Packet acquisition and channel tracking for a wireless communication device configured in a zero intermediate frequency architecture

Abstract

A method of controlling operation of a wireless device configured in a zero intermediate frequency architecture including a DC loop and a gain loop. The method includes processing energy in a wireless medium to generate a corresponding receive signal, monitoring the receive signal via a predetermined measurement window, detecting a changed condition in the channel, holding the gain feedback control loop at a constant gain level, and operating the DC loop in an attempt to search a stable DC value for the receive signal while the gain loop is held constant. A first case is DC saturation, where the gain is held constant until DC is controlled. A second case is clear channel assessment, where a prior stored gain setting is applied to the gain loop after detecting the end of the packet. A third case is preparation for receiving an expected acknowledgement packet after transmitting a packet, where again a prior stored gain setting is applied to the gain loop and DC is searched.

1. A method of controlling operation of a wireless communication device configured in a zero intermediate frequency (ZIF) architecture including a DC feedback control loop and a gain feedback control loop, the method comprising:
 processing energy in a wireless medium to generate a corresponding receive signal; 
 monitoring the receive signal via a predetermined measurement window; 
 detecting a changed condition in the wireless medium; 
 holding the gain feedback control loop at a constant gain level after detecting the changed condition; and 
 operating the DC feedback control loop in an attempt to search a stable DC value for the receive signal while the gain feedback control loop is held at the constant gain level. 
 
     
     
       2. The method of  claim 1 , further comprising wherein:
 said processing comprising comprises processing noise energy in the wireless medium while no packets are being transmitted; 
 said detecting a changed condition comprising comprises detecting DC saturation of the measurement window; 
 said operating the DC feedback control loop comprising comprises adding opposite polarity DC to the receive signal to reduce DC level of the receive signal until the measurement window is no longer DC saturated; and 
 wherein the method further comprises, when the measurement window is no longer DC saturated, operating the DC feedback control loop to control the DC level of the receive signal and releasing the gain feedback control loop to control power level of the receive signal to a predetermined target power level. 
 
     
     
       3. The method of  claim 2 , further comprising:
 detecting gain saturation in which the measurement window is clipped at both of predetermined minimum and maximum values above a predetermined clip rate and relatively balanced between the predetermined minimum and maximum values; and 
 operating the gain feedback control loop to perform a clip-step procedure to reduce gain of the receive signal. 
 
     
     
       4. The method of  claim 3 , wherein said clip-step procedure includes using a graduated clip gain adjustment in which gain is adjusted based on an amount of clipping of the receive signal. 
     
     
       5. The method of  claim 1 , further comprising: wherein said processing comprising comprises processing noise energy in the wireless medium while no packets are being transmitted;, the method further comprising:
 operating the gain feedback control loop until a noise floor gain value is determined; and 
 storing the noise floor gain value. 
 
     
     
       6. The method of  claim 5 , further comprising: wherein said detecting a changed condition in the wireless medium comprising comprises detecting an end of transmission of a packet in the wireless medium; wherein said holding the gain feedback control loop at a constant gain level comprises holding the gain at the retrieved noise floor gain value during a predetermined quiet period; the method further comprising:
 retrieving and applying the stored noise floor gain value in the gain feedback control loop; 
 said holding the gain feedback control loop at a constant gain level comprising holding the gain at the retrieved noise floor gain value during a predetermined quiet period; and 
 after expiration of the quiet period, releasing the gain feedback control loop. 
 
     
     
       7. The method of  claim 6 , further comprising:
 prior to transmission of the packet, determining a DC noise value of the DC feedback control loop; 
 storing the DC noise value; and 
 after detecting an end of transmission of the packet in the wireless medium, retrieving and applying the DC noise value to the DC feedback control loop. 
 
     
     
       8. The method of  claim 5 , further comprising: wherein said detecting a changed condition in the wireless medium comprising comprises detecting an end of transmission of a packet being transmitted in the wireless medium; and wherein said holding the gain feedback control loop at a constant gain level comprising comprises retrieving and applying the stored noise floor gain value in the gain feedback control loop for a predetermined period of time; and the method further comprising determining whether the DC feedback control loop converges to a stable DC level within the predetermined period of time. 
     
     
       9. The method of  claim 8 , further comprising: determining that the wireless medium is busy if the DC feedback control loop does not converge to a stable DC level within the predetermined period of time. 
     
