JPS5842961B2 - Automatic gain control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, good automatic gain control is performed on signal components in a predetermined frequency band, the transfer function of the automatic gain control system is set to 1 when no control is performed, and The purpose of this invention is to provide an automatic gain control system with a simpler configuration than conventional automatic gain control systems.

2. Description of the Related Art Automatic gain control systems in which automatic gain control is performed on signal components in a specific frequency band in a signal are widely known in the art, for example, in noise reduction circuits and other various devices.

FIGS. 1 and 3 are block diagrams showing configuration examples of conventional automatic gain control systems in various fields, respectively.

First, in the conventional automatic gain control method shown in FIG.
1 is a signal input terminal, 29 is an output terminal, and the input signal applied to input terminal 1 is sent out as an output signal from output terminal 29 via buffer amplifier 2, variable attenuation network VN, and buffer amplifier 20. Ru.

In the figure, the variable attenuation network VN described above has a resistor 3 and a coil 4.
, 7, capacitors 5, 8, control element 6°9, resistor 10.
a variable attenuation network portion for signal components in a specific frequency band with fl as the center frequency of the band, and
f consisting of resistor 3, coil 12゜15, capacitor 13.16, control element 14.17, resistor 18.19, etc.
Although only variable attenuation network parts are shown for signal components in a specific frequency band where n is the center frequency of the band, many variable attenuation network parts for signal components in many frequency bands having various center frequencies may be added as necessary. A net portion is provided.

Further, SG is a control signal generator, and this control signal generator SG is capable of individually supplying control signals to each variable attenuation network portion of the variable attenuation network VN described above. A control signal generation circuit is provided, and in the illustration, a bandpass filter 21 and an amplifier 22 are provided.
, a control signal generation circuit composed of a double-wave rectifier circuit 23, an integrating circuit 24, etc., a bandpass filter 25, an amplifier 26, a double-wave rectifier circuit 27 . A control signal generation circuit configured with an integrating circuit 28 and the like is illustrated.

This control signal generator SG extracts signals in frequency bands corresponding to the frequency bands to be attenuated in each variable attenuation network portion of the variable attenuation network Vl'am from the output signal using bandpass filters 21 and 25. Then, it is amplified by amplifiers 22 and 26, and then passed through the double wave rectifier circuit 23.
．． Rectifying at 27 and integrating at integrator circuits 24 and 28 generates a control signal corresponding to the envelope of the output signal to control element 6 in each corresponding variable attenuation network section.
, 9 (14, 17) to resistance 10.11 (18, 19)
It is given through.

In the conventional automatic gain control system shown in FIG. 1, the variable attenuation network VN includes coils 4, 7, .
. . . and control elements 6, 9 . . . and the control elements 6, 9, .・・・
By changing the internal resistance (channel resistance) of the channel, the amount of attenuation of the signal component in a predetermined frequency band can be changed. As shown in the curve diagram shown in Figure 2, there is a problem in that the frequency response characteristics change widely depending on the control, and the frequency response characteristics are not uniform within the band. In some cases, the large number of coils in series resonant circuits required for this purpose increases the size of the device, and
In addition to the disadvantage of being expensive, in order to achieve control with a flat frequency response characteristic over a wide frequency band, many coils and capacitors are used in series resonant circuits. This method has a disadvantage in that it requires an extremely troublesome adjustment process in which variations in the resonance sharpness Q of each series resonant circuit due to variations in the loss resistance of the series resonant circuits must be adjusted.

On the other hand, in the conventional automatic gain control system shown in FIG.
.about.33 into n frequency band signals, and then automatically gain-controlled each of the above-mentioned signals by automatic gain control circuits 34-36 provided separately,
The output signals from each of the automatic gain control circuits 34 to 36 described above are mixed by a mixing circuit made up of mixing resistors 31 to 39, and the mixture is sent to the output terminal 40 as an output signal. In the automatic gain control system shown in FIG. 3, since the frequency band to be controlled is divided into n parts by n bandpass filters 31 to 33, each adjacent bandpass filter has (n-1) Therefore, even in low signal level conditions where no gain control is performed, the transfer function between the output terminals 30 and 40 does not become 1, and high fidelity is achieved. The drawback was that it could not transmit signals.

