JPH0738358A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To exactly execute automatic gain control even in the case an output of an A/D converting part is saturated. CONSTITUTION:A voltage control attenuating part 2 attenuates a spreaded spectrum signal in accordance with a control voltage and applies it to an A/D converting part 3. An output of the A/D converting part 3 is subjected to reverse diffusion by a PN code in a multiplying part 4, integrated by an integrating part 5, and its absolute value is calculated by an absolute value calculating part 6. Saturation detecting/switching parts 11 and 7 detect saturation of the output of the A/D converting part 3, and in the case it is detected, an output of the absolute value calculating part 6 is outputted, and in the case it is not detected, a constant value is outputted. Outputs of the saturation detecting/ switching parts 11 and 7 are provided to a comparing part 9 through a D/A converting part 8, compared with a reference voltage Vref, and an output of the comparing part 9 is low-pass-filtered by a low-pass filter part 10, and provided to the voltage control attenuating part 2 as a control voltage. The constant value is selected to a value by which an output of the D/A converting part 8 becomes maximum.

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, and more particularly to an automatic gain control circuit for a digital signal processing type spread spectrum receiver.

[0002]

2. Description of the Related Art Automatic gain control of a spread spectrum receiver is disclosed in, for example, Japanese Unexamined Patent Publication Nos. 1-101040 and 2-10.
-69033, JP-A-60-249445, JP-A-61-33025 (using a PN generator), JP-A-61-242431 and the like.

In the spread spectrum receiver of the digital signal processing type, if the signal processing for automatic gain control is also performed by the digital signal processing, it is possible to take advantage of the advantages of the digital signal processing such as being strong against the temporal change. At that time, if it is desired to change the signal band for which the automatic gain control is performed, the automatic gain control loop has an integrating unit that can change the number of integrations. An example of this case is shown in FIG.

The automatic gain control circuit of FIG. 2 receives a spread spectrum signal from an input terminal 1 and attenuates the received signal according to a control voltage, and a voltage control attenuator 2 which outputs an A / D signal. The A / D conversion unit 3 for conversion and the output of the A / D conversion unit 3 are PN (pseudonois)
e) A multiplication unit 4 that despreads with a code (pseudo-random code), an integration unit 5 that integrates the output of this multiplication unit 4, and an absolute value calculation unit 6 that calculates the absolute value of the output of this integration unit 5.
And a D / A converter 8 for receiving the output of the absolute value calculator 6 as a conversion input signal and D / A converting the conversion input signal.
And a comparison unit 9 which compares the output of the D / A conversion unit 8 with a reference voltage V _rcf and outputs a comparison result, and an output of the comparison unit 9 which _undergoes reduction filtering and outputs the _filtered signal as the control voltage. And a reduction filtering section 10 for

[0005]

Generally, in digital signal processing, a signal is represented by 2's complement. Considering now that the synchronization of the PN code is not achieved, in the circuit shown in FIG. 2, the output of the A / D conversion unit 3 and the output of the multiplication unit 4 are both noise-like. When the output of the A / D conversion unit 3 is not saturated, the effective value σ _{A / D of the} output of the A / D conversion unit 3, the effective value σ _{ACC of the} output of the integration unit 5, and the number of integration times N have the following relationships.

Σ _ACC = σ _{A / D} / N ^{0.5 In the} circuit shown in FIG. 2, automatic gain control is performed at a desired level when the input rises faster than the response speed of the automatic gain control circuit, such as when the power is turned on. There is a problem of not being forgotten. The reason for this will be described below.

Now, when the output of the reduction filter 10 is turned off and the open loop characteristic is considered, from the above equation, when the input of the A / D converter 3 is not saturated, the output of the integrator 5 increases as the signal input increases. The output of the effective value / absolute value calculation unit 6 increases. However, when the signal input further increases and the output of the A / D conversion unit 3 begins to saturate, many positive maximum values and negative maximum values begin to appear in the output of the A / D conversion unit 3, and they cancel each other when they are added to each other. Therefore, the effective value of the output of the integrator 5 and the output of the absolute value calculator 6 do not monotonically increase but start to decrease with respect to the signal input of a certain level abnormality. That is, the automatic gain control circuit having such an open loop characteristic may have a plurality of operating points.

An object of the present invention is to provide an automatic gain control circuit which realizes a monotonically increasing detection characteristic even when the output of the A / D converter is saturated and enables accurate automatic gain control. .

[0009]

According to the present invention, a spread spectrum signal is received, a voltage control attenuator for attenuating the received signal according to a control voltage, and an output A / D for converting the output of the voltage control attenuator. / D conversion unit, a multiplication unit that despreads the output of this A / D conversion unit with a PN code, an integration unit that integrates the output of this multiplication unit, and an absolute value that calculates the absolute value of the output of this integration unit. The calculation unit and the output of this absolute value calculation unit are received as a conversion input signal, and this conversion input signal is received by the D / A.
A D / A converter for conversion, a comparator for comparing the output of the D / A converter with a reference voltage and outputting a comparison result, an output of the comparator for reduction filtering, and a filtered signal for the control voltage. In the automatic gain control circuit including a reduction filtering unit that outputs as, the saturation of the output of the A / D conversion unit is detected, and when detected, the output of the absolute value calculation unit is output to the D / A conversion unit. An automatic gain control circuit is provided which has a saturation detection switching unit that supplies a constant value to the D / A conversion unit as the conversion input signal when it is supplied as the conversion input signal and is not detected.

