Automatic gain control and DC offset compensation

1. A signal receiver configured to process two receive phase signals, having a gain control circuit comprising:

detection means configured to identify for each phase signal: (a) a first number of samples during a part of a training period for which that phase signal exceeds a first threshold, (b) a second number of samples during a part of the training period for which that phase signal is below minus the first threshold, and to determine for each phase signal a respective minimum value that is equal to a smaller of the first and second numbers of samples;

a first gain stimulus generator configured to generate a first gain stimulus in dependence on the two minimum values;

averaging means configured to compute an average of the signal received by the receiver during the training period;

a second gain stimulus generator configured to generate a second gain stimulus in dependence on the average estimated by the averaging means during the training period; and

a gain control signal generator configured to generate a gain control signal for the receiver in dependence on the first gain stimulus and the second gain stimulus.

2. The receiver as claimed in claim 1 , comprising an amplifier for amplifying received signals, the amplifier being configured to apply a level of gain that is dependent on the gain control signal.

3. The receiver as claimed in claim 1 , wherein the first gain stimulus generator is configured to generate the first gain stimulus in dependence on a larger of the two minimum values.

4. The receiver as claimed in claim 3 , wherein the averaging means is configured to estimate the average of the signal received by the receiver during the training period as being the average over the part of the training period of the phase signal whose minimum value is larger.

5. The receiver as claimed in claim 1 , wherein one of the receive phase signals is an in-phase signal and one of the receive phase signals is a quadrature signal.

6. The receiver as claimed in claim 1 , wherein the first gain stimulus generator is configured to generate the first gain stimulus such that it is at least approximately proportional to an inverse error function of a representation of excess amplitude.

7. The receiver as claimed in claim 1 , wherein the first gain stimulus detector comprises a look-up table configured to output the first gain stimulus in response to receiving a representation of excess amplitude.

8. The receiver as claimed in claim 1 , wherein the second gain stimulus detector is configured to generate the second gain stimulus such that it is at least approximately proportional to an error function of the average estimated by the averaging means during the training period.

9. The receiver as claimed in claim 1 , wherein the second gain stimulus detector comprises a look-up table configured to output the second gain stimulus in response to receiving the average estimated by the averaging means during the training period.

10. The receiver as claimed in claim 1 , wherein the gain control signal generator is configured to generate the gain control signal for the receiver by summing the first gain stimulus and the second gain stimulus.

11. The receiver as claimed in claim 1 , comprising means for performing DC offset compensation in dependence on the signal received during the said training period.

12. The receiver as claimed in claim 1 , wherein:

the detection means is configured to identify minimum amplitudes during each of a series of training periods of the signal received by the receiver;

the first gain stimulus generator is configured to generate a series of first gain stimuli, each being generated in dependence on a minimum amplitude identified by the detection means during a respective training period;

the averaging means is configured to compute the average of each signal whose gain is to be controlled by the circuit as received by the receiver during each training period;

the second gain stimulus generator is configured to generate a series of second gain stimuli, each being generated in dependence on the average estimated by the averaging means during a respective training period; and

the gain control signal generator is configured to generate a series of gain control signals for the receiver in dependence on the first gain stimulus and the second gain stimulus dependent on the signal received during a respective training period.

13. The receiver as claimed in claim 12 , wherein the receiver is for receiving signal frames composed of a series of training periods followed by traffic data, and the receiver is configured to use the gain control signal generated by the gain control signal generator in dependence on the first gain stimulus and the second gain stimulus dependent on the signal received during a final training period of a frame for reception of the traffic data of the frame.

14. The receiver as claimed in claim 13 , wherein each training period occupies a part of a training symbol of the received signal.

15. The receiver as claimed in claim 1 , wherein the receiver is an ultra wide band (UWB) signal receiver.

16. A method for receiving a signal by means of a signal receiver configured to process two receive phase signals, the method comprising:

identifying for each phase signal: (a) a first number of samples during a part of a training period for which that phase signal exceeds a first threshold, (b) a second number of samples during a part of the training period for which that phase signal is below minus the first threshold, and determining for each phase signal a respective minimum value that is equal to a smaller of the first and second numbers of samples;

generating a first gain stimulus in dependence on the two minimum values;

computing an average of the signal received by the receiver during the training period;

generating a second gain stimulus in dependence on the average estimated during the training period; and

generating a gain control signal for the receiver in dependence on the first gain stimulus and the second gain stimulus.