Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-08-30
2003-02-25
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S109000, C331S158000, C331S175000
Reexamination Certificate
active
06525619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to crystal-oscillator circuits for phase-locked loop (PLL) circuits for use in image display devices having television tuners and radio frequency (RF) modulators.
2. Description of the Related Art
In image display devices having television tuners and RF modulators, the television tuners and the RF modulators are provided with PLL circuits. Each PLL circuit is provided with a crystal-oscillator circuit employed as a reference oscillation circuit.
FIG. 3
shows the structure of a conventional crystal-oscillator circuit. The crystal-oscillator circuit includes a first crystal-oscillator circuit
20
employed for a PLL circuit of a television tuner and a second crystal-oscillator circuit
30
employed for a PLL circuit of an RF modulator. The first crystal-oscillator circuit
20
and the second crystal-oscillator circuit
30
share a single quartz crystal resonator
40
.
The first crystal-oscillator circuit
20
is formed by a first oscillation transistor
21
, the quartz crystal resonator
40
, and the like. The second crystal-oscillator circuit
30
is formed by a second oscillation transistor
31
, the quartz crystal resonator
40
, and the like. In
FIG. 3
, DC bias circuits for the oscillation transistors
21
and
31
are omitted.
In the first crystal-oscillator circuit
20
, the collector of the first oscillation transistor
21
is grounded at a high frequency by a ground capacitor
22
. A feedback capacitor
23
extends between the emitter and the ground, and a feedback capacitor
24
extends between the base and the emitter. A Clapp capacitor
41
is provided in series with the quartz crystal resonator
40
between the base and the ground. The Clapp capacitor
41
is connected to the base, whereas the quartz crystal resonator
40
is connected to the ground. An oscillation signal is output from the emitter of the first oscillation transistor
21
and is input to the PLL circuit of the television tuner (not shown).
In contrast, in the second crystal-oscillator circuit
30
, the collector of the second oscillation transistor
31
is grounded at a high frequency by a ground capacitor
32
. A feedback capacitor
33
extends between the emitter and the ground, and a feedback capacitor
34
extends between the base and the emitter. A Clapp capacitor
42
is provided in series with the quartz crystal resonator
40
between the base and the ground. The Clapp capacitor
42
is connected to the base, whereas the quartz crystal resonator
40
is connected to the ground. An oscillation signal is output from the emitter of the second oscillation transistor
31
and is input to the PLL circuit of the RF modulator (not shown).
In the above arrangement, the single quartz crystal resonator
40
is shared by the two crystal-oscillator circuits
20
and
30
. With regard to one crystal-oscillator circuit, it seems that the oscillation transistor of the other crystal-oscillator circuit is connected in parallel with the quartz crystal resonator
40
. Hence, the former crystal-oscillator circuit has a significantly small apparent Q-factor of the quartz crystal resonator
40
, failing to ensure a sufficient load resistance required for oscillation. This may cause oscillation to stop.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a crystal-oscillator circuit that prevents oscillation stoppage due to a reduction in the apparent Q-factor of a quartz crystal resonator when an oscillation signal is extracted.
To this end, a crystal-oscillator circuit according to the present invention includes an oscillation transistor having the collector or the base thereof at a ground potential. A first capacitor is connected between the base and the emitter of the oscillation transistor. A second capacitor is connected between the emitter and the collector. A quartz crystal resonator and a capacitor are connected in series between the base and the collector. An oscillation signal is extracted from a node between the quartz crystal resonator and the capacitor.
The collector of the oscillation transistor may be grounded. The quartz crystal resonator may be disposed at the base side. The capacitor may be disposed at the ground potential side.
According to a crystal-oscillator of the present invention, no other circuit is connected in parallel with the crystal-oscillator circuit. Hence, the apparent Q-factor of the crystal-oscillator is not reduced, preventing stopping of oscillation. Also, the crystal-oscillator circuit of the present invention forms a Colpitts oscillator circuit that prevents the stopping of oscillation.
REFERENCES:
patent: 5025229 (1991-06-01), Hasegawa et al.
patent: 5309116 (1994-05-01), Stone
patent: 6271734 (2001-08-01), Satoh
Koyama et al., “Precise Measurement of Resonance Current and Frequency Characteristics of Quartz Oscillators for Oven-Controlled Crystal Oscillators”, Electronics and Communications in Japan, Part 2, vol. 79, No. 4, 1996, pp. 39-45.
Kumaki Masataka
Shimizu Takeshi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kinkead Arnold
LandOfFree
Crystal-oscillator circuit for preventing stopping of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Crystal-oscillator circuit for preventing stopping of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Crystal-oscillator circuit for preventing stopping of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3156146