     
       10. A method of operating a wireless communication device to perform initial acquisition of a packet being transmitted in a wireless medium, the wireless communication device configured in a zero intermediate frequency (ZIF) architecture including a DC feedback control loop and a gain feedback control loop, said the method comprising:
 processing radio frequency (RF) energy in the wireless medium to generate a corresponding receive signal; 
 determining if a DC threshold condition of the receive signal is exceeded; 
 if the DC threshold condition is exceeded, holding the gain feedback control loop at a constant gain level and operating the DC feedback control loop to reduce DC of the receive signal until the DC threshold condition of the receive signal is met; and 
 when the DC threshold condition of the receive signal is met, operating the DC feedback control loop to control the DC level of the receive signal and operating the gain feedback control loop to control a power level of the receive signal to a predetermined target power level. 
 
     
     
       11. The method of  claim 10 , wherein said operating the DC feedback control loop to control the DC level of the receive signal comprises controlling the DC level to within a predetermined maximum DC level. 
     
     
       12. The method of  claim 10 , wherein the receive signal comprising comprises an analog signal, the method further comprising: sampling the receive signal with an analog to digital converter (ADC) to generate corresponding digital samples, the ADC having a sufficient range to maintain signal integrity without covering a total potential signal range of the receive signal. 
     
     
       13. The method of  claim 12 , the digital samples ranging between a minimum value and a maximum value, wherein the DC threshold condition is exceeded when a percentage of digital samples at the minimum value or a percentage of digital samples at the maximum value exceed a predetermined threshold percentage of a total number of digital samples. 
     
     
       14. The method of  claim 13 , wherein the predetermined threshold percentage is 90 percent. 
     
     
       15. The method of  claim 13 , wherein said operating the DC feedback control loop to reduce the DC level of the receive signal comprises adding a DC offset to the receive signal in an attempt to meet the DC threshold condition. 
     
     
       16. The method of  claim 15 , wherein said adding a DC offset comprises conducting a step search procedure by repeatedly adding a predetermined DC offset voltage amount until the DC threshold condition is met. 
     
     
       17. The method of  claim 15 , wherein said adding a DC offset comprises performing a successive approximation DC offset voltage search procedure until the DC threshold condition is met. 
     
     
       18. The method of  claim 12 , the digital samples ranging between a minimum value and a maximum value, the method further comprising:
 detecting a gain saturation state in which clipped digital samples occur at both of the minimum and maximum levels at a rate greater than a predetermined clip ratio threshold and in which a number of digital samples at the minimum level is relatively balanced with a number of digital samples at the maximum level; and 
 operating the gain feedback control loop in a clipping mode while in the gain saturation state. 
 
     
     
       19. The method of  claim 18 , further comprising: adjusting the gain level of the gain feedback control loop based on an amount of clipping using a graduated clip gain adjustment. 
     
     
       20. The method of  claim 19 , wherein said graduated clip gain adjustment includes a corresponding one of a predetermined plurality of gain level adjustments for each of a plurality of predetermined clip ratio ranges. 
     
     
       21. The method of  claim 20 , wherein said graduated clip gain adjustment is graduated between a high gain adjustment for a high clip ratio and a low gain adjustment for a low clip ratio. 
     
     
       22. A method of operating a wireless transceiver device in preparation for an expected acknowledgment packet, the wireless transceiver device configured in a zero intermediate frequency (ZIF) architecture and including a DC feedback control loop and a gain feedback control loop, the method comprising:
 holding a gain level of the gain feedback control loop constant during a predetermined quiet period after transmission of a packet; 
 operating the DC feedback control loop during the predetermined quiet period in an attempt to resolve DC level while the gain feedback control loop is held constant; and 
 after the quiet period, releasing the gain feedback control loop to operate in a normal packet acquisition mode. 
 
     
     
       23. The method of  claim 22 , further comprising:
 prior to transmission of the packet, storing a gain level value of the gain feedback loop; and 
 after transmission of the packet, retrieving the stored gain level value and holding the gain feedback control loop at the retrieved gain level value during the predetermined quiet period. 
 
     
     
       24. The method of  claim 22 , further comprising:
 prior to said transmitting a packet, storing a DC value of the DC feedback control loop; and 
 applying the stored DC value after transmitting the packet. 
 