The present invention aims to provide an automatic gain control method that does not have the drawbacks of the conventional automatic gain control methods as described above, and the specific contents thereof will be clarified below with reference to the accompanying drawings. .

FIG. 4 is a block diagram of an embodiment of the automatic gain control system of the present invention. In FIG. 4, 41 is a signal input terminal, 42 is an output terminal, and VA is a signal input terminal for signals in a specific frequency band. The variable attenuator (hereinafter referred to as variable attenuator) and C8G are control signal generators.

The signal supplied to input terminal 41 is applied to variable attenuator VA and control signal generator C8G, and variable attenuator VA
Then, gain control is performed on signal components in a specific frequency band according to the control signal given from the control signal generator C8G, and an output signal is sent to the output terminal 42.

In the automatic gain control system of the present invention shown in FIG. 4, the variable attenuator VA is a subtracter SUB and an amplifier AMP.

First bandpass filter BPF1, gain constant circuit GC, second bandpass filter BPF2, adder ADD, variable gain circuit V
It is composed of a control signal generator C8G, and a control signal generator C8G.
is a bandpass filter BPF, a double-wave rectifier circuit WR1, an integrator circuit I
It consists of a setting circuit SC for the TC1 operation start signal level, etc.

In the variable attenuator VA, the first bandpass filter BPF1 is a first-order high-pass filter H whose cutoff frequency value is fh.
PF1 and the cutoff frequency value is fe (however, the frequency value f4
is a frequency value that satisfies the relationship fb<fl with the frequency value fh described above). and its passband width is between the cutoff frequency fl in the first-order low-pass filter LPF1 and the cutoff frequency fh in the first-order high-pass filter HPF1,
Further, it exhibits a passband characteristic in which the slope of the frequency response characteristic curve from the passband to the cutoff band is 6 dB per octave.

The second bandpass filter BPF2 described above is a second-order high-pass filter HP whose cutoff frequency value is fh.
F2 and a second-order low-pass filter LPF2 whose cut-off frequency value is the above-mentioned fl are connected in series, and whose pass band width is the above-mentioned second-order low-pass filter. It is between the cutoff frequency fl in LPF2 and the cutoff frequency fh in the second-order high-pass filter HPF2, and the slope of the frequency response characteristic curve from the passband to the cutoff band is 12 dB per octave. This shows the passband characteristics.

In the above description, the cut-off frequency value of each low-pass filter is expressed as fl, and the cut-off frequency value of each high-pass filter is expressed as f.
h, and these frequency values fl.

fl> may be standardized so that the center frequency of the passband of the bandpass filter is 1, and the frequency value U mentioned above may be expressed by n1fh in Akira. The values fl and fh may be expressed as scaled frequency values n and Vn, respectively.

The first and second bandpass filters BPF1. The output signal from the subtracter SUB is applied to BPF2 via the amplifier AMP, and the output signal from the first bandpass filter BPF1 is set to an appropriate signal level in the gain constant circuit GC. Later, it is added as one input signal to adder ADD.

Further, the output signal from the second bandpass filter BPF2 described above is added to the adder ADD as the other input signal.

The output signal from the adder ADD described above is applied to the subtracter SUB as its subtracted signal via the variable gain circuit VG.

FIG. 5 is a block diagram used to explain the principle of construction and operation of the variable attenuator VA described above.
In each block of the illustrated block diagram, characteristics of each block are illustrated.

In the block diagram shown in FIG. 5, the amplifier AMP has a gain of 1, the gain constant circuit GC has a gain constant of 1, and the variable gain circuit VG has a gain of 1. Furthermore, the first bandpass filter BPF1 has cutoff frequency values above and below the normalized frequency values n, -! - When expressed as -, the transfer characteristic H1 is Hl-=
The next high-pass filter HPF1, denoted by L, and the transmission 1-characteristic u or H2
The first-order low-pass filter S+nLPFl as shown by = is connected in series, and the second bandpass filter BPF2 has a transfer characteristic H3 of 2H3=82+2ζ.

+± (However, ζ is damping n2 A second-order high-pass filter HPF22 as shown by and・transfer characteristic n7”・”−8”+2ζ.

