Gain compensation based on a first gain factor and a second gain factor with time-varying compensation

1. A device comprising a processing circuit (B 1 ; B 1 , B 11 ) with a predetermined limited dynamic range, and an automatic gain control circuit comprising:

a gain determining circuit (B 2 ) for determining a first gain factor (g),

a first gain controller (B 3 ) for controlling an amplitude of an input signal (S 1 ) with the first gain factor (g) to supply a gain controlled signal (S 3 ) to the processing circuit (B 1 ; B 1 , B 11 ),

a compensation circuit (B 5 ) for determining a second gain factor (dg) based on the first gain factor (g) and input parameters (DL, TR, DV) defining a time variation of the second gain factor (dg), and

a second gain controller (B 1 ; B 10 ) for receiving an output signal of the processing circuit (B 1 ; B 1 , B 11 ) and the second gain factor (dg) to obtain a compensated output signal (S 2 ) being substantially compensated for an amplitude change of the gain controlled signal (S 3 ) due to a change of the first gain factor (g).

2. A device as claimed in claim 1 , wherein the processing circuit (B 1 ; B 1 , B 11 ) comprises an analog to digital converter (B 1 ) for converting the gain controlled signal (S 3 ) into a digital signal (S 4 ; S 2 ), the output signal of the processing circuit (B 1 ; B 1 , B 11 ) being a digital signal (S 4 ), and the compensated output signal (S 2 ) being a compensated digital signal (S 2 ).

3. A device as claimed in claim 2 , wherein the gain determining circuit (B 2 ) has inputs for receiving the gain controlled signal (S 3 ) and/or the digital signal (S 4 ) and an output for supplying the first gain factor (g), the first gain factor (g) being determined to obtain the amplitude of the gain controlled signal (S 3 ) fitting within an operating range of the analog to digital converter (B 1 ).

4. A device as claimed in claim 3 , wherein the gain determining circuit (B 2 ) is arranged for adapting the first gain factor (g) in steps.

5. A device as claimed in claim 4 , wherein the steps comprise powers of the number two.

6. A device as claimed in claim 2 , wherein the analog to digital converter (B 1 ) is of a single bit sigma-delta type.

7. A device as claimed in claim 2 , wherein the analog to digital converter (B 1 ) comprises the second gain controller (B 1 ; B 10 ) for controlling the gain of the digital signal (S 4 ) to supply the compensated digital signal (S 2 ).

8. A device as claimed in claim 2 , wherein the second gain controller (B 1 ; B 10 ) is arranged for controlling the gain of the digital signal (S 4 ) supplied by the analog to digital converter (B 1 ).

9. A device as claimed in claim 2 , wherein the processing circuit (B 1 ; B 1 , B 11 ) comprises a digital processing circuit (B 11 ) for processing the digital signal (S 4 ) supplied by the analog to digital converter (B 1 ) to obtain a processed digital signal (S 5 ), and wherein the second gain controller (B 10 ) is arranged for controlling a gain of the processed digital signal (S 5 ) with the second gain factor (dg).

10. A device as claimed in claim 9 , further comprising a digital gain controller (B 12 ) being arranged between the analog to digital converter (B 11 ) and the digital processing circuit (B 11 ), the digital gain controller (B 12 ) being controlled by a further digital gain factor (dga).

11. A device as claimed in claim 1 , wherein the compensation circuit (B 5 ) comprises a delay circuit (B 6 ) for delaying a start instant of a change of the second gain factor (dg) in response to the change of the first gain factor (g) to substantially compensate for a processing time of the processing circuit (B 1 ; B 1 , B 11 ) causing a time delay (TD) between the gain controlled signal (S 3 ) and the compensated output signal (S 2 ).

12. A device as claimed in claim 1 , wherein the compensation circuit (B 5 ) comprises a waveform generating circuit (B 7 ) for generating a waveform (WF) of the time variation of the second gain factor (dg).

13. A device as claimed in claim 12 , wherein the waveform generating circuit (B 7 ) comprises a bandwidth limitation circuit, or a linear interpolation circuit, or a higher order interpolation circuit, or a table look up circuit, or a line drawing algorithm circuit.

14. A device as claimed in claim 1 , wherein the compensation circuit (B 5 ) comprises a level adaptating circuit (B 8 ) for generating a DC-offset of the second gain factor (dg) to substantially compensate for a static level deviation (E) of the compensated output signal (S 2 ).

15. A device as claimed in claim 1 , further comprising an automatic calibration circuit (B 13 ) being arranged for, during a test period (TP), repeatedly:

generating a reference signal (RS) being supplied as the input signal (S 1 ),

adapting the first gain factor (g) with a predetermined amount,

providing a first set of input parameters (DL, TR, DV),

checking whether a change of amplitude occurs of the compensated output signal (S 2 ), and

adapting at least one of the input parameters (DL, TR, DV), until substantially no change of amplitude occurs of the compensated output signal (S 2 ), and

finally storing the input parameters (DL, TR, DV) determined, for use during normal operation.

16. A method of automatic gain control in a device comprising a processing circuit (B 1 ; B 1 , B 11 ) with a predetermined limited dynamic range, the method comprising:

determining (B 2 ) a first gain factor (g),

controlling (B 3 ) an amplitude of an input signal (S 1 ) with the first gain factor (g) to supply a gain controlled signal (S 3 ) to the processing circuit (B 1 ; B 1 , B 11 ),

determining (B 5 ) a second gain factor (dg) based on the first gain factor (g) and input parameters (DL, TR, DV) defining a time variation of the second gain factor (dg), and

controlling (B 1 ; B 10 ) with the second gain factor (dg) an output signal of the processing circuit (B 1 ; B 1 , B 11 ) to obtain a compensated output signal (S 2 ) being substantially compensated for an amplitude change of the gain controlled signal (S 3 ) due to a change of the first gain factor (g).

17. A method of automatic gain control as claimed in claim 16 , further comprising an automatic calibration (B 13 ) comprising, during a test period, repeatedly:

generating a reference signal (RS) being supplied as the input signal (S 1 ),

adapting the first gain factor (g) with a predetermined amount,

providing a first set of input parameters (DL, TR, DV),

checking whether a change of amplitude occurs of the compensated output signal (S 2 ), and

adapting at least one of the input parameters (DL, TR, DV), until substantially no change of amplitude occurs of the compensated output signal (S 2 ), and

finally storing the input parameters (DL, TR, DV) determined, for use during normal operation.

18. An audio apparatus comprising a processing circuit (B 1 ; B 1 , B 11 ) with a predetermined limited dynamic range, and an automatic gain control circuit comprising:

a gain determining circuit (B 2 ) for determining a first gain factor (g),

a first gain controller (B 3 ) for controlling an amplitude of an input signal (S 1 ) with the first gain factor (g) to supply a gain controlled signal (S 3 ) to the processing circuit (B 1 ; B 1 , B 11 ),

a compensation circuit (B 5 ) for determining a second gain factor (dg) based on the first gain factor (g) and input parameters (DL, TR, DV) defining a time variation of the second gain factor (dg), and

a second gain controller (B 1 ; B 10 ) for receiving an output signal of the processing circuit (B 1 ; B 1 , B 11 ) and the second gain factor (dg) to obtain a compensated output signal (S 2 ) being substantially compensated for an amplitude change of the gain controlled signal (S 3 ) due to a change of the first gain factor (g).