JPH05160656A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To follow up the amplitude change without time delay at the time of the amplitude change from a low level signal to a high level signal and to limit the amplitude without distortion. CONSTITUTION:This circuit is provided with a variable gain amplifying circuit 2 to which an input signal is supplied and from which the amplified signal is outputted, a slicing circuit 7 which slices an output signal of the variable gain amplifying circuit 2 by a prescribed level, and a peak level holding circuit 8 which holds the peak level of the sliced signal obtained on the output side of the slicing circuit 7, and the gain of the variable gain amplifying circuit 2 is controlled by the output signal of the peak level holding circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control circuit suitable for use in, for example, a magnetic recording device.

[0002]

2. Description of the Related Art Generally, in a magnetic recording apparatus, in order to prevent distortion of a recording signal during recording, an amplitude of an input signal having a large amplitude exceeding a recording dynamic range of a magnetic tape or the like is limited.

Conventionally, an automatic gain control circuit as shown in FIG. 5 and a limiter circuit as shown in FIG. 7 have been proposed to limit the amplitude of the input signal.

In FIG. 5, reference numeral 1 denotes an input terminal of a recording signal to which a signal to be recorded is supplied. The recording signal supplied to the input terminal 1 is supplied to a variable gain amplifying circuit 2 and the variable gain amplifying circuit 2 is supplied. The amplified recording signal obtained at the output side of the circuit 2 is supplied to the output terminal 3 for supplying the magnetic head. The output signal of the variable gain amplifier circuit 2 is supplied to a low-pass filter circuit 5 forming a smoothing circuit via a rectifier circuit 4 for detecting the level, and the output signal of the low-pass filter circuit 5 causes the variable gain amplifier circuit 2 to output Control the gain.

In the example shown in FIG. 5, when the input signal is at a low level, the gain of the variable gain amplifier circuit 2 increases in accordance with the small level of the input signal, and when the input signal is at a high level, the variable gain amplification circuit 2 is operated. The circuit 2 operates so that the gain of the circuit 2 decreases according to the level of the input signal level and the level of the output signal becomes constant.

In the example shown in FIG. 7, the recording signal supplied to the input terminal 1 is supplied to the output terminal 3 via the limiter circuit 6. The limiter circuit 6 has a variable resistor 6a for setting the limit level. The limit level is set to a predetermined level by and a signal limited to a predetermined level or lower is supplied to the output terminal 3.

[0007]

However, in the automatic gain control circuit shown in FIG. 5, when a signal changing from a small level to a large level as shown in FIG. 6A is supplied to the input terminal 1, its output signal As shown in FIG. 6B, since the level gradually becomes a constant level from a large level due to the time constant of this automatic gain control circuit, there is a disadvantage that effective amplitude limitation is not performed.

Further, the limiter circuit 6 shown in FIG.
8A is input, a signal whose amplitude is limited to a predetermined level as shown in FIG. 8B is obtained at the output terminal 3, but the signal component lost by the limiter circuit becomes a distortion. was there.

In view of the above point, the present invention is to follow an amplitude change from a small level signal to a large level signal without any time delay, and to perform amplitude limitation without distortion. To aim.

[0010]

The automatic gain control circuit according to the present invention includes a variable gain amplifier circuit 2 to which an input signal is supplied and an amplified signal is output, as shown in FIG. The slice circuit 7 for slicing the output signal at a predetermined level and the peak level holding circuit 8 for holding the peak level of the slice signal obtained at the output side of the slice circuit 7 are provided. Thus, the gain of the variable gain amplifier circuit 2 is controlled.

The automatic gain control circuit of the present invention is shown in FIG.
, A variable gain amplifier circuit 2 which is supplied with an input signal and outputs an amplified signal, and a frequency selection circuit 9 which selects the frequency of the output signal of the variable gain amplifier circuit 2,
It has a slice circuit 7 for slicing the output signal of the frequency selection circuit 9 at a predetermined level, and a peak level holding circuit 8 for holding the peak level of the slice signal obtained at the output side of the slice circuit 7. The output signal of the holding circuit 8 controls the gain of the variable gain amplifier circuit 2.

[0012]

According to the present invention, when the input signal is below the slice level of the slice circuit 7, the variable gain amplifying circuit 2 has a constant gain and operates as a fixed gain amplifying circuit, and the input signal is above this slice level. In this case, since the output signal of the peak level holding circuit 8 holding the peak level of this slice signal controls the gain of the variable gain amplifier circuit 2, the amplitude of the large-amplitude input signal can be limited. Since the peak level holding circuit 8 detects when the amplitude changes from the small level signal to the large level signal, it is possible to follow up without a time delay, and the gain of the variable gain amplifier circuit 2 is controlled to limit the signal amplitude. Therefore, the amplitude of the signal can be limited without causing distortion.

