Receiver circuit for mobile radio receivers with automatic gain control

1. A receiver circuit for a mobile radio receiver, comprising:

a controllable amplifier having a variable gain level;

an analog-digital converter stage connected downstream of said controllable amplifier in a signal path through the receiver circuit;

a digital filter configuration for channel selection connected downstream of said converter stage, said digital filter configuration for channel selection being a cascade filter composed of a plurality of filter stages including an input-end filter stage, intermediate filter stages, and an output-end filter stage, said intermediate filter stages and said output-end filter stage being minimum-phase filter stages;

a signal strength estimator for determining a signal strength in a selected user channel; and

a feedback connected between said signal strength estimator and said amplifier for controlling said amplifier in dependence on a function of the signal strength of the user-channel determined by said signal strength estimator.

2. The receiver circuit according to claim 1 , wherein said minimum-phase filter stages are selected from the group consisting of wave digital filters and bridge wave digital filters.

3. A receiver circuit for a mobile radio receiver, comprising:

a controllable amplifier having a variable gain level;

an analog-digital converter stage connected downstream of said controllable amplifier in a signal path through the receiver circuit;

a digital filter configuration for channel selection connected downstream of said converter stage, said digital filter configuration for channel selection being a cascade filter composed of a plurality of filter stages including an input-end filter stage and intermediate filter stages, said intermediate filter stages being minimum-phase filter stages;

a signal strength estimator for determining a signal strength in a selected user channel; and

a feedback connected between said signal strength estimator and said amplifier for controlling said amplifier in dependence on a function of the signal strength of the user-channel determined by said signal strength estimator.

4. The receiver circuit according to claim 3 , wherein: said controllable amplifier comprises a plurality of amplifier stages; and an evaluation device is connected to receive a signal representing the user-channel signal strength determined by said signal strength estimator; and a respective said amplifier stage is connected into the circuit whenever said evaluation device detects that a signal-to-noise ratio in the user signal has dropped below a predefined value.

5. The receiver circuit according to claim 4 , wherein the predefined value of the signal-to-noise ratio is approximately 20 db.

6. The receiver circuit according to claim 4 , which further comprises: a memory device connected to said signal strength estimator for storing signal strength values for the user channel and for adjacent channels; and said

evaluation device is connected to read out the signal strength values stored in said memory device.

7. The receiver circuit according to claim 6 , wherein: at least some of said amplifier stages of said controllable amplifier have different gain levels; and

respective said amplifier stages are selected for connection into the circuit in dependence on the signal strength values read out from said memory device.

8. The receiver circuit according to claim 3 , wherein said controllable amplifier comprises between 3 and 6 amplifier stages.

9. The receiver circuit according to claim 3 , wherein said controllable amplifier comprises 4 amplifier stages.

10. The receiver circuit according to claim 3 , wherein said analog-digital converter stage is a delta-sigma converter.

11. The receiver circuit according to claim 3 , wherein said minimum-phase filter stages are selected from the group consisting of wave digital filters and bridge wave digital filters.

12. The receiver circuit according to claim 3 , which comprises a digital IF mixer stage connected in the signal path between said analog-digital converter stage and said digital filter configuration.

13. A method for processing a received signal in a mobile radio receiver; which comprises the following steps:

amplifying the received signal with a controllable amplifier having a variable gain;

digitizing the amplified signal with an analog-digital converter stage to form a digitized signal;

limiting a bandwidth of the digitized signal with a digital filter configuration for channel selection, the digital filter configuration for channel selection being a cascade filter composed of a plurality of filter stages including an input-end filter stage, intermediate filter stages, and an output-end filter stage, the intermediate filter stages and the output-end filter stage being minimum-phase filter stages;

determining a signal strength of a selected user-channel signal with a signal strength estimator; and

controlling the controllable amplifier in dependence on the signal strength of the user-channel determined by the signal strength estimator.

14. A method for processing a received signal in a mobile radio receiver, which comprises the following steps:

amplifying the received signal with a controllable amplifier having a variable gain;

digitizing the amplified signal with an analog-digital converter stage to form a digitized signal;

limiting a bandwidth of the digi&ized signal with a digital filter configuration for channel selection, the digital filter configuration for channel selection being a cascade filter composed of a plurality of filter stages including an input-end filter stage and intermediate filter stages, the intermediate filter stages being minimum-phase filter stages; determining a signal strength of a selected user-channel signal with a signal strength estimator; and

controlling the controllable amplifier in dependence on the signal strength of the .user-channel detetmined by the signal strength estimator.

15. The method according to claim 14 , which comprises: implementing changes in a gain level only with incremental changes; and changing from one amplification stage into an amplification stage with a higher gain level if a signal-to-noise ratio in the user-channel signal drops below a predefined value.

16. The method according to claim 15 , which comprises: storing signal strength values for the user channel and for adjacent channels in a memory device; and when a change in the gain level is requested, reading out stored signal strength values from the memory device with an evaluation device and selecting a suitable stage level of the gain taking into account the read-out signal strength values.