JPS5854688B2 - line equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an S/
Concerning N improvement and parts saving.

When broadcasting signals are transmitted through a carrier broadcasting line, the transmission and reception of signals between the broadcasting station and the carrier end station is carried out using a cable (Cable).
e).

This cable causes signal deterioration (amplitude distortion, frequency characteristic deviation) and loss, so a line equalizer (Cab
leEQL) performs equalization and compensation.

Here, Cable EQL must accommodate a wide range of changes in cable length and also a wide range of usage level changes.

Furthermore, the circuit type must be simple in structure and easy to operate.

Let us now consider a case where an attenuated signal sent from a broadcasting station via a cable is equalized and amplified.

Normally, ■Cable length varies depending on the situation (
For example, in the range of 0 to 16 km).

■ The required equalization step is on the order of 1 km.

■ Broadcasting stations transmit signals at a flat frequency level from low to high frequencies, but there is a wide range of transmission levels.

■ Cable loss is small in the low range and large in the high range (see Figure 1).

Therefore, the signal reaching the terminal station is greatly attenuated in the high frequency range, and is not attenuated very much in the reduction.

It can be said.

Cable EQL must not only level out the frequency characteristics but also meet the above conditions in terms of dynamic range and S/N.

In Fig. 1, the curve Cv1 is 8km Cab l.
e, curve Cv2 is 4km Cab le, curve Cv3 is 2km Cab le, curve C
V4 indicates the case of 1 km Cab 1 e, respectively.

For this reason, the configuration of Cable EQL conventionally used is as follows.

■ For example, cab le with a width of O~16krT1
To equalize, equalization circuit blocks (EQL blocks) for 1, 2, 4, and 8 km cables are prepared and used in combination.

(2) The characteristic shape of each EQL block is a downward-sloping characteristic that approximates the inverse characteristic of the Cable characteristic.

(2) The frequency of a reference point that defines the C level (for example, O 0.8 KHz) and the amount of attenuation at that point are defined as odB.

(2) Even if any number of EQL blocks are used in any combination, the amount of attenuation at, for example, 0.8 KHz is determined to be odB.

Here, the overall characteristic function of each EQL block is a linear function (
This is a combination of multiple stages (bypass type).

Considering the case of a three-stage type, its characteristic function (loss function) is as follows.

A specific example of the function is shown below (Fig. 1 8 kmCabl
e for 4 Ihi).

A=0.17018. Person'=0.12066B=0.9
4560, B'=0.55677C=18.7559
, C'-1,83560H=0.083031 This characteristic curve is shown in FIG. 2 as curve C■5.

At the same time, the characteristic images of the 1 and 2.4km EQL blocks are shown in the figure, respectively, with curves C and 8. C■7. Indicated by C■6.

Here, the overall characteristic function expressed by equation (1) is usually decomposed to create first-order partial functions, and realized by cascade-connecting partial circuits that individually realize the first-order partial functions.

There are various combinations of these, and when you change the combination, the characteristics will change in various ways.

Which combination to use and in what order to connect them is determined by taking into consideration the saturation level, noise level, and level diagram.

An example of decomposition is shown below.

This is simply a combination of coefficients with similar coefficient values.

For example, H1=0.10667, H2=0.9891
If we set 8°H3=0.78691, the characteristics of each stage will be the third
Curve C■0. C■1o and C■1 (both odBatO18KHz).

However, under the conditions described above, it is not a good idea to configure each EQL circuit with a passive circuit (constant resistance type circuit).

It is better to implement each stage in the EQL block with an active circuit.

The active circuit will be described below.

Examples of primary CR type active circuits having linear function characteristics include those shown in FIG. 4 a, b, c, and d.

Their high input impedance, low output impedance allows direct connections between stages.

In this case, direct connection between the EQI and the blocks is possible, which is advantageous.

However, it is necessary to install input and output buffer amplifiers for connection with external circuits.

The entire configuration of CableEQL at this time is shown in FIG.

In the figure, BA□ and BA2 are buffer amplifiers, EQL
1 to EQLn are cabs each consisting of multiple stages of circuits.
This is an eEQL block.

Multiple CableEQL blocks are available, and
They are appropriately combined and cascaded according to the BLE length.

However, CableEQL shown in FIGS. 4 and 5 has the following drawbacks.

[Yes] In active circuits, operational amplifiers generate noise.

■ Since a large number of operational amplifiers are used in CableEQL of this configuration, securing S/N is an important issue.