     
     
       25. A method of operating a wireless communication device to determine clear channel assessment of a wireless medium, the wireless communication device configured in a zero intermediate frequency (ZIF) architecture and including a DC feedback control loop and a gain feedback control loop, the method of comprising:
 storing a gain level value of the gain feedback control loop; 
 detecting a packet being transmitted; 
 after transmission of the packet is completed, retrieving the stored gain level value and holding the gain feedback control loop at the retrieved gain level value; 
 operating the DC feedback control loop to search a stable DC level; and 
 determining whether the DC loop converges to a stable DC level. 
 
     
     
       26. The method of  claim 25 , wherein said storing a gain level value is performed while no packets are being transmitted via the wireless medium. 
     
     
       27. The method of  claim 25 , further comprising:
 storing a DC value of the DC feedback control loop prior to said detecting a packet being transmitted; and 
 applying the stored DC gain setting after packet transmission. 
 
     
     
       28. The method of  claim 25 , further comprising:
 holding the gain level of the gain feedback control loop constant during a predetermined quiet period; and 
 releasing the gain feedback control loop after the predetermined quiet period to operate in a normal mode. 
 
     
     
       29. The method of  claim 25 , further comprising:
 determining if the DC feedback control loop converges to a stable DC level within a predetermined period; and 
 if the DC feedback control loop converges within the predetermined period, operating the DC feedback control loop and the gain feedback control loop in a normal mode. 
 
     
     
       30. The method of  claim 25 , further comprising: determining that the wireless medium is busy if the DC feedback control loop does not converge to a stable DC level within a predetermined period of time. 
     
     
       31. An apparatus for controlling DC offset voltage comprising:
 an automatic gain control (AGC) amplifier having a gain control input configured to set a gain of the AGC amplifier;   a gain feedback control loop connected to the gain control input configured to set the gain of the AGC amplifier, wherein the gain feedback control loop is configured to detect a changed condition in a wireless medium and to responsively hold the gain of the AGC amplifier constant;   a DC feedback control loop configured to generate a DC offset correction signal to reduce a DC offset voltage while the gain feedback control loop is held constant.   
     
     
       32. The apparatus of claim 31, wherein the DC feedback control loop includes a DC digital to analog converter (DAC) configured to generate the DC offset correction signal. 
     
     
       33. The apparatus of claim 31, wherein the gain feedback control loop includes an AGC digital to analog converter (DAC) configured to generate the DC offset correction signal. 
     
     
       34. The apparatus of claim 31, further comprising an analog to digital converter (ADC) coupled to the AGC amplifier, wherein the changed condition is a rail condition of the ADC. 
     
     
       35. The apparatus of claim 31, wherein the DC control loop includes a DC offset estimator configured to generate a DC estimate signal. 
     
     
       36. The apparatus of claim 35, further comprising a gain converter circuit configured to use the AGC gain to alter the DC estimate signal. 
     
     
       37. The apparatus of claim 36, wherein the gain converter circuit is a look up table. 
     
     
       38. The apparatus of claim 36, wherein the gain converter circuit includes an adjust memory. 
     
     
       39. The apparatus of claim 31, wherein the DC control loop includes a look up table. 
     
     
       40. The apparatus of claim 31, further comprising a calibration circuit configured to inject a predetermined or arbitrary DC level. 
     
     
       41. An apparatus for controlling DC offset voltage comprising:
 an automatic gain control (AGC) amplifier;   an AGC gain signal generator connected to the AGC amplifier;   a DC offset signal generator configured to generate a DC offset correction signal,   compensation logic circuitry connected to the AGC gain signal generator and the DC offset signal generator, and configured to detect a changed condition in a wireless medium and to responsively hold the gain of the AGC amplifier constant while controlling the DC offset signal generator to reduce a DC offset.   
     
     
       42. The apparatus of claim 41, wherein the DC offset signal generator is a DC digital to analog converter (DAC). 
     
     
       43. The apparatus of claim 42, wherein the DC DAC is configured to generate a DC offset correction signal for an in phase channel and for a quadrature channel. 
     
     
       44. An apparatus comprising:
 a zero intermediate frequency (ZIF) transceiver; and   a baseband processor configured to detect a changed condition in the wireless medium, wherein the baseband processor further comprises:
 a gain feedback control loop configured to maintain a constant gain level after detection of the changed condition; and 
 a DC feedback control loop configured to search for a stable DC value for the receive signal while the gain feedback control loop is maintained at the constant gain level. 
   