Further, according to the present invention, the signal whose frequency is selected by the frequency selecting circuit 9 is supplied to the slice circuit 7, and when the signal whose frequency is selected becomes equal to or higher than the slice level of this slice circuit 7, this slice Since the gain of the variable gain amplifier circuit 2 is controlled by the output signal of the peak level holding circuit 8 which holds the peak level of the signal, frequency selective amplitude limiting can be performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the automatic gain control circuit of the present invention will be described below with reference to the drawings. 1 and 3, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, the recording signal supplied to the input terminal 1 is supplied to the output terminal 3 via the variable gain amplifying circuit 2, and the output signal of the variable gain amplifying circuit 2 is connected to the level detecting circuit. It is supplied to the slicing circuit 7 via the rectifying circuit 4 that constitutes the rectifying circuit. The slice level S _L of the slice circuit 7 is a target value for amplitude limitation and is determined according to the recording dynamic range.

The slice signal obtained at the output side of the slice circuit 7 is supplied to the peak level holding circuit 8. As shown in FIG. 2D, the peak signal 8a of the peak level holding circuit 8 does not have a time delay because its rising is held at the peak, and its falling has a time constant determined by the hold capacitor C _H and the discharge resistor R _r . .. The peak signal 8a of the peak level holding circuit 8 is supplied to the inverting amplifier circuit 10, and the output signal of the inverting amplifier circuit 10 is supplied to the gain control terminal of the variable gain amplifier circuit 2 as the gain control signal 10a.

In this case, the variable gain amplifier circuit 2 is designed so that the gain is controlled according to the voltage supplied to the gain control terminal. Further, in this case, the bias voltage of the output signal of the inverting amplifier circuit 10 is set to a predetermined fixed voltage V _N, and the output signal of the variable gain amplifier circuit 2 is set to the above predetermined slice level S _L.
In the following cases, the gain of the variable gain amplifier circuit 2 is set to a constant gain determined by this fixed voltage V _N.

[0018] Since this embodiment is constructed as described above, when the recording signal 1a which becomes such a slice level S _L slice level S _L or more from the following shown in FIG. 2A is supplied to the input terminal 1 is of the rectifier circuit 4 On the output side, as shown in Fig. 2B,
A rectified signal 4a of the positive direction of the recording signal 1a is obtained, the rectified signal 4a is supplied to the slice circuit 7, and the slice level S of the rectified signal 4a as shown in FIG. A slice signal 7a of _L or more is obtained. In this case, the size of the slice signal 7a is determined by the size of the recording signal 1a. The slice signal 7a is supplied to the peak level holding circuit 8, a peak signal 8a as shown in FIG. 2D is obtained at the output side of the peak level holding circuit 8, and the peak signal 8a is supplied to the inverting amplifier circuit 10. A gain control signal 10a as shown in FIG. 2E is obtained at the output side of the inverting amplifier circuit 10.
The gain of the variable gain amplifier circuit 2 is controlled by a.

Therefore, the gain of the variable gain amplifier circuit 2 is a constant gain determined by the fixed voltage V _N when the recording signal 1a is below the slice level S _L , and when the recording signal 1a is above the slice level S _L. Is controlled so that the gain of the variable gain amplifying circuit 2 becomes smaller according to the value larger than the slice level S _L, and an output signal as shown in FIG. 2F is obtained at the output terminal 3, and the recording signal 1a is obtained. The large amplitude part of is amplitude limited.

In this case, when the amplitude of the recording signal 1a changes from the small level signal to the large level signal, this is detected by the peak level holding circuit 8, so that the peak level holding circuit 8 can follow the time signal without delay and the variable gain amplifying circuit 2 can follow. Since the gain is controlled to limit the amplitude of the signal, there is an advantage that the amplitude of the signal can be limited without causing distortion.

FIG. 3 shows another embodiment of the present invention. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. In this example of FIG. 3, a low-pass filter that passes a frequency of 200 Hz or less is inserted as a frequency selection circuit 9 between the variable gain amplifier circuit 2 of FIG. 1 and the rectifying circuit 4 for level detection.

Generally, the recording characteristics of a magnetic tape are saturated at a low level at a low frequency, and the level at which distortion is generated is low as compared with the frequency in the middle range. Therefore, it is necessary to limit the amplitude of this low frequency signal. This example of FIG. 3 is configured similarly to the example of FIG. 1 except for the above.