This is because the band is vast, and the EQL characteristic is of a high-frequency emphasis type, and the high-frequency gain is thick.

- The longer the distance, the greater the amount of equalization and amplification in EQL, and the greater the number of stages, so the degree of S/N deterioration is greater.

Even if you try to use an operational amplifier with as low noise as possible, the S
/N may be difficult to completely satisfy.

The following methods can be considered as measures to reduce such noise.

■) The buffer amplifier (BAI) has a flat gain over all frequencies, and the level is raised in the first stage of the multiple stages, and the S/
There are ways to improve N, but there are dynamic range limitations.

In other words, low frequency signals are nearly lossless, so if they are sent out at a high level from a broadcasting station, a large signal will come in.

If this is greatly amplified, it will become saturated.

2) How to apply emphasis and de-emphasis.

Even if you don't amplify the entire band, it will be effective if you amplify only the high range, so applying emphasis and de-emphasis is effective.

No oversaturation. However, this method requires extra stages for emphasis and de-emphasis.

As shown in FIG. 5, if the buffer amplifier BA1. Even if it is constructed using BA2, the extra C and R parts will be required.

Additionally, extra amplitude distortion (frequency characteristic deviation) occurring in the emphasis and de-emphasis parts cannot be ignored.

In this way, both methods 1) and 2) are impossible.

From the above circumstances, ■ Effective countermeasures on the circuit for noise reduction.

■ The challenge is to suppress and save the number of operational amplifiers as much as possible.

The present invention aims to solve the above-mentioned problem, and by effectively utilizing a common module buffer amplifier, it simultaneously achieves a reduction in noise and a reduction in the number of operational amplifiers.

The present invention will be described below based on Examples.

FIG. 6 shows an embodiment of the present invention, in which OP is an operational amplifier, ta and tb are switching terminals, C is a capacitor, and R is a resistor.

In the present invention, the circuit configured as shown in FIG.
Insert it into the buffer amplifier BA1 part of the figure.

When the switching terminals ta and tb are open, it is used as a buffer amplifier, and when the switching terminals ta and tb are connected, it is used as the first stage of Cable EQ L with the first stage circuit removed.

That is, when the switching terminals ta and tb are connected, the capacitor C1 has a certain frequency characteristic due to the resistor R.

To explain the above more specifically using FIG. 5, for example, if the first stage circuit is deleted in EQLn, the terminals ta and tb will be connected when EQLn is used as a combination. Make it.

Thereby, desired equalization characteristics can be achieved.

As a result, for the EQLn, one operational amplifier, which is a noise source, disappears in the input part where S/N is important, and the S
/N is significantly improved.

The EQL block for which the first-stage circuit is deleted is usually the one that has the largest number of stages and is for the longest distance, which causes S/H problems.

Furthermore, since it is effective to place a high-frequency emphasis type characteristic in the first stage of the arrangement in the book, such a characteristic (function) is usually determined and assigned.

However, this is determined by taking into account the constraints on the level diagram.

As described above, by utilizing the common part input amplifier as one stage of the equalization circuit, 1) improvement of the S/N ratio 2) reduction of one OP-AMP can be achieved.

Although the switching work in the buffer amplifier BA1 section increases, since only one strap is added, this is hardly a problem and is extremely useful in terms of practical application of Cable EQL.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the frequency characteristics of the line, FIG. 2 is a diagram showing the characteristics of the equalization amount block, FIG. 3 is a diagram showing the characteristics of each stage of the equalization amount block, and FIGS. 4 a and b. FIG. 5 is a diagram showing the overall structure of the line equalization amount, and FIG. 6 is a diagram showing an example of the input buffer amplifier used in the present invention. In the figure, EQL1 to EQLn are equalization amount blocks, BAl. BA2 is a buffer amplifier, OP is an operational amplifier, C is a capacitor, R is a resistor, and ta and tb are switching terminals.

Claims (1)

[Claims] It includes a plurality of equalizer blocks formed by connecting a plurality of single-cover sofa amplifiers and a plurality of first-order CR active circuits each having linear function characteristics, and by connecting the equalizer blocks in combination, desired equalization characteristics can be obtained. In a line equalizer having a line equalizer, the primary CR type active circuit at the first stage of a specific equalizer block is omitted, and the input buffer amplifier is switched so that it operates as the first stage of the specific equalizer block. 1. A line equalizer characterized in that the line equalizer is configured to switch when the specific equalizer block is used.