8+.・Second-order low-pass filter LPF2 as shown in 7.
are connected in series, and therefore,
The transfer function G(S) between the output terminals 41 and 42 of the variable attenuator VA is expressed by the following equation (1).

G(S)=□+2(K1.Ho-H2-1-H3-H
4) """(") FIG. 6 is a characteristic curve diagram showing an example of the frequency-amplitude characteristic of the transfer function G(S) as shown by the above equation (1). For example, the frequency response characteristic curve group of the second-order high-pass filters HPF2 and 2 constituting the second bandpass filter BPF2 is
The damping coefficient ζ in the next low-pass filter LPF2 is set to 0.4, the gain constant set in the gain constant circuit GC is set to 1 to 0.7, and the first and second bandpass filters BPF1. B
If the cutoff frequency n is standardized so that the center frequency of the passband in PF2 is 1, and Akira is a station, then the gain constant in the variable gain circuit VG is 2.
This is an example of a group of characteristic curves obtained while varying the .

As can be seen from the characteristic curve group shown in FIG. 6, the variable attenuator VA shown in FIGS. 4 and 5 is connected to the first and second bandpass filters BPF1. Low pass filters LPF1., respectively used in BPF2. The cutoff frequency n of LPF,
High-pass filter HPF1. The gain constant of the variable gain circuit VG is shifted in parallel in the vertical direction according to the magnitude of 2, while the frequency range between the cutoff frequency of the HPF2 remains flat.

In the variable attenuator VA described above, the frequency band in which the amount of attenuation is made variable while remaining in a flat state is defined by the first and second bandpass filters BPF1. Each high-pass filter HPF1. used in the configuration of BPF2. Cutoff frequency % in HPF2 and each low pass filter LPF1. The shape X of the frequency response characteristic curve of the attenuation characteristic near the cut-off frequency and n is determined by the cutoff frequency n of the second bandpass filter BPF2.
The damping coefficient in the low-pass filter LPF2 and high-pass filter HPF2 used in the configuration is determined by this value, and furthermore, the attenuation characteristic near the boundary between the frequency band where the amount of attenuation is variable and the frequency band where it is not attenuated. The shape Y of the frequency response characteristic curve of the gain constant circuit G
It is determined by the value of 1 for the gain constant set in C.

FIG. 7 is a block circuit diagram showing a specific circuit example of the variable attenuator VA described above, in which each block in FIG. 1 is replaced by each block in FIGS. Blocks corresponding to 1 and 2 are given the same drawing numerals as those used in FIGS. 4 and 5 to clarify their mutual correspondence.

In the block circuit diagram shown in FIG. 1, the circuit SUB, AMP consisting of the amplifier 44 and the resistor 49.50 corresponds to the attenuator SUB block and the amplifier A in FIGS. 4 and 5.
A negative feedback amplifier configured to have the functions of both the MP block and the MP block, the output signal of which is
An output terminal 42 and first and second bandpass filters BPF1. B
PF2.

The first bandpass filter BPF1 includes a first-order high-pass filter HPF1 consisting of a buffer amplifier 45, a capacitor 64, and a resistor 51, and a first-order low-pass filter consisting of a buffer amplifier 64, a resistor 52, and a capacitor 65. LP
F1, and the second bandpass filter BPF2 includes a buffer amplifier 4γ and resistors 53 and 54.
and a second-order high-pass filter HPF2 consisting of a capacitor 60.66, a buffer amplifier 48, and a resistor 55°5.
6 and a second-order low-pass filter LPF2 consisting of capacitors 62 and 63.

Further, the circuits ADD and GC consisting of the inverting amplifier 61 and the resistors 51 to 59 are the adder A in FIGS. 4 and 5.
This circuit is configured to have the functions of both the DD block and the gain constant circuit GC block.

Furthermore, the variable gain circuit VG consisting of a multiplier is configured so that the gain constant in equation (1) described above is changed by 2 in response to a control signal supplied to the control signal input terminal 43.

The first and second bandpass filters BPF1 . Since the BPF 2 does not use a coil in its configuration, it will be readily understood that a variable attenuator VA with less variation in characteristics can be easily obtained with such a configuration.

