Oscillators – Plural oscillators – Selectively connected to common output or oscillator...
Reexamination Certificate
2000-06-14
2001-09-25
Grimm, Siegfried H. (Department: 2817)
Oscillators
Plural oscillators
Selectively connected to common output or oscillator...
C331S1170FE, C331S167000, C331S17700V
Reexamination Certificate
active
06294961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to selectable oscillation circuits and, more particularly, relates to a selectable oscillation circuit that achieves low power consumption by reducing the amount of current that flows through the inactivated oscillation circuit, when either of two oscillation circuits is inactivated using a selector circuit.
2. Description of the Related Art
Among the mobile communication systems used worldwide, Digital Cellular System (“DCS”) is employed in the United Kingdom, Germany, France, and part of Asia, and Global System for Mobile Communications (“GSM”), which was adopted as an European standard method for digital cellular phones in 1982, is employed in Europe, the United States, Africa, and part of Asia.
DCS has 374 working channels and employs Gaussian Minimum Shift Keying (“GMSK”) modulation method. In DCS, a frequency band of 1805 MHz to 1880 MHz is assigned to a base station, a frequency band of 1710 MHz to 1785 MHz is assigned to a mobile station, and a 1700 MHz oscillation frequency is assigned to the voltage-controlled oscillator (“VCO”) of the cellular phone. GSM has 124 working channels and employs GMSK as a modulation method. In GSM, a frequency band of 925 MHz to 960 MHz is assigned to a base station, a frequency band of 880 MHz to 915 MHz is assigned to a mobile station, and a 900 MHz oscillation frequency is assigned to the VCO of the cellular phone.
Since these two mobile communication systems, DCS and GSM, employ different communication methods, two cellular phones are required in order to subscribe to both DCS and GSM mobile communication systems: a cellular phone adopting the DCS method and a cellular phone adopting the GSM method.
However, since both DCS and GSM methods employ GMSK modulation method, and only their assigned operating frequencies are different, there has been proposed a cellular phone that can be used for both DCS and GSM modes. In this cellular phone, there is provided a selectable oscillation circuit that has a first voltage-controlled oscillation circuit oscillating at 1700 MHz, a second voltage-controlled oscillation circuit oscillating at 900 MHz, and a selector circuit. This cellular phone is controlled so as to select and properly use one of the two voltage-controlled oscillation circuits, in accordance with a control signal from the selector circuit.
In this cellular phone, having both DCS and GSM modes, when mobile communication is performed using DCS method, by causing the selector circuit to activate the first voltage-controlled oscillation circuit and to inactivate the second voltage-controlled oscillation circuit, the oscillation output can be obtained from the first voltage-controlled oscillation circuit. On the other hand, when mobile communication is performed using GSM method, by causing the selector circuit to inactivate the first voltage-controlled oscillation circuit and to activate the second voltage-controlled oscillation circuit, the oscillation output can be obtained from the second voltage-controlled oscillation circuit.
FIG. 2
shows one example of a conventional selectable oscillation circuit in a cellular phone having both DCS and GSM modes. As shown in
FIG. 2
, the selectable oscillation circuit includes a first voltage-controlled oscillation circuit
21
oscillating at 1700 MHz, a second voltage-controlled oscillation circuit
22
oscillating in the 900 MHz band, a selector circuit
23
, a first oscillation-signal output terminal
24
, a second oscillation-signal output terminal
25
, a selector-signal supply terminal
26
, a first selector terminal
27
, a second selector terminal
28
, a power supply terminal
29
, a first frequency-setting voltage supply terminal
30
, and a second frequency setting voltage-supply terminal
31
.
The first voltage-controlled oscillation circuit
21
includes a first oscillation transistor
211
, an emitter load resistor
21
2
, a varactor diode
21
3
, an inductor
21
4
, coupling capacitors
21
5
and
21
6
, a direct-current-decoupling capacitor
21
7
, a buffer resistor
21
8
, base-bias resistors
21
9
and
21
10
, and a bypass capacitor
21
11
. These circuit elements
21
1
to
21
11
are interconnected as shown in FIG.
2
. The varactor diode
21
3
and the inductor
21
4
mainly constitute a first resonator circuit that determines the oscillation frequency of the first voltage-controlled oscillation circuit
21
. A predetermined frequency of 1700 MHz, which is obtained by changing a first frequency-setting voltage provided via the first frequency-setting voltage-supply terminal
30
to the varactor diode
21
3
, is set as the resonant frequency of the first resonant circuit.
The second voltage-controlled oscillation circuit
22
, which has substantially the same construction as the above-described oscillation circuit
21
, includes a second oscillation transistor
22
1
, an emitter load resistor
22
2
, a varactor diode
22
3
, an inductor
22
4
, coupling capacitors
22
5
and
22
6
, a direct-current-decoupling capacitor
22
7
, a buffer resistor
22
8
, base-bias resistors
22
9
and
22
10
, and a bypass capacitor
22
11
. These circuit elements
22
1
to
22
11
are interconnected as shown in FIG.
2
. The varactor diode
22
3
and the inductor
22
4
mainly constitute a second resonator circuit that determines the oscillation frequency of the second voltage-controlled oscillation circuit
22
. A predetermined frequency of 900 MHz, which is obtained by changing a second frequency-setting voltage provided via the second frequency-setting voltage-supply terminal
31
to the varactor diode
22
3
, is set as the resonant frequency of the second resonant circuit.
The selector circuit
23
includes a first switching transistor
23
1
, a second switching transistor
23
2
, and resistors
23
3
,
23
4
,
23
5
,
23
6
, and
23
7
, which are connected as shown in FIG.
2
.
The conventional selectable oscillation circuit having the above-described construction operates as follows. In the cellular phone, when mobile communication is performed using the DCS method, a HIGH-level (saturated) selector signal is provided to the selector-signal supply terminal
26
of the selector circuit
23
, which switches the first switching transistor
23
1
on and the second switching transistor
23
2
off. At this time, the emitter load resistor
21
2
connected to the first oscillation transistor
21
1
is grounded via the collector-emitter path of the first switching transistor
23
1
, which allows an operating current to flow through the collector-emitter path of the first oscillation transistor
21
1
. Accordingly, normal oscillation occurs in the first voltage-controlled oscillation circuit
21
. The first oscillation signal, whose oscillation frequency is at 1700 MHz, is provided from the emitter of the first oscillation transistor
21
1
via the coupling capacitor
21
6
to the first oscillation-signal output terminal
24
. Finally, the first oscillation signal is provided to an application circuit (not shown). At this time, since the second switching transistor
23
2
is switched off, the emitter load resistor
22
2
connected to the second oscillation transistor
22
1
is not grounded, which prevents an operating current from flowing via the collector-emitter path of the second oscillation transistor
22
1
. Accordingly, the second voltage-controlled oscillation circuit
22
does not oscillate.
On the other hand, when mobile communication is performed using the GSM method, a LOW-level selector signal (non-conducting) is provided to the selector-signal supply terminal
26
of the selector circuit
23
, which switches the first switching transistor
23
1
off and the second switching transistor
23
2
on. At this time, since the second switching transistor
23
2
is switched on, the emitter load resistor
22
2
connected to the second oscillation transistor
22
1
is grounded via the collector-emitter path of the second switching transistor
23
2
, which allows the operating current to flow through the colle
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Grimm Siegfried H.
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