JPS6322110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quantization feedback circuit used for compensating for low-frequency cut-off characteristics and regenerating DC components in a digital transmission type regenerative repeater.

In general, in digital transmission type regenerative repeaters, the power to operate the repeater is superimposed on the transmitted signal and supplied through the same transmission path, so there is no low-frequency loss or disconnection at the input and output of each repeater. Although a power separating waveform with special characteristics is inserted, intersymbol interference occurs in the transmission line equalized and amplified signal due to this low frequency cutoff. Quantization feedback has been proposed as one method for reducing intersymbol interference due to low-frequency distortion.

FIG. 1 shows a block diagram of a conventional quantization feedback circuit and its peripheral circuits. 1 is a low-frequency cutoff circuit of the transmission line equalization amplifier including a power separation waveform, 2 is a quantization feedback circuit, 11 is a branch circuit, 12 is an inversion circuit, 13 is a delay circuit, 14 and 18 are 15 and 16 are 2-input adder circuits, and 1
7 is an identification and reproducing circuit. Also, point a is the output point of the previous repeater, point b is the output point of the transmission line equalized amplified signal that has been distorted by the low frequency cutoff of the low frequency cutoff circuit 1, and point c is the output point of the low frequency cutout. Point d is the output point of the transmission line equalized amplified signal after the distortion caused by disconnection circuit 1 has been compensated for by quantization feedback, and point d is the output point of the signal obtained by identifying and reproducing the signal at point c.

Here, if the overall transfer function from point a to point c in FIG. 1 is T ₀ (S), then T ₀ (S) is expressed by the formula.

T ₀ (S)=P(S)・(1−Q ₁ (S)・e ^-STx
)+Q ₂ (S)・e ^-STd )... Here, P(S) is the transfer characteristic of the low-pass cutout circuit 1, Q ₁ (S) is the transfer characteristic of the low-pass wave generator 14,
Q ₂ (S) is the transfer characteristic of the low frequency converter 18, T _x is the delay time in the delay circuit 13, and T _d is the delay time from point c to point d and back to point c.

Next, if we set P(S)=1−P ₁ (S), then P ₁ (S)
is the low frequency characteristic, and the equation becomes Eq.

T ₀ (S) = 1-P ₁ (S) + P ₁ (S)・Q ₁ (S)・e ^-
STx −Q ₁ (S)・e ^-STx +Q ₂ (S)・e ^STd ... If the shearing frequency of Q ₁ (S) is set sufficiently higher than the shearing frequency of P ₁ (S), P ₁ (S)・Q ₁ (S)≒P ₁
(S), and the formula is obtained.

T ₀ (S) = 1-P ₁ (S) (1-e ^-STx ) - {Q ₁ (
S) e ^-STx -Q ₂ (S)・e ^-STd }... From the above formula, when Q ₁ (S) = Q ₂ (S) and T _x = T _d
T ₀ (S) becomes T ₀ (S)=1-P ₁ (S) (1-e ^-STd )... As a result, if the characteristics of Q ₁ (S) and Q ₂ (S) are matched and the delay amount of T _x is made equal to T _d , T ₀ (S) = 1 after the delay time T _d seconds, and low frequency It can be seen that the influence of the shear cut P(S) disappears.

However, this quantization feedback circuit has the following drawbacks. First, the relative accuracy of Q ₁ (S) and Q ₂ (S) is required. Second, Q ₁ (S) and Q ₂ (S)
Since the cut-off frequency is lower than the code transmission speed, the element value becomes large, and therefore the implementation scale becomes large. Third, the delay must be precisely adjusted so that T _x = T _d , but this is extremely difficult. In other words, since the signal that has passed through the low-pass wave filter 14 or 18 has passed through the low-pass wave filter, its amplitude is small and its rising and falling edges are also poor. Since the main signal with a large amplitude that has not passed through the wave transmitter is also added, it is difficult to observe only the signal that has passed through the low frequency wave transmitter 14 or 18. It is difficult to precisely match the time positions of the signals.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
It is an object of the present invention to provide a quantization feedback circuit that can be constructed with waveformers that do not require precision, has a small implementation scale, and is easy to adjust.

A structural block diagram of the present invention is shown in FIG. 11 to 17 and b to d in the figure are the same as each circuit and each point in FIG. 1, respectively. Further, point e is an observation terminal for delay adjustment. The quantization feedback circuit of the present invention branches an input signal into two at the branch circuit 11, connects the branched first output to the first input of the first addition circuit 15, and identifies and reproduces the output of the 15. It is connected to the input of circuit 17, and at the same time the output of circuit 15 is used as an output signal.
The second output of the branch circuit 11 is connected to the first input of the adder circuit 16 and the second output of the branch circuit 11 is connected to the inverter circuit 12 and the delay circuit 1.
3 to the second input of the adder circuit 16, and the output is connected to the adder circuit 15 via the low-pass wave generator 14.
by connecting it to the second input of the.

Next, the circuit operation of the present invention will be described. Note that the signal entering the input terminal point b in FIG. 2 is the signal from the output point a of the preceding repeater that has passed through the low-frequency cutoff circuit 1, as in FIG. The overall transfer function from point a to point c is T ₁ (S), the characteristics of the low-pass filter 14 are Q ₁ (S), and P (S), T _x , and T _d are the same as those in the equation. Then, T ₁ (S) becomes Eq.

T ₁ (S) = P(S) + (e ^-STd -P(S)・e ^-STx )・Q ₁
(S)=P(S)・(1−Q ₁ (S)・e ^−STx )+Q ₁ (S
)・e ^-STd ... Q ₁ (S) and Q ₂ (S) in the formula are Q ₁ (S) = Q ₂
(S), then T ₀ (S) in the equation is T ₁ (S) in the equation
is equal to Therefore, it can be seen that the quantization feedback circuit according to the present invention functions in the same manner as the conventional circuit shown in FIG. In addition, the conventional circuit required two low-pass waveformers, but now only one circuit is required.
Therefore, relative accuracy between the two circuits is not required, and the implementation scale is halved. In addition, if you observe the waveform at point e, you can observe a waveform with a large amplitude rise and a good fall because it does not pass through the low-pass waver, and the main signal is also separated, so the delay circuit It is possible to perform this with high precision.

As described above, according to the present invention, it is possible to realize a quantization feedback circuit that has a small packaging scale, does not require element precision, and is easy to adjust.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional quantization feedback circuit and its peripheral circuits, and FIG. 2 is a block diagram of a quantization feedback circuit according to the present invention. 1...Low frequency cutoff circuit, 2...Quantization feedback circuit, 11...Branch circuit, 12...Inversion circuit, 13
...Delay circuit, 14...Low pass wave generator, 15,
16... Addition circuit, 17... Discrimination reproducing circuit.

Claims (1)

[Claims] 1 The input signal supplied to the input terminal is branched into two, one of which is used as the first input of the first addition circuit, the output of the addition circuit is used as the input of the identification and regeneration circuit, and the output of this identification circuit is used as the input of the first addition circuit. The other of the branched input signals is used as the second input of the second adder circuit through an inversion circuit and a delay circuit, and the output of this second adder circuit is used as a low-pass signal. 1. A quantization feedback circuit, characterized in that the quantization feedback circuit is configured by inputting the signal to the second input of the adder circuit through a waveform generator, and having the output of the discrimination circuit as the output terminal.