As is clear from the above explanation, in the variable attenuator VA in FIG. Subtractor SUB as signal
The circuit arrangement with frequency selection characteristics provided in the negative feedback path means that it has a frequency of 12 per octave.
a second bandpass filter BPF2 exhibiting a cutoff characteristic with a slope of dB;
and a first bandpass filter BPF1 exhibiting a cutoff characteristic with a slope of 6 dB per octave are provided in parallel, so that the amount of attenuation for signal components in a predetermined frequency range can be controlled. It can be stably controlled according to the control code supplied from the signal generator C8G.

Now, the control signal generator C8G in the block diagram shown in FIG.
As described above, the bandpass filter BPF has a characteristic that allows a signal in a frequency band corresponding to the frequency band to be attenuated in the variable attenuator VA to pass through, and the bandpass filter BPF described above. It consists of a double-wave rectifier circuit WR that double-wave rectifies the output signal, an integrating circuit ITC that integrates (smoothes) the output signal from the double-wave rectifier circuit WR, and a circuit SC that sets the operation start signal level. This control signal generator C8G generates a signal obtained by rectifying and filtering a signal component in a specific frequency band extracted by a bandpass filter BPF from the input signal supplied to it using a double-wave rectifier circuit WR, an integrating circuit ITC, etc. When the signal level becomes equal to or higher than the signal level set by the operation start signal level setting circuit SC, it is supplied as a control signal to the control signal input terminal 43 of the variable attenuator VA.

Now, if the variable attenuator VA has a configuration as shown in FIG. S in equation (1) can be determined as jω, but since the central angular frequency is ω-1 as described above, the absolute value of the gain at central angular frequency 1 is equal to S in equation (1). can be determined by setting j to be expressed by the following equation (2).

The value in the parentheses of the second term in the denominator on the right side of equation (2) above is a constant, and the control signal voltage given to the variable gain circuit VG is Vc, and the gain constant in the variable gain circuit VG is 2 and the control signal voltage Vc. The relationship between 2 oCV
Since it is expressed as c, the above two equations can be transformed into the following (
3) It is expressed as the formula.

Therefore, the input signal voltage is ei, and the output signal voltage is e.

Then, the relationship between the person and the output signal voltages ei and eo is expressed by the following equation (4).

Now, the output signal voltage e.

is a constant value eth in the region of ei≧eth, then the relationship between the input signal voltage ei and eth is as follows (5)
It is shown by the formula.

Therefore, from equation (5), the control signal voltage Vc is as follows (6
) can be calculated as follows.

Therefore, in the control signal generator C8G in FIG. 4, if the conversion efficiency of the bandpass filter BPF, the double-wave rectifier circuit WR, the integrator circuit ITC, etc. is 1, then the operation start signal level setting circuit The SC may be configured to generate the control signal voltage VC as shown in equation (6).

Note that the threshold voltage eth is the variable gain circuit VG.
This is the set voltage at which the multiplier that constitutes enters the operating state.

FIG. 8 is an example of a frequency response/input characteristic curve of an embodiment of the automatic gain control system of the present invention. Curve 2 in the figure indicates that the control signal from the control signal generator C8G is applied to the variable attenuator VA. If it is not given, that is, the signal level of the signal component in a specific frequency band (in the example shown, the frequency band with n-th frequency value) in the input signal is low, and the signal from the integrating circuit ITC in the control signal generator C8G is shows the transfer characteristics between the output terminals 41 and 42 when the output voltage does not reach the threshold voltage set by the operation start signal level setting circuit SC. When the control signal generated based on the signal component of the band exactly reaches the threshold voltage, output terminal 4
1.42, and curves (1) to (V) show examples of curves when the output signal level of a specific frequency band is made constant by a control signal.

In the curve in FIG. 8, the slope of the portion indicated by α and β in the figure is the slope of the second bandpass filter BPF in the variable attenuator VA.
Low-pass filter LPF2 and high-pass filter HPF2 that constitute 2
By choosing the damping coefficients ζ equally at and,
It will be clear from the above that it is possible to make them equal during automatic gain control operation.

