Digital automatic gain control method and device

1. A method for attenuating a wideband analog signal before reception by an ADC:

selecting as a peak value the larger of a current output of the ADC or a previous output of the ADC;

determining an out-of-range indicator value, the out-of-range indicator value a multiple of the peak value if the current output exceeds an out of range value and the out-of-range indicator value the same as the peak value if the current output does not exceed an out-of-range value;

determining an error signal, the error signal based on the difference between the out-of-range indicator value and a target value; and

setting an attenuation level based on the error signal.

2. The method of claim 1 wherein the step of setting an attenuation level further comprises:

determining a new integrator value by adding the error signal to an existing integrator value; and

determining the attenuation level based on the new integrator value.

3. The method of claim 2 wherein the integrator value falls between one and a maximum upper range.

4. The method of claim 3 further comprising converting the new integrator value to a digital measure of attenuation and converting the digital level of attenuation to a decibel level.

5. The method of claim 1 wherein the step of selecting as a peak value further comprises reducing the previous output of the ADC by a decay factor.

6. The method of claim 1 wherein the step of determining an error signal further comprises setting the target value near the saturation point of the ADC.

7. The method of claim 1 further comprising increasing the error signal by a gain value after the step of determining an error signal.

8. The method of claim 1 further comprising adding the attenuation level to an output of the ADC.

9. The method of claim 1 further comprising determining a temperature based attenuation level.

10. An automatic gain control device comprising:

a peak detector configured to receive a current output of an ADC and compare it to a previous output to produce a peak value;

an out-of-range indicator configured to receive an out-of-range signal if an input to the ADC exceeds the dynamic range of the ADC, the out-of-range indicator operable to increase the peak value if the out-of-range indicator receives the out-of range signal;

an error detector coupled to the out-of-range indicator and the peak detector and operable to produce an error level, the error level the difference of an output of the out-of-range indicator and a pre-selected target value, the pre-selected target value chosen to attenuate interference signals that exceed the dynamic range of the ADC but minimize the attenuation of communication signals;

an integrator coupled to the error detector and configured to sum the error level with an integrator value to determine a new integrator value; and

a quantizer coupled to the integrator and operable to receive the new integrator value and determine a new level of attenuation.

11. The automatic gain control device of claim 10 further comprising a volt-to-decibel converter to convert the new level of attenuation to an amount of decibel attenuation.

12. The automatic gain control device of claim 10 further comprising a temperature attenuation compensator for determining an attenuation value based on the temperature of the automatic gain control.

13. The automatic gain control device of claim 10 further comprising a gain recovery unit operable to restore the output of the ADC to its original signal strength.

14. The automatic gain control device of claim 10 wherein the integrator has a minimum value of one to prevent any negative attenuation.

15. The automatic gain control device of claim 10 wherein the quantizer further comprises a lookup table relating the integrator output to an attenuation level.

16. The automatic gain control device of claim 10 wherein the previous output is decreased by a decay factor prior to each time the previous output is compared with the current output.

17. A receiver for receiving two or more communication channels in the presence of interference, the receiver comprising:

an antenna operable to receive an analog signal comprising two or more communication channels;

an analog to digital converter coupled to the antenna and configured to sample the analog signal and to convert the analog signal into a digital representation;

an attenuator coupled to the antenna and configured to attenuate the analog signal prior to the analog-to-digital converter sampling the analog signal; and,

an automatic gain control coupled to the output of the analog to digital converter and an input of the attenuator, the automatic gain control comprising:

a peak detector configured to receive a current output of an ADC and compare it to a previous output to produce a peak value;

an out-of-range indicator configured to receive an out-of-range signal if an input to the ADC exceeds the dynamic range of the ADC, the out-of-range indicator operable to increase the peak value if the out-of-range indicator receives the out-of range signal;

an error detector coupled to the out-of-range indicator and operable to produce an error level, the error level the difference of an output of the out-of-range indicator and a pre-selected target value chosen to attenuate interference signals that exceed the dynamic range of the ADC but minimize the attenuation of communication signals;

an integrator coupled to the error detector and configured to sum the error level with an integrator value to determine a new integrator value; and

a quantizer coupled to the integrator and operable to receive the new integrator value and determine a new level of attenuation.

18. The receiver of claim 17 further comprising a channelizer to separate the analog signal into the two or more communication channels.

19. The receiver of claim 17 further comprising a temperature attenuation compensator for determining an attenuation value based on the temperature of the automatic gain control.

20. The receiver of claim 17 further comprising a gain recovery unit operable to restore the output of the ADC to its original signal strength.