Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2000-10-23
2003-02-11
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S133000
Reexamination Certificate
active
06518843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable gain type amplifier.
2. Description of the Related Art
An amplifier having a large amplification gain or amplification quantity is composed of a plurality of amplifying circuits connected tin series. The plurality of amplifying a signal step by step. Generally, each of the plurality of amplifying circuits has a gain control function. An amplifier having a gain control function is called a variable gain type amplifier.
FIG. 1
shows a conventional variable gain type amplifier. Referring to
FIG. 1
, a variable gain type amplifier
1
is composed of a first amplifying circuit
11
, a second amplifying circuit
12
and an attenuating circuit
13
.
The first amplifying circuit
11
is connected with the output of the attenuating circuit
13
. The second amplifying circuit
12
is connected with the output of the first amplifying circuit
11
. An input signal S
1
is supplied to the attenuating circuit
13
. The second amplifying circuit
12
outputs an output signal S
2
. A power supply voltage VDD and a control voltage VAGC are applied to the attenuating circuit
13
. The power supply voltage VDD is applied with the first amplifying circuit
11
and the second amplifying circuit
12
.
The first amplifying circuit
11
is composed of a transistor circuit which amplifies the input signal. The second amplifying circuit
11
is composed of a transistor circuit which amplifies the input signal. The attenuation circuit
13
is composed of a transistor circuit which attenuates the input signal.
The amplification quantity (Gp
1
) of the first amplifying circuit
11
is fixed, and is set to 12 dB. The first amplifying circuit
11
has a noise figure of 2 dB (NF
1
). The amplification quantity (Gp
2
) of the second amplifying circuit
12
is fixed, and is set to 12 dB. The second amplifying circuit
12
has a noise figure of 3 dB (NF
2
). The attenuation quantity of the attenuating circuit
13
is changed in accordance with the value of the control voltage VAGC. The attenuation quantity of the attenuating circuit
13
is varied from a range of 40 to 1 dB when the value of the control voltage VAGC is varied from a range of 40 to 1 dB when the value of the control voltage VAGC is varied from a range of 0.5 to 2.5 V. During the operation of the variable gain type amplifier
1
, the power supply voltage VDD is kept constant. In this way, the gain of the variable gain type amplifier
1
is determined based on the control voltage VAGC.
Hereinafter, the relation of a total amplification quantity (Gp-A) and the total noise figure (NF-A) in the variable gain type amplifier
1
will be described with reference to the total noise figure (NF-B) of FIG.
7
. When the control voltage VAGC is 2.5 V, the attenuation quantity of the attenuating circuit
13
is set to 1 dB. In this case, the total amplification quantity (Gp-A) of the variable gain type amplifier
1
is set to 23 dB. Also, the total noise figure (NF-A) of the variable gain type amplifier
1
is set to 4.7 dB.
When the control voltage VAGC is decreased to 2.0 V, the attenuation quantity of the attenuating circuit
13
is set to 6 dB. In this case, the total amplification quantity (Gp-A) of the variable gain type amplifier
1
is set to 18 dB. Also, the total noise figure (NF-A) of the variable gain type amplifier
1
is set to 7.7 dB.
When the control voltage VAGC is decreased to 1.5 V, the attenuation quantity of the attenuating circuit
13
is set to 11 dB. In this case, the total amplification quantity (Gp-A) of the variable gain type amplifier
1
is set to 13 dB. Also, the total noise figure (NF-A) of the variable gain type amplifier
1
is set to 11.7 dB.
The technique relating to distortion control of the variable gain type amplifier is disclosed in Japanese Laid Open Patent Application (JP-A-Showa 62-226705). In this reference, an attenuating circuit is arranged between two amplifying circuits. However, in this reference, only an attenuation quantity of the attenuating circuit is controlled based on a control voltage.
When a variable gain type amplifier is provided in an amplification stage of a transmitter section of a handheld phone, the variable gain type amplifier generates reception interfering wave to other handheld phones which are in the reception state in the neighborhood. The reception band noise figure (dBm/Hz) indicates the degree of the reception interference and can be expressed by Gp+NF+IM+ thermal noise. Here, Gp is a total amplification quantity of the amplifier, NF is a total noise figure of the amplifier, IM is an intermodulation distortion of the amplifier, and the thermal noise is called kTB noise, and is calculated by use of the Boltzman's constant, temperature and bandwidth. The thermal noise is constant to be −173.9 (dBm/Hz) in the temperature of 25° C.
When a handheld phone is used, it is necessary to control the magnitude of the output signal based on its position from a base station in order to save power. Such reception band noise does not cause any problem since the other users are hardly in the neighborhood, when the position for the handheld phone to be used is far from the base station. On the other hand, when the position of the handheld phone is near the base station, the probability of reception interference is high because a lot of other users are in the neighborhood. Therefore, when the position of the handheld phone is near the base station, i.e., when the transmission output is made small, the reception band noise should be made small. For this purpose, it is necessary to decrease the reception band noise when the total amplification quantity is decreased in the variable gain type amplifier provided in the amplification stage of the transmitter section.
However, as shown in
FIG. 7
, even when the total amplification quantity (Gp-A) is decreased in the conventional variable gain type amplifier
1
, the total noise figure (NF-B) is largely increased. Therefore, the reception band noise index (TXN-B) is almost unchanged. Therefore, when the conventional variable gain type amplifier
1
is used for the amplification stage of the transmitter section in the handheld phone, the conventional variable gain type amplifier
1
gives large reception interference to other handheld phones near the base station.
Also, in the variable gain type amplifier having the structure disclosed in Japanese Laid Open Patent Application (JP-A-Showa 62-226705), the attenuating circuit is arranged between two amplifying circuits. Therefore, when the attenuation quantity of the attenuating circuit is large in order to decrease the total amplification quantity, the intermodulation distortion (IM) increase. Also, the reception band noise can't be small when the total amplification quantity is decreased.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a variable gain type amplifier, in which reception band noise can be decreased or not changed when an attenuation quantity of an attenuating circuit is increased.
Another object of the present invention is to provide a variable gain type amplifier, which is suitable for use for an amplification stage of a transmitter of a handheld phone.
In order to achieve an aspect of the present invention, a variable gain type amplifier includes a first amplifying circuit, an attenuating circuit connected to an output of the first amplifying circuit, and a second amplifying circuit connected to an output of the first amplifying circuit. An amplification of the first amplifying circuit is adjusted based on a control voltage, and an attenuation of the attenuating circuit is adjusted based on the control voltage.
Here, it is desirable that the attenuation of the attenuating circuit is increased based on the control voltage, when the control voltage is decreased in a predetermined voltage range. In this case, the amplification of the first amplifying circuit is not substantially changed when the control voltage is changed in a first ra
Dickstein Shapiro Morin & Oshinsky LLP.
Mottola Steven J.
NEC Compound Semiconductor Devices Ltd.
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