JPS6048929B2 - Filter for vestigial sideband communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a filter used in a vestigial sideband communication system,
By reducing fluctuations in attenuation and delay characteristics within the required band, distortion in communication content is reduced, and the required characteristics can be easily achieved even when the ratio of (communication bandwidth)/(carrier frequency) is relatively large. The purpose of the present invention is to make it possible to reduce the size and weight by configuring the circuit with a circuit including active elements.

The vestigial sideband communication method has already been used in the past, and is a very effective means for transmission (especially analog amounts) within a limited communication band.

However, when sending signals using the vestigial sideband communication method,
The amplitude and delay characteristics of the filter within the communication band must satisfy certain conditions, and these characteristics determine the quality of the communication content. Generally, (communication bandwidth) / (carrier frequency)
Those with relatively small values (television image signals, etc.)
It is possible to achieve the desired characteristics relatively easily by using a resonant circuit of inductance and capacitance, but for devices with relatively large values (such as facsimiles), it is quite complicated to obtain the desired characteristics. It is necessary to use means. In other words, since the bandwidth is wide, a series or parallel resonant circuit of inductance and capacitance as passive elements is used to sequentially match the swing characteristics within the required band to the desired value, and then the delay time is made constant. A phase shift circuit is constructed of inductance and capacitance, which are connected in cascade. As a result, the resonance characteristics of each inductance and capacitance interfere with each other, making adjustment of the resonance characteristics complicated.As a result, adjustment of the transfer circuit to correct the phase characteristics that occur is complicated, and the linearity of the delay characteristics is affected. It is difficult to ensure this, and as a result, it is accompanied by considerable difficulty in ensuring the characteristics after detection of the vestigial sideband communication system. The present invention eliminates the above-mentioned drawbacks, and by cascading circuits having independent predetermined transfer functions, the present invention can be used as a wave filter for the vestigial sideband communication system to greatly increase the amplitude characteristics within the communication band. The aim is to significantly improve the linearity of the detected output. First, for convenience of explanation, the well-known vestigial sideband communication system will be briefly explained with reference to FIG.

When creating a communication signal using the carrier frequency WCl, a certain sideband filter Wal is created on both sides of the center frequency WOl, and W
Pl, W.P. In contrast, in the case of the vestigial sideband communication method, substantially half of the modulated wave is used to reduce the bandwidth.In other words, the solid line A1 ( As shown in (6), the amplitude characteristics of the non-attenuated portion (from WPl to WP3) are amplitude A., 1/2A0.at carrier frequency Wcl, and substantially zero at Wp4, reduced area Bll, and additional area. Bl2 is point P
Make it point symmetrical with l3 as the center. Also, this band WPL
~WP4, when the delay characteristic TlO(W) takes a constant value TlO, when the carrier wave frequency WCl is detected, a detection output in which the additional area Bl2 is folded back to the reduced area Bll is obtained, and the modulated wave is completely regenerated. be done. Therefore, in this case, the communication band of WP2 to WP4 is reduced, allowing efficient communication. Also, in this case, WP2 is W. The closer the value is to l, the more effective the communication will be. Therefore, the conditions required for an offshore wave device are WPl as the amplitude characteristic.
~WP3 is a constant value AO, the value of 1I2A0 is maintained at the carrier frequency, and the reduction area Bll and the additional area Bl2 maintain point-symmetrical characteristics about the carrier frequency point Pl3.

Further, the delay characteristic T(W) within the required band may maintain a constant value. An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, the first polarized low-pass p-wave circuit B2l?
It is a modified version of Muffin T, and the resistance R2ll'VR
2l7) It consists of a capacitor C2ll'' C2l3 ~ operational amplifier (operational amplifier) A2l. The transmission function Tl, S) of this circuit B2. is determined by the attenuation pole frequency WNl and the zero point frequency WOl.
, using the sharpness Q1, it is expressed as (here, S=JW).

Similarly, the second polarized low-pass furnace wave circuit B22 has a resistor R2
2l to R227, capacitors C22l to C223, and an operational amplifier A22, and is similarly expressed as a transfer function T2L).

The first phase shift circuit B23 has resistors R23l to R235 and a capacitor C
23l, C2 consisting of a small operational amplifier A23, zero point frequency W.

3 and the sharpness Q3 to express the transfer function T3OS).

Similarly, the second phase shift circuit B24 has resistors R24l to R245.
, capacitance Q4l, C242, operational amplifier A. , and the transfer function T4(3,
is expressed as .

The above four sets of transfer functions T, (.

