Automatic gain control for a WLAN system

• US 20060068733A1
• Filed: 09/28/2004
• Published: 03/30/2006
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: VIA Technologies Incorporated (VIA Technologies)
• Original Assignee: VIA Technologies Incorporated (VIA Technologies)
• Inventors: Wang, Chih-Chia, Kao, Kai-Pon
• Granted Patent: US 7,187,915 B2
• Time in Patent Office: Days
• US Class Current: 455/234.100
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H04W 52/52 using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

An Automatic Gain Control (AGC) method and system thereof. The power of a detected signal is first checked to ensure that it is large enough for AGC process. A power average of the detected signal is computed and compared to a first threshold in order to determine whether to proceed with a coarse tune procedure or enter a fine tune procedure. Both Low Noise Amplifier (LNA) gain and Variable Gain Amplifier (VGA) gain are tuned during coarse tune, whereas only the VGA gain is tuned during fine tune. The LNA and VGA gains are tuned to predetermined values during coarse tune, and the VGA gain is adjusted according to a difference between a computed average of power and a second threshold.

Claims

1. An Automatic Gain Control (AGC) method, comprising:

setting a gain of a Low Noise Amplifier (LNA) and a gain of a Variable Gain Amplifier (VGA) according to preset upper boundaries LNA0 and VGA0 respectively;

detecting and comparing the power of a signal to a first power level until it exceeds the first power level, wherein the first power level exceeds an average noise power;

tuning the gains of the LNA and the VGA according to maximum preset values LNA1 and VGA1;

computing a second power level depending on an average power of the signal;

comparing the second power level to a first threshold, and moving to execute fine tune procedures if the second power level is less than or equal to the first threshold;

tuning the gain of the LNA and the VGA according to medium preset values LNA2 and VGA2 if the second power level exceeds the first threshold;

recalculating the second power level and comparing it to the first threshold, if the recalculated second power level is less than or equal to the first threshold, moving to execute fine tune procedures;

tuning the gain of the LNA and the VGA according to minimum preset values LNA3 and VGA3 if the recalculated second power level exceeds the first threshold;

beginning fine tune procedures by computing a third power level depending on an average power of the signal; and

tuning the gain of the VGA according to a difference between the third power level and a second threshold.

2. The AGC method according to claim 1, wherein the first power level is an ideal 16-point average power predetermined by the system.

3. The AGC method according to claim 1, wherein the AGC process is accomplished by digital computation.

4. The AGC method according to claim 3, wherein the second power level, the third power level, the first threshold, the second threshold, and the LNA and VGA gains are represented in logarithm unit decibels.

5. The AGC method according to claim 1, wherein the second power level is obtained by calculating a 16-point average power of the signal.

6. The AGC method according to claim 5, wherein the first threshold is determined by considering a gain allowance and an ideal power level of 16 sample points.

7. The AGC method according to claim 1, wherein the third power level is obtained by calculating a 32-point average power of the signal.

8. The AGC method according to claim 7, wherein the second threshold is determined by an ideal power level of 32 sample points.

9. The AGC method according to claim 1, wherein the preset upper boundary for the LNA gain (LNA0) is greater than or equal to the maximum preset value for the LNA gain (LNA1), LNA1 is greater than or equal to the middle preset value for the LNA gain (LNA2), and LNA2 is greater or equal to the minimum preset value for the LNA gain (LNA3).

10. The AGC method according to claim 1, further comprising recalculating the third power level and tuning the gain of the VGA according to a difference between the recalculated third power level and the second threshold.

11. A system for Automatic Gain Control (AGC), comprising:

a detection logic, detecting and comparing the power of a signal to a first power level, and outputting an AGC activating signal when the detected power exceeds the first power level, wherein the first power level exceeds an average noise power;

a Low Noise Amplifier (LNA) gain controller, initializing an LNA gain to a preset upper boundary LNA0, tuning the LNA gain to a maximum preset value LNA1 if the detection logic outputs the AGC activating signal, and sequentially to a medium preset value VNA2 and a minimum preset value LNA3 if receiving a coarse tune signal;

a Variable Gain Amplifier (VGA) gain controller, initializing a VGA gain to a preset upper boundary VGA0, tuning the VGA gain to a maximum preset value VGA1 if the detection logic outputs the AGC activating signal, sequentially to a medium preset value VNA2 and a minimum preset value LNA3 if receiving the coarse tune signal, and further tuning the VGA gain according to a fine tune signal;

a second power computing unit, calculating a second power level depending on an average power of the signal;

a coarse gain decision unit, comparing the second power level to a first threshold, instructing the LNA and VGA gain controllers to tune the gains to LNA2 and VGA2 respectively by sending the coarse tune signal and requesting the second power computing unit to recalculate the second power level if the second power level exceeds the first threshold, then comparing the recalculated second power level to the first threshold, instructing the LNA and VGA gain controllers to tune the gain to LNA3 and VGA3 respectively by sending the coarse tune signal if the recalculated second power level exceeds the first threshold;

a third power computing unit, calculating a third power level depending on an average power of the signal; and

a fine gain decision unit, instructing the VGA gain controller to tune the VGA gain according to a difference between the third power level and a second threshold as the fine tune signal.

