JPH01177706A - Frequency separation filter circuit - Google Patents

Abstract

PURPOSE:To reduce the loss at a high frequency band and to facilitate the design of a compensation circuit by designing the circuit such that a signal with lower frequency passes through more number of filters and a signal with higher frequency passes through less number of filters. CONSTITUTION:A filter 2A synthesizes signals SA1-SA4 of plural bands to be a composite signal CS, which to fed is a coaxial cable 1. The signal SA1 is processed by an LPF1-21A, synthesized with a signal being the result of processing the signal SA2 at an HPF1-22A and the resulting signal is processed by an LPF2-23A. The output is synthesized with a signal being the result of processing the signal SA4 at an LPF4-27A and an HPF3-26A and the resulting signal CS is fed to the cable 1. A filter 2B demultiplexes the signal CS in nearly opposite processing to form SB1-SB4 of plural bands.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a frequency separation filter circuit used for multiplexing, for example, television signals. Related to frequency separation filter circuit with suppressed loss reduction [Prior art] Conventional frequency separation filter circuits of this type are used for multiplexing, for example, television signals, and are symmetrical through signal lines that transmit complex signals. A filter connected to
The circuit is configured so that signals of multiple bands can be combined into a composite signal and sent to the signal line, and the composite signal sent via the signal line can be converted to a signal of multiple bands.

FIG. 2 is a circuit diagram showing an example of the configuration of such a conventional frequency separation filter circuit.

In Figure 2, SA, SB are 0 to 4.5 [M7]
Signals in the band, SA2, SB2 are 5.5 to 7.5
CM)tz) band signal, SA3. SB3 is 9.2
~23[M&) band signal, SA,.

SB is a signal in the band of 39 to 47 (MHz).

This frequency separation filter circuit is composed of filters 2a and 2b symmetrically connected via a coaxial cable 1, which is a signal line for transmitting a composite signal C8. The filter 2a has a circuit configuration so that the signals SA, -SA4 of multiple bands can be synthesized to form a composite signal C8 and sent to the coaxial cable l. Further, the filter 2b is configured to convert the composite signal C8 sent via the coaxial cable 1 into signals SB, -SB4 of multiple bands. Note that filter 2a and filter 2b are reversible, and both are input and output! Can be used.

Furthermore, the configurations of filter 2a and filter 2b will be explained.

Filter 2a is configured as follows. That is,
A low-pass filter 21a that processes the signal SA+ and a bypass filter 22a that processes the composite signal of the signals SA2 to SA3 are connected on the composite signal C8 side and connected to the coaxial cable l.

This bypass filter 22a is connected to a connection point where a low-pass filter 23a for processing the signal SA2 and a bypass filter 24a for processing the combined signal SA3-SA40 are connected on the composite signal C5 side. This bypass filter 24a is connected to a connection point where a low-pass filter 25a that processes the signal SA3 and a bypass filter 26a that processes the signal SA are connected on the composite signal O8 side. This bypass filter 26a is connected to the input terminal of the signal SA via a low-pass filter 27a. This low-pass filter 27a is 0 to
This is for removing harmonics from signals in the 47 [M) [z] band.

Filter 2b is configured as follows. That is,
A low-pass filter 21b that processes the signal SB, and a bypass filter 22b that processes the composite signal of the signals SB, -SB are connected on the composite signal CS side and connected to the coaxial cable 1.

This bypass filter 22b is connected to a connection point where a low-pass filter 23b that processes the signal SB2 and a bypass filter 24b that processes the composite signal of the signal SB3°SB are connected on the side of the composite signal C8. This bypass filter 24b is connected to a connection point where a low-pass filter 25b for processing the signal SB3 and a bypass filter 26b for processing the signal SB'4 are connected on the composite signal C8 side. This bypass filter 26
b c) Connected to the input terminal of the signal SB via the low-pass filter 27b. This low pass filter 27
b is for harmonic removal of signals in a band of 0 to 47 [MHz].

Here, the low-pass filter 218.21b has a cutoff frequency of 4.5 [:MHz], the bypass filter 22a,
22b has a cutoff frequency of 5.5 (Ml(z)), and the 0-bus filters 23a and 23b have a cutoff frequency of 7.5 [Ml(z)].
Hz], the bypass filters 24a and 24b have a cut-off frequency of 9.5 (MHz), and the low-pass filters 25a and 2
5b has a cut-off frequency of 23 [MHz], bypass filters 26a and 26b have a cut-off frequency of 39 [Ml(z]), and low-pass filters 27a and 27b have a cut-off frequency of 47 (MHZ).
z).

