Oscillators – Plural oscillators – Selectively connected to common output or oscillator...
Reexamination Certificate
2000-07-11
2002-04-30
Kinkead, Arnold (Department: 2817)
Oscillators
Plural oscillators
Selectively connected to common output or oscillator...
C331S179000, C331S1170FE, C331S074000, C331S046000
Reexamination Certificate
active
06380813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a frequency-characteristic switchable buffer circuit, and particularly to a frequency- characteristic switchable buffer circuit wherein high frequency selective characteristics are respectively added to signals having selectively-supplied first and second frequencies, whereby selected frequency signal components are outputted in a state in which non-selected frequency signal components are sufficiently attenuated.
2. Description of the Related Art
As mobile communication systems employed in all the countries of the world, there are known a DCS (Digital Cellular System) employed in England, Germany, Italy, France and partial countries in Asia, and a GSM (Global System for Mobile Communications) which is the European unified standard system for a digital portable cellular phone, which has been adopted in 1982, and which is used in partial countries in Europe, America, Africa and Asia.
In this case, the DCS is a mobile communication system wherein 1805 MHz through 1880 MHz, 1710 MHz through 1785 MHz and a 1700 MHz band are respectively assigned to a base-station frequency, a mobile-station frequency, and an oscillating frequency generated from a voltage-controlled oscillator (VCO) of a portable cellular phone, the number of channels to be used is 374, and GMSK (Gaussian Minimum Shift Keying) is used as a modulation scheme. On the other hand, the GSM is a mobile communication system wherein 925 MHz through 960 MHz, 880 MHz through 915 MHz and a 900 MHz band are respectively assigned to a base-station frequency, a mobile-station frequency, and an oscillating frequency generated from a voltage-controlled oscillator (VCO) of a portable cellular phone, the number of channels to be used is 124, and the GMSK (Gaussian Minimum Shift Keying) is used as a modulation scheme.
Since these two mobile communication systems, i.e., the DCS and GSM are originally mobile communication systems different in system from each other, two portable cellular phones: a portable cellular phone used when mobile communications are performed by the DCS and a portable cellular phone used when mobile communications are made by the GSM, are needed to enter the two mobile communication systems of DCS and GSM.
Since, however, the DCS and GSM are both GMSK in use modulation scheme and simply different from each other in assignment use frequency as described above, a portable cellular phone capable of being shared between the DCS and GSM has already been proposed wherein two voltage-controlled oscillators: a first voltage-controlled oscillator for oscillating a first frequency lying within a 1700 MHz band and a second voltage-controlled oscillator for oscillating a second frequency lying within a 900 MHz band, and a switching type oscillator having a switching circuit are placed within the portable cellular phone, and the switching circuit of the switching type oscillator is controlled to thereby allow the proper use of the two voltage-controlled oscillators.
In the portable cellular phone capable of being shared between the DCS and GSM, when the mobile communications are performed by the DCS, the switching circuit is used to bring the first voltage-controlled oscillator to an operating state and bring the second A voltage-controlled oscillator to a non-operating state, whereby an oscillating signal having a first frequency is outputted from the first voltage-controlled oscillator.
On the other hand, when the mobile communications are carried out by the GSM, the switching circuit is used to bring the second voltage-controlled oscillator to an operating state and bring the first voltage-controlled oscillator to a non-operating state, whereby an oscillating signal having a second frequency is outputted from the second voltage-controlled oscillator. Further, the oscillating signal having the first frequency or the oscillating signal having the second frequency is selected and amplified by a buffer circuit capable of performing switching between frequency characteristics, followed by supply to an available circuit.
The frequency-characteristic switchable buffer circuit used at this time has a parallel resonance circuit (frequency selection circuit). When the first voltage-controlled oscillator is kept in the operating state or the second voltage-controlled oscillator is kept in the operating state, the parallel resonance circuit is supplied with a first switching voltage or a second switching voltage to thereby select its characteristic selective characteristic. When the first switching voltage is supplied to the parallel resonance circuit, the parallel resonance circuit selects and outputs the oscillating signal having the first frequency- When the second switching voltage is supplied thereto, the parallel resonance circuit selects and outputs the oscillating signal having the second frequency.
FIG. 5
is a circuit diagram showing one example of a configuration of a conventional frequency-characteristic switchable buffer circuit employed in the portable cellular phone capable of being shared between the DCS and GSM.
As shown in
FIG. 5
, the conventional frequency-characteristic switchable buffer circuit
50
has an amplifying stage with a transistor
51
, base bias resistors
55
and
56
, an emitter resistor
57
, and a bypass capacitor
58
; a parallel resonance circuit (frequency selection circuit)
52
; coupling capacitors
53
and
54
; a frequency switching voltage generator
71
with a one-circuit two-contacts selector switch
59
, switching-voltage setting resistors
60
and
61
, and a bypass capacitor
62
; a buffer resistor
63
; a signal input terminal
64
; a signal output terminal
65
; and a power terminal
66
. These circuit elements are electrically connected to one another as shown in FIG.
5
.
Further, the parallel resonance circuit
52
comprises a first inductor
52
1
, a second inductor
52
2
, a first capacitor
52
3
, a second capacitor
52
4
, a third capacitor
52
5
, and a switching diode
52
6
. These circuit elements
52
1
through
52
6
are electrically connected to one another as shown in FIG.
5
.
As shown in
FIG. 5
, a first voltage-controlled oscillator
67
for oscillating a first frequency, in this case, each of frequencies lying within a 1700 MHz band, a second voltage-controlled oscillator
68
for oscillating a second frequency, in this case, each of frequencies lying within a 900 MHz band, a power supply or battery
69
, and a one-circuit two-contacts selector switch
70
are placed on the preceding stage side of the frequency-characteristic switchable buffer circuit
50
. These circuit elements
67
through
70
are electrically connected to one another as shown in FIG.
5
. In this case, the selector switch
59
and the selector switch
70
are selected or changed in interlock with each other by a control signal to be described later.
The conventional frequency-characteristic switchable buffer circuit
50
having the above-described configuration is operated as follows:
When the portable cellular phone is used in a mobile communication based on the DCS, movable contacts of the selector switch
59
and the selector switch
70
are respectively changed over from positions indicated by solid lines shown in
FIG. 5
to positions indicated by dotted lines illustrated in
FIG. 5
according to a first control signal outputted from a controller (not shown). Owing to the changeover, the first voltage-controlled oscillator
67
is electrically connected to the power supply
69
so that it is brought to an operating state. Thus, a signal having a first frequency (corresponding to any of the frequencies lying within the 1700 MHz band) is outputted from the first voltage-controlled oscillator
67
. On the other hand, the second voltage-controlled oscillator
68
is electrically disconnected from the power supply
69
so that it is brought to a non-operating state. Owing to the changeover of the movable contact of the selector switch
59
to the position indicated by the dotted line, a first switching vo
Baba Toshiki
Noumi Hiroki
Alps Electric Co. ,Ltd.
Kinkead Arnold
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