JPH09266422A - Automatic gain control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily and smoothly converge the level of an input signal on a target level. SOLUTION: This circuit is equipped with a gain control amplifier 11 which adjusts the level of an input signal, gain control means 13, 14, 15, 18, and 19 which control the gain of this amplifier 11, and a coefficient control circuit 20 which applies a variable coefficient to the gain control means to adjust follow-up characteristics as to the level variation of the input signal. As the coefficient, an initial value β(1) with fastest follow-up characteristics corresponding to a rise time and a convergence value β(n) with high stability corresponding to ordinary reception are set, and this coefficient is monotonously varied from the initial value β(1) and converted on the convergence value β(n) a certain time later. An operation time τ(i) is made longer and the coefficient value β(i) smaller with time. Consequently, the level of the input signal is made to speedily follow up the target level in the beginning and then converged gently and smoothly thereafter.

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 for automatically maintaining the level of a received signal in an optimum state.

[0002]

2. Description of the Related Art In a receiver for digital signal processing,
An automatic gain control circuit is used to keep the received signal level optimal. Especially, in the terminal of digital mobile communication, the dynamic range of the average received power is 70 dB.
In addition to the above, instantaneous level fluctuation due to fading is added to this, and therefore control of the received signal level by the automatic gain control circuit is important.

As a conventional automatic gain control circuit, one having a structure as shown in FIG. 2 is known. In the figure, an analog reception signal r (t) is first amplified by a gain control amplifier 1 and then converted into a digital reception signal r (n) by an AD converter 2. Here, n indicates the sampling time. The r (n) is directly input to the demodulation processing unit (not shown) and also input to the average power calculation unit 3. After the average power Ld (n) of the received signal r (n) is calculated in the average power calculation unit 3, the error power Δ with the target power Lr is calculated in the subtractor 4.
L is calculated. The error power ΔL is multiplied by a coefficient β described later in the multiplier 5, and integrated by the integrator including the adder 6 and the register 7. The output M (n) of this integrator is converted into a voltage in the DA converter 8 and output as the control voltage V _AGC of the gain control amplifier 1.

This automatic gain control circuit constitutes a feedback system, and the operation time constant of the loop is determined by the value of the coefficient β. That is, if the coefficient β is large, the time constant becomes small and the followability to the level fluctuation of the received signal is improved, and as a result, the control value vibrates and becomes unstable. On the other hand, if the coefficient β is small, the time constant becomes large, the followability to the level fluctuation of the received signal deteriorates, and the coefficient becomes stable. In this way, there is a trade-off relationship between the tracking performance and stability of the control loop. When prioritizing the tracking performance, such as when starting up a communication terminal, increase the value of coefficient β, and during normal reception operation When the priority is given to stability as described above, the value of the coefficient β is reduced. Set this coefficient β to a predetermined value,
The control is performed using the value.

[0005]

However, in the above-mentioned conventional automatic gain control circuit, when the communication terminal is started up and the control of the automatic gain control circuit is started, the reception level is affected by the fading or the like as described above. May fluctuate significantly. In this case, if the value of the coefficient β is set to a large value, the control value may vibrate and may not converge to an appropriate value. On the contrary, if the value of the coefficient β is set small, it is possible to avoid unnecessary reaction to the level fluctuation due to fading, but there is a problem that the convergence is delayed.

[0006]

In order to solve the above-mentioned problems, a first aspect of the present invention relates to a variable gain amplifying means for adjusting the level of an input signal, a gain control means for controlling the gain of the amplifying means, and The gain control means is provided with a coefficient control means for adjusting the followability with respect to the level fluctuation of the input signal by adding a variable coefficient to the gain control means. A highly stable convergence value corresponding to reception is set, and this coefficient is controlled so as to monotonically change from the initial value as time elapses from the start-up and converge to the convergence value after a lapse of a certain time. It is characterized by

By using the coefficient of the initial value at the time of start-up, the time constant becomes small, and the level of the input signal is quickly tracked to near the target level. After that, as the time from the start-up progresses, the coefficient is brought closer to the convergence value, the time constant is gradually increased, and the level of the input signal is converged to the target level.

