JPH06350364A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To allow a control circuit to cope with a large level fluctuation by providing a loop filter generating a steady-state fluctuation component corresponding to a steady-state fluctuation of an input analog signal level in a pre- stage of an integration device in a feedback loop so as to improve the tracking performance against a steady-state level fluctuation. CONSTITUTION:An analog signal received from an input terminal 10 is inputted to a level calculation means 3 via an A/D converter 2 to calculate an average power of the received signal. Then a logarithmic transformation means 8 transforms the power in a dB and a difference device 4 obtains a difference DELTAm between the signal subjected to dB transformation and a reference level. A loop filter 9 multiplies a constant beta2 by the difference DELTAm and obtains a DELTAM being the sum of an alpha0 being the integration of the result and a beta1XDELTAm. Then an integration device 5 integrates an output DELTAM from the filter 9 and its output Mn is converted into an analog signal by a D/A converter and it is converted into a control signal Gn by a response function (G)7. The gain is controlled by the signal Gn so that an output level of the amplifier 1 is made constant.

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 used in a digital communication receiver or the like.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional automatic gain control circuit.

This automatic gain control circuit holds the output level of the amplifier constant by controlling the gain of the amplifier. That is, in FIG. 2, the input analog signal is amplified by the amplifier 1, converted into a digital signal by the AD converter 2, and the level calculating means 3 calculates the average power of the output of the amplifier 1. Then, the difference device 4 calculates the difference between the average power and a preset reference level, the integration circuit 5 integrates the difference, and the DA converter 6 converts the difference into an analog signal. This analog signal is supplied to the amplifier 1 through the response function 7, and the gain of the amplifier 1 is controlled so that the level of the output signal becomes constant even if the level of the input signal changes.

[0004]

By the way, in a receiver of a mobile station in digital mobile communication, the level of the received signal fluctuates drastically due to fading, and as the mobile station approaches or moves away from the base station, its reception is performed. The signal level fluctuates almost linearly (hereinafter, this fluctuation is called steady fluctuation). Therefore, it is required that the automatic gain control circuit used for the receiver of the mobile station operates stably even under the fluctuation of the received signal level due to the fading and can sufficiently follow the steady fluctuation. To be done.

However, in the conventional automatic gain control circuit having the above configuration, if the response function 7 is set so as to operate stably under the fluctuation of the received signal due to fading, the followability to the steady fluctuation is lowered, and If the response function 7 is set so as to be able to sufficiently follow the dynamic fluctuation, there is a problem that the operation becomes unstable under the fluctuation of the received signal due to fading.

Further, in the above-mentioned receiver of the mobile station, the level of the received signal fluctuates in a wide range due to fading, so that the operating range of the automatic gain control circuit used in the receiver must be set wide accordingly. .

However, in order to set a wide operating range of the conventional automatic gain control circuit having the above-mentioned configuration, AD
Since it is necessary to set the converter 2, the level calculation means 3, and other digital parts so as to handle data having a large number of digits, there is a problem that the device to be used becomes large and the cost becomes high.

The present invention has been made in order to solve the above problems, and by providing a loop filter in the feedback loop, the feedback loop operates stably even under drastic fluctuations in the level of the received signal, and steady fluctuations occur. It is an object of the present invention to provide an excellent automatic gain control circuit which is capable of sufficiently following the above, and is sufficiently adapted to a received signal whose level fluctuates in a wide range by providing a logarithmic conversion means.

[0009]

In order to achieve the above object, the present invention provides an amplifier for amplifying an input signal, level calculation means for calculating an average level of the output of the amplifier, and the average level and a preset reference. A difference device for calculating the difference with the level, and an integrator for integrating the value of the difference,
An automatic gain control circuit that controls the gain of the amplifier based on the output of the integrator so that the output level of the amplifier is constant. The average level calculated by the level calculating means is logarithmically converted and output to the differencer. A logarithmic conversion unit and a loop filter for adding a value obtained by integrating the difference value to the difference value calculated by the difference unit and outputting the added value to the integrator are provided.

[0010]

Since the loop filter generates the component corresponding to the steady fluctuation of the input signal and outputs it to the integrator, it is possible to follow the steady fluctuation. Further, by providing the logarithmic conversion means, it is possible to cope with an input signal having a large level fluctuation.

[0011]

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

In this embodiment, a logarithmic conversion means 8 is inserted between the level calculation means 3 and the difference unit 4 of the conventional automatic gain control circuit shown in FIG. 2, and a loop is provided between the difference unit 4 and the integrator 5. A filter 9 is inserted, and the amplifier 1, the AD converter 2, the level calculating means 3, the difference unit 4, the integrator 5, the DA converter 6 and the response function 7 have the same reference numerals in FIG. It is similar. The portion handling the digital signal from the level calculation means 3 to the integrator 5 is a single DSP (Digital Signal Proc).
can be implemented as an essay).

Next, the operation of this embodiment will be described with reference to FIG.

