TWI228345B - Automatic gain control device and its control method - Google Patents

Abstract

The invention provides an automatic gain control device and its control method. An average power computation unit computes the power of the received signal, and a power range monitor unit monitors its change. If the power of the signal bounces around a threshold, an acquisition mode is entered and the gain is resumed to a certain table value. If the power of the signal is still higher than the upper limit of the tracking range, a gain decrement unit is employed to decrease the gain. If the power of the signal is smaller than the lower limit of the tracking range, a gain increment unit is employed to increase the gain. Such increment and decrement are executed until the power is in the tracking range and then a tracking mode is entered from which a response is made in real time to the change of the received signal, thereby rapidly adjusting the gain.

Description

1228345 V. Description of the invention α) [Technical field to which the invention belongs] The present invention relates to an automatic gain controller and a control method thereof, in particular to a fast automatic gain device and a control method thereof used in a wireless communication network. [Previous technology] In the wireless communication network, because the distance between devices and the difference between the obstacles, when the signal reaches the receiving end, the magnitude of the intensity change cannot be predicted in advance. The received signal must be adjusted to a certain table value for reception The machine achieves the best dynamic range. A commonly used method is to use an Automatic Gain Control (AGC). In a wireless local area network system, the automatic gain controller calculates the required gain according to the preamble signal placed in front of the packet to adjust the received signal strength to a predetermined level. However, due to the existence of noise and interference, the required gain estimation has a certain error. This error will cause an error in the adjusted signal level. To avoid this situation, generally only one small step value (S ΐ e p S i z e) is adjusted when adjusting the gain, and multiple adjustments are used to approach the set level. As shown in Figure 1, it is a schematic diagram of the automatic gain controller in the prior art. During automatic gain control, the analog signal received is amplified by a Variable Gain Amplifier (VGA). An analog digital converter (Ana 1 og-Digita 1 Conver ΐ er, ADC) 2 0 is converted into a digital signal and input to the automatic gain controller AGC 30. In AGC 3 0, it can generally include an average power calculation Unit 3 1 0, logic control unit 3 2 0, and a tracking unit 3 3 0, tracking unit 3 3 0

1228345 5. Invention description (2) may include a comparison device 3301, a step adjustment unit 3302, and a loop filter 3 3 0 3. The average power of the current received signal is calculated by the average power calculation unit 3 1 0. Under the control of the control unit 3 2 0, after comparing the comparison device 3 3 0 1 (which can be implemented by an adder) with the set target power, the step adjustment unit 1 2 0 2 (which can be implemented by a multiplier) ) After adjustment, input a loop filter 1 2 0 3 in a certain ratio, and then control the control voltage of the variable gain amplifier through digital digital converter DAC to analog signal to adjust the gain. The main purpose of this control loop is to adjust the signal level when entering the analog-to-digital converter. It must be within its set range to match its dynamic range (D y n a m i c R a n g e). However, with the small tracking method described above, although the target gain can be approached gradually, it takes a long time, and for some systems that require fast gain adjustment, this method cannot meet the requirements. Therefore, how to quickly adjust the gain is An important issue. Under actual circumstances, due to the influence of noise, interference and other factors, the estimation of the average power has a certain error. Therefore, the characteristics of the gain adjustment loop must be carefully considered. Generally speaking, the design of this loop must take into account two factors. First, the convergence speed of gain adjustment; and second, the error of gain adjustment. Among them, one of the important factors affecting the two is the step size. As shown in Fig. 2 and Fig. 3, they are schematic diagrams of the loop characteristic curves when the gain is adjusted in a small step and the gain is adjusted in a large step. When a small step is selected, as shown in Figure 2, the gain can be adjusted to a more precise range but takes a longer time. When choosing a large step, as shown in Figure 3,