A second aspect of the invention is characterized in that a plurality of values that are monotonically changed are used as the coefficient, and the operation time at each coefficient value is increased as the time from the start-up progresses.

As described above, by increasing the time for operating each coefficient value as the time from the start-up increases, the coefficient value changes from the initial value rapidly at the beginning and gradually thereafter. It converges to the convergence value. Thereby, the level of the input signal quickly follows the target level at the time of start-up, and then smoothly converges to the target level as the coefficient value converges to the convergent value.

In the third aspect of the invention, coefficient control is performed to reduce the amount of change in the coefficient as time elapses from the start-up, and the amount of change in time at which each coefficient value operates as the time elapses from the start-up. It is characterized in that one or both of the time control for increasing the time is performed.

As described above, as the time from the start-up progresses, the amount of change in the coefficient is gradually decreased so as to be, for example, half of the coefficient immediately before, and the time for operating at each coefficient value is changed to, for example, immediately before. The coefficient value can be converged more quickly and smoothly from the initial value to the converged value by gradually increasing the value so as to be twice the time. As a result, the level of the input signal follows the target level more quickly and converges smoothly.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. 1 is a block diagram showing a configuration of an automatic gain control circuit according to the present invention, FIG. 3 is a block diagram showing a coefficient control circuit, and FIG. 4 is a graph showing a control pattern of a coefficient value and an operation time in the coefficient control circuit. .

The overall configuration of the automatic gain control circuit according to this embodiment is almost the same as that of the conventional automatic gain control circuit.
Specifically, as shown in FIG. 1, a gain control amplifier 11 as a gain varying amplifier that adjusts the level of a reception signal that fluctuates irregularly to a constant value, and an analog signal output from the gain control amplifier 11. Is converted into a digital signal, an average power calculator 13 that calculates the average value of the power of the output signal from the AD converter 12, an average power calculated by the average power calculator 13, and preset The subtracter 14 that calculates the error power ΔL from the target power Lr by taking the difference from the calculated target power, the error power ΔL calculated by the subtractor 14, and the coefficient β (i from the coefficient control circuit 20 described later. ) And a multiplier 15, an integrator 18 including an adder 16 and a register 17, which integrates an output value ΔM (n) from the multiplier 15, and a digital output value M (n) from the integrator 18. Analog And a DA converter 19 for converting the signal into a signal of. The output signal from the DA converter 19 is output to the gain control amplifier 11 as a gain control voltage V _AGC for controlling the gain control amplifier 11. Then, the average power calculation unit 13, the subtractor 14, the multiplier 1
5, the DA converter 18 and the DA converter 19 constitute a gain control means for controlling the gain of the gain control amplifier 11.

The coefficient β (i) multiplied by the error power ΔL from the subtractor 14 in the multiplier 15 is the coefficient control circuit 2
Output from 0. The coefficient β (i) is added to the gain control means to change the time constant of the gain control means to adjust the followability to the level fluctuation of the input signal. As shown in FIG. 3, the coefficient control circuit 20 mainly includes a timer 21, an address generator 22, and a coefficient memory 23.

The timer 21 is reset by the start-up of the communication terminal, starts counting, and outputs a count signal to the address generator 22.

The address generator 22 has an operating time τ (1)
To τ (n) are stored. This operating time τ (i)
(I = 1, 2, ..., N) is a coefficient β (i) (i corresponds to τ (i) above) corresponding to each of them,
= 1, 2, ..., N) is set to output to the multiplier 15.

The operating times τ (1) to τ (n) can be set arbitrarily, and τ (j-1) <τ (
j) (j = 2, 3, ..., N) is set so that the relationship holds. That is, as the coefficient β (i) becomes smaller, the operation time τ (i) operating at that value is set to monotonically increase. Specifically, as shown in the time axis of FIG. 4, t ₁ , t
₂ , ..., 0 to t ₁ is τ (1), t ₁ to t
_The amount of change in time {τ (2
j) −τ (j−1)} is set to be gradually increased. In addition, in FIG. 4, almost {τ (j) = 2τ (j-1)}
Are set to hold. This allows
When the communication terminal is started up, the coefficient β (i) switches at short intervals and then at longer intervals, resulting in the final convergence value β
It gradually converges to (n). Note that n
Is an arbitrary numerical value, and a small numerical value is used for rough control, and a large numerical value is used for fine control.

