RU2778438C1 - Automatic gain control device - Google Patents

Abstract

FIELD: automatic gain control devices.

SUBSTANCE: invention relates to devices for automatic gain control and can be used in receivers, in particular in radio relay receivers. The device for automatic gain control additionally contains N identical blocks for registering the input signal level, an intermediate frequency amplifier (10), a splitter (11), a logarithmic detector/controller (14). Each of the N blocks for registering the input signal level contains the first (2) and second (5) comparators, an analog key (4) and the first (3) and second (6) latches. The inputs of the blocks for recording the input signal level are combined and connected to the output of the logarithmic detector. The outputs of the input signal level registration units are connected to the corresponding inputs of the control unit (7), the output of which is connected to the control input of the digital attenuator (8).

EFFECT: increasing the dynamic range of the automatic gain control device.

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Description

The technical solution relates to devices for automatic gain control and can be used in receiving devices, in particular in radio relay communication receiving devices.

Known devices for automatic gain control, for example, described in [1] page 101, [2] page 134, [4] page 223. However, these devices do not have a sufficiently large dynamic range.

The closest analogue in technical essence to the proposed is the device described in [3], pages 87-89, taken as a prototype.

The functional diagram of the prototype device is shown in Fig. 1, where the following designations are introduced:

9 - analog attenuator;

12 - low-pass filter;

13 - DC amplifier;

15 - amplitude detector.

The prototype device contains series-connected amplitude detector 15, a DC amplifier 13, a low-pass filter 12, the output of which is connected to the control input of the analog attenuator 9, the input of which is the input of the device, and the output is the output of the device and is connected to the signal input of the amplitude detector 15, the second input of which is the threshold.

The automatic gain control device works as follows.

Automatic gain control ensures that the output of the analog attenuator 9 maintains a signal level high enough and stable enough to reproduce messages from radio stations of different power, located at different distances and in changing conditions of radio wave propagation. The input of the device receives an intermediate frequency signal of the receiver, which is fed through the analog attenuator 9 to the input of the amplitude detector 15. The amplitude detector 15 detects this signal and produces at its output a low-frequency signal proportional to the level of the input signal of the intermediate frequency. Further, this signal is amplified by the DC amplifier 13 and through the low-pass filter 12 is fed to the control input of the analog attenuator 9. The attenuation of the analog attenuator 9 increases with an increase in the input signal of the device or decreases with its decrease. Thanks to this regulation, the level of the intermediate frequency signal at the output of the prototype device is maintained almost constant.

Also, a delay voltage can be introduced into the detector, which does not allow a voltage to appear at its output until the input signal of the amplitude detector 15 exceeds a certain threshold U _C .

However, the prototype device does not have a sufficiently large dynamic range.

The task is to increase the dynamic range of the proposed device.

To solve this problem, the automatic gain control device containing a series-connected DC amplifier and a low-pass filter, the output of which is connected to the control input of an analog attenuator, according to the invention , N identical input signal level detection units are introduced, the inputs of which are combined and connected to the output of a logarithmic detector, the output of each block for recording the input signal level is connected to the corresponding input of the control unit, the output of which is connected to the control input of the digital attenuator, the output of which is connected to the input of the analog attenuator (ААт), the output of which is connected through the intermediate frequency amplifier (IFA) to the input of the splitter, one output of which is the output of the device, and the other output through a logarithmic detector/controller (LD-K) is connected to the input of the DC amplifier, while the other input of the LD-K is the input of the reference voltage; the inputs of the logarithmic detector and the digital attenuator are combined and are the input of the device, in addition, each of the N blocks for registering the input signal level contains the first comparator and the first latch connected in series, the output of which is the output of the block for registering the input signal level and is connected to the control input of the analog switch , the output of which, through the second comparator and the second latch connected in series, is connected to the reset input of the first latch, the signal inputs of the first comparator and the analog switch being combined and being the input of the input signal level registration unit; the second inputs of the first and second comparators are the inputs of the first and second reference voltages, respectively.

In FIG. 2 shows a functional diagram of the proposed automatic gain control device, where the following designations are introduced:

1 - logarithmic detector (LD);

I, II, N - blocks for recording the level of the input signal;

2.1, 5.1 - first and second comparators (K);

3.1, 6.1 - the first and second latch triggers (T-Z);

4.1 - analog key (AK);

7 - control unit (BU);

8 - digital attenuator (DAt);

9 - analog attenuator (ААт);

10 - intermediate frequency amplifier (IFA);

11 - splitter (P);

12 - low-pass filter (LPF);

13 - DC amplifier (UPT);

14 - logarithmic detector/controller (LD-K).

