Oscillators – Automatic frequency stabilization using a phase or frequency... – Particular frequency control means
Reexamination Certificate
2001-06-12
2003-03-25
Pascal, Robert (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Particular frequency control means
C331S167000, C331S179000
Reexamination Certificate
active
06538521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage controlled oscillator (VCO), and more particularly, to a voltage controlled oscillator (VCO) connected and disposed in a phase locked loop (PLL) and capable of switching oscillation frequency bands by supplying a band switching signal to an LC resonator circuit.
2. Description of the Related Art
Hitherto, there are known, as the mobile telecommunication systems used in respective countries in the world, DCS (Digital Cellular system ) used in England, Germany, Italy, France, and some countries of Asia and GSM (Global System for Mobile Communications) used in Europe, the United States, Africa, and some countries in Asia as European Standard System for digital hand-held phones. Since DCS and GSM are mobile telecommunication systems employing a different telecommunication system, users must be provided with two hand-held phones, that is, a hand-held phone used for DCS (hand-held phone dedicated for DCS) and a hand-held phone used for GSM (hand-held phone dedicated for GSM) in order to subscribe to both of DCS and GSM.
However, since both of DCS and GSM use GMSK (Gaussin Minimum Shift keying) as a signal modulation system while they employ a different communication system, they are different from each other only in that their usable frequency band is different. Accordingly, hand-held phones which can be commonly used by both of DCS and GSM are being developed in place of using two hand-held phones dedicated for DCS and GSM and several commonly usable hand-held phones have been proposed.
These previously proposed hand-held phones which are commonly usable in DCS and GSM include two voltage controlled oscillators, that is, a first voltage controlled oscillator for generating a local oscillation signal suitable for a DCS band receiving frequency and a second voltage controlled oscillator for generating a local oscillation signal suitable for a GSM band receiving frequency, and they selectively use the first and second voltage controlled oscillators based on whether they are used in DCS or in GSM. These previous commonly usable hand-held phones use the two voltage controlled oscillators as well as connect them to individual phase locked loops, which inevitably increases the size of the commonly usable hand-held phones as well as increases the number of parts thereof, which makes the cost of the previous commonly usable hand-held phones expensive.
Hand-held phones commonly usable in the DCS and the GSM, which were proposed after the development of the previous hand-held phones to improve the disadvantages of them (improved-type hand-held phones), employ one voltage controlled oscillator connected to one phase locked loop and are switched to DCS and GSM by switching the resonance circuit of the voltage controlled oscillator in response to a band switching signal. That is, the switching of the resonance circuit in response to the band switching signal permits the voltage controlled oscillator to output a local oscillation signal having an oscillation frequency suitable for the receiving frequency of the DCS band and a local oscillation signal having an oscillation frequency suitable for the receiving frequency-of the GSM band, respectively.
FIG. 4
is a block diagram showing an example of the arrangement of a phase locked loop to which one voltage controlled oscillator used in an improved-type hand-held phone is connected, and
FIG. 5
is a circuit diagram showing an example of the arrangement of the main portion of the voltage controlled oscillator connected to the phase locked loop shown in FIG.
4
.
As shown in
FIG. 4
, the phase locked loop (PLL) includes a voltage controlled oscillator (VCO)
31
, a loop filter (LPF)
32
, a phase comparison circuit (COMP)
33
, a reference frequency signal input terminal
34
, and an oscillation signal output terminal
35
.
The output terminal (oscillation signal output terminal) of the voltage controlled oscillator
31
is connected to the oscillation signal output terminal
35
and to one input terminal of the phase comparison circuit
33
, and the input terminal (control voltage input terminal) thereof is connected to the output terminal of the loop filter
32
. The output terminal of the phase comparison circuit
33
is connected to the input terminal of the loop filter
32
, and the other input terminal thereof is connected to the reference frequency signal input terminal
34
.
As is known well, the operation of the phase locked loop is such that the phase comparison circuit
33
compares the phase of the oscillation signal of the voltage controlled oscillator with the phase of a reference frequency signal, outputs an error signal indicating the error between the phases of the oscillation signal and the reference frequency signal, and supplies the error signal to the loop filter
32
. The loop filter
32
smooths the inputted error signal, outputs it as a control voltage and supplies the control voltage to the LC resonator circuit of the voltage controlled oscillator. In the voltage controlled oscillator
31
, the resonance frequency of the LC resonator circuit is controlled in correspondence to the control voltage supplied thereto, whereby the frequency of an oscillation signal is adjusted to a normal frequency.
As shown in
FIG. 5
, the voltage controlled oscillator (VCO)
31
includes the LC resonator circuit
41
, an amplifier stage
42
, a control voltage input terminal
43
, an oscillation signal output terminal
44
, a band switching signal input terminal
45
, a shunt capacitor
46
, a series inductor
47
, a coupling capacitor
48
, and a series resistor
49
. In this case, the LC resonator circuit
41
includes a varactor diode
41
1
, a first inductor
41
2
, a second inductor
41
3
, a first direct current preventing capacitor
41
4
, a second direct current preventing capacitor
41
5
, and a switching diode
41
6
. Note that, the same reference numerals as used in
FIG. 4
are used in
FIG. 5
to denote the same components.
In the LC resonator circuit
41
, the anode of the varactor diode
41
1
is connected to the ground, the cathode thereof is connected to one end of the first direct current preventing capacitor
41
4
and to the other end of the series inductor
47
. One end of the first inductor
41
2
is connected to the other end of the first direct current preventing capacitor
41
4
and to one end of the coupling capacitor
48
, and the other end thereof is connected to one end of the second inductor
41
3
and to one end of the second direct current preventing capacitor
41
5
. The other end of the second inductor
41
3
is connected to the ground. The other end of the second direct current preventing capacitor
41
5
is connected to the anode of the switching diode
41
6
and to one end of the series resistor
49
. The cathode of the switching diode
41
6
is connected to the ground. Further, the input terminal of the amplifier stage
42
is connected to the other end of the coupling capacitor
48
, and the output terminal thereof is connected to the oscillation signal output terminal
44
. In addition to the above, one end of the shunt capacitor
46
is connected to the control voltage input terminal
43
and to one end of the series inductor
47
. The other end of the shunt capacitor
46
is connected to the ground. The other end of the series resistor
49
is connected to the band switch signal input terminal
45
.
The voltage controlled oscillator
31
arranged as described above will operate as follows. When the voltage controlled oscillator
31
is used as the local oscillator for DCS, a band switching signal of a positive voltage is supplied to the band switching signal input terminal
45
. The band switching signal of the positive voltage is applied to the anode of the switching diode
41
6
through the series resistor
49
to thereby turn on the switching diode
41
6
so as to electrically short circuit the second inductor
41
3
. Further, the control voltage supplied to the control voltage input terminal
43
is su
Chiba Yutaka
Ikarashi Yasuhiro
Kobayashi Hiroki
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Glenn Kimberly E
Pascal Robert
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