1228345 5. Description of the invention (3) shows that the gain can be quickly adjusted to the vicinity of the target gain but the accuracy is reduced. From the analysis of Fig. 2 and Fig. 3, the gain adjustment can be divided into two modes: Acquisition and Tracking. When the gain is extremely far from the target gain, the gain adjustment must be quickly acquired. (A cquisiti ο η mode), and when the gain is close to the target gain, the gain adjustment must be reduced to avoid overshooting (.Tracking mode). An ideal gain adjustment example is shown in Figure 4. The key to achieve this ideal adjustment is to use large step adjustment when the gain is far from the target gain, and use small step fine adjustment when the gain is close to the target gain. In a wireless local area network system, data is transmitted in the form of packets. The receiver cannot know when the packet is received. The receiver may be turned on at any time. In this case, the receiver must The signal strength adjusts the gain, and if the signal strength changes again after the gain adjustment is completed, the gain adjuster must quickly adjust the gain again to an appropriate value. Figure 5 shows an example of the gain change process when the receiver is receiving noise from the packet. In the actual operation process, the receiver cannot know when the packet enters the receiver, and the gain must converge quickly. The most important factor is that the gain adjuster must enter the acquisition to quickly adjust the gain in large steps, so the gain The regulator must accurately determine when it should enter capture mode and then when it should enter tracking mode. In the US patent US 6, 4 2 0, 9 3 4, an automatic gain control circuit is disclosed. As shown in FIG. 6, the signal amplified by AGC 6 0 1 passes through a received signal strength indicator (Receive Signal Strength

1228345 V. Description of the invention (4)

Indicator (RSSI) 6 0 4 to indicate the strength of the received signal, and then compare it with a number of preset thresholds (Threshold) through the comparison device 6 0 5 to determine the strength of the received signal. A logic 6 0 is determined based on the judgment result. 6 to determine whether the AGC works in fast acquisition mode or small tracking mode. However, this method cannot calculate the true receiving strength when the signal is greatly saturated and truncated (C 1 ippi ng). Moreover, due to the influence of noise and errors, the selection of a series of critical values is not easy. . [Summary of the Invention] The present invention is to provide an automatic gain controller and a control method thereof for solving the above problems, so as to quickly respond to changes in the strength of a received signal and speed up the process of gain adjustment. The invention provides an automatic gain controller, which is applied to a wireless communication network and uses the signal saturation characteristics as a basis for entering the acquisition mode to quickly adjust the gain. The automatic gain controller includes an average power calculation unit for calculating a received signal. Average power; power range monitoring unit to monitor the change of the power range of the received signal; logic control unit to control the transmission of the signal in the automatic gain controller according to the change of the power range; tracking control unit to The control of the logic unit performs gain tracking; the fetch control unit is used to perform gain fetching according to the control of the logic unit, and the fetch unit further includes: a gain regression unit to recall the current gain to a certain table value ; Gain increasing unit for increasing the current gain value; gain decreasing unit for reducing the current gain value. The invention further provides an automatic gain control method, which is applied to a wireless communication network and uses signal saturation characteristics as a basis for entering the acquisition mode.

1228345 V. Description of the invention (5) To quickly adjust the gain, this method first calculates the average power of the received signal and monitors the change in the power range of the received signal. When the monitored signal power jumps from below the saturation threshold to above the saturation threshold Enter the acquisition mode, and then recall the current gain to a certain built-in gain value, and then calculate the average signal power again. If the monitored power does not fall within the tracking range, the current gain is increased or decreased according to its value until the signal average After the power falls within the tracking range, it enters the gain tracking mode to track and control the gain. The invention uses the signal saturation characteristic as the basis for entering the acquisition mode, so that it can accurately and timely determine when to perform gain adjustment in the acquisition mode, and through strategies such as regression gain and fixed steps, the noise and calculation errors can be significantly reduced. In response to changes in the received signal in time, quickly adjust the gain to the range of the tracking mode. [Embodiment] The present invention provides an automatic gain controller, which is applied to a wireless communication network and uses signal saturation characteristics as a basis for entering the acquisition mode to quickly adjust the gain. As shown in FIG. 7, this is the automatic gain control of the present invention. Schematic diagram of the controller. The automatic gain controller includes an average power calculation unit 701, a logic control unit 702, a power range monitoring unit 703, a tracking control unit 704, and an acquisition control unit 705. The fetch control unit 7 0 5 further includes a gain returning unit 7051, a gain increasing unit 705 2 and a gain decreasing unit 7 0 5 3. Among them, the average power calculation unit 701 is used to calculate the average power of the received signal, the power range monitoring unit 703 is used to monitor the change in the power range of the received signal, and the logic control unit 702 is used to monitor the power range according to the monitored signal.

