Impedance-matching method and circuit at different frequences

Details Impedance-matching method and circuit at different frequences Impedance-matching method and circuit at different frequences

1999-05-11

2001-12-11

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

With impedance matching

C333S033000

Reexamination Certificate

active

06329886

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an impedance-matching method and an impedance-matching circuit and more particularly, to an impedance-matching method and an impedance-matching circuit capable of matching the impedance between two circuits at different frequencies, which are suitably used for wireless communication systems using radio frequency (RF) signals.
2. Description of the Prior Art
Conventionally, impedance matching circuits have been used to maximize the performance of electronic devices used in RF circuits of wireless communication systems.
FIG. 1
is a schematic circuit diagram showing an application example of conventional impedance-matching circuits.
In
FIG. 1
, first and second impedance-matching circuits
110
and
120
are connected to input and output terminals
132
and
133
of a RF circuit
140
, respectively. The first impedance-matching circuit
110
serves to match or accord the output impedance of a RD circuit (not shown) located at a prior stage to the circuit
140
with the input impedance of the RF circuit
140
. The second impedance-matching circuit
120
serves to match the output impedance of the RF circuit
140
with the input impedance of an RF circuit (not shown) located at a next stage to the circuit
140
.
For the sake of simplification, the RF circuit
140
is illustrated as a RF amplifier equipped with only one npn-type bipolar transistor Tr in
FIG. 1
, which is an alternate-current (ac) equivalent circuit. The transistor Tr has an emitter connected to the ground, a base connected to the input terminal
132
, and a collector connected to the output terminal
133
.
The first impedance-matching circuit
110
is comprised of two coils or inductors
111
and
112
. Two terminals of the inductor
111
are connected to the terminals
131
and
132
, respectively. Two terminals of the inductor
112
are connected to the terminal
131
and the ground, respectively. The circuit
110
has a so-called “L—L matching” configuration. The second impedance-matching circuit
120
is comprised of two capacitors
121
and
122
. Two terminals of the capacitor
121
are connected to the terminals
133
and
134
, respectively. Two terminals of the capacitor
122
are connected to the terminal
134
and the ground, respectively. The circuit
120
has a so-called “C—C matching” configuration.
The first impedance-matching circuit
110
, which serves to match the output impedance of the prior-stage RF circuit with the input impedance of the RF circuit
140
, has a problem that impedance matching is realized only at single frequency. Thus, to realize impedance matching at different frequencies between the RF circuit
140
and its preceding-stage circuit, some contrivance is needed. This is applied to the second impedance-matching circuit
120
also.
An example of the contrivance is explained below with reference to FIG
2
, which shows a schematic circuit configuration of a single superheterodyne receiver of a portable phone of the Personal Digital Cellular (PDC) type that has been used in Japan.
In the receiver circuit of
FIG. 2
, an antenna
101
receives a RF signal in the 820 MHz band of frequencies. A RF amplifier
102
amplifies the RF signal received by the antenna
101
to produce an amplified RF signal. A frequency mixer
103
frequency-mixes the amplified RF signal from the RF amplifier
102
with a local signal of 950 MHz sent from a local oscillator
104
, producing an intermediate Frequency (IF) signal of an IF frequency 130 MHz which is equal to the difference between the two frequencies of 950 MHz and 820 MHz. An IF amplifier
105
amplifies the IF signal from the frequency mixer
103
to produce an amplified IF signal. A demodulator
106
demodulates the amplified IF signal from the IF amplifier
105
according to the specified demodulation method, thereby deriving the transmitted information from the amplified IF signal.
In the circuit of
FIG. 2
, if two adjacent ones of the RF circuits handling the RF signal, such as the RF amplifier
102
, the frequency mixer
103
, the local oscillator
104
, and the IF amplifier
105
, are connected to each other through the conventional impedance matching circuit
110
or
120
shown in
FIG. 1
, the configuration of the impedance matching circuit
110
or
120
is designed in such a way that the impedances of the two RF circuits to be connected are matched with each other at a specific single frequency (e.g., 820 MHz) within the frequency band (i.e., the 820 MHz band) of the received signal. In this case, the RF amplifier
102
has a frequency response or characteristic of the Voltage Standing-Wave Ratio (VSWR) shown in
FIG. 5
, where f is the frequency of the received signal. In other words, since the necessary band of frequencies is only the 820 MHz band, the configuration of the impedance matching circuit
110
or
120
is designed so that the output impedance of one of the RF circuits to be connected is equal to the input impedance of the other at a frequency of 180 MHz.
In recent years, however, technological advances have been rapidly accomplished in the radio communication equipment and systems and as a result, there has been the need to enable RF receivers to handle the RF signals within two separated bands of frequencies. An example of the RF receivers coping with this need is a telephone capable of handling the RF signal in the 820 MHz band used for the PDC-type portable phone system and that of the 1.9 GHz (i.e., 1900 MHz) band used for the Personal Handy-phone System (PHS). Two examples of the conventional circuit configurations of this two-band telephone is shown in
FIGS. 3 and 4
.
In the circuit configuration of
FIG. 3
, there are provided with a circuit block for handling the received signal in the 820 MHz band comprising a RF amplifier
102
a
, a frequency mixer
103
a
, a local oscillator
104
a
, and an IF amplifier
105
a
, and a circuit block for handling the received signal in the 1900 MHz band comprising a RF amplifier
102
b
, a frequency mixer
103
b
, a local oscillator
104
b
, and an IF amplifier
105
b
. The two circuit blocks for the 820 MHz and 1900 MHz bands are alternatively used by switches
107
and
108
. The local oscillators
104
a
and
104
b
generate local signals having local frequencies of 950 and 1770 MHz, respectively.
In the circuit configuration of
FIG. 3
, each of the RF amplifiers
102
a
and
102
b
provides the VSWR-f characteristic shown in FIG.
6
A. Specifically, impedance matching is carried out only at a specific frequency (e.g., 820 MHz) within the 820 MHz band with respect to the circuit block for the 820 MHz band. Simultaneously with this, impedance matching is carried out only at a specific frequency (e.g., 1900 MHz) within the 1900 MHz band with respect to the circuit block for the 1900 MHz band.
Since the two circuit blocks for the 820 MHz and the 1900 MHz bands are alternatively used by the switches
107
and
108
according to the frequency band of the received signal, the VSWR-f characteristic of each of the RF amplifiers
102
a
and
102
b
is given by the curve shown in
FIG. 6B
produced by combining the two curves in
FIG. 6A
with each other.
In the circuit configuration of
FIG. 4
, which is a variation of the configuration of
FIG. 3
, there are provided with a common frequency mixer
103
and a common IF amplifier
105
for handling the received signals in the 820 and 1900 MHz bands instead of the dedicated local oscillators
104
a
and
104
b
and the dedicated frequency mixers
105
a
and
105
b
in
FIG. 3
Also, according to this difference, a switch
109
for selecting one of the outputs of the RF amplifiers
102
a
and
102
b
and a switch
110
for selecting one of the outputs of the local oscillators
104
a
and
104
b
provided instead of the switch
108
in FIG.
3
. The other part of the circuit configuration of
FIG. 4
is the same as that of FIG.
3
. In this case, similar to the configuration of
FIG. 3
, each of the RF amplifiers
102
a
and
102
b
provides th

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