Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2002-12-19
2004-10-26
Nguyen, Khanh Van (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S278000, C330S296000
Reexamination Certificate
active
06809592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a high-frequency circuit having a function of switching a band in a plurality of circuit blocks each of which deals with a high-frequency signal.
2. Description of the Related Art
FIG. 1
is a circuit diagram of a conventional high-frequency circuit
40
for driving one of bands in a power amplifier which accomplishes a dual-band power amplification module.
The illustrated high-frequency circuit
40
is comprised of a main transistor
50
, a bias circuit
51
which supplies a current to a base of the main transistor
50
, a band-switching circuit
52
for switching a band, and a gain control circuit
53
.
The main transistor
50
is electrically connected through a collector thereof to a power source voltage terminal Vcc through which a power source voltage is supplied, and further electrically connected through a base thereof to an input terminal Vin through which a high-frequency signal is input.
The bias circuit
51
is comprised of a first transistor
54
, a second transistor
55
, and a first resistor
56
.
The first transistor
54
is electrically connected through a collector thereof to the power source voltage terminal Vcc, and further electrically connected through an emitter thereof to both a base of the main transistor
50
and a base of the second transistor
55
.
The second transistor
55
is electrically connected through a collector thereof to the power source voltage terminal Vcc through the first resistor
56
, and further electrically connected through a base thereof to both a base of the main transistor
50
and an emitter of the first transistor
54
.
The band-switching circuit
52
is comprised of a third transistor
57
, a fourth transistor
58
, a fifth transistor
59
, a second resistor
60
, a third resistor
61
, and a fourth resistor
62
.
The third transistor
57
is electrically connected through a base thereof to a band-switching voltage terminal Vsw through which a band-switching voltage is supplied, through the second resistor
60
, and further electrically connected through a collector thereof to the power source voltage terminal Vcc through the third resistor
61
.
The fourth transistor
58
is electrically connected through a base thereof to a node D at which a collector of the third transistor
57
and the third resistor
61
are electrically connected to each other, and further electrically connected through a collector thereof to the power source voltage terminal Vcc through the fourth resistor
62
.
The fifth transistor
59
is electrically connected through a base thereof to a node at which a collector of the fourth transistor
58
and the fourth resistor
62
are electrically connected to each other, and further electrically connected through a collector thereof to a node at which a collector of the second transistor
55
and the first resistor
56
are electrically connected to each other.
The gain control circuit
53
is electrically connected to a gain control voltage terminal Vagc through which a gain control voltage is supplied, and further electrically connected to a node C at which a collector of the fifth transistor
59
and a node at which a collector of the second transistor
55
and the first resistor
56
are electrically connected to each other are electrically connected to each other.
In the conventional high-frequency circuit
40
illustrated in
FIG. 1
, a gain of the main transistor
50
is controlled by the gain control circuit
53
, and a band is switched when a band-switching voltage supplied through the band-switching voltage terminal Vsw is changed between high and low levels. Specifically, a band is turned off when a reference current I
1
running through the bias circuit
51
runs through the fifth transistor
59
as a current I
2
, whereas a band is turned off when a path through which the current I
2
runs is interrupted. Thus, a band is switched on or off by allowing the reference current I
1
to run through a path or interrupting the path.
The conventional high-frequency circuit
40
illustrated in
FIG. 1
, for instance, receives a plurality of high-frequency signals which are identical with one another or different from one another, and then, amplifies each of the received high-frequency signals, or converts frequencies of the received high-frequency signals.
A high-frequency circuit such as one illustrated in
FIG. 1
is presently frequently used in a mobile communication device such as a cellular phone.
It is quite important for a cellular phone driven by a battery arranged therein, to be fabricated in a smaller size and designed to be driven with smaller power consumption.
To this end, the high-frequency circuit
40
illustrated in
FIG. 1
is required to reduce a current running through the power source voltage terminal Vcc down to a range of about 10 to about 30 &mgr;A when the gain control voltage is lowered to 0.1V. A smaller current running through the power source voltage terminal Vcc is more preferable, since the current defines a period of time in which a battery arranged in a cellular phone can work.
However, a band in the conventional high-frequency circuit
40
illustrated in
FIG. 1
was switched merely by converting a direction in which the reference current I
1
ran, and accordingly, it was not possible in the conventional high-frequency circuit
40
to reduce a current running through the power supply voltage terminal Vcc when a gain control voltage was set at 0.1V.
Japanese Unexamined Patent Publication No. 10-65466, which is based on the U.S. patent application Ser. No. 08/664,972 filed on Jun. 3, 1996, has suggested an amplifier for amplifying a signal having one of predetermined frequencies. The suggested amplifier is comprised of a plurality of amplifying units each of which operates under one of the predetermined frequencies, and a controller which allows one of amplifying units to operate in accordance with one of the predetermined frequencies, and disallows the rest of the amplifying units to operate.
Japanese Unexamined Patent Publication No. 10-313259 has suggested a high-frequency circuit comprised of a plurality of circuit blocks into which received radio-frequency signals are input. Each of the circuit blocks includes a DC switching transistor which interrupts a current path through which a dc bias current runs in a circuit block in accordance with a received signal indicating that the circuit block is not selected.
The above-mentioned problem remains unsolved even in the above-identified Publications.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional high-frequency circuits, it is an object of the present invention to provide a high-frequency circuit which is capable of reducing a current running through a power supply voltage terminal down to tens of microamperes (&mgr; A), even if a gain control voltage is relatively low, for instance, at about 0.1V.
The present invention provides a high-frequency circuit having a function of switching a band in a bias circuit of a power amplifier module, used in a dual mode, and accomplishing band-switching without an increase in a circuit current when a power amplifier is off.
There is provided a high-frequency circuit including (a) a bias circuit to which a gain control voltage is input and which controls gains of transistors arranged in the bias circuit in accordance with the gain control voltage, and (b) a band-switching circuit which switches a band and through which a reference current runs, wherein the band-switching circuit includes a transistor which cuts off a current path through which the reference current runs, in synchronization with the gain control voltage.
There is provided a high-frequency circuit including (a) a bias circuit to which a gain control voltage is input and which controls gains of transistors arranged in the bias circuit in accordance with the gain control voltage, and (b) a band-switching circuit which switches a band and through which a reference current runs, wherein the band-switching circuit
Hayes & Soloway P.C.
NEC Compound Semiconductor Devices Ltd.
Nguyen Khanh Van
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