According to the frequency separation filter circuit configured in this way, when transmitting a signal from the filter 2a to the filter 2b, for example, the following operation occurs.

In the filter 2a, the signal SA4 is given to the bypass filter 26a via the low-pass filter 27a, and only the signal components of 39 to 47 (MHz) are converted to the signal SA3 sent via the low-pass filter 25a.
and is sent to the next stage through the bypass filter 24a. A composite signal of the signal SA3°SA is combined with the signal SA2 sent through the low-pass filter 23a, and sent to the next stage through the bypass filter 22H.

A composite signal obtained by combining the signals SA2 to SA is combined with the signal SA1 sent through the low-pass filter 21a to form a composite signal C3, which is sent to the coaxial cable 1.

A composite signal C3 sent from the coaxial cable 1 to the filter 2b is processed by a low-pass filter 21b to form a signal SB+, and also processed by a bypass filter 22b to form a composite signal including signals SB2 to SB3. Ru. The composite signal including the signals SB2 to SB2 is processed by the bypass filter 22b to produce the signal S
B2 and a bypass filter 24b.
is separated into a composite signal including signals SB3 and SB.

A composite signal including such signals SB3 and SB is separated into a signal SB3 by the low-pass filter 25b, and into a signal SB4 by the bypass filter 26b. Signal SB.

is 0 to 47 (MHz) by the low-pass filter 27b.
) removes harmonics of the signal in the band.

The above-described conventional frequency separation filter circuit operates in this manner, and the filter 2a and filter 2b are capable of combining and separating signals of various frequency bands.

[Problem that the invention seeks to solve]

However, according to the conventional frequency separation filter circuit described above, the signal A (n is an arbitrary integer) is passed through the filter 2a.
The loss lost when taking out the signal SB, (n is an arbitrary integer) from the filter 2b through the coaxial cable 1 is the sum of the loss of each filter element and the loss of the coaxial cable 1. . Here, let's compare what kind of loss occurs in the signals of each band. To simplify the comparison, each filter 21a to 27a, 21b to 27
It is assumed that the insertion loss per piece b is 1.5 (dB), and coaxial cable 1 carries 5C2V for 500 (m).
To explain the loss situation that occurs when using
The explanatory diagram of FIG. 4 will be used. Note that the loss of the coaxial cable 1 is due to the center frequency.

As can be understood from this explanatory diagram, as the frequency increases, the frequency separation filter circuit shown in FIG.
There is a problem in that both the loss of the filter and the loss of the coaxial cable 1 increase, and the loss increases rapidly as the passband rises, making it extremely difficult to design a compensation circuit connected to these frequency separation filter circuits. There was also the problem of becoming

The present invention has been made in order to solve the above-mentioned problems, and it aims at averaging the loss depending on the frequency band, suppressing the reduction in loss in the high frequency band, and facilitating the design of the compensation circuit. The purpose is to provide a filter circuit.

[Means for solving problems]

The frequency separation filter circuit according to the present invention can combine signals of multiple bands and send the composite signal to the signal line by using filters that are symmetrically connected via the signal line that transmits the composite signal. In a frequency separation filter circuit that converts a composite signal sent through a multi-band signal into a multi-band signal, the side where signals in a low frequency band are processed is the first low-pass filter, and the side where signals in a band higher than this signal are processed is the first low-pass filter. is the first high-pass filter, the combined signal sides of the two filters are connected, and the side that processes the signal at the connection point on the combined signal/signal side is the second low-pass filter, and the side that processes the signal at the connection point on the combined signal side is the second low-pass filter. The present invention is characterized in that it has at least a circuit configuration in which the side that processes signals in a higher frequency band than the signal is a second high-pass filter, and the combined signal sides of both second filters are connected.

According to the frequency separation filter circuit of the present invention configured as described above, low frequency signals are made to pass through as many filters as possible, high frequencies are made to pass through as many filters as possible, and high frequency signals are made to pass through as many filters as possible. Since the loss associated with passage through the filter is suppressed, the loss can be averaged by frequency band, the loss can be reduced in the high frequency band, and the design of the compensation circuit becomes easier.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a frequency separation filter circuit according to the present invention.

