Pulse or digital communications – Receivers – Automatic gain control
Reexamination Certificate
2000-06-09
2004-08-10
Fan, Chieh M. (Department: 2634)
Pulse or digital communications
Receivers
Automatic gain control
C375S130000, C375S316000, C455S245200
Reexamination Certificate
active
06775336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiver and a gain control method thereof, and more particularly to a control scheme of a gain control amplifier provided in a radio section forming part of a receiver in mobile communication.
2. Description of the Related Art
Generally, in radio communication such as mobile communication, it is known that received power at an antenna terminal of a receiver largely varies due to the strength of radio waves depending on the distance between a transmitter and the receiver or due to the strength of radio waves depending on topographic conditions of a site where the transmitter communicates with the receiver. When the received power at the antenna terminal varies, there exists not only the need for setting a wide range of input power to a demodulator forming part of the receiver, but also the problem of failing to ensure stable reception characteristics due to the varying received power.
To address the problems, the receiver is provided with a gain control amplifier capable of controlling gain in a relatively later stage in a radio section forming part of the receiver and in a stage previous to the demodulator such that the gain of the gain control amplifier is controlled in accordance with variations in received power at the antenna terminal to maintain constant input power to the demodulator and to ensure stable reception characteristics.
Next, the control method of the gain control amplifier is described in detail. First, a received signal is demodulated in the receiver and the received power amount is derived from the demodulated received signal. Next, the derived received power amount is compared with a target value held in the receiver, and if the derived received power amount is lower than the target value, control is performed such that the gain of the gain control amplifier is increased. On the other hand, if the derived received power amount is higher than the target value, control is performed such that the gain of the gain control amplifier is reduced. In this manner, the input power amount to the demodulator is adjusted to be constant and stable reception characteristics can be realized.
FIG. 1
shows a configuration of the aforementioned receiver. The receiver shown in
FIG. 1
comprises antenna
101
for receiving signals transmitted from a base station and for transmitting signals transmitted from a mobile station, antenna sharing device
102
for separating received signals and transmitted signals, high frequency amplifier
103
for amplifying a received signal in a radio frequency band, high pass filter
104
for passing only the frequency band of the received signal, frequency converter
105
for frequency converting the received signal in the radio frequency band into a received signal in an intermediate frequency band, channel filter
106
for passing only the signal of a received channel of the frequency converted received signal, gain control amplifier
107
capable of controlling gain, orthogonal demodulator
108
, baseband filters
109
and
110
, local signal oscillators
111
and
112
, transmitter
113
, and digital signal processing unit
114
.
In the receiver configured as shown in
FIG. 1
, the received signal received at antenna
101
is inputted to high frequency amplifier
103
for amplification through antenna sharing device
102
. The amplified output is inputted to frequency converter
105
through high pass filter
104
. At frequency converter
105
, the received signal in the radio frequency band is frequency converted into a received signal in the intermediate frequency band using a locally oscillated signal outputted from local signal oscillator
111
, and then the converted signal is outputted.
The received signal in the intermediate frequency band outputted from frequency converter
105
is inputted to orthogonal demodulator
108
through gain control amplifier
107
after channel filter
106
filters out any interference wave existing near the received channel. At orthogonal demodulator
108
, the received signal in the intermediate frequency band is frequency converted into a received signal in a baseband using a locally oscillated signal outputted from local signal oscillator
112
, and the received signal is orthogonal demodulated for output as a received I component signal and a received Q component signal. Thereafter, the received I component signal and the received Q component signal are inputted to digital signal processing unit
114
through baseband filters
109
and
110
, respectively.
Digital signal processing unit
114
converts analog signals into digital signals and performs digital signal processing such as error correction, and in addition, calculates the received power from the received signal to perform gain control of gain control amplifier
107
.
Next, the control operation of gain control amplifier
107
is described in detail with reference to FIG.
2
. It should be noted that
FIG. 2
shows the details of the portions for processing the received signal in the intermediate frequency band and the portions for processing the received signal in the baseband (corresponding to digital processing unit
114
in
FIG. 1
) forming part of the aforementioned receiver, and the components equivalent to those in
FIG. 1
are denoted with the same reference numerals. Since the portions of the receiver for processing the received signal in the high frequency band overlaps with the portions in
FIG. 1
, the description thereof is omitted.
Digital signal processing unit
114
comprises A/D converters
206
and
207
for receiving outputs from baseband filters
109
and
110
as their inputs, respectively, baseband digital filters
208
and
209
, baseband signal processing unit
210
, control signal generating unit
211
, and power calculator
212
.
The received I component signal and the received Q component signal outputted from orthogonal demodulator
108
are inputted to baseband filters
109
and
110
, respectively, where any interference wave existing near the received signals is removed. Thereafter, the received I and Q signals are converted from analog signals into digital signals at A/D converters
206
and
207
, respectively, and inputted to baseband digital filters
208
and
209
. Baseband digital filters
208
and
209
respectively filter out any interference wave existing near the received channel and limit the bands for preventing intersymbol interference in the digital signals, and then the signals are inputted to baseband signal processing unit
210
and to power calculator
212
, respectively.
Baseband signal processing unit
210
performs digital signal processing such as error correction. The interference wave existing near the received channel is sufficiently attenuated in three stages using channel filter
106
, baseband filters
109
and
110
, and baseband digital filters
208
and
209
. Power calculator
212
calculates the received power amount from the received I and Q components signals and outputs the calculation result of the received power to control signal generating unit
211
.
Control signal generating unit
211
compares the received power amount inputted from power calculator
212
with a target value held in control signal generating unit
211
, and controls gain control amplifier
107
in accordance with the comparison result. Specifically, if the received power amount is lower than the target value, a control signal for increasing the gain of gain control amplifier
107
is generated to cause gain control amplifier
107
to increase its gain. Alternatively, if the received power amount is higher than the target value, a control signal for reducing the gain of gain control amplifier
107
is generated to cause gain control amplifier
107
to reduce its gain. The target value held in control signal generating unit
211
is a predetermined value so as to prevent saturation at input ends of A/D converters
206
and
207
.
Next, a case is considered where the conventional receiver shown in FIG.
1
and
F
Chang Edith
Dickstein, Shapiro, Morin & Oshinksy, LLP.
Fan Chieh M.
NEC Corporation
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