Oscillators – Electromechanical resonator – Crystal
Reexamination Certificate
2001-10-26
2003-04-29
Mis, David C. (Department: 2817)
Oscillators
Electromechanical resonator
Crystal
C331S1160FE, C331S075000, C331S173000, C331S057000
Reexamination Certificate
active
06556094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillator circuit having an amplifier circuit for amplifying the oscillation output from a piezoelectric oscillator such as a quartz oscillator and to an integrated circuit for oscillation. More particularly, the invention relates to an oscillator circuit adapted for high-frequency operation and to an integrated circuit for oscillation.
2. Description of the Related Art
Conventionally, an oscillator circuit equipped with an amplifier circuit for amplifying the oscillation output from a piezoelectric oscillator such as a quartz oscillator as shown in
FIG. 17
is available. In this circuit, a quartz oscillator XL is connected between the input terminal in and the output terminal out of the CMOS inverter INV acting as an amplifier portion. Also, a feedback resistor Rf is connected between these input and output terminals. The input terminal in and output terminal out are connected with a power-supply terminal VSS (0 V) via capacitive elements CG and CD, respectively, serving as load capacitors.
Today, oscillator circuits are required to operate at higher frequencies. As the operating frequency is made higher, the size of the quartz oscillator decreases. Concomitantly, the oscillation output, i.e., the electric current (hereinafter may be referred to as “quartz current”) flowing through the quartz oscillator, becomes weaker. Therefore, in the configuration of
FIG. 17
, oscillation is possible for a quartz oscillator up to where a