Automatic gain control

• US 20030148745A1
• Filed: 02/15/2002
• Published: 08/07/2003
• Est. Priority Date: 02/16/2001
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Konradsson, Per, Nystrom, Christian, Grasbeck, Ari
• Granted Patent: US 7,082,291 B2
• Time in Patent Office: Days
• US Class Current: 455/136
• CPC Class Codes: H03G 3/001 Digital control of analog signals
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence

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 (I_P-LP; Q_−LP) are digitised in A/D-converters (110; 111 ) for further processing in a digital signal processor (112). The resulting signal components (I_P-LP; Q_P-LP) are also fed to a respective signal level detector (113; 114) whose output signals ([I]; [Q]) are combined (115) into a combined signal (V_Σ). This signal (V_Σ) 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 (I_P-LP; Q_P-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 (V_Σ) sends a pulse signal (R) to the digital signal processor (112) if the time derivative parameter (V_Σ) on basis of the combined signal (V_Σ) . A ramp generator (118) receiving the time derivative parameter (V_Σ) sends a pulse signal (R) to the digital signal processor (112) if the time derivative parameter (V_Σ) exceeds a threshold value (V_T). 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 (V_Σ) has a comparatively high value, and vice versa.

Claims

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 (I_p-LP;

Q_P-LP) resulting from amplified radio frequency signals (RF_P), 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 (V_Σ

) of the at least one down converted signal (I_p-LP;

Q_p-LP) such that the automatic gain control signal (c) is adapted to a power variation rate of the received radio frequency signals (RF).