Amplifiers – With semiconductor amplifying device – Including plural stages cascaded
Reexamination Certificate
2002-07-02
2003-07-29
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural stages cascaded
C330S051000, C330S285000
Reexamination Certificate
active
06600377
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an amplifier a gain of which can be changed.
BACKGROUND OF THE INVENTION
FIGS. 6 and 7
show a prior-art gain control amplifier, respectively.
The gain control amplifier shown in
FIG. 6
is configured to amplify a signal inputted from an input terminal
1
by an emitter-grounded transistor
3
and output the signal at an output terminal
2
. The amplifier has a high-gain mode in which a power supply voltage is applied to a collector of the transistor
3
from a power supply
10
through a load
9
and a collector-emitter of a base-grounded transistor
4
and a low-gain mode in which the power supply voltage is applied to the collector of the transistor
3
from the power supply
10
through the load
9
, a resistance
7
, and a collector-emitter of a base grounded transistor
6
. Reference number
11
denotes a bias power supply generating a bias voltage that determines an operation point of the transistor
3
.
The high-gain mode or low-gain mode is selected by a selector switch
12
.
To select the high-gain mode, the selector switch
12
is turned to contact
12
a
. This causes the bias voltage to be applied only to a base of the transistor
4
out of the bases of the transistors
4
and
6
from a bias power supply
13
and the power supply voltage to be applied to the transistor
3
through the transistor
4
. The signal amplified by transistor
3
is outputted from the output terminal
2
through a branch
5
.
To select the low-gain mode, the selector switch
12
is turned to a contact
12
b
. This causes the bias voltage to be applied from the bias power supply
13
only to the base of the transistor
6
and the power supply voltage to be applied to the transistor
3
through the transistor
6
. The signal amplified by the transistor
3
is outputted from the output terminal
2
through a branch
8
. The gain in the low-gain mode is controlled through the resistance
7
.
The gain control amplifier shown in
FIG. 7
is different from the one shown in
FIG. 6
in that gain control is accomplished by controlling the current ratio between a branch
25
and a branch
27
and current control is accomplished by controlling a base voltage of a base-grounded transistor
6
.
In particular, a signal RFin inputted through an input terminal
1
is amplified by an emitter-grounded transistor
3
and outputted at an output terminal
2
. Reference number
11
denotes a bias power supply generating a bias voltage that determines an operation point of the transistor
3
.
The amplifier has a high-gain mode in which a power supply voltage is applied to a collector of the transistor
3
from a power supply
10
through a load
9
and the collector-emitter of a base-ground transistor
4
, and a low-gain mode in which the power supply voltage is applied to the collector of the transistor
3
from the power supply
10
through the collector-emitter of the base-grounded transistor
6
.
Base voltage is applied to the bases of the transistors
4
and
6
from power supplies
29
and
30
, respectively. Current control is accomplished by changing an output voltage of the power supply
30
to control the base voltage of the base-grounded transistor
6
and the current ratio between the branches
24
and
27
is controlled.
As an example circuit in which a gain control amplifier is used, there can be cited a head amplifier provided at a front end of a radio frequency receiver. As shown in
FIG. 8
, band-pass filters
709
and
710
are connected in input and output stages, respectively, of a head amplifier A in order to improve selectivity. Reference number
711
denotes a mixer circuit.
Because the band-pass filters
709
and
710
are designed to satisfy an required pass frequency property at predetermined input and output impedances, a gain of the head amplifier A is switched between high-gain and low-gain modes in accordance with electric field strength in an area in which the radio frequency receiver is used.
Therefore, it is required that the predetermined input and output impedances be maintained independently of switching between the high-gain mode and the low-gain mode.
However, in the gain control method in
FIG. 6
, the output impedance varies depending on the high-gain and low gain modes and therefore it is difficult to achieve output impedance matching in both of the high-gain and low-gain modes.
According to the gain control method shown in
FIG. 7
, in which the control of the current ratio between the branches
25
and
27
is accomplished by controlling the base voltage of the base-grounded transistor
6
, it is difficult to control the gain because the gain changes by 1 dB when the base voltage of the transistor
6
changes by 0.02 volts, for example.
DISCLOSURE OF THE INVENTION
The present invention has been achieved to solve the problems of the prior art and it is an object of the present invention to provide a gain control amplifier in which the amount of variation in output impedance between the high-gain mode and low-gain mode is small and gain control can be performed easily and accurately.
To solve these problems, the gain control amplifier of the present invention has a configuration in which a load is provided in an output circuit of a first transistor, an output circuit of a second transistor is provided between the output circuit of the first transistor and the load, an input signal supplied to the input of the first transistor is amplified, and the amplified signal is taken out from a connection point between the load and the second transistor. In the high-gain mode, only a control bias for the second transistor out of the second transistor and a third transistor is turned on, and in the low-gain mode, control biases for both of the second and third transistors are turned on.
According to the first aspect of the present invention, there is provided a gain control amplifier in which a load is provided in an output circuit of a first transistor, an output circuit of a second transistor is provided between the output circuit of the first transistor and the load, the input signal supplied to the input of the first transistor
1
is amplified, and the amplified signal is taken out from a connecting point between the load and the second transistor, wherein an output circuit of a third transistor is connected in parallel with a series circuit of the output circuit of the second transistor and the load and switch means for turning on and off a control bias for the third transistor is provided, the switching means is turned off to turn on a control bias only for the second transistor out of the second and third transistors in a high-gain mode, and the switch means is turned on to turn on the control bias for both of the second and third transistors in a low-gain mode.
According to this configuration, the amount of variation in the output impedance between the high-gain mode and low-gain mode is small and an output current is determined by the size ratio between the base-grounded transistors, therefore the gain can be controlled easily and accurately without depending on the control bias.
According to the second aspect of the present invention there is provided gain control amplifier in which a load is provided in an output circuit of a first transistor, an output circuit of a second transistor is provided between the output circuit of the first transistor and the load, the input signal supplied to the input of the first transistor is amplified, and the amplified signal is taken out at a connecting point between the load and the second transistor, wherein an output circuit of a third transistor is connected in parallel with a series circuit of the output circuit of the second transistor and the load, control terminals of the second and third transistors are connected with each other through switch means, the switching means is turned off to turn on a control bias only for the second transistor out of the second and third transistors in a high-gain mode, and the switch means is turned on to turn on the control bias for both o
Choe Henry
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
LandOfFree
Gain control amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gain control amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gain control amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3065209