| 摘要 |
The present invention relates to an automatic gain control circuit (AGC) in a receiver for a digital radio telephone. Most of the total gain control of the received signal is accomplished in the base band frequency sections, in the I and Q branches whereof the signal amplification is controlled step by step, and only a minor part of the total gain control is performed in the RF stage. High amplification steps are formed by means of amplifiers (9a, 10a, 11a, 12a; 9b, 10b, 11b, 12b), of which the desired amplifier is activated by means of a digitally controlled (A, B) multiplexer (13a, 13b), and low amplification steps are formed by means of a resistance attenuator (14a, 14b), in which a signal of desired level is selected by means of a digitally controlled (C, D, E) multiplexer (15a, 15b). In addition, the RF amplifier (2) has two amplification levels, of which the desired amplification is selected by means of a digital control (F). By means of different digital control combinations (A, B, C, D, E, F) the entire gain control range required of the receiver can be covered.
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