The proposed device contains serially connected digital attenuator 8, analog attenuator 9, intermediate frequency amplifier 10, the output of which is connected to the input of the splitter 11, one output of which is the output of the device, and the other output is connected to the signal input of the logarithmic detector/controller 14, the other input of which is reference voltage input U _op . In this case, the output of the logarithmic detector/controller 14 is connected through a series-connected DC amplifier 13 and a low-pass filter 12 to the second input of the analog attenuator 9.

The output of the logarithmic detector 1 is connected to the inputs of N identical blocks for recording the level of the input signal I, II...N. Each of the N blocks for recording the input signal level contains the first comparator 2 connected in series, the first trigger-latch 3, the output of which is connected to the control input of the analog key 4, the output of which is connected through the second comparator 5 and the second trigger-latch 6 connected in series to the reset input of the first trigger-latch 3, the output of which is the output of the input signal level registration unit and is connected to the corresponding input of the control unit 7. The first input of the first comparator 2 is the input of the input signal level registration unit. The second input of the first comparator 2 is the input of the first threshold voltage U ₁ . The second input of the second comparator 5 is the input of the second threshold voltage U ₂ . The outputs of the remaining (N-1) blocks for registering the input signal level are connected to the corresponding inputs of the control unit 7, the output of which is connected to the control input of the digital attenuator 8.

The inventive automatic gain control device operates as follows.

The input signal of the device through the digital attenuator 8 is fed to the first input of the analog attenuator 9, which operates as part of an automatic gain control (AGC) loop, consisting of an analog attenuator 9, an intermediate frequency amplifier 10, a splitter 11, a logarithmic detector/controller 14, a DC amplifier 13 and low-pass filter 12. The intermediate frequency amplifier 10 provides amplification of the input signal of the proposed device to the minimum level required for the normal operation of the logarithmic detector/controller 14. The voltage U _op applied to the reference input of the logarithmic detector/controller 14 sets the output signal level of the analog loop AGC that is kept constant.

In modern receivers, the input signal level can vary widely: from 60 dB in radio receivers to 120 dB in radar receivers. Normal operation of the terminal device requires that the changes in the receiver output signal do not exceed 4-6 dB. To meet these requirements, the depth of amplifier control by the AGC system should be 56-116 dB [6] (p. 32).

The signal level at the receiver input can vary depending on the distance to the correspondent's transmitter or depending on the intensity of precipitation on the path, which is especially important for communication lines operating in the microwave and EHF bands.

Since the analog attenuator in the prototype device provides a control range of no more than 30 - 35 dB (see, for example, attenuators MA4VAT2000-1277T f. M / A-COM, SVA-2000 f. Mini-Circuits), in the receive path to increase the range regulation, a second digital attenuator 8 is introduced, which will additionally increase the control range by 31 dB (see, for example, attenuators MAATCC0009 f. M/A-COM, CHT4012-ODG f. UMS). The total attenuation of the two attenuators, and, consequently, the control range will be 61 - 66 dB.

Let us consider the operation of the proposed device using the example of using a device with two input signal level detection units shown in Fig. 3. The input signal level of the proposed device is measured by a logarithmic detector with a linear response in dB, having a dynamic range of at least 60 dB.

Let's say that the input level of the device has increased by 19 dB. An analog AGC loop consisting of an analog attenuator 9, an IF amplifier 10, a splitter 11, a logarithmic detector/controller 14, a DC amplifier 13, and a low pass filter 12 will compensate for this increase in the input signal by increasing the attenuation of the analog attenuator 9 by 19 dB, maintaining the output level of the device is unchanged. The voltage U _op applied to the reference input of the logarithmic detector/controller 14 sets the output signal level of the analog AGC loop, which is maintained constant.

With an increase in the input signal level of the device, the voltage at the output of the logarithmic detector 1 increases and, with an increase in the input signal level by 19 dB, exceeds the threshold U _1.1 of the comparator 2.1 of the first block for recording the input signal level I. The first comparator 2.1 changes the logic level at its output and thereby leads to actuation of the first trigger-latch 3.1. The output signal of the trigger-latch 3.1 is fed to the control unit 7, which generates a command to increase the attenuation of the digital attenuator 8 by 15 dB.

The analog attenuator is then forced to reduce the attenuation by 15 dB to bring the AGC loop back to equilibrium. In this case, the attenuation of the analog attenuator 9 will be 4 dB. If the input signal fluctuates and decreases somewhat, the analog attenuator 9 will compensate for this decrease with a 4 dB attenuation margin. Thus, there will be no chaotic switching of the digital attenuator from a state of 10 dB to a state of 0 dB and vice versa.