Also in the embodiment shown in FIG. 1, the same components as in the conventional example will be described with the same reference numerals.

In FIG. 1, this frequency separation filter circuit is composed of filters 2A and 2B symmetrically connected via a coaxial cable 1, which is a signal line for transmitting a composite signal C8. The filter 2A receives signals SA of multiple bands, ~
The circuit is configured so that SA4 can be synthesized into a composite signal C5 and sent to the coaxial cable 1. The filter 2B also receives a composite signal C sent via the coaxial cable 1.
The circuit is configured to generate signals of multiple bands from 8 to SB+ to SB. In addition, filter 2A, filter 2B
are reversible and can be used on both the input and output sides.

Furthermore, the configurations of filter 2A and filter 2B will be explained.

Filter 2A is configured as follows. That is,
The side where the signal SA in the low frequency band is processed is the 10th
- A pass filter 21A is used, and the side where this signal SA and higher band signal SA2 are processed is a first high-pass filter 22A, and the combined signal sides of both first filters 21A and 22A are connected, and the combined signal side is connected. Point signal SA,
.

The side that processes the composite signal including SA is the 20th-pass filter 23A, and the signal (S
A second high-pass filter 24A is used to process the signal SA3 in a higher frequency band than AI, SA2).
and both second filters (23A.

24A> is connected to the composite signal side.

In addition, the signals S/'z, S at the connection point on the composite signal side
The side that processes the composite signal including A2 and SA3 is the 30th-
A pass filter 25A is used, and the signals at the connection point on the composite signal side (SAI, SA2) are connected to the pass filter 25A.

A third high-pass filter 26A is used to process the signal SA4 in a higher frequency band than 5A3), and the combined signal sides of both second filters (25A, 26A) are connected to the coaxial cable 1. In addition, low-pass filter 2
7Δ is inserted to provide the same effect as the low-pass filter 27a of the conventional frequency separation filter circuit.

Filter 2B is configured as follows. That is,
The side where the signal SB in the lower frequency band is processed is the first low-pass filter 21B, and the side where this signal SB and the signal SB2 in the higher band are processed is the first high-pass filter 22B, and both of the first filters 21B are , 22B, and the signal SB+ at the connection point of this composite signal side.
.

The side that processes the composite signal including SB2 is the 20th-pass filter 23B, and the signal (S
The second high-pass filter 24B is the side that processes the signal SB3 in a frequency band higher than B+, SB2), and both second filters (23B.

The circuit configuration is such that the combined signal side of 24B) is connected.

Also, the signals SB, SB2 at the connection point on the composite signal side
, SB3 is used as the third low-pass filter 25B, and the signal (
SB, , SB, .

The third high-pass filter 26B processes the signal SA in a higher frequency band than 5B3), and the combined signal sides of both second filters (25B, 26B) are connected to the coaxial cable 1. In addition, low-pass filter 2
7B is inserted to perform the same function as the low-pass filter 27b of a conventional frequency separation filter circuit.

Here, the cutoff frequency of the tenth bus filters 21A and 21B is 4.5 (MHz), and the first bypass filter 2
2A and 22B have a cutoff frequency of 5.5 (M7), 20th-
The pass filters 23A and 23B have cutoff frequencies of 7 and 5.
CMHz'3, second bypass filters 24A, 24B
has a cut-off frequency of 9.5 (MHz), the 30th bus filters 25A and 25B have a cut-off frequency of 23 [MHz], and the third high-pass filter 26A.

26B has a cutoff frequency of 39 [M7], and the 40th bus filters 27A and 27B have a cutoff frequency of 47 [M7].

The operation of the embodiment configured in this way will be explained.

In this embodiment, for example, from filter 2A to filter 2B
Let us now explain the operation when transmitting a signal to.