     
     
       45. The apparatus of claim 44, wherein the baseband processor is further configured to process energy in a wireless medium to generate a receive signal and monitor the receive signal via a predetermined measurement window to detect the changed condition. 
     
     
       46. The apparatus of claim 45, wherein the baseband processor is configured to process noise energy in the wireless medium while no packets are being transmitted and detect DC saturation of the measurement window, and wherein the DC feedback control loop is configured to add opposite polarity DC to the receive signal to reduce a direct current level of the receive signal until the measure window is no longer DC saturated. 
     
     
       47. The apparatus of claim 45, wherein the baseband processor is configured to process noise energy in the wireless medium while no packets are being transmitted, and wherein the gain feedback control loop is configured to operate until a noise floor gain value is determined, and wherein the baseband processor is further configured to store the noise floor gain value. 
     
     
       48. The apparatus of claim 47, wherein the gain feedback control loop is configured to maintain a constant gain level at the retrieved noise floor gain value during a predetermined quiet period associated with a packet, and after expiration of the predetermined quiet period, operate normally. 
     
     
       49. The apparatus of claim 48, wherein the baseband processor is further configured to determine a DC noise value of the DC feedback control loop prior to transmission of the packet, store the DC noise value, and after detection of the transmission of the packet in the wireless medium, retrieve and apply the DC noise value to the DC feedback control loop. 
     
     
       50. An apparatus comprising:
 a processor configured to determine if a DC threshold condition of a receive signal is exceeded; wherein the processor further comprises:
 a gain feedback control loop configured to maintain a constant gain level in response to a determination that the DC threshold condition of the receive signal is exceeded and control a power level of the receive signal at a predetermined target power level in response to a determination that the DC threshold condition of the receive signal is not exceeded; and 
 a DC feedback control loop configured to reduce a direct current level of the receive signal until the DC threshold condition of the receive signal is met in response to the determination that the DC threshold condition of the receive signal is exceeded and control the direct current level of the receive signal in response to the determination that the DC threshold condition of the receive signal is not exceeded. 
   
     
     
       51. The apparatus of claim 50, wherein the processor further comprising an analog to digital converter (ADC) configured to sample the receive signal to generate digital samples. 
     
     
       52. The apparatus of claim 51, wherein the digital samples range between a minimum value and a maximum value, and wherein the DC threshold condition is exceeded when a percentage of the digital samples at the minimum value or a percentage of the digital samples at the maximum value exceed a predetermined threshold percentage of a total number of the digital samples. 
     
     
       53. The apparatus of claim 52, wherein the DC feedback control loop is configured to reduce the direct current level of the receive signal by adding a DC offset to the receive signal. 
     
     
       54. The apparatus of claim 53, wherein the DC feedback control loop is configured to conduct a step search procedure by repeatedly adding a predetermined DC offset voltage amount until the DC threshold condition is met. 
     
     
       55. The apparatus of claim 51, wherein the digital samples range between a minimum value and a maximum value, wherein the processor is configured to detect a gain saturation state in which clipped digital samples occur at both of the minimum and maximum levels at a rate greater than a predetermined clip ratio threshold, and wherein the gain feedback control loop is configured to operate in a clipping mode while in the gain saturation state. 
     
     
       56. The apparatus of claim 55, wherein the gain feedback control loop is further configured to adjust the gain level based on an amount of clipping using a graduated clip gain adjustment. 
     
     
       57. An apparatus comprising:
 a processor including:
 a gain feedback control loop configured to maintain a gain level constant during a predetermined quiet period after transmission of a packet and operate in a normal packet acquisition mode after the quiet period; and 
 a DC feedback control loop configured to resolve a direct current level while the gain feedback control loop maintains the constant gain level. 
   
     
     
       58. The apparatus of claim 57, wherein the quiet period corresponds to a period during an ACK receive priority mode between an indication of an end of an original packet and a detected onset of an ACK packet. 
     
     
       59. The apparatus of claim 57, wherein the processor is configured to store a gain level value of the gain feedback loop prior to transmission of a packet and, after transmission of the packet, retrieve the stored gain level value and maintain the gain feedback control loop at the retrieved gain level value during the predetermined quiet period. 
     
     
       60. The apparatus of claim 57, wherein the processor is configured to store a DC value of the DC feedback control loop prior to transmission of a packet and apply the stored DC value after transmission of the packet.