Further, according to the automatic gain control method of the present invention, good gain control is performed in a specific frequency band (in the illustrated example, a frequency band with a frequency value of n to %). It is clear that the problems encountered in the prior art system described above do not exist.

In the automatic gain control system according to the embodiment of the present invention shown in FIG. , due to the presence of various factors, the gain control operation is performed with a certain time delay with respect to the input signal, since the time of application of the input signal is delayed.

The block diagram shown in FIG. 9 is a block diagram of an example of an embodiment of the automatic gain control method of the present invention that can solve the above-mentioned problems in the embodiment of the automatic gain control method of the present invention shown in FIG. 9, VA is a variable attenuator, C8G is a control signal generator, and DL is a delay circuit.

The variable attenuator VA and control signal generator C8G in FIG. 9 are replaced by the variable attenuator V shown in the block diagram shown in FIG.
A, the control signal generator C8G, etc. may have a similar configuration.

Further, the delay circuit DL provided between the input terminal 41 and the variable attenuator VA transmits the control signal generated by the control signal generator C8G based on the input signal supplied to the input terminal 41 to the variable attenuator VA. A delay circuit having a delay time such that an input signal is applied to the variable attenuator VA at the time when it is applied to the control signal input terminal 43 of the variable gain circuit VG in VA, and is configured as shown in FIG. In the automatic gain control system of the present invention, the problems in the automatic gain control system shown in the block diagram of FIG. 4 described above can be satisfactorily solved.

Next, FIGS. 10 and 11 show that by using a plurality of variable attenuators VA and control signal generators C8G in the block diagram shown in FIG. 4 and the block diagram shown in FIG. 10 and 11, VAl, VA2...VAn are ,
Each center frequency f1. A variable attenuator configured to vary the amount of attenuation of a signal in a frequency band (see FIG. 12) having f2...fn, and
C8G1. C8G2...C3Grl are each variable attenuator ■A1. ■A2...A control signal generator configured to be able to individually supply required control signals to each VAn, and furthermore, D in FIG. 11.
L is a delay circuit similar to the delay circuit DL described with reference to FIG.

10 and 11, the plurality of variable attenuators VA1. VA, 2...VAn are connected in cascade to the signal transmission path, and a plurality of control signal generators C8G1... Since input signals are applied to C8G2...C3Gn, each variable attenuator VA, 1■A2...
・Control signal generator C8 attached to VAn individually
G1. By performing individual control using control signals from C8G2...C3Gr1, it is possible to uniformly control the entire band, or to perform different control for each individual band.

As is clear from the above detailed explanation, the automatic gain control method of the present invention does not require the use of expensive coils that are required in the configuration of the conventional band control type automatic gain control method. In addition, since no coil is used, a large space is not required, making it possible to provide a compact and inexpensive device.Furthermore, it is easy to adjust and achieve stable control, and settings within the control band are also easy.
In addition, the frequency response and characteristics during gain control are good, and even when no control is performed, the transfer function between the person and the output terminal is 1, that is, a flat frequency response characteristic and a transmission characteristic without phase rotation are easily achieved. In addition, it is possible to provide an automatic gain control method with excellent characteristics such as the following: In addition, the time delay of the control signal generated in the control signal generator is provided in the path of the input signal to the variable attenuator. By performing compensation using a delay circuit, it was possible to provide an automatic gain control system that performs control without time delay.

[Brief explanation of drawings]

Figures 1 and 3 are block diagrams of conventional automatic gain control systems, Figure 2 is an example of frequency response characteristic curves for the automatic gain control system shown in Figure 1, and Figures 4 and 9 to 11 are A block diagram of an embodiment of the automatic gain control system of the present invention, FIG. 5 is a block diagram of a variable attenuator, FIG. 6 is an example of a frequency response characteristic curve of the variable attenuator, and FIG. 1 is a variable attenuation diagram. The block circuit diagram of the device, FIG. 8 and FIG. 12 are examples of frequency response characteristic curves of the automatic gain control system of the present invention. 1.41...Input terminal, 29,42...
・Output terminal, VN...Variable attenuation network, SG...
...Control signal generator, VA...Variable attenuator, C8G...Control signal generator, SUB...
...Subtractor, AMP...Amplifier, BPFl...
...First bandpass filter, BPF2...Second
bandpass filter, GC...gain constant circuit, ADD
... Adder, VG ... Variable gain circuit,
DL...Delay circuit, BPF...Band filter, WR...Double wave rectifier circuit, ITC...
...Integrator circuit, SC... Operation start signal level setting circuit.

