Automatic gain controller for radio communication system

Details Automatic gain controller for radio communication system Automatic gain controller for radio communication system

1998-10-29

2001-04-24

Williams, Howard L. (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Nonlinear

C455S138000

Reexamination Certificate

active

06222472

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic gain controller for compensating for an amplitude variation of a received signal in a radio communication system and more particularly relates to an automatic gain controller for reducing a code size of a digital signal processor (DSP).
2. Description of the Related Art
Radio communication systems often suffer from a fading phenomenon which causes an amplitude variation in a received signal. To compensate for the amplitude variation, radio communication systems often utilize an automatic gain controller (AGC). AGC circuits provide a substantially constant output amplitude in response to a varying input signal amplitude.
FIG. 1
illustrates a block diagram of a conventional automatic gain controller. Referring to the drawing, an automatic gain control (AGC) amplifier
11
amplifies an input signal according to an AGC control signal. An analog-to-digital (A/D) converter
12
converts an analog signal output from the AGC amplifier
11
to a digital signal. A power estimator
13
estimates a power of a signal output from the A/D converter
12
. An AGC controller
14
receives an AGC reference value and the power estimated in the power estimator
13
to calculate an AGC gain. The power estimator
13
converts the calculated AGC gain to a digital dB (decibel) value. A digital-to-analog (D/A) converter
15
converts the digital dB value output from the AGC controller
14
to the analog AGC control signal and provides the AGC control signal to the AGC amplifier
11
.
Conventionally, the AGC controller
14
is a complex structure, since it must calculate the AGC reference value and the estimation value of the power estimator
13
in real time. With advances in digital signal processor (DSP) chips, there is an increasing tendency to utilize a DSP chip as a processor for the communications system and have the DSP perform the function of the automatic gain controller. However, utilizing the DSP as the AGC controller
14
places a significant calculation burden on the DSP, which may result in an overload on the DSP chip. In addition, to incorporate additional functions into the DSP chip, it is necessary to reduce the DPS code in size (or length) for respective software modules.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an automatic gain controller for reducing a DSP code in size.
To achieve the above object, there is provided an automatic gain controller including an automatic gain control amplifier and an A/D converter for converting an analog signal output from the AGC amplifier to a digital signal. In the automatic gain controller, a power estimator connected to the A/D converter, estimates a power of a signal input from the A/D converter. A filter connected to the power estimator filters the power output from the power estimator to attenuate noises and interferences. A comparator connected to the filter receives the filtered power output from the filter and generates an AGC control gain. A dB-to-D/A input converter connected to the comparator converts the AGC control gain output from the comparator to a D/A input signal. A D/A converter connected to the dB-to-D/A input converter converts the D/A input signal output from the dB-to-D/A input converter to an analog AGC control signal and provides the AGC control signal to the AGC amplifier.


REFERENCES:
patent: 5659582 (1997-08-01), Kojima
patent: 5784410 (1998-07-01), Nakano
patent: 5-075664 (1993-03-01), None
JPO Abstract and front page of JP 7-288485, Kojima and Uchiki Oct. 31, 1995.

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