Page 10 1228345 V. Description of the invention (6) The transmission of the change control signal in the automatic gain controller, the tracking control unit 7 0 4 is used for gain tracking according to the control of the logic unit, and the acquisition control unit 7 0 5 is used The gain is retrieved according to the control of the logic unit. The gain return unit 7 0 5 1 is used to recall the current gain to a certain table value. The gain increasing unit 7 0 5 2 is used to increase the current gain value. The gain decreasing unit 7 is 0 5 3 is used to decrease the current gain value. The power range monitored by the power range monitoring unit 703 is: transition from below the saturation threshold to above the saturation threshold; greater than the upper limit of the tracking range; less than the lower limit of the tracking range; and falling within Within tracking range. When the power range monitoring unit 7 0 3 monitors that the received signal power transitions from below the saturation threshold to above the saturation threshold, the logic control unit 7 0 2 switches the automatic gain controller to the capture mode and passes The gain return unit 7 0 5 1 adjusts the gain to a certain built-in gain value. When the power range monitoring unit 7 0 3 monitors that the received signal power is greater than the upper limit of the tracking range, the logic control unit 7 0 2 uses the gain decreasing unit 7 0 5 3 in the acquisition mode to adjust the current gain according to a table Decreasing value. When the power range monitoring unit 7 0 3 monitors that the received signal power is less than the lower limit of the tracking range, the logic control unit 7 0 2 sets the current gain according to a table through the gain increasing unit 705 2 in the acquisition mode. The value is incremented. When the power range monitoring unit 703 monitors that the received signal power falls within the tracking range, the logic control unit 702 switches the automatic gain controller to the tracking mode for gain tracking. Referring to FIG. 8, the present invention further provides an automatic gain control method. First, the average power of the received signal is calculated and the power range of the received signal is monitored.

Page 11 1228345 V. Description of the invention (7) Peripheral change (step 8 0 1); When the monitored signal power jumps from below the saturation power threshold to above the saturation power threshold, it enters the capture mode (step 8 0 2); Call back the current gain to a built-in gain value (step 8 0 3); Calculate the average signal power again. If the monitored signal power does not fall within the target power range, the current gain is increased or decreased according to its value. Until the average power of the signal falls within the target power range (step 804); enter the gain tracking mode and perform tracking control on the gain (step 805).

Among them, after the automatic gain control enters the acquisition mode, when the received signal power is greater than the upper limit of the tracking range, the current gain is reduced; when the received signal power is less than the lower limit of the tracking range, the current gain is increased. Among them, the increase or decrease of the current gain may be to increase or decrease the current gain according to a certain table value.

In the example of the wireless network application environment, as shown in Figure 5, when the automatic gain controller has adjusted the gain to an appropriate range in the noise section, and when the packet enters, because the packet power is greater than the power of the noise, Enlarging the packet with the gain adjusted by the noise at that time will cause the packet signal level to exceed the upper limit acceptable by the analog-to-digital converter, resulting in a truncation (C 1 ipping) phenomenon, leading to an error in the calculation of the average power, and The calculation of the reception intensity is not allowed for the bird. Figure 9 shows the changes in the average power and gain of IEEE802.il g signals with different strengths after being amplified and truncated. It can be seen from the figure that the average power also has a saturation phenomenon, and the saturated average power is also equal. Therefore, this saturated average power can be used to detect whether there is a large change in the signal strength, thereby determining whether it should enter the acquisition mode. Take Figure 9 as an example, assuming the noise power is -9 0 d B m and the packet