[0023] between the low frequency signal 1a ₁ and middle band signal 1a ₂ frequency is 1kHz to the input terminal 1 is the frequency as shown in FIG. 4A the slice level S _L or more from the following 100Hz slice level S _L in FIG. 3 When the recording signal 1a is supplied, only the low frequency signal 1a ₁ of this recording signal 1a is obtained at the output side of the frequency selecting circuit 9 as shown in FIG. 4B, and this low frequency signal 1a ₁ is a level detecting rectifier circuit. 4 is supplied. At the output side of the rectifier circuit 4, as shown in FIG. 4C, the rectified signal 4 of the positive direction signal of the low frequency signal 1a ₁
a is obtained, the rectified signal 4a is supplied to the slice circuit 7, and the output side of the slice circuit 7 is as shown in FIG.
A slice signal 7a having a slice level S _L or higher of the rectified signal 4a is obtained. In this case, the size of the slice signal 7a is determined by the size of the low frequency signal 1a ₁ .

The slice signal 7a is supplied to the peak level holding circuit 8, a peak signal 8a as shown in FIG. 4E is obtained at the output side of the peak level holding circuit 8, and the peak signal 8a is supplied to the inverting amplifier circuit 10. Then, the gain control signal 10a as shown in FIG. 4F is obtained at the output side of the inverting amplifier circuit 10, and the gain of the variable gain amplifier circuit 2 is controlled by the gain control signal 10a.

Therefore, the gain of the variable gain amplifier circuit 2 is low.
Frequency signal 1a₁Is the slice level S _LWhen and when
Area signal 1a₂When, the fixed voltage V_NConstant gain determined by
And this low frequency signal 1a₁Is the slice level S_LSince
When it is above, the gain of this variable gain amplifier circuit 2 is
Slice level S_LSmaller according to the greater value
The output terminal 3 is controlled as shown in FIG. 4G.
Low frequency signal 1a of recording signal 1a₁The large amplitude part of
A signal whose width is limited is obtained.

In this case, when the amplitude of the low frequency signal 1a ₁ changes from the small level signal to the large level signal, this is detected by the peak level holding circuit 8, so that it can be followed without a time delay and the variable gain amplifier circuit can be followed. Since the gain of 2 is controlled to limit the amplitude of the signal, there is an advantage that the amplitude of the signal can be limited without causing distortion.

In the above embodiment, the frequency selection circuit 9 uses the low pass filter, but a band pass filter, a high pass filter or the like may be used if necessary. Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0028]

According to the present invention, when the amplitude of the input signal changes from the small level signal to the large level signal, this is detected by the peak level holding circuit 8. Therefore, the peak level holding circuit 8 can follow the variable without delay and change the level. Since the gain of the gain amplification circuit 2 is controlled to limit the amplitude of the signal, there is an advantage that the amplitude of the signal can be limited without causing distortion.
Further, according to the present invention, there is a practical effect that the frequency selective type amplitude limitation can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an automatic gain control circuit of the present invention.

FIG. 2 is a diagram used to explain FIG.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a diagram used for explaining FIG.

FIG. 5 is a configuration diagram showing an example of a conventional automatic gain control circuit.

6 is a diagram used to explain FIG. 5. FIG.

FIG. 7 is a configuration diagram showing an example of a limiter circuit.

8 is a diagram used to explain FIG. 7. FIG.

[Explanation of symbols]

 1 Input Terminal 2 Variable Gain Amplifier Circuit 3 Output Terminal 4 Rectifier Circuit 7 Slice Circuit 8 Peak Holding Circuit 9 Frequency Selection Circuit

Claims (2)

[Claims] 1. A variable gain amplifier circuit to which an input signal is supplied and which outputs an amplified signal, a slice circuit which slices the output signal of the variable gain amplifier circuit at a predetermined level, and an output side of the slice circuit. And a peak level holding circuit for holding the peak level of the obtained slice signal, wherein the gain of the variable gain amplifier circuit is controlled by the output signal of the peak level holding circuit. .. 2. A variable gain amplifier circuit to which an input signal is supplied and which outputs an amplified signal, a frequency selection circuit for selecting the frequency of the output signal of the variable gain amplifier circuit, and an output signal of the frequency selection circuit. And a peak level holding circuit for holding the peak level of the slice signal obtained at the output side of the slice circuit, and the variable gain amplifier circuit according to the output signal of the peak level holding circuit. An automatic gain control circuit characterized in that the gain of the control circuit is controlled.