The coefficient memory 23 has a preset coefficient β.
(i) (i = 1, 2, ..., N) is stored. The coefficient β (i) is output to the multiplier 15 only during the corresponding operation time τ (i). That is, only during the operation time τ (i), the address generator 22 moves to the coefficient memory 2
According to the control signal output to 3, the coefficient β (i) corresponding to the operating time τ (i) stored in the coefficient memory 23 is output to the multiplier 15 only during the operating time τ (i). It has become.

The value of the coefficient β (i) is set so that the initial value β (1) at the start-up of the communication terminal is set large and gradually decreased so as to monotonically decrease. That is, β (
j−1)> β (j) (j = 2, 3, ..., N). Further, the amount of decrease of this coefficient {β (j-1) -β (j)} is set to be gradually smaller. In addition, in FIG. 4, almost {2/3 · β (
It is set so that the relationship of (j-1) = β (j)} is established. As a result, the coefficient β (i) changes greatly immediately after the terminal starts up, together with the setting of the operating time τ (i),
That is, at the beginning, the coefficient β (i) sharply decreases, and thereafter, the amount of decrease gradually becomes small, and the time becomes short, so that the final convergence value β (n) slowly approaches. Here, the initial value β (1) is set to a sufficiently large value so that it can optimally follow a large fluctuation in the reception level, that is, the followability becomes the fastest. Also, the convergence value β
(n) is set to a sufficiently small value so that the control value does not unnecessarily follow level fluctuations due to fading or the like, that is, high stability is obtained.

[Operation] The automatic gain control circuit configured as described above operates as follows. The overall operation of the automatic gain control circuit is almost the same as that of the conventional automatic gain control circuit. That is, the analog reception signal r (t) is amplified by the gain control amplifier 11, converted into the digital reception signal r (n) by the AD converter 12, and input to the demodulation processing unit (not shown). At the same time, it is input to the average power calculation unit 13. The average power calculator 13 calculates the average power Ld (n) of the received signal r (n), and the subtractor 14 calculates the error power ΔL with the target power Lr. This error power ΔL is output to the multiplier 15, in which the coefficient β (i) from the coefficient control circuit 20 is multiplied and integrated by an integrator consisting of an adder 16 and a register 17 to output M (n) is converted into a control voltage V _AGC by the DA converter 18 and output to the gain control amplifier 11.

In the coefficient control circuit 20, a reset signal is output to the timer 21 when the communication terminal is started up. As a result, the timer 21 newly starts counting and the signal is output to the address generator 22. In the address generator 22, the signal from the timer 21 outputs the address signal of the coefficient β (i) corresponding to it to the coefficient memory 23 only during the operation time τ (i). As a result, the coefficient β (i) is output from the coefficient memory 23 to the multiplier 15 only during the operation time τ (i), and as shown in the graph of FIG. Only τ (1) is output. Then, the coefficient β (i) becomes gradually smaller and the operating time τ
(i) becomes longer. As a result, the coefficient β (i) changes largely and rapidly at the beginning, then gradually and gradually changes to a final value β (n) smoothly.

As a result, the gain control means is changed from a state in which the followability is emphasized to a state in which the stability is emphasized, that is, the followability at the time of start-up is the fastest, and the followability gradually becomes dull and the stability is high. It is possible to quickly and smoothly shift to the reception state. As a result, the average power of the received signal quickly follows the target power at startup, and then gradually converges to the target power.

After the coefficient β (i) has changed to the final convergence value β (n), it is fixed to this convergence value β (n) so that the control value does not unnecessarily follow level fluctuations due to fading or the like. To

[Effect] As described above, the initial value β of the coefficient
(1) is set to a large value so that the tracking capability at the time of start-up of the communication terminal is set to be the fastest so that it can optimally follow large level fluctuations, so the average power of the received signal quickly follows the target power at start-up. Can be made.

Furthermore, since the operating time τ (i) is made longer and the coefficient β (i) is made smaller as time elapses from the start-up, the coefficient β (i) is set to the coefficient at start-up. It is possible to quickly and smoothly converge from β (1) to the coefficient β (n) for normal reception. As a result, the average power of the received signal, which is made to quickly follow the target power at startup, can be gradually and smoothly converged to the target power.