Page 121228345 V. Description of the invention (8) The power is -1 5 dBm, when the noise is adjusted to the target power, the gain is about 90 dB, and when the packet enters (path 1), it is amplified by this large gain. The packet causes the signal to be significantly truncated, resulting in a calculated average power of approximately 17dB. If a saturation threshold is set to the level of acquisition judgment (for example, 15 dB), then the automatic gain controller can decide to enter the acquisition. It must be noted that the current gain value is far from the target gain. When the noise power is -40dBm and the packet power is -15dB m, the gain when the noise is adjusted to the target power is about 50 dB, and when the packet enters (path 2), the gain is amplified by the packet. The signal was also greatly truncated so that the calculated average power was about 17dB. At this time, the automatic gain controller also decided to enter the acquisition, but the current gain value is not too far from the target gain. The above two examples show that the calculated average power can determine whether the gain has changed too much and caused the signal to be significantly truncated. However, due to this saturation characteristic, the distance between the current gain and the target gain is still unknown. At this time, a regression gain and fixed step strategy can be adopted to greatly adjust the gain. Take Figure 10 as an example. When the noise power is -90dBm and the packet power is -1 5dBm, it is assumed that the gain has been adjusted in the noise section. To the vicinity of the target gain (9 0 d B), when the packet enters, the calculated average power jumps to the saturation power exceeding the critical value (Overflow Unlock) and judges to enter the acquisition (path 1). At this time, regardless of the gain, the gain returns To a table value G init (path 2). If the calculated average power is still greater than the critical value, the gain starts to decrease from a certain value (such as 30 dB) from this value until the gain falls within the tracking range (path 3). As shown in Figure 11, when the noise power is -40dBm and the packet power is-

1228345 V. Description of the invention (9) At 5dBm, it is assumed that the gain has been adjusted to around the target gain (50dB) in the noise section. When the packet enters, the calculated average power jumps to the saturation power and exceeds the critical value to determine the capture (path 1), and then the gain returns to G init (path 2). ◦ At this time, the calculated average power is still greater than the critical value. The gain is This value starts to decrease by a certain table value (for example, 30 dB) until the gain falls within the tracking range (path 3).

As shown in Figure 12, when the noise power is -9 0 d B m and the packet power is -40 dBm, it is assumed that the gain is adjusted to around the target gain (90 dB) in the noise section. When the packet enters, the average power is calculated to jump to the saturation power exceeding the critical value to determine the acquisition (path 1), and then the gain returns to G i n i t (path 2). At this time, the calculated average power is smaller than the tracking range, and the gain is increased by a value (for example, the difference between the estimated calculated average power and the target power) to the tracking range (path 3). The above are only the preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention; that is, all equivalent changes and modifications made in accordance with the scope of the patent application for this creation are covered by the scope of the creation patent .

Page 14 1228345 Brief description of the diagram. Figure 1 is a schematic diagram of the principle of the prior art automatic gain controller. Figure 2 is a schematic diagram of the loop characteristic curve with a small step to adjust the gain process. Figure 3 is a process with a large step to adjust the gain. Schematic diagram of the loop characteristic curve; Fig. 4 is a schematic diagram of the loop characteristic curve with a large step coarse adjustment and a small step fine adjustment to adjust the gain process, and Fig. 5 is a schematic diagram of the receiver's gain change process from noise to packet; Fig. 6 is a schematic diagram of an automatic gain control circuit disclosed in US Patent US 6, 4 2 0, 9 3 4; Fig. 7 is a schematic diagram of an automatic gain controller of the present invention; Fig. 8 is an automatic gain control of the present invention Method flow chart; Figure 9 is the average power and gain change of IEEE 8 0 2.1 lg signals with different strengths after being truncated; Figure 10 is the noise power -90dBm packet power -1 of the present invention A schematic diagram of the gain adjustment process of the embodiment of 5dBm; FIG. 11 is a schematic diagram of the gain adjustment process of the embodiment of the present invention using a noise power of -40dBm packet power -1 5dBm; and FIG. 12 This is a schematic diagram of the gain adjustment process of the embodiment in which the noise power of the present invention is -90 dBm and the packet power is -40 dBm. [Illustration of Symbols]