Further, according to the present invention, the saturation detection switching unit detects the saturation of the output of the A / D conversion unit, and when the saturation detection unit detects the saturation,
The output of the absolute value calculation unit is supplied to the D / A conversion unit as the conversion input signal, and when the saturation is not detected, the constant value is supplied to the D / A conversion unit as the conversion input signal. An automatic gain control circuit having a switching unit is obtained.

According to the present invention, there is also provided an automatic gain control circuit characterized in that the constant value is selected to be a value that maximizes the output of the D / A converter.

[0012]

The present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. The input signal or the intermediate frequency signal is input from the terminal 1, passes through the voltage control attenuator 2, and is A / D converted by the A / D converter 3.
To be converted. The output of the A / D conversion unit 3 is output to the PN in the multiplication unit 4.
It is despread by being multiplied with the code. The output of the multiplication unit 4 is integrated by the integration unit 5, the absolute value is calculated by the absolute value calculation unit 6, and then input to one of the two inputs of the switching unit 7. The output of the switching unit 7 is D by the D / A conversion unit 8.
A / A conversion is performed, and the comparison unit 9 compares it with the reference voltage. The output of the comparison unit is subjected to reduction filtering by the reduction filtering unit 10. The output of the reduction filter unit 10 is input as a control voltage to the voltage control attenuator unit 2 and negative feedback is applied. A constant that maximizes the output of the D / A conversion unit is input to the other one of the two inputs of the switching unit 7. Further, the saturation detection unit 11 is an A / D
Saturation of the output of the conversion unit 3 is determined, and if it is saturated, the output of the absolute value calculation unit 6 is switched to the output of the switching unit 7, and if not saturated, the constant is switched to the output of the switching unit 7.

Generally, in an automatic gain control device, the gain control characteristic in the open loop is required to be monotonous, but a monotonous open loop gain control characteristic can be obtained with a relatively simple circuit. Further, by changing the integration time of the integrating section 5, the signal band for which the automatic gain control is performed can be changed relatively easily.

As described above, in this embodiment, the input signal is A /
The digital signal is converted into a digital signal in the D conversion unit 3, PN despreaded in the multiplication unit 4, and averaged in the integration unit 5. Further, the absolute value calculation unit 6 converts the absolute value. On the other hand, the saturation detector 10
Detects the saturation of the A / D conversion unit 1, and the switching unit 7
When the output of the / D conversion unit 3 is not saturated, the absolute value calculation unit 6 output is selected, and when it is saturated, the D / A conversion unit 8 is selected.
Select the maximum input value. The D / A converter 8 receives the signal selected by the switch 7 and outputs an analog signal. The analog output is passed through the reduction pass filter 9 and negative feedback is applied to the voltage control attenuator 2. As a result, even if the input of the A / D converter is saturated, a monotonically increasing detection characteristic can be realized and the gain can be automatically controlled.

[0016]

As described above, the present invention has the advantages that an accurate automatic gain control circuit can be realized with a relatively simple circuit and the signal bandwidth of automatic gain control can be varied relatively easily.

[Brief description of drawings]

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

FIG. 2 is a block diagram of an example of a conventional technique.

[Explanation of symbols]

 1 Input Terminal 2 Voltage Control Attenuation Section 3 A / D Conversion Section 4 Multiplication Section 5 Integration Section 6 Absolute Value Calculation Section 7 Switching Section 8 D / A Conversion Section 9 Comparison Section 10 Reduction Filter Section 11 Saturation Detection Section

Claims (3)

[Claims] 1. A voltage control attenuator for receiving a spread spectrum signal and attenuating the received signal according to a control voltage, an A / D converter for A / D converting the output of the voltage control attenuator, and the A / D converter. A multiplication unit that despreads the output of the conversion unit with a PN code, and an integration unit that integrates the output of this multiplication unit,
An absolute value calculation unit that calculates the absolute value of the output of this integration unit,
The output of this absolute value calculation unit is received as a conversion input signal, and the output of this D / A conversion unit and the D / A conversion unit that performs D / A conversion of this conversion input signal are compared with the reference voltage and the comparison result is output. An automatic gain control circuit including: a comparison unit; and a reduction filtering unit that reduces and filters the output of the comparison unit and outputs the filtered signal as the control voltage. Detects saturation of the output of the A / D conversion unit. If detected, the output of the absolute value calculation unit is supplied to the D / A conversion unit as the conversion input signal, and if not detected, a constant value is supplied to the D / A conversion unit as the conversion input signal. An automatic gain control circuit having a saturation detection switching unit for supplying. 2. The saturation detection switching unit detects a saturation of an output of the A / D conversion unit, and outputs an output of the absolute value calculation unit when the saturation detection unit detects the saturation. A switching unit which supplies the D / A conversion unit as the conversion input signal and supplies the constant value to the D / A conversion unit as the conversion input signal when the saturation is not detected. The automatic gain control circuit according to claim 1. 3. The automatic gain control circuit according to claim 1, wherein the constant value is selected to be a value that maximizes the output of the D / A conversion unit.