JPH0681001B2 - Automatic gain control circuit - Google Patents

Description

The present invention relates to an automatic gain control circuit, and more particularly to an automatic gain control circuit suitable for sample value control.

〔Overview〕

The present invention is an automatic gain amplifier configured to sample a received signal that has been distorted by a transmission line, input it to a variable gain circuit, detect the peak value of its output waveform, and apply negative feedback to the variable gain circuit as a control signal. The control circuit is configured to detect the peak value after adding the output of the variable gain circuit and the output obtained by differentiating the output once or twice, so that an accurate peak is obtained regardless of the sampling phase. The value can be detected, stability is improved, and digitalization facilitates integration into an integrated circuit.

[Conventional technology]

Conventionally, in the automatic gain control circuit suitable for sample value control,
For example, The Bell System techntcal Journal, November 1982, 2
As shown on page 743, the peak value is detected for the output waveform of the automatic gain control circuit by the diode clip analog technology, and the variable gain circuit is controlled by the result.

[Problems to be solved by the invention]

The conventional automatic gain control circuit described above has a drawback in that the loop gain increases if the variable gain width is widened, and the stability of the system is lost. Further, since analog technology is used, it is difficult to form an integrated circuit and it is difficult to reduce the cost.

An object of the present invention is to provide an automatic gain control circuit which is suitable for a sample value control system, has high stability, and can be easily integrated into an integrated circuit by eliminating the above drawbacks.

[Means for solving problems]

According to the present invention, a sampling circuit that samples a reception signal that has been distorted by a transmission path, a variable gain circuit that inputs the output of the sampling circuit and performs gain control, and a peak value of an output waveform of the variable gain circuit are detected. In the automatic gain control circuit including a peak detection circuit and a control circuit that controls the gain of the variable gain according to the output of the peak detection circuit, a differentiation circuit that inputs the output of the variable gain circuit and performs differentiation a predetermined number of times, It is characterized by including an arithmetic circuit for adding the output of the differentiating circuit and the output of the variable gain circuit and outputting the sum to the peak detecting circuit.

Further, in the present invention, it is preferable that the differentiating circuit is a differentiating circuit that performs one-time differentiation.

Further, in the present invention, it is preferable that the differentiating circuit is a differentiating circuit that performs twice differentiation.

Further, in the present invention, it is preferable that the differentiating circuit is a 90-degree phase circuit whose band is limited.

[Work]

The output waveform from the arithmetic circuit is the sum of the output of the variable gain circuit and the output of the differentiating circuit obtained by differentiating the output of this variable gain circuit, for example, once or twice. When the time slot is T, the output waveform of the variable gain circuit from -T to T and its waveform are 1
Only the 1st or 2nd derivative is superposed with the output waveform, and as a result, in the case of the 1st derivative, -T / 2 to 0
In the case of the second differentiation, the waveform has a substantially constant amplitude between −2 / T and T / 2.

Therefore, if the sampling period of the sampling circuit is set shorter than T / 2 or T of the time slot T, the output of the peak detection circuit can detect the correct level corresponding to the amplitude of the received signal regardless of the sampling phase. It is possible to improve stability. Furthermore, the differentiating circuit and the arithmetic circuit can be easily integrated into a digital circuit, and a circuit that is easy to integrate as a whole can be realized.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the first embodiment of the present invention.

In this embodiment, a sampling circuit 1 for sampling a reception signal which is distorted by a transmission line, and this sampling circuit 1
Of the variable gain circuit 2 for inputting the output of the variable gain circuit 2, the peak detection circuit 5 for detecting the peak value of the output waveform of the variable gain circuit 2, and the gain of the variable gain circuit 2 according to the output of the peak detection circuit 5. In an automatic gain control circuit including a control circuit 6 for controlling, a peak value is obtained by adding the output of the variable gain circuit 2 to the differentiating circuit 3 for differentiating and the output of the differentiating circuit 3 with the output of the variable gain circuit 2. The arithmetic circuit 4 output from the detection circuit 5 is included.

A feature of the present invention is that the differentiating circuit 3 and the arithmetic circuit 4 are provided in FIG.

Next, the operation of this embodiment will be described with reference to FIGS.
This will be described with reference to the waveform charts of (c) and each part shown in FIG.

2 (a), (b) and (c) are waveform diagrams of the output A of the variable gain circuit 2, the output B of the differentiating circuit 3 and the output C of the arithmetic circuit 4, respectively, and the horizontal axis is the time axis. The vertical axis represents the amplitude, and T is the time slot of the received signal.

