Variable gain amplifying device

Details Variable gain amplifying device Variable gain amplifying device

1999-02-19

2001-01-09

Pascal, Robert (Department: 2817)

Amplifiers

Combined with automatic amplifier disabling switch means

C330S12400D, C330S129000

Reexamination Certificate

active

06172559

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a variable gain amplifying device. More to particularly this invention relates to a variable gain amplifying device having variable gain amplifiers which are capable of being changed respective gains.
DESCRIPTION OF THE PRIOR ART
At the present time, there is proposed various kinds of variable gain amplifying devices in order to use outputted signals for various kinds of uses.
There is described a configuration of a conventional variable gain amplifying device referring to FIG.
1
.
FIG. 1
is a circuit view showing one example of a configuration of the conventional variable gain amplifying device. As shown in
FIG. 1
, variable gain amplifiers
11
to
14
constituted by n stages are connected to a control circuit
3
by gain control signal lines
41
to
44
. The control circuit
3
enables gain of the variable gain amplifiers
11
to
14
to be established in every respective amplifiers through the gain control signal lines
41
to
44
. With respect to the variable gain amplifiers
11
to
14
, generally, the maximum gain is of approximately degree of 15 to 20 dB in every one stage, and the minimum gain is of approximately degree of −10 dB to −30 dB.
Consequently, the signal inputted from an input terminal
1
is outputted from an output terminal
2
with a required gain.
Here, in the above described conventional variable gain amplifying device, negative gain appears to be realizable, however when it permits the gain to be amplified, distortion becomes problem in many cases, therefore, gain establishment range is established to approximately 0 dB to the maximum gain in the majority of cases.
Furthermore, by way of a control method of the gain, there is used a descent type control method in which a point of time of the maximum gain establishment is set as a starting point, and there is obtained required gain while decreasing gain gradually from this point in the majority of cases.
Moreover, by way of methods for decreasing gain, there are many control methods. A first control method is to reduce gain from the initial stage of a variable gain amplifier previously. A second control method is to reduce gain from the final stage of a variable gain amplifier previously. A third control method is to reduce gain from the second stage of the variable gain amplifier previously. A fourth control method is to reduce gain simultaneously of the whole stages of the variable gain amplifiers. The selection out of these control methods is implemented in such a way that more appropriate control method is selected in accordance with required characteristic of the system of the whole device in which the variable gain amplifying device is used.
Moreover, the Japanese Patent Application Laid-open No. SHO 56-90612 discloses “GAIN CONTROL METHOD IN LIGHT SIGNAL OBSERVATION DEVICE” by way of similar prior art to the present invention.
The method of the literature is that when there is observed the light signal, it is capable of being changed gain widely without damaging frequency characteristic in wide band width.
For that reason, the method enables 1 time, 10 times, and 100 times of gain change to be executed by a gain changing device such that the first fixed gain amplifier (wide band width amplifier ) or the second fixed gain amplifier of the gain changing device is provided with the by-pass for passing through the signal, as shown in the drawings of the literature.
The Japanese Patent Application Laid-open No. HEI 8-18348 discloses “VARIABLE GAIN AMPLIFIER” by way of the similar prior art to the present invention.
The object of the VARIABLE GAIN AMPLIFIER is to provide a variable gain amplifier which is capable of achieving reduction of power consumption.
For that reason, the VARIABLE GAIN AMPLIFIER causes input/output of the first, the second, and the third fixed gain amplifiers to be changed by the gain changing switches, and causes the power supply switches to be changed timely, to achieve reduction of the power consumption.
The Japanese Patent Application Laid-open No. HEI 9-148852 discloses TRANSMISSION OUTPUT VARIABLE DEVICE by way of the similar prior art to the present invention.
The object of the TRANSMISSION OUTPUT VARIABLE DEVICE is to provide a variable gain amplifier which achieves reduction of the power consumption, together with, which is capable of achieving improvement of CIN distortion.
For that reason, the TRANSMISSION OUTPUT VARIABLE DEVICE enables the power amplifier as the fixed gain amplifier to be provided with the by-pass line so that the signal passes through the by-pass line, furthermore, the change of the gain itself is executed by the variable gain amplifier. Due to the above method, it enables the control characteristic with the exception of the power amplifier, and noise, and distortion characteristic to be improved so that it is capable of being reduced greatly the power consumption caused by the power amplifier which consumes power of the transmission system mainly.
However, there are following problems in the above-described prior art. The first problem is that for instance, in the variable gain amplifiers
11
to
14
as shown in
FIG. 1
, since a noise figure (simply referring to NF) deteriorates in proportion to reduction of the gain, when individual variable gain amplifier is established to low gain, the NF becomes bad by way of the variable gain amplifying device as a whole. In particular, it is ascertained that when there is established gain of the variable gain amplifying device to the minimum gain, the NF becomes the worst value. Here, there is described change of the value of the NF referring to FIG.
2
.
FIG. 2
is a graph showing a relationship between the NF and the gain in the conventional variable gain amplifying device. However, the variable gain amplifying device which is assumed here is a variable gain amplifying device in which the variable gain amplifier is of the three stages configuration. Now, the conventional variable gain amplifying device which has characteristic of the graph shown in
FIG. 2
possesses the same constitution as that of the variable gain amplifying device shown in
FIG. 1
with the exception that the variable gain amplifier is of the three stages configuration. Hereinafter, there is described it referring to
FIG. 1
which shows the conventional variable gain amplifying device.
Furthermore, the result shown in
FIG. 2
is a result which is obtained by executing simulation that the variable gain range in every one stage of the variable gain amplifier is set to 0 dB to 20 dB and the relationship between the gain and the NF has the characteristic shown in FIG.
9
. Here,
FIG. 9
is a graph showing the relationship between the gain in every one stage of the variable gain amplifier used in the present invention and the conventional variable gain amplifying device and the NF.
Moreover, there is implemented four control methods in which it causes the gain to increase to the maximum gain initially by way of gain control method, subsequently, the first control method is to decrease the gain previously from the variable gain amplifier of the initial stage, the second control method is to decrease the gain previously from the variable gain amplifier of the last stage, the third control method is to decrease the gain previously from the variable gain amplifier of the second stage, and the fourth control method is to decrease the gain simultaneously from the variable gain amplifier of the whole stages.
As shown in
FIG. 2
, there is a difference in the value of the NF at the time of intermediate gain depending on the control method. In all cases, the NF becomes the worst value at the time of minimum gain. At this case, the NF becomes approximately 30 dB.
Consequently, when there is used such the variable gain amplifying device for the receiver's sake of the communication device, the NF of the variable gain amplifier deteriorates the NF of the whole receiver, thus deteriorating property of the receiver.
Next, the second problem is that since the variable

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