Automatic gain control

Abstract

The invention relates to gain control for an amplifier for received radio signals by means of an automatic gain control signal (c). A down converter (103) produces signal components (I; Q) from received radio frequency signals (RF). The signal components (I; Q) are amplified in a respective amplifier (104; 105), low pass filtered (106; 107) and further amplified (108; 109). Then, the resulting signal components (IP-LP; Q−LP) are digitised in A/D-converters (110; 111 ) for further processing in a digital signal processor (112). The resulting signal components (IP-LP; QP-LP) are also fed to a respective signal level detector (113; 114) whose output signals ([I]; [Q]) are combined (115) into a combined signal (VΣ). This signal (VΣ) is forwarded to a gain control unti (116), which produces the automatic gain control signal (c). The automatic gain control signal (c) controls the gain of the amplifiers (104; 105) such that the resulting signal components (IP-LP; QP-LP) are maintained at signal level ([I]; [Q]) less than a predetermined limit level being adapted to the A/D converters (110; 111). A derivation unit (117) generates a time derivative parameter (VΣ) sends a pulse signal (R) to the digital signal processor (112) if the time derivative parameter (VΣ) on basis of the combined signal (VΣ) . A ramp generator (118) receiving the time derivative parameter (VΣ) sends a pulse signal (R) to the digital signal processor (112) if the time derivative parameter (VΣ) exceeds a threshold value (VT). The digital signal processor (112) produces a time constant value (set-D), which forms a basis for a time constant (T) of the automatic gain control signal (c). The digital signal processor (112) also influences the time constant (T) such that it obtains a relatively small value if the time derivative parameter (VΣ) has a comparatively high value, and vice versa.

Dependencies are inferred from the claim text.