That is, the output C has a form in which the waveform of the output A and the waveform of the output B are superimposed, and the amplitude value is substantially constant in the section from -T / 2 to 0.

Therefore, in the peak detection circuit 5, by setting the sampling period in the sampling circuit 1 to be shorter than T / 2, even if the sampling phase is deviated, a correct constant level corresponding to the received signal amplitude is obtained. Can be detected.

FIG. 3 is a waveform diagram of the output C showing this relationship. In the figure, output C ₀ is standard output, output C ₁ is below standard output,
The output C ₂ indicates an output higher than the standard. As a result, the peak detection circuit 5 detects a correct peak value corresponding to the amplitude value of the received signal, and controls the gain of the variable gain circuit 2 via the control circuit 6 so as to reach the standard value determined. To do.

FIG. 4 is a block diagram showing the second embodiment of the present invention. In the present embodiment, two differentiating circuits (1) 3a and (2) 3b are provided for differentiating the output of the variable gain circuit 2 twice. This is the same as the first embodiment.

The feature of the present invention resides in that the differentiating circuit (1) 3a, the differentiating circuit (2) 3b and the arithmetic circuit 4 are provided in FIG.

Next, the operation of this embodiment will be described with reference to FIGS.
This will be described with reference to the waveform diagrams of the respective parts shown in (c) and (d).

FIGS. 5 (a), (b), (c) and (d) show the output A of the variable gain circuit 2 and the output of the differentiating circuit (1) 3a, respectively.
B ₁ , the output B _{2 of} the differentiation circuit (2) 3b and the output of the arithmetic circuit 4
It is a waveform diagram of Ca.

That is, the output Ca has a form in which the waveform of the output A and the waveform of the output B ₂ are superposed, and has a substantially constant amplitude value from −T / 2 to T / 2. Therefore, the second embodiment is more complicated than the first embodiment by adding one differentiating circuit, but the width of a constant level of the output waveform of the arithmetic circuit 5 is doubled. That is, sampling can be performed at intervals of T or more, and more stabilization can be achieved.

The differentiating circuits 3, 3a, 3b and the arithmetic circuit 4 can be realized by digital circuits, which facilitates the integrated circuit circuit of the entire circuit.

As the differentiating circuit, instead of the so-called differentiating circuit shown in the above-mentioned embodiment, the above-mentioned respective signal waveforms are equivalent and the same effect can be obtained even if a 90-degree phase circuit with a limited band is used.

〔The invention's effect〕

As described above, the present invention can detect the correct peak value corresponding to the amplitude of the received signal regardless of the sampling phase, and has the effect of improving the stability.
Further, since a digital circuit such as a differentiating circuit and an arithmetic circuit is used, there is an effect that it can be easily integrated into a circuit and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention. 2 (a), (b), (c) and FIG. 3 are output waveform charts of respective parts showing the operation. FIG. 4 is a block diagram showing the second embodiment of the present invention. FIGS. 5 (a), (b), (c) and (d) are waveform diagrams of outputs of respective parts showing the operation. 1 ... Sampling circuit, 2 ... Variable gain circuit, 3 ...
Differentiation circuit, 3a ... Differentiation circuit (1), 3b ... Differentiation circuit (2), 4 ... Arithmetic circuit, 5 ... Peak detection circuit, 6 ...
... control circuit, 7 ... input terminal, 8 ... output terminal, A,
B, B ₁ , B ₂ , C ₀ , C ₁ , C ₂ , Ca ... Output.

Claims (4)

[Claims] 1. A sampling circuit (1) for sampling a reception signal distorted by a transmission line, a variable gain circuit (2) for inputting the output of this sampling circuit and performing gain control, and an output of this variable gain circuit. An automatic gain control circuit including a peak detection circuit (5) for detecting a peak value of a waveform and a control circuit (6) for controlling the gain of the variable gain circuit according to the output of the peak detection circuit, A differentiating circuit (3, 3a, 3b) that receives an output and performs differentiation a predetermined number of times, and an arithmetic circuit (4) that adds the output of the differentiating circuit and the output of the variable gain circuit and outputs the sum to the peak detecting circuit. An automatic gain control circuit characterized by including. 2. The automatic gain control circuit according to claim 1, wherein the differentiating circuit is a differentiating circuit that performs one-time differentiating. 3. The automatic gain control circuit according to claim 1, wherein the differentiating circuit is a differentiating circuit that performs twice differentiation. 4. The automatic gain control circuit according to claim 1, wherein the differentiating circuit is a 90-degree phase shift circuit with a band limited.