) to T4(1) are combined to configure a filter having the desired characteristics. In order to achieve a smooth characteristic that meets the purpose, the sharpness Q is used at a relatively low value, and the amplitude characteristic and delay time are configured by combining those with a peak and those without a peak near the zero point frequency. First polarized low-pass Toba circuit B. , has a quadratic transmission function as shown in equation (1), and its amplitude characteristic is expressed as A1(W
), and the delay characteristics also have the characteristics of T and (W) in FIG. Then, the amplitude characteristic A, (W) is the sharpness Q
, is set low, there is no peak up to the attenuation pole frequency WNI. Also, the zero point frequency WO is the carrier frequency W. , is set to a lower value. Further, at this time, since the value of Q is low, the delay characteristic T1(W) has a peak at a frequency lower than the zero point frequency. Similarly, a second polarized low-pass Toba circuit B. . is the formula (2
), it has a quadratic transmission function, and the amplitude and delay characteristics are respectively A2 in Fig. 3. w,,t. , w. This amplitude characteristic A. (W) is the attenuation pole frequency W
Since N2 is set to a higher frequency than WN, and the sharpness Q2 is slightly higher than the sharpness Q of the first wave generator, the zero point frequency W wave. There is a peak nearby, but the sharpness is Q. is not very high, so it does not completely match Wc.
Also, at this time, the delay characteristic T2 (W) also has its peak near the zero point frequency WO2. The combination of these two is shown in FIG. 3 as the amplitude characteristic Al2 (w), and the carrier wave frequency Wc, The special issue has an attenuation pole at WNI.Therefore, as the amplitude characteristic, the above method v is sufficient to achieve the purpose.On the other hand, the delay characteristic T,.
w, Jt. (The composite of W is the delay characteristic T, .
w, is shown in Figure 3, and each zero point frequency W〇,
Otsu W. It has the characteristic of having one peak between 2ι
This T,2.

Two phase shift circuits B23 and B2 are used to make the characteristics of w, substantially unaffected. Use. This phase shift circuit B
2a, B2. The transmission function of is expressed by the above equations (3) and (4). In other words, the amplitude characteristic of this phase shift circuit T3 (W) is constant regardless of the frequency, and the delay characteristic T3 (W)
, T4(W) changes depending on the frequency. Therefore, the above delay characteristic T,. ,w, can be corrected. This phase shift circuit B23 has a zero point frequency W. 3, but the sharpness Q3 is the above-mentioned first and second wave plate.

The sharpness of Q,,Q. Since it is much lower than the zero point frequency W
. No peak appears near 3.

Rather, it has a shape without a peak. Also, this zero point frequency W. . is W. , is set to a lower value. Also, a second phase shift circuit. has zero frequency WO, and sharpness Q. is the first and second furnace wave device B. ,,B. .
The sharpness of Q,,Q. Since the zero point frequency WO is somewhat higher than
It has a peak nearby. And this zero point frequency W. .
is the zero point frequency W of the second J polar low-pass Toba circuit 2.
. set to a higher frequency. When these delay characteristics Tl2(W), T3(W), and T4(W) are combined, TO(w) in Figure 3 is obtained, and the line between the lower limit WB and upper limit WB2 of the required band is almost a straight line, which is the required characteristic. is obtained. Ma? In addition, as the amplitude characteristic, the upper limit WB of the required band. Since it is possible to have an attenuation pole frequency WN near the upper limit WB, unnecessary bands near the upper limit WB can be rapidly attenuated. FIG. 4 shows a comparison between the characteristics of a conventional product, which is said to be very well designed with conventional inductance and capacitance, and the characteristics of the exemplary circuit of the present invention as a furnace wave device.

As shown in the amplitude characteristic A(W) (in the case of FIG. 4, a linear scale is adopted), the amplitude characteristic A of this circuit. . w, is the amplitude characteristic A5 of the conventional product. It is very superior to w,15. This is also clear from the amplitude detection characteristic D(W).
That is, the detection characteristic of this circuit is D,. (w) is almost a straight line within the band, but the detection characteristic D5 (W, of the conventional product) does not maintain linearity. This is because the point symmetry with respect to point P, 3 of the amplitude characteristic is In addition, the delay characteristic t(W) of this circuit also maintains a nearly straight line, but in the case of conventional products, it is always excellent within the required band. The meandering is conspicuous, and this circuit is far superior.The door waver for the vestigial sideband communication system of the present invention will be further explained, including the results.

By using the polarized low-pass waveform circuit using active elements as described above, each attenuation pole frequency WN, ,
WN2, zero point frequency W.

,,WO2, and the sharpness Q,,Q2 can be arbitrarily selected, so the attenuation pole frequencies WN,,WN. The carrier frequency W
Additional area bird even if it gets close to c. , reduction region B, , can be maintained, and the required bandwidth can be sufficiently reduced.
At the same time, at this time, the attenuation value at the carrier frequency can be easily set to 112, and its characteristics are the detection characteristics D, as shown in FIG. (W, and delay characteristics TO(W
, very excellent characteristics can be obtained with both. In this case, an equivalent circuit can be realized using two or more polarized low-pass Toba circuits. Also, the first polarized low-pass furnace wave circuit B
2, the attenuation pole frequency WN, approaches the carrier wave frequency Wc, the upper limit of the required band WB, approaches the carrier wave frequency Wc, to reduce the required band, and the sharpness Q, is set to a low value. The peak of the characteristic is eliminated, the amplitude characteristic A, (W) in the vicinity of the carrier wave frequency 2 wave number Wc is made smooth, and the attenuation pole frequency W.
．． By setting 2 to a higher frequency than the attenuation pole frequency WN, the amplitude attenuation characteristic at a high frequency is satisfied, and at the same time, the amplitude two-width characteristic A near the carrier wave frequency Wc.