[Modification] (1) In the above embodiment, the coefficient β (i) and the operating time τ
The change in (i) was set as shown by the curve 31 in FIG.
These differ depending on various conditions such as the type of communication terminal, and may be set so as to converge at other rates of change, such as the curves 32, 33, 34 in FIG. 4 according to them. Also, the magnitude of the coefficient β (i) and the length of the operating time τ (i) are
It is set appropriately according to the type of communication terminal used.

Further, the coefficient β (i) may be set so as to change at equal intervals, and the operating time τ (i) may be set so that the amount of change gradually increases as shown in FIG. β (i)
4 may be set so that the amount of change may gradually decrease, and the operating time τ (i) may be set to change at equal intervals.

(2) In the above embodiment, the communication terminal for wireless communication has been described as an example, but the same operation and effect as in the above embodiment can be obtained by applying the present invention even in the case of wired communication. You can

(3) Further, in the above embodiment, the control signal M (n) (V
_AGC ) is reviewed according to the output signal ΔM (n) from the multiplier 15 and basically shown to be always changed.
As described in the specification of Japanese Patent Application No. 7-165565 and the drawings, when a predetermined condition is satisfied, it may be maintained at the next time n + 1. That is, time n
Assuming that the control signal M (n) at time n is maintained at time n + 1, time n predicted from the received signal level at time n
When the predicted value of the average power at +1 and the observed value of the average power at time n + 1 are almost equal, the time n at the adder 16
The addition operation of the signal ΔM (n + 1) at +1 is prohibited, and the time n +
The control signal M (n + 1) at 1 is the control signal M at time n.
(n) may be output as it is.

As described above, the characteristic configuration of the above embodiment,
When the feature configuration described in the specification of Japanese Patent Application No. 7-165565 and the drawings is combined, the stability in the normal state is maintained while maintaining the high-speed followability at the time of startup in the above embodiment. It will be possible to improve it beyond the form.

[0031]

As described above in detail, according to the automatic gain control circuit of the present invention, the following effects can be obtained.

When the communication terminal is started up, the coefficient is set to be the fastest so that it can optimally follow a large level fluctuation, so that at the time of startup, the input signal level can be made to quickly follow the target level. .

Further, as the time from the start-up progresses, the time for operating each coefficient is made longer and the coefficient is made smaller. Therefore, the coefficient is set from the initial value at the start-up to the convergence value at the normal reception. In addition, it becomes possible to converge quickly and smoothly. As a result, the level of the input signal, which is made to promptly follow the target level at the time of startup, can be gradually and smoothly converged to the target level thereafter.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a conventional automatic gain control circuit.

FIG. 3 is a block diagram showing a coefficient control circuit according to the present invention.

FIG. 4 is a graph showing a control pattern of a coefficient value and an operation time in the coefficient control circuit according to the present invention.

[Explanation of symbols]

11: gain control amplifier, 12: AD converter, 13: average power calculation unit, 14: subtractor, 15: multiplier: 16: adder 1, 17: register: 18: DA converter, 19: DA
Converter, 20: coefficient control circuit.

Claims (3)

[Claims] 1. A variable gain amplifying means for adjusting the level of an input signal, a gain control means for controlling the gain of the amplifying means, and a variable coefficient added to the gain control means to follow a level fluctuation of the input signal. And a coefficient control means for adjusting the stability, and as the coefficient, an initial value having the fastest followability corresponding to startup and a highly stable convergence value corresponding to normal reception are set. Is controlled so as to monotonically change from the initial value as time elapses from the start-up and converge to the converged value after a lapse of a certain time. 2. The automatic gain control circuit according to claim 1, wherein a plurality of values that monotonically change is used as the coefficient, and the time to operate with each coefficient value increases as the time from the start-up progresses. An automatic gain control circuit characterized by. 3. The automatic gain control circuit according to claim 1, wherein the coefficient control reduces the amount of change in the coefficient as time elapses from the start-up, and each coefficient value as the time elapses from the start-up. An automatic gain control circuit, characterized by performing one or both of time controls for increasing the amount of change in the operating time.