Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
2003-02-28
2004-05-18
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S310000
Reexamination Certificate
active
06737923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency circuit including an amplifying element. In particular, the present invention relates to a high-frequency circuit including amplifying blocks arranged in multi-stages.
2. Description of the Related Art
Hereinafter, a conventional high-frequency circuit will be described with reference to FIG.
7
.
FIG. 7
is a circuit diagram showing one example of a conventional high-frequency circuit.
FIG. 7
gives an example of the high-frequency circuit in which amplifying blocks are arranged in two stages.
As shown in
FIG. 7
, a first-stage amplifying block includes an amplifying element
101
, a choke inductor
111
, and a by-pass capacitor
121
. Similarly, a second-stage amplifying block includes an amplifying element
102
, a choke inductor
112
, and a by-pass capacitor
122
.
In the first-stage amplifying block, a power terminal of the amplifying element
101
is connected to one end of the choke inductor
111
, the other end of the choke inductor
111
is connected to one end of the by-pass capacitor
121
, and the other end of the by-pass capacitor
121
is grounded. Similarly, in the second-stage amplifying block, a power terminal of the amplifying element
102
is connected to one end of the choke inductor
112
, the other end of the choke inductor
112
is connected to one end of the by-pass capacitor
122
, and the other end of the by-pass capacitor
122
is grounded.
The choke inductors
111
and
112
achieve low impedance with respect to a direct-current component from a common power terminal
143
, thereby forming power supply lines to the amplifying elements
101
and
102
, respectively. On the other hand, with respect to an alternating-current component from an input terminal
141
, the choke inductors
111
and
112
achieve high impedance (an open-circuit state). The by-pass capacitors
121
and
122
ground a high-frequency component (an alternating-current component) from the power supply voltage side of the choke inductors
111
and
112
, respectively.
In this high-frequency circuit, a signal input from the input terminal
141
is input to the amplifying element
101
via a matching circuit
131
, and is output from the amplifying element
101
after being amplified. The signal output from the amplifying element
101
is then input to the amplifying element
102
via a matching circuit
132
, and is output from the amplifying element
102
after being further amplified. The signal output from the amplifying element
102
is then output to the outside of the circuit via a matching circuit
133
and an output terminal
142
.
By the way, for efficient signal transmission in a high-frequency circuit, impedance matching is important. The impedance matching is to bring about a condition in which the impedances of two amplifying blocks connected with each other are equal in magnitude but opposite in phase in Smith chart (such a condition is referred to as a “conjugate match”). For example, when an amplifying block A and an amplifying block B are connected with each other, the impedance matching is to adjust the impedance of the amplifying block A to [R+jX (&OHgr;)] and the impedance of the amplifying block B to [R−jX (&OHgr;)]. In this case, reflection of signals can be avoided, thus allowing 100% of signals to be transmitted.
In general, in the high-frequency circuit as shown in
FIG. 7
, the impedance of the signal line is designed to be 50 &OHgr;, and the impedance of the input and output also is designed to be 50 &OHgr;. However, in many cases, the impedance of the amplifying elements is different from 50 &OHgr;. On this account, the matching circuits
131
,
132
, and
133
are arranged to achieve impedance matching by creating a conjugate match between the impedances of the amplifying blocks, thus allowing efficient signal transmission.
In the high-frequency circuit with the two-stage amplifying blocks shown in
FIG. 7
, to decrease the number of power terminals, electric power is supplied from the common power terminal
143
to the amplifying elements in the respective amplifying blocks via the choke inductor
111
or
112
. This brings about a condition in which the first-stage amplifying block and the second-stage amplifying block are coupled with each other directly. In this case, unless both the by-pass capacitors
121
and
122
have an infinite capacitance, an undesired peak is generated so that a desired frequency characteristic cannot be obtained.
FIG. 8
is a graph showing the result of a simulation performed to examine a frequency characteristic of the conventional high-frequency circuit shown in FIG.
7
. In
FIG. 8
, the horizontal axis indicates a frequency (GHz) from 0.1 (GHz) to 10.1 (GHz) graduated in 1 (GHz) increments. On the other hand, the vertical axis indicates a forward gain [Gain] (dB) from −50 (dB) to
50 (
dB) graduated in 10 (dB) increments. In
FIG. 8
, the mark “M1” indicates a forward gain at a design frequency of 5.84 (GHz), and I1 indicates a frequency (GHz) at a point where the measurement is carried out.
As can be seen from
FIG. 8
, in the high-frequency circuit shown in
FIG. 7
, a forward gain of about 18.6 (dB) is obtained at the design frequency of 5.84 (GHz). However, as indicated by the mark “M2”, after a forward gain of about −1.0 (dB) is obtained at a frequency of 2.28 (GHz), the forward gain drops, thereby generating an undesired peak.
The cause of the undesired peak is considered to be as follows. As described above, because the by-pass capacitors
121
and
122
in the respective amplifying blocks have a limited capacitance, sufficient high-frequency grounding is not attained at the frequency at which the undesired peak is generated. More specifically, because the grounding of the high-frequency component from the choke inductors
111
and
112
is not perfect, feedback of high frequency signals is caused between the first-stage amplifying block and the second-stage amplifying block, thereby causing the undesired peak to be generated.
However, the capacitance of the by-pass capacitors
121
and
122
is limited to a certain value as long as the area of the chip is limited. Thus, obtaining an infinite capacitance is almost impossible. On this account, in a high-frequency circuit shown in
FIG. 9
, a high-frequency separation element
151
is arranged between a first-stage amplifying block and a second-stage amplifying block to prevent the feedback of the high frequency signals from being caused between the first-stage amplifying block and the second-stage amplifying block.
FIG. 9
is a circuit diagram showing another example of a conventional high-frequency circuit. In the high-frequency circuit shown in
FIG. 9
, the high-frequency separation element
151
is arranged between the first-stage amplifying block and the second-stage amplifying block to prevent an undesired peak. As the high-frequency separation element
151
, a &lgr;/4 line or an inductor generally is used.
In this high-frequency circuit, electric power is supplied to a power terminal of an amplifying element
101
via a common power terminal
143
, the high-frequency separation element
151
, and a choke inductor
111
. On the other hand, electric power is supplied to a power terminal of an amplifying element
102
via a choke inductor
112
.
However, the &lgr;/4 line and the inductor are elements taking up a large area on a chip. Therefore, such elements inhibit the reduction in area of the chip, thereby causing a problem in that the reduction in size of a chip provided with a high-frequency circuit cannot be achieved.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-described problem and to provide a high-frequency circuit that can prevent the generation of an undesired peak and contribute to the reduction in area of a chip.
To achieve the above-described object, a high-frequency circuit according to the present invention includes a plurality of amplifying blo
Takagi Tsunehiro
Tara Katsushi
Yamamoto Shinji
Choe Henry
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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