. w) is made gentle and the sharpness Q2 is set somewhat high to give the amplitude characteristic A2(W) a slight peak, thereby obtaining the amplitude characteristic A of the first polarized low-pass Toba circuit.
By correcting w, the symmetry of the reduced region B, , and the additional region B,2 and the attenuation characteristics of the unnecessary band can be significantly improved. Of course, even in this case, the same effect can be obtained even if two or more polar low-pass wave circuits are used.

Further, as described above, the amplitude characteristics A, of the first and second polar low-pass Toba circuits. w,,A2. A,2 as the comprehensive property 35 of W,. It can be realized to have w, **
However, in that case, the total delay characteristic T,. . It is possible to correct the characteristics of the polar low-pass waveform circuit using a small number of phase shift circuits so that w, has one peak, and as a result, the meandering property is significantly improved. In addition, in this case, as an example, two phase shift circuits are used.

However, it is possible to achieve this with only one phase shift circuit (B., only), although the delay characteristics in high bands will be somewhat worse. In this connection, a low frequency phase shift circuit B. 3 has no peak. This allows one phase shift J circuit to correct all delay characteristics on the low frequency side. Therefore, the configuration is simple, and at the same time, the meandering nature of the delay characteristics can be significantly improved.
In the illustrated circuit, the zero point frequency W of each circuit is
.

l,W. 2, W, 3, W.

4 and attenuation pole frequencies WN,,WN.

As mentioned above, they are arranged as follows. That is,
WO3<WO, <WO2<WN, <WO. <WN2. This combination consists of two polarized low-pass reactor wave circuits B1, 2, and two second-order phase shift circuits 2, 2, and 2. This shows the optimal design method when using . Here, almost the same characteristics can be obtained even if the phase shift circuit Bm is omitted as described above, but in that case, the above zero point frequency WO, is eliminated, W
O3<W. , <WO2<WN, <WN2. In both of these examples, the zero frequency W. ,,To W. ,W. .
and sharpness Q,,Q. By establishing a certain relationship between ,Q, and Q, an optimal configuration can be achieved as a vestigial sideband door transducer. That is, as shown in Table 1, the polar low-pass Toba circuit B is used. ,,B. . , phase shift circuit B. The zero point frequency of each of 3 is kept as WO3<WO, <WO2, and the sharpness is kept as U<Q, <Q. By keeping the width characteristics required for vestigial sideband communication, the symmetry with respect to points P and 3 of the carrier skin frequency shown in Fig. As shown in Fig. 3 and Fig. 4, the delay characteristic T can be improved. , w, can be significantly improved. However, predetermined characteristics can be obtained with the configuration having the smallest number of stages.

These three circuits described above constitute the main part of the door waver for the vestigial sideband communication system, and have the same effect even if they are accompanied by ancillary circuits.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the vestigial sideband communication system, FIG. 2 is an electrical circuit diagram showing an embodiment of the door waver for the vestigial sideband communication system according to the present invention, and FIG. FIG. 4 is a characteristic diagram comparing the characteristics of the product of the present invention and the conventional product.

Claims (1)

[Claims] 1. A plurality of polarized low-pass filter circuits having different attenuation pole frequencies, zero-point frequencies, and sharpnesses are configured using active elements, and the polarized low-pass filter circuits are configured using active elements. By cascading, the amplitude characteristic of the carrier frequency is set to 1/2 of the non-attenuated portion in the passband, and the overall delay characteristic of these multiple polar low-pass filter circuits becomes one. 1. A filter for a vestigial sideband communication system, characterized in that the delay characteristic of the passband is linearized using at least one second-order phase shift circuit. 2 A transfer circuit circle used for correcting delay characteristics in a frequency band lower than the peak frequency of the overall delay characteristics of a plurality of polarized low-pass filter circuits, whose delay characteristics have a maximum value at least within the required band. 2. A filter for a vestigial sideband communication system according to claim 1, characterized in that the value of sharpness is set low so that the sharpness does not occur. 3 Zero point frequency W_O_1, W_O_2, sharpness Q_1
, Q_2;
Using one phase shift circuit with zero point frequency W_O_3 and sharpness Q_3, the above zero point frequency is set as W_O_3<W_O_
When 1<W_O_2, the above sharpness is Q_3<Q_1<
The filter for vestigial sideband communication system according to claim 1, characterized in that Q_2. 4 Sharpness Q_1, Q_2, Q_3 are each 0.3<Q_
3<0.8, 0.5<Q_1<1.2, 1.2<Q_2
<Claim 3 characterized in that it is defined in 2.5.
A filter for the vestigial sideband communication system described in .