Claims (1)

[Scope of Claims] 1. Means for supplying a human input signal to a subtractor as a minuend signal, a means for supplying an output signal from the subtractor to an output terminal, and a means for supplying the output signal from the subtractor to a frequency value fl, fb is fl >fb, and a first bandpass filter consisting of a first-order low-pass filter with a cut-off frequency fd and a first-order high-pass filter with a cut-off frequency fh, and a first-order high-pass filter with a cutoff frequency fh.
means for providing a second bandpass filter consisting of a second-order low-pass filter of d and a second-order high-pass filter of cutoff frequency fh;
Means for providing the output signal of the first bandpass filter as one input signal of the adder via the gain constant circuit, and means for providing the output signal of the second bandpass filter as the other input signal of the adder. means for applying the output signal of the adder to the variable gain circuit; and means for applying the output signal of the variable gain circuit to the subtracter as a subtraction signal; A variable attenuator that can vary the amount of attenuation of a signal in a frequency band, and a signal in a frequency band to be attenuated in the variable attenuator is extracted from the input signal applied to the variable attenuator. means for double wave rectifying said extracted signal; means for providing an output signal from said double wave rectifying means to an integrating circuit; and a predetermined signal level in the output signal from said integrating circuit. and a control signal generator comprising means for extracting the above signal and using it as a control signal, and controlling the gain of the variable gain circuit in the variable attenuator by the control signal from the control signal generator. automatic gain control method. 2. A plurality of variable attenuators each configured to be able to individually vary the amount of attenuation of the signal in each frequency band for signals in different specific frequency bands are connected in cascade, and each of the different plurality of variable attenuators For each variable gain circuit in the variable attenuator, an individual signal is generated from a signal in a frequency band corresponding to the frequency band to be attenuated in each variable attenuator in which each variable gain circuit is provided. 2. The automatic gain control system according to claim 1, wherein the control signal is provided from a separate control signal generator. 3 Means for supplying the human input signal to the subtractor as a minuend signal, supplying the output signal from the subtractor to the output terminal, and transmitting the output signal from the subtractor to the frequency value f71! ,
If fh is in the relationship fd>fh, then the cutoff frequency is fl
a first-order low-pass filter with a cut-off frequency of fh, and a second-order low-pass filter with a cut-off frequency of fl and a first-order high-pass filter with a cut-off frequency of fh. and means for providing the output signal of the first bandpass filter as one input signal of the adder via a gain constant circuit. and means for supplying the output signal of the second bandpass filter as the other input signal of the adder; means for supplying the output signal of the adder to the variable gain circuit; and the output of the variable gain circuit. a variable attenuator that is capable of varying the amount of attenuation of a signal in a specific frequency band in an input signal; means for extracting a signal in a frequency band targeted for attenuation; means for double-wave rectification of the extracted signal; means for providing an output signal from the double-wave rectification means to an integrating circuit; A control signal generator comprising a means for extracting a signal of a predetermined signal level or higher from the output signal from the integrating circuit and using it as a control signal, and an input signal applied to the variable attenuator described above, A variable gain circuit in the variable attenuator includes a delay circuit configured to provide a time delay corresponding to the time delay occurring between the input signal to the control signal generator and the output control signal in the control signal generator. An automatic gain control method in which the gain is controlled by a control signal from the control signal generator described above. 4. Having a predetermined delay time for a plurality of cascaded variable attenuators, each of which is configured to be able to individually vary the amount of attenuation of the signal in each of the different specific frequency bands. An input signal is applied through a delay circuit, and attenuation is applied to each variable attenuator in each of the plurality of variable attenuators of various fields described above, in which each variable attenuator is provided with the variable gain circuit. 4. The automatic gain control system according to claim 3, wherein individual control signals generated from signals in frequency bands corresponding to the target frequency band are provided from individual control signal generators.