12. The system for AGC according to claim 11, further comprising a first power computing unit calculating the first power level according to an ideal 16-point average power.

13. The system for AGC according to claim 11, wherein the AGC apparatus is a digital implementation.

14. The system for AGC according to claim 13, wherein the second power level, the third power level, the first threshold, the second threshold, and the LNA and VGA gains are represented in logarithm unit decibels.

15. The system for AGC according to claim 11, wherein the second power computing unit obtains the second power level by calculating a 16-point average power of the signal.

16. The system for AGC according to claim 15, wherein the first threshold is determined by considering a gain allowance and an ideal power level of 16 sample points.

17. The system for AGC according to claim 11, wherein the third power computing unit obtains the third power level by calculating a 32-point average power of the signal.

18. The system for AGC according to claim 17, wherein the second threshold is determined by an ideal power level of 32 sample points.

19. The system for AGC according to claim 11, wherein the preset upper boundary for the LNA gain (LNA0) is greater than or equal to the maximum preset value for the LNA gain (LNA1), LNA1 is greater than or equal to the middle preset value for the LNA gain (LNA2), and LNA2 is greater or equal to the minimum preset value for the LNA gain (LNA3).

20. The system for AGC according to claim 11, wherein the fine gain decision unit instructs the third power computing unit to recalculate the third power level and retune the VGA gain according to a difference between the recalculated third power level and the second threshold.

21. An Automatic Gain Control (AGC) method of controlling a wireless receiver having a gain of a Low Noise Amplifier (LNA) and a gain of a Variable Gain Amplifier (VGA) for determining a final gain setting LNAFinal and VGAFinal of the LNA and VGA, comprising:

(i) setting initial gains for the LNA and the VGA corresponding to a maximum gain;

(ii) detecting and determining whether the power of a received RF signal is within a valid receiving range;

(iii) coarse-tuning the gains of the LNA and the VGA according to a subsequent preset value if the power of the received RF signal is not within the valid receiving range;

wherein a plurality of preset values for the gains are arranged in order so that the subsequent preset value is lower than the antecedent preset value;

(iv) repeating steps (ii) and (iii) if the power of the received RF signal is still outside the valid receiving range, else fixing the current gain of the LNA as LNAFinal;

(v) computing an average power of the received RF signal; and

(vi) fine-tuning the gain of the VGA to be VGAFinal according to a difference between the average power and a threshold.

22. The AGC method according to claim 21, wherein the valid receiving range is set according to an ideal 16-point average power predetermined by the system.

23. The AGC method according to claim 21, wherein the AGC process is accomplished by digital computation.

24. The AGC method according to claim 21, wherein the average power level is obtained by calculating a 32-point average power of the signal.

25. The AGC method according to claim 24, wherein the threshold is determined by an ideal power level of 32 sample points.

26. The AGC method according to claim 21, further comprising:

(vii) recalculating the average power level and tuning the gain of the VGA according to a difference between the recalculated average power level and the threshold.

27. An Automatic Gain Control (AGC) apparatus of controlling a wireless receiver having a gain of a Low Noise Amplifier (LNA) and a gain of a Variable Gain Amplifier (VGA) for determining a final gain setting LNAFinal and VGAFinal of the LNA and VGA, comprising:

means for setting initial gains for the LNA and the VGA corresponding to a maximum gain;

means for detecting and determining whether the power of a received RF signal is within a valid receiving range;

means for coarse-tuning the gains of the LNA and the VGA according to a subsequent preset value if the power of the received RF signal is not within the valid receiving range;

wherein a plurality of preset values for the gains are arranged in order so that the subsequent preset value is lower than the antecedent preset value;

means for computing an average power of the received RF signal; and

means for fine-tuning the gain of the VGA to be VGAFinal according to a difference between the average power and a threshold;

wherein the detecting and determining means requests the coarse-tuning means to tune the gains of the LNA and VGA again if the power of the received RF signal is still outside the valid receiving range, else fixes the current gain of the LNA as LNAFinal.

28. The AGC apparatus according to claim 27, wherein the valid receiving range is set according to an ideal 16-point average power predetermined by the system.

29. The AGC apparatus according to claim 27, wherein the AGC apparatus is operated in digital computation.

30. The AGC apparatus according to claim 27, wherein the average power level is obtained by calculating a 32-point average power of the signal.

31. The AGC apparatus according to claim 30, wherein the threshold is determined by an ideal power level of 32 sample points.

32. The AGC apparatus according to claim 27, further comprising:

means for recalculating the average power level and tuning the gain of the VGA according to a difference between the recalculated average power level and the threshold.