparatus of the present invention is not necessarily limited to that used in the CATV head end or CATV system.

Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 Signal input part 2 Down converter 2a Image rejection filter 2b, 3b Amplification part 2c Mixer 3, 3A IF processing part 3a IF band pass filter 3c, 12 Branch part 4 A / D conversion part 5 Orthogonal demodulation part 6 Digital filter 7 Multi Pass-scancera 8 Orthogonal demodulation D / A conversion unit 9 Signal output unit 10 Detection unit 11 Local oscillation unit 13 Calculation unit 14 Control unit 100, 200 Signal processing device BF1, BF2 Transmission band BS band BU Unnecessary band S1 Desired FM signal S2, S3 FM signal SIF1, SIF2 Desired IF signal SL1, SL2 Local oscillation frequency signal SU1, SU2 Unnecessary signal A CATV system B CATV headend C Antenna D FM receiver E Demultiplexer F Amplifier G Mixer H Transmitter I Signal transmission path J Subscriber home K Subscriber home equipment

Claims (8)

A down converter that converts an input high frequency signal into an intermediate frequency signal;
A local oscillator for supplying a local oscillation frequency signal to the down converter;
An intermediate frequency processing unit having a band-pass filter that selectively transmits a predetermined band of the intermediate frequency signal;
An A / D converter for A / D converting the intermediate frequency signal transmitted through the band-pass filter;
A baseband converter that generates a baseband signal from the A / D converted intermediate frequency signal;
A digital filter that performs digital signal processing that selectively transmits a predetermined band of the baseband signal;
A D / A converter for D / A converting a baseband signal transmitted through the digital filter into a high-frequency signal;
An image rejection filter disposed in the preceding stage of the down converter or the down converter;
With
The high-frequency signal is an FM signal,
The down-converter converts the input high-frequency signal into an intermediate frequency signal having a frequency equal to or lower than a half of the upper limit value of the band of the high-frequency signal and a frequency higher than 10.7 MHz. Processing equipment. A down converter that converts an input high frequency signal into an intermediate frequency signal;
A local oscillator for supplying a local oscillation frequency signal to the down converter;
An intermediate frequency processing unit having a band-pass filter that selectively transmits a predetermined band of the intermediate frequency signal;
An A / D converter for A / D converting the intermediate frequency signal transmitted through the band-pass filter;
A baseband converter that generates a baseband signal from the A / D converted intermediate frequency signal;
A digital filter that performs digital signal processing that selectively transmits a predetermined band of the baseband signal;
A D / A converter for D / A converting a baseband signal transmitted through the digital filter into a high-frequency signal;
An image rejection filter disposed in the preceding stage of the down converter or the down converter;
With
The high-frequency signal is a terrestrial digital signal,
The down-converter converts the input high-frequency signal into an intermediate frequency signal having a frequency equal to or lower than a half of the upper limit value of the band of the high-frequency signal and a frequency higher than 37.15 MHz. Processing equipment.   The signal processing apparatus according to claim 1, further comprising a multipath scancer that suppresses multipath noise included in the baseband signal that has passed through the digital filter and outputs the same to a D / A converter. The baseband conversion unit orthogonally demodulates the A / D converted intermediate frequency signal to obtain an I signal and a Q signal, and the D / A conversion performs an orthogonal modulation process using the I signal and the Q signal. The signal processing apparatus according to claim 1 , wherein the high-frequency signal is generated. A branching part for branching a part of the intermediate frequency signal;
A detector for detecting a level of the branched intermediate frequency signal;
An output adjusting unit that adjusts a gain for at least one of the high-frequency signal and the intermediate-frequency signal to be constant based on the level of the detected intermediate-frequency signal;
The signal processing apparatus according to claim 1, comprising: A branching part for branching a part of the baseband signal transmitted through the digital filter;
A calculation unit for calculating the level of the intermediate frequency signal from the branched baseband signal;
An output adjusting unit that adjusts a gain for at least one of the high-frequency signal and the intermediate-frequency signal to be constant based on the level of the calculated intermediate-frequency signal;
The signal processing apparatus according to claim 1, comprising: A signal processing device according to any one of claims 1 to 6 and a plurality of signal processing devices that respectively perform signal processing on a high-frequency signal distributed by the distribution unit that distributes a high-frequency signal, and the signal processing device. A mixing unit that mixes the high-frequency signal signal-processed by the receiver, and
A transmission device for transmitting a high-frequency signal output from the reception device;
A CATV head end comprising: A CATV headend according to claim 7 provided in a CATV station;
A signal transmission path for transmitting a high-frequency signal transmitted from the CATV headend transmitter;
A subscriber premises device provided in the subscriber premises that receives the high-frequency signal transmitted through the signal transmission path; and
A CATV system comprising:

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