Switch-type oscillating circuit for providing isolation...

Details Switch-type oscillating circuit for providing isolation... Switch-type oscillating circuit for providing isolation...

2000-06-23

2001-09-11

Mis, David (Department: 2817)

Oscillators

Plural oscillators

Selectively connected to common output or oscillator...

C331S077000, C331S1170FE, C331S173000, C331S17700V

Reexamination Certificate

active

06288615

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to switch-type oscillating circuits, and more particularly, to a switch-type oscillating circuit in which switch circuits selectively switch one of two oscillating circuits to an operating state and sufficient isolation is provided between the two oscillating circuits when the output ends of the two oscillating circuits are coupled with the input end of a common circuit through a coupling circuit.
2. Description of the Related Art
As mobile communication systems used in the world, there are a digital cellular system (DCS) used in Great Britain, Germany, Italy, France, and a part of Asian nations, and a global system for mobile communications (GSM), which was adopted in 1982 as the European integrated standard method for digital portable telephones, used in Europe, the United States of America, Africa, and a part of Asian nations.
In the DCS, a local-station frequency is assigned to 1805 MHz to 1880 MHz, a mobile-station frequency is assigned to 1710 MHz to 1785 MHz, the oscillation frequency of a voltage-controlled oscillating circuit (VCO) in a portable telephone is assigned to the 1700 MHz band, the number of used channels is 374, and the Gaussian minimum shift keying (GMSK) modulation method is used. In the GSM, a local-station frequency is assigned to 925 MHz to 960 MHz, a mobile-station frequency is assigned to 880 MHz to 915 MHz, the oscillation frequency of a voltage-controlled oscillating circuit (VCO) in a portable telephone is assigned to the 900 MHz band, the number of used channels is 124, and the Gaussian minimum shift keying (GMSK) modulation method is used.
Since these two mobile communication systems, the DCS and the GSM, are essentially different in method, it is necessary to use two portable telephones, one for mobile communication in the DCS and the other for mobile communication in the GSM, to subscribe to the two mobile communication systems.
Because the DCS and the GSM use the GMSK modulation method, as described above, and only differ in assigned frequency, a portable telephone which can be used both in the DCS and the GSM has already been proposed, provided with a switch-type oscillating circuit which includes two voltage-controlled oscillating circuits, a first voltage-controlled oscillating circuit for oscillating at a frequency of the 1700 MHz band and a second voltage-controlled oscillating circuit for oscillating at a frequency of the 900 MHz band, and switch circuits; and in which the two voltage-controlled oscillating circuits are selectively used under the control of the switch circuits.
When this portable telephone, which can be used both in the DCS and the GSM, is used for mobile communication in the DCS, the switch circuits switch the first voltage-controlled oscillating circuit to an operating state and the second voltage-controlled oscillating circuit to a non-operating state so as to obtain an oscillation output from the first voltage-controlled oscillating circuit. When the portable telephone is used for mobile communication in the GSM, the switch circuits switch the first voltage-controlled oscillating circuit to a non-operating state and the second voltage-controlled oscillating circuit to an operating state so as to obtain an oscillation output from the second voltage-controlled oscillating circuit.
FIG. 3
is a circuit diagram showing an example structure of a known switch-type oscillating circuit in a portable telephone which can be used both in the DCS and the GSM.
As shown in
FIG. 3
, the known switch-type oscillating circuit is provided with a first voltage-controlled oscillating circuit
31
for oscillating at a frequency of the 1700 MHz band, a second voltage-controlled oscillating circuit
32
for oscillating at a frequency of the 900 MHz band, a coupling circuit
33
, a common circuit
34
, a first-oscillation-signal output terminal
35
, a second-oscillation-signal output terminal
36
, a common input terminal
37
, a signal output terminal
38
, a first-switch-signal supply terminal
39
, a second-switch-signal supply terminal
40
, a power terminal
41
, a first-frequency-setting-voltage supply terminal
42
, and a second-frequency-setting-voltage supply terminal
43
.
The first voltage-controlled oscillating circuit
31
is formed of a first oscillation transistor
31
1
, a first switching transistor
31
2
, an emitter load resistor
31
3
, an isolation inductor
31
4
, a varactor diode
31
5
, an inductor
31
6
, a bypass capacitor
31
7
, resonant capacitors
31
8
and
31
10
, a resonant inductor
31
9
, base bias resistors
31
11
, and
31
12
, feedback capacitors
31
13
and
31
14
, a series resistor
31
15
, and a grounding capacitor
31
16
. These circuit elements
31
1
, to
31
16
are connected as shown in FIG.
3
.
The first switching transistor
31
2
constitutes a first switch circuit, goes on when a first switch signal sent to the first-switch-signal supply terminal
39
has a positive polarity (high level), and goes off when the first switch signal has a ground potential (low level). The varactor diode
31
5
, the resonant inductor
31
9
, and the resonant capacitors
31
8
and
31
10
, constitute a first resonant circuit for specifying the first oscillation frequency of the first voltage-controlled oscillating circuit
31
. The resonant frequency of the first resonant circuit is set to a predetermined frequency in the 1700 MHz band by changing a first frequency setting voltage sent to the varactor diode
31
5
through the first-frequency-setting-voltage supply terminal
42
.
The second voltage-controlled oscillating circuit
32
has almost the same structure as the first voltage-controlled oscillating circuit
31
, and is formed of a second oscillation transistor
32
1
, a second switching transistor
32
2
, an emitter load resistor
32
3
, an isolation inductor
32
4
, a varactor diode
32
5
, an inductor
32
6
, a bypass capacitor
32
7
, resonant capacitors
32
8
and
32
10
, a resonant inductor
32
9
, base bias resistors
32
11
and
32
12
, feedback capacitors
32
13
and
32
14
, a series resistor
32
15
, and a grounding capacitor
32
16
. These circuit elements
32
1
to
32
16
are connected as shown in FIG.
3
.
The second switching transistor
32
2
constitutes a second switch circuit, goes on when a second switch signal sent to the second-switch-signal supply terminal
40
has a positive polarity (high level), and goes off when the second switch signal has a ground potential (low level). The varactor diode
32
5
, the resonant inductor
32
9
, and the resonant capacitor
32
8
and
32
10
, constitute a second resonant circuit for specifying the second oscillation frequency of the second voltage-controlled oscillating circuit
32
. The resonant frequency of the second resonant circuit is set to a predetermined frequency in the 900 MHz band by changing a second frequency setting voltage sent to the varactor diode
32
5
through the second-frequency-setting-voltage supply terminal
43
.
The coupling circuit
33
is formed of a first coupling capacitor
33
1
, an inductor
33
2
, a capacitor
33
3
, a second coupling capacitor
33
4
, an inductor
33
5
, and a capacitor
33
6
. These circuit elements
33
1
to
33
6
are connected as shown in FIG.
3
. The inductor
33
2
and the capacitor
33
3
form a first trap circuit which resonates at the second oscillation frequency of the second voltage-controlled oscillating circuit
32
. The inductor
33
5
and the capacitor
33
3
form a second trap circuit which resonates at the first oscillation frequency of the first voltage-controlled oscillating circuit
31
. The coupling circuit
33
provides sufficient isolation between the first voltage-controlled oscillating circuit
31
and the second voltage-controlled oscillating circuit
32
since the first trap circuit and the second trap circuit are connected as shown in FIG.
3
.
The common circuit
34
is formed of an amplifying transistor
34
1
, a collector load inductor
34
2
, an emitter resistor
34
3
, a groundin

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