With a further increase in the input signal level by 19 dB, the voltage at the output of the logarithmic detector 1 increases and exceeds the threshold U _1.2 of the comparator 2.2 of the second block for recording the input signal level. Comparator 2.2 changes the logic level at its output and thereby switches the latch 3.2. The output signal of the trigger-latch 3.2 is fed to the control unit 7, which generates a command to increase the attenuation of the digital attenuator 8 by 15 dB (total 30 dB). The analog attenuator 9 is then forced to reduce the attenuation by 15 dB to bring the AGC loop back into equilibrium. In this case, the attenuation of the analog attenuator will be 8 dB.

By further increasing the input signal level, the analog attenuator 9 will be able to increase the attenuation by another 22 dB. Thus, the total attenuation of digital attenuator 8 and analog attenuator 9 will be 60 dB.

When the input signal level decreases, the signal from the output of the analog switch 4.2 becomes less than the threshold U _2.2 of the second comparator 5.2, the comparator fires and switches the second latch 6.2, which in turn resets the first latch 3.2 to its original state. The signal from the output of the latch 3.2 reduces the attenuation of the digital attenuator 8 by 15 dB, and further control of the gain of the receiving path is carried out by the analog attenuator 9.

We examined the operation of the device using the example of using two blocks for registering the input signal level. In this case, the step of changing the attenuation of the digital attenuator 8 was chosen to be 15 dB. When using more blocks for registering the input signal level, the step Δ of attenuation of the digital attenuator 8 will decrease in accordance with the expression: Δ=A/N, where A is the total attenuation of the digital attenuator 8 and N is the number of blocks for registering the input signal level.

The implementation of the newly introduced blocks is well known and does not present any difficulties. For example, the control unit can be implemented in the form of a logical decoder, a logarithmic detector in the form of an HMC601LP4 chip f. Analog Devices or 1313UF2U AEYAR.431000.688-03TU, logarithmic detector/controller in the form of an AD8317 chip f. Analog Devices or 1313UF1AU AEYAR.431000.688-02TU, analog attenuator in the form of a MA4VAT2000-1277T chip f. M/A-COM, digital attenuator in the form of a chip CHT4012-ODG f. UMS or M44750 APNT.434820.053TU.

Thus, the introduction of new blocks and connections into the claimed device allows increasing the dynamic range of the automatic gain control device.

Sources of information

1. A.A. Makarenko, M.Yu. Plotnikov. Devices for receiving and converting signals. St. Petersburg, ITMO University Editorial and Publishing Department, 2019

2. V.P. Pushkarev. Analog and digital radio receivers. Tomsk, 2018

3. Yu.V. Markov, A.S. Bokov. Designing devices for receiving and processing signals. Yekaterinburg, Ural University Press, 2015

4. Devices for receiving and processing signals. Ed. V.S. Plaxienko M.: Educational and Methodological Publishing Center "Educational Literature", 2004.

5. US Patent No. 5,721,757. 1998 Automatic gain control loop.

6. N.P. Nikitin, V.V. Kiyko. Design of radio receivers based on analog blocks. Yekaterinburg: GOU VPO USTU-UPI, 2004.

Claims (1)

An automatic gain control device containing a series-connected DC amplifier and a low-pass filter, the output of which is connected to the control input of an analog attenuator, characterized in that N identical input signal level detection units are introduced, the inputs of which are combined and connected to the output of a logarithmic detector, the output of each of the input signal level registration unit is connected to the corresponding input of the control unit, the output of which is connected to the control input of the digital attenuator, the output of which is connected to the input of the analog attenuator (ААт), the output of which is connected through the intermediate frequency amplifier (IFA) to the input of the splitter, one output of which is the output of the device, and the other output through a logarithmic detector/controller (LD-K) is connected to the input of the DC amplifier, while the other input of the LD-K is the input of the reference voltage; the inputs of the logarithmic detector and the digital attenuator are combined and are the input of the device, in addition, each of the N blocks for registering the input signal level contains the first comparator and the first latch connected in series, the output of which is the output of the block for registering the input signal level and is connected to the control input of the analog switch , the output of which, through the second comparator and the second latch connected in series, is connected to the reset input of the first latch, the signal inputs of the first comparator and the analog switch being combined and being the input of the input signal level registration unit; the second inputs of the first and second comparators are the inputs of the first and second reference voltages, respectively.

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