10 VGA

1228345 Brief description of the diagram 20 ADC 30 AGC 310 Average power calculation unit 320 Logic control unit 330 Tracking unit 330 Tracking unit 3 3 0 1 Comparator 3 3 0 2 Step adjustment unit 3 3 0 3 Loop filter 601 AGC 602 ADC 603 CPU logic 604 received signal strength indicator 605 comparison device 606 decision logic 701 average power calculation unit 702 logic control unit 703 power range monitoring unit 704 tracking control unit 705 capture control unit 7 0 5 1 gain return unit 7 0 5 2 gain transfer Adding unit 7 0 5 3 Gain decreasing unit

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Claims (1)

1228345 6. Application patent scope 1. An automatic gain controller, which is applied to wireless communication networks and uses signal saturation characteristics as a basis to enter the acquisition mode to quickly adjust the gain. The automatic gain controller includes: an average power calculation unit, Used to calculate the average power of the received signal; a power range monitoring unit to monitor the change in the power range of the received signal; a logic control unit to control the transmission of the signal in the automatic gain controller according to the change in the power range ; A tracking control unit for gain tracking according to the control of the logic unit; and an acquisition control unit for gain acquisition according to the control of the logic unit, wherein the acquisition unit further includes: a gain return unit, It is used to recall the current gain to a certain table value; a gain increasing unit is used to increase the current gain value; and a gain decreasing unit is used to decrease the current gain value. 2. The automatic gain controller according to item 1 of the scope of patent application, wherein the logic control unit, when the power range monitoring unit monitors that the received signal power transitions from below the saturation threshold to above the saturation threshold, The automatic gain controller is switched to the acquisition mode, and the gain is adjusted to a certain built-in gain value through the gain regression unit. 3. The automatic gain controller described in item 1 of the patent application range, wherein the logic control unit, when the power range monitoring unit monitors that the received signal power is greater than the upper limit of the tracking range, passes through the acquisition mode The gain decrement unit decrements the current gain by a certain table. Page 17 1228345 6. Patent application scope 4. The automatic gain controller as described in item 1 of the patent application scope, wherein the logic control unit monitors that the received signal power is less than the lower limit of the tracking range in the power range monitoring unit. In the acquisition mode, the current gain is incremented by a certain table value through the gain increasing unit. 5. The automatic gain controller according to item 1 of the scope of patent application, wherein the logic control unit switches the automatic gain controller to tracking when the power range monitoring unit monitors that the received signal power falls within the tracking range. Mode for gain tracking. 6. An automatic gain control method, which is applied to a wireless communication network and uses the signal saturation characteristics as a basis to enter the acquisition mode to quickly adjust the gain. The method includes: calculating the average power of the received signal and monitoring the change in the power range of the received signal; when When the monitored signal power transitions from below the saturation threshold to above the saturation threshold, the acquisition mode is entered; the current gain is recalled to a certain built-in gain value; the average power of the signal is calculated again, if the monitored power does not fall into Within the tracking range, the current gain is increased or decreased according to its value until the average power of the signal falls within the tracking range; and enters the gain tracking mode to track and control the gain. 7. The automatic gain control method as described in item 6 of the patent application range, wherein after the automatic gain control enters the acquisition mode, when the received signal power is greater than the upper limit of the tracking range, the current gain is reduced. 8. The automatic gain control method described in item 7 of the scope of patent application, wherein the step of reducing the current gain is to decrease the current gain according to a certain table value. Page 18 1228345 6. Patent application scope 9. The automatic gain control method described in item 6 of the patent application scope, wherein after the automatic gain control enters the acquisition mode, when the received signal power is less than the lower limit of the tracking range, Increase the current gain. 10. The automatic gain control method as described in item 9 of the scope of patent application, wherein the step of increasing the current gain is to increase the current gain by 0 according to a certain table. Page 19