Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-06-05
2002-06-25
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S134000, C333S206000
Reexamination Certificate
active
06411176
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a duplexer for use in a microwave band, for example, and a communication apparatus.
2. Description of the Related Art
A transmission frequency band required for the transmission side circuit of a duplexer for use in PCS is 1850-1910 MHz, and a reception frequency band for a reception side circuit is 1930-1990 MHz. It is necessary for both of the transmission side circuit and reception side circuit to have a wide pass-band of 60 MHz. On the other hand, the separation assured to separate the transmission frequency band from the reception frequency band is 20 MHz. That is, the separation between the both bands is very narrow.
Further, the duplexer composes the phase of the transmission side circuit and that of the reception side circuit. In the case of PCS, the phase of the transmission side circuit and that of the reception side circuit are ideally composed by setting the transmission side circuit to have a high impedance (open) in the reception frequency band of 1930-1990 MHz, and setting the reception side circuit to have a high impedance (open) in the transmission frequency band of 1850-1910 MHz.
FIG. 8
shows an example of the circuit configuration of a prior art duplexer
1
. In the case of a PCS system, the separation between the transmission frequency band and reception frequency band is narrow, namely, 20 MHz. Accordingly, the transmission frequency band is divided into two ranges of 1850-1880 MHz and 1880-1910 MHz, and also, the reception frequency band is divided into two ranges of 1930-1960 MHz and 1960-1990 MHz. That is, the frequency bands become narrow, and the separations are wide. In particular, reactance elements (PIN diode) are connected to resonators, respectively, and control the voltages of the resonators, so that the two types of pass-bands of each of the transmission side circuit
25
and the reception side circuit
26
can be changed over, resulting in reduction of the number of the filter stages. Like this, it is attempted to downsize the duplexer and give high qualities thereto. In
FIG. 8
, a transmission terminal is designated by Tx, a reception terminal by Rx, an antenna terminal by ANT, resonators in the transmission side circuit
25
by 2 and 3, resonators in the reception side circuit
26
by 4 to 6, coupling coils by L
1
and L
11
, coupling capacitors for determining a rejection-band attenuation by C
1
and C
2
, capacitors by C
5
, C
6
, and C
24
, frequency band variable capacitors by C
3
, C
4
, and C
7
to
9
, PIN diodes by D
2
to D
6
, choke coils by L
2
, L
3
, and L
6
to
8
, control voltage supply resistances and capacitors by R
1
and R
2
, and C
22
and C
23
, respectively, coils and capacitors constituting phase circuits by L
20
and L
21
, and C
15
, respectively, and coupling capacitors by C
11
to C
14
.
CONT
1
designates a voltage control terminal for controlling the voltages of the PIN diodes D
2
and D
3
of the transmission circuit
25
, and CONT
2
a voltage control terminal for controlling the voltages of the PIN diodes D
4
to D
6
. When positive voltages are applied to the voltage control terminals CONT
1
and CONT
2
, the PIN diodes D
2
to D
6
are in the on state, and the duplexer
1
operates through the LOW channel. That is, as shown in
FIG. 9
, the pass-band of the transmission side circuit
25
becomes 1850-1880 MHz, and that of the reception side circuit
26
becomes 1930-1960 MHz. To the contrary, when the control voltages are zero with no voltages being applied to the voltage control terminals CONT
1
and CONT
2
, the PIN diodes D
2
to D
6
turn off, and the duplexer
1
operates through the HIGH channel. That is, as shown in
FIG. 9
, the pass-band of the transmission side circuit
25
becomes 1880-1910 MHz, and that of the reception side circuit
26
becomes 1960-1990 MHz.
A portable telephone is put on standby for a reception wave except the time when speech is carried out. In case the frequency during the reception wave standby is 1930 MHz and the reception wave standby is carried out with positive voltages being applied to the voltage control terminals CONT
1
and CONT
2
, the battery of the portable telephone is quickly exhausted, which causes the problem that the reception wave standby time becomes short.
It may be supposed that as countermeasures against the problem, the control voltage of the voltage control terminal CONT
1
is set at 0V and a positive voltage is applied to the voltage control terminal CONT
2
only. Since a consumption current flows through only the reception side circuit
26
during the reception wave standby, the exhaustion of the battery can be suppressed. However, as to a system such as PCS in which the frequency of the transmission frequency band is lower than that of the reception frequency band, the separation between the pass-band (1880-1910 MHz) of the transmission side circuit
25
and that (1930-1960 MHz) of the reception side circuit
26
is very narrow, as shown in
FIG. 10
, when the PIN diodes D
2
and D
3
in the transmission side circuit
25
is turned off (in the off state) and the PIN diodes D
4
to D
6
in the reception side circuit
26
is turned on (in the on state). Therefore, it is difficult to set the transmission side circuit
25
to have a high impedance (open) in the reception frequency band of 1930-1960 MHz. Thus, there arises the in problem that the insertion loss of the reception side circuit
26
is large.
FIG. 11
is a graph showing the measurement results of the band-pass characteristic S
32
and reflection characteristic S
22
(see
FIG. 8
) of the reception side circuit
26
obtained when positive voltages are applied to the voltage control terminals CONT
1
and CONT
2
. In this case, the insertion loss of the reception side circuit
26
was 3.3 dB. On the other hand,
FIG. 12
is a graph showing the measurement results of the band-pass characteristic S
32
and reflection characteristic S
22
of the reception side circuit
26
obtained when a positive voltage is applied to the voltage control terminal CONT
2
only. In
FIG. 12
, the waveform is distorted in the part thereof shown by a circle A. In this case, the insertion loss of the reception side circuit
26
was deteriorated to be 5.0 dB.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide a duplexer of which the consumption current is small and the insertion loss is low, and a communication apparatus.
One preferred embodiment of the present invention provides A duplexer comprising: a first external terminal; a second external terminal; an antenna terminal; a first frequency variable filter electrically connected between the first external terminal and the antenna terminal, and composed of at least one resonator and a reactance element electrically connected to the resonator and capable of being voltage-controlled; a second frequency variable filter electrically connected between the second external terminal and the antenna terminal, and composed of at least one resonator and a reactance element electrically connected to the resonator and capable of being voltage-controlled; the predetermined reactance element of the first frequency variable filter being in the on state when the reactance element of the second frequency variable filter is in the on state.
Hereupon, the first frequency variable filter is a transmission filter, for example, and the second frequency variable filter is a reception filter, for example. As the reactance elements, for example, PIN diodes and variable capacitance diodes are used.
When the reactance element of the second frequency variable filter is in the on state, the predetermined reactance element of the first frequency variable filter is in the on state. Thereby, the impedance of the first frequency variable filter is enhanced in the resonant frequency band of the second frequency variable filter. Accordingly, the insertion loss of the second frequency variable filter is suppressed. In addition, since only t
Atokawa Masayuki
Tsunoda Kikuo
Bettendorf Justin P.
Chang Joseph
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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