An analog signal input from the input terminal 10 is amplified by the amplifier 1 and converted into a digital signal by the AD converter 2. The level calculating means 3 calculates the average power of the received signal using the digital signal according to the equation (1).

[0015]

[Equation 1]

Next, the RCV-P is converted by the logarithmic conversion means 8.
OW is converted to dB by the equation (2).

L _D = 10 log ₁₀ (RCV-POW) (2) By this dB conversion, L _D can be suppressed below a certain value even if the value of PCV-POW becomes large, so the reception level becomes large. However, the digital portion from the difference unit 4 to the DA converter 6 does not overflow.

Next, the difference Δm between the signal L _D, which has been dB-converted by the differentiator 4, and a preset reference level Lr.
Is calculated by the equation (3).

[0019] Δm = L _D -Lr (3) the output level of the amplifier 1 will come determined by the reference level Lr.

Next, the loop filter 9 executes the calculations represented by the equations (4) and (5) for the Δm.

Α _n = α _n-1 + β ₂ Δm (4) ΔM = α _n + β ₁ Δm (5) However, β ₁ and β ₂ are constants.

That is, the loop filter 9 includes the differentiator 4
The difference Δm output from the above is multiplied by a constant β ₂ , and α _n obtained by integrating this is added to β ₁ Δm obtained by multiplying the difference Δm by a constant β ₁ (5 ) Is used to calculate ΔM.

Here, the value of the constant β ₁ is greatly affected by the fluctuation of the output of the amplifier 1 even when the level of the analog signal input to the amplifier 1 is greatly changed due to the influence of fading or the like. It is set so that it converges stably to a predetermined value without However, in this way the constant β ₁
If the value of is set, the followability to the steady fluctuation of the level of the analog signal input to the amplifier 1 is deteriorated, and it becomes difficult to control the output level of the amplifier 1 to be constant. Therefore, in the present embodiment, the difference Δm output from the differentiator 4 is multiplied by a constant β ₂ and integrated to generate a component α _n proportional to a steady fluctuation, and the component α _n is output to the integrator 5. The gain of the amplifier 1 is controlled to reduce steady fluctuations in the output of the amplifier 1. The constant β ₂ is set so that the steady fluctuation in the output of the amplifier 1 is minimized.

In the conventional automatic gain control circuit shown in FIG. 2, the stability of the output of the amplifier 1 at the time of convergence and the speed of convergence are adjusted by changing the hardware of the response function (f) 7. It wasn't easy to do because I had to do it. However, in the present embodiment, the loop filter 9 shown in FIG.
It is adjusted by changing the value of the constant β ₁ of. Therefore, if the digital portion including the loop filter 9 is realized by a DSP, the value of the constant β ₂ can be easily changed, and the above-mentioned stability at the time of convergence and swiftness at the time of convergence can be easily adjusted. Become.

Next, the integrator 5 integrates the output ΔM from the loop filter 9. The output M _n of the integrator 5 is expressed by equation (6).

M _n = M _n-1 + ΔM (6) The output M _n of the integrator 5 is converted into an analog signal by the DA converter 6, and converted into a control signal G _n by the response function (G) 7. The gain is controlled by the control signal G _n so that the output level of the amplifier 1 becomes constant. As the response function, for example, the linear form represented by the equation (7) is used.

G _n = aM _{n + b} (7) where a and b are constants.

The constants β ₁ and β _{2 of} the loop filter 9 are
The position for multiplying by is not limited to the above-mentioned embodiment, and if the same effect is given, at other positions,
It may be multiplied by β ₁ and β ₂ .

[0029]

As described above in detail, according to the present invention, the loop filter for generating the steady fluctuation component corresponding to the steady fluctuation of the input analog signal level is provided at the front stage of the integrator of the feedback loop. Since it is provided in the above, it becomes possible to follow the above-mentioned steady fluctuation and compensate for this. Therefore,
INDUSTRIAL APPLICABILITY The present invention is suitable for an automatic gain control circuit or the like used in a receiver of a mobile station whose received signal level constantly fluctuates.

Further, since the logarithmic conversion means for logarithmically converting the value of the input signal is provided in the preceding stage of the digital portion of the feedback loop, it is possible to handle an input analog signal having a large level fluctuation.

[Brief description of drawings]

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 amplifier 2 AD converter 3 level calculation means 4 difference device 5 integrator 6 DA converter 7 response function 8 logarithmic conversion means 9 loop filter

Claims (1)

[Claims] 1. An amplifier for amplifying an input signal, level calculating means for calculating an average level of the output of the amplifier, a differencer for calculating a difference between the average level and a preset reference level, and a difference calculator for calculating the difference. An automatic gain control circuit having an integrator that integrates a value, and controlling the gain of the amplifier based on the output of the integrator so that the output level of the amplifier is constant, the average level calculated by the level calculation means A logarithmic conversion means for logarithmically converting and outputting the logarithmic difference to the difference unit, and a loop filter for adding to the difference value calculated by the differencer a value obtained by integrating the difference value and outputting the added value to the integrator. An automatic gain control circuit characterized by the above.