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) that are amplified in a respective amplifier (104, 105). Then, the resulting signal components (IP-LP; QP-LP) are digitised in A / D-converters (110; 111) for further processing in a digital signal processor (112) and are also fed to a respective signal level detector (113; 114) whose output signals ([I]; [Q]) are combined (115) into a combined signal (VSigma). This signal (VSigma) is forwarded to a gain control unit (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).

Description

THE BACKGROUND OF THE INVENTION AND PRIOR ART[0001] The present invention relates generally to automatic gain control in a radio frequency receiver. More particularly the invention relates to a method of controlling gain of an amplifier for received radio signals in a radio receiver, according to the preamble of claim 1. The invention also relates to a computer program, for instance in the form of a digital processor algorithm, according to claim 12, a computer readable medium according to claim 13 and an arrangement according to the preamble of claim 14.[0002] A problem that arises in most radio communications receivers concerns the wide variation in power level of the radio signals received at the antenna. This variation is due to a variety of causes. For example, the distance between the transmitter and the receiver can vary considerably. Different transmitters may also utilise different power levels. Since, disregarding the influence of any screening objects, the received signal...

AI Technical Summary

Benefits of technology

"The present invention relates to a method for controlling the gain of an amplifier for received radio signals in a radio receiver. The method is characterized by varying the time constant of the automatic gain control signal in response to a time derivative parameter of the at least one down converted signal. This allows for a quick and accurate AGC that can meet the requirements of modern packet data protocols. The invention provides a reliable and flexible AGC solution that is fast and flexible, and can be used in bursty communication systems."

Problems solved by technology

A problem that arises in most radio communications receivers concerns the wide variation in power level of the radio signals received at the antenna.

Furthermore, these variations may occur very rapidly due to changes in the radio conditions.

However, besides capable A / D- and D / A-converters, digital AGC also requires an amount of processing power, which in turn is correlated with power consumption and costs.

Moreover, a large bandwidth places relatively demanding requirements on the A / D- and D / A-converters, particularly if a high digital resolution is necessary.

However, it is both technically complicated and expensive to accomplish an AGC function involving digital signal level detection with sufficient accuracy and within such short time limits by utilising today's A / D converters, D / A converters and digital signal processors.

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