Automatic gain control
First Claim
1. A method for controlling gain of an amplifier for received radio signals in a radio receiver, the radio receiver having a controllable gain responsive to an automatic gain control signal (c), the method comprising:
- amplifying received radio frequency signals (RF), level detecting at least one down converted signal (Ip-LP;
QP-LP) resulting from amplified radio frequency signals (RFP), and generating the automatic gain control signal (c) in response to at least one down converted signal level ([I];
[Q]) such that the controllable gain maintains the at least one down converted signal level ([I];
[Q]) at less than a predetermined limit level, characterised by varying a time constant (T) of the automatic gain control signal (c) in response to a time derivative parameter (VΣ
) of the at least one down converted signal (Ip-LP;
Qp-LP) such that the automatic gain control signal (c) is adapted to a power variation rate of the received radio frequency signals (RF).
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Accused Products
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.
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Citations
1 Claim
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1. A method for controlling gain of an amplifier for received radio signals in a radio receiver, the radio receiver having a controllable gain responsive to an automatic gain control signal (c), the method comprising:
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amplifying received radio frequency signals (RF), level detecting at least one down converted signal (Ip-LP;
QP-LP) resulting from amplified radio frequency signals (RFP), andgenerating the automatic gain control signal (c) in response to at least one down converted signal level ([I];
[Q]) such that the controllable gain maintains the at least one down converted signal level ([I];
[Q]) at less than a predetermined limit level, characterised by varying a time constant (T) of the automatic gain control signal (c) in response to a time derivative parameter (VΣ
) of the at least one down converted signal (Ip-LP;
Qp-LP) such that the automatic gain control signal (c) is adapted to a power variation rate of the received radio frequency signals (RF).
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Specification