In the filter 2A, the signal SA, is applied to the input terminal of the 20th-pass filter 23A via the first low-pass filter 21A, and the signal SA2 is applied to the input terminal of the 20th-pass filter 23A via the first high-pass filter 22A. given, this 20th-pass filter 23A
A composite signal including the signal SA and the signal SA2 is generated at the input terminal of the signal SA and the signal SA2, and is passed through the second low-pass filter 23A. The composite signal (S
A,,SA2) is the second pass filter 24A
The composite signal (SA,
, SA2) and is combined with a signal SA3 having a higher frequency than the signal SA2, and is applied to the 30th pass filter 25A. This third
The composite signal (SA+
, SA2, SA3) are the composite signals (S/'z, SA
2, SA3) and is combined with a signal SA4 having a higher frequency than that of the signal SA3, and is sent to the coaxial cable 1.

, On the other hand, in the filter 2B, the composite signal C5 sent from the coaxial cable 1 is passed through the third high-pass filter 26.
B separates the signal SB, and the 30th pass filter 25'B separates the combined signal (SBI, S
B2. SB3”).

Signal SB has unnecessary harmonics removed by the 40th-pass filter 27B. In addition, the composite signal (SB1,
SB2. SB3) is the second high-pass filter 24B
and the second low-pass filter 23B, and the second high-pass filter 24B separates the signal SB, and the second low-pass filter 23B separates the composite signal (SB).
SB+, SB2) are separated. This composite signal (SB+, SB2) is passed through the first high-pass filter 22B and! 10-pass filter 21B,
The first high-pass filter 22B separates the signal into a signal SB2, and the first low-pass filter 21B separates into a signal S81.

Such an action transfers the signal from filter 2B to filter 2
The same applies to the case of sending toward Δ.

In this example, the loss from sending the signal SAh of each band through the filter 2A to the signal SB obtained through the coaxial cable filter 2B was examined under the same conditions as the conventional frequency separation filter circuit. is an explanatory diagram of FIG. 3.

As can be understood from this figure, the center frequency is 2 (M
Hz), the signal path is SA, -3B.

Since the number of pass filters is 6, the total filter loss is 9CdB], and the loss of the coaxial cable 1 is 5[:dB], resulting in a total loss of 11[dB]. On the other hand, the center frequency is 43 [MHz
), the signal path is SA, →SB, and the number of pass filters is 4, so the total filter loss is 6 [dB], and the loss of coaxial cable 1 is 28 [dB].
[dB], resulting in a total loss of 34 [dB]. And the frequencies between these are also as shown in Figure 3.
It will show the total loss of each.

As mentioned above, in this embodiment, the loss of the coaxial cable 1,
It can be seen that since the filter loss has a value in the opposite direction to the change in the center frequency, the total loss is averaged and the absolute value of the loss is also reduced.

Although the above embodiment has been described in the case of four human input signals/output signals, it goes without saying that the present invention is not limited to this, and can be configured as long as there are three or more input signals/output signals.

〔Effect of the invention〕

As explained above, the present invention allows low-frequency signals to pass through a large number of filters, high-frequency signals to pass through a small number of filters, and suppresses the loss associated with high-frequency signals passing through a certain number of filters. Therefore, it is possible to average out the loss depending on the frequency band, reduce the loss in the high frequency band, and facilitate the design of the compensation circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional example, Fig. 3 is an explanatory diagram shown to explain the present invention in detail, and Fig. 4 is a circuit diagram showing a conventional example. It is an explanatory diagram shown in order to explain an effect. 1...Coaxial cable, 2A, 2B...Filter, 21A, 21B...10th pass filter, 2
2A, 22B...First high-pass filter, 23
A, 23B...20th pass filter, 24A
, 24B... Second high-pass filter. Applicant NEC Corporation Agent Patent Attorney Umeo Yamauchi Figure 3, Figure 4

Claims (1)

[Claims] Filters that are symmetrically connected through the signal line that transmits the composite signal can combine signals of multiple bands and send the composite signal to the signal line, and also combine the signals of multiple bands from the composite signal sent through the signal line. In the frequency separation filter circuit, a side where signals in a low frequency band are processed is a first low-pass filter, a side where signals in a band higher than this signal are processed is a first high-pass filter,
The composite signal sides of both first filters are connected, and the side that processes the signal at the connection point on this composite signal side is used as a second low-pass filter, and the signal in a higher frequency band than the signal at the connection point on this composite signal side is processed. 1. A frequency separation filter circuit comprising at least a circuit configuration in which a second high-pass filter is used for processing the second filter, and the combined signal sides of both the second filters are connected.