JPS5863218A - Equalizer - Google Patents

Abstract

PURPOSE:To obtain a cosine equalizer, by using a delaying circuit which has a cascade connection of the primary and secondary all pass circuits. CONSTITUTION:The reproduced waveform given from an input terminal Ti is turned into waveforms A, B and C of different phases and with no change of form through the delaying circuits 30 and 40. Each of the circuits 30 and 40 has a cascade connection of the primary and secondary all pass circuits. The waveforms B and C are synthesized by resistances R51 and R52 plus a variable resistance RV1 with a proper ratio and then fed to a differential amplifier 51. The output B+C of the amplifier 51 is controlled by a variable resistance RV2 for its amplitude and added with the waveform A at the next differential amplifier 52. Thus a waveform D having a narrowed width is delivered to an output terminal T0. Thus the size is reduced for an equalizer which corrects the reproduced waveform of a digital signal recorded with high density.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an equalizer that restores a waveform reproduced from a tape on which a digital signal is magnetically recorded on q#, or a waveform that is distorted in a transmission path.

In devices that record and play back digital signals on magnetic tape, generally speaking, increasing the density of data recorded on the magnetic tape will result in a relative decrease in the playback speed of the magnetic tape. Frequency components are lost and an accent occurs.

Accurate data cannot be obtained.

Therefore, use an equalizer to equalize the waveform.

Techniques for increasing recording density by equalizing reproduced waveforms are known.

No. 111j (aH) This shows a cosine equalizer that equalizes a waveform like this. This cosine equalizer is used for the reproduced waveform A as shown in FIG. 1(b).
A waveform B whose phase is advanced by 7 times, and a waveform C whose phase is delayed by 7 times are formed by the delay circuits 1 and 2Wc, and the waveforms are formed by the reproduced waveform A and the coefficient circuits 3 and 4 that set an appropriate amplitude value. By calculating waveform B and waveform C using the addition/subtraction circuit 5, that is, by subtracting waveform B and waveform C from the reproduced waveform A, a waveform with a narrowed pulse width can be obtained without changing the peak point of the reproduced waveform. If the magnetic tape to be formed is relatively small, delay lines or the like can be used as delay circuits 1 and 2, but the relative speed between the magnetic tape and the magnetic head is relatively small (for example, when the tape has a standard force of When high-density recording is performed at a speed of 4.8 cm/sω, the delay amount τ1,
A τ snow of about 10 to 15 μm is required, and a passing type delay line has a very large shape and is not practical.

This invention was made in view of this point.

5 in order to provide the active circuit with the necessary delay characteristics and to form a compact equalizer.

The equalizer of this invention will be explained below.

First, general phase characteristics in a passive all-pass circuit formed by impedance elements and CK will be described.

As shown in FIG. 2, it is known that when a second-order all-bus circuit 10 and a second-order all-bus circuit 20 are connected in cascade, their respective transmission coefficients are expressed by.

However, S=j ω ω; angular frequency ω, center angular frequency of the knee-order all-bus circuit 10 (angular frequency at which the phase rotates 90°) ω. The central angular frequency (angular frequency at which the phase rotates 180 degrees) of the second-order all-bus circuit 20 is shown.

From these equations, the delay characteristics of the all-bus circuit 10 are as follows.

2ω− τ, (ω)=□ ・・・・・・・・・・・・・・・・・・
...(3) ω2+ω2 What is the delay characteristic of the secondary all-bus circuit 20?

become.

This equation (3) has an angular frequency of 1 as shown by τ and IC in Figure 3.
1 shows a curve in which VC sequentially decreases as the number ω increases, and the (4)
The formula is τ, as shown by the central angular frequency ω. It becomes a unimodal curve IIIVc which decreases left and right with the peak point being the peak point.

Therefore, as shown in FIG.
From this diagram of τ=τ, (S+τbcm), the total delay amount when the secondary all-bus circuit 20 is connected in cascade is as follows.
The total delay amount τ is ω2 in the band from ω to ω.
．． ω. By appropriately setting and Q, a fairly flat delay amount τ can be obtained, and the signal band from ω to ω has the same function as the delay characteristic of the delay line. Be able to do that.

Now, in the case where the required frequency band is about 50 KHz and the delay amount in that frequency band is lO~15μ, the central angular frequency ω1. ω. As a result of considering and Q, -=l~1. If s, Q = 0.7ωa ~ 0.85, a very satisfactory delay characteristic can be obtained4.
I confirmed that.

Therefore, the cosine equalizer shown in FIG. 1 described above deals with 5 frequency bands of approximately 50 KHz.

Delay time τ1 of delay circuit 1.2. τ, 10 to 15
μ itself, the above-mentioned first-order all-bus circuit 10
．． The delay circuit 1.2 can be realized by a circuit in which the second-order all-bus circuit 20 and the second-order all-bus circuit 20 are connected in series, and the circuit can be made compact without using a delay line.

FIG. 4 shows an embodiment in which the primary and secondary all-bus circuits are realized by active circuits using CR, and the -th all-bus circuit 10 is a differential amplifier 11 . Resistors R11+R+*, R111(-) and capacitor Css form the secondary all-pass circuit 20, which is a differential amplifier 21. Resistors R□, R2th R*
s.

It is formed by R 4 and capacitor C□+C2x+.

In this circuit, the central angular frequency ω of the -th all-bus circuit 10 is ω'''C,,R,T.

If the resistance value and capacitance QiVc are shown in the diagram, then ω, Q3
1.26KHz, ω. It becomes 40.86KHz in the middle, -! ” - I was able to make it 1st and 3rd year of junior high school.

ωa becomes.

The jlE5 diagram shows the resistance values shown in the circuit diagram of the liA diagram.

This figure shows data obtained by actually measuring the delay characteristics of a circuit made using a capacitor and a capacitor. From this figure, about 5
At a bandwidth of 0 KHz, the delay time τ is 12.5
It can be seen that μB is almost constant.

FIG. 6 shows an embodiment of the above-mentioned cosine equalizer using the delay circuit shown in FIG. A delay circuit formed by adding an all-bus circuit, 50 indicates a subtractable circuit.

The addition/subtraction circuit 50 includes two differential amplifiers 51 and 52, resistors Ril to R1m, and a variable resistor RV.

It is composed of Rv3. The delay circuit 30.40 is the fourth
Use the one shown in the diagram.

This circuit operates in the same manner as the cosine equalizer shown in FIG. 1(a) described above. In other words, the reproduced waveform input from the input terminal T+ is transferred to the delay circuit 30 without changing its waveform. and 40, said FIG. 1(b
) waveforms A, B, and C having different phases are formed. Waveforms B and C are resistance R1゜R,1 and variable resistance RV,
The signals are combined at an appropriate ratio and input to the differential amplifier 51. The amplitude of the B+C waveform output from the differential amplifier 51 is further adjusted by a variable resistor RV.11. It is added to the waveform A in the next differential amplification s52, and the output terminal T,
A waveform In with a narrower K width is output.

In addition, the bandwidth is 50K)I, and the delay amount is 125μ.
The delay circuit set to m is + pk when playing a PCM audio signal at a cassette tape speed of 4.8 cm/a.
It goes without saying that LK is required for the cosine equalizer used.

As detailed above, in the equalizer of the present invention, the primary and secondary all-bus circuits are formed as delay circuits by 7-acting circuits, so a cosine equalizer can be formed without using a delay line, and the tape speed is slow. In the reproduction circuit of digital signals recorded at high density,
It has the advantage that the equalizer for restoring the waveform can be formed in a small size.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are block diagrams of the cosine equalizer and their respective waveform diagrams, Figure 12 is a dependent connection diagram of the primary and secondary all-bus circuits, and Figure 3 is the delay characteristic M of the second factor.
, FIG. 4 is a delay circuit diagram showing one embodiment of the present invention, and FIG.
The figure is the 41st!21st characteristic diagram, and the sixth factor is a circuit diagram showing the equalizer of the present invention. Figure 1 (a) Δ Figure 2 Figure 3 tAJI ωa woW
2ω To C ~? −. +-11

Claims (1)

[Claims] A cosine equalizer includes a first-order all-bus circuit with a center angular frequency of ω and a center angular frequency of ω. A delay circuit is formed by cascade-connecting secondary all-bus circuits, and the ratio of the central angular frequencies is set to ω = 1 to 1.5. Qω of the secondary all-bus circuit
Ibrizer's characteristic is that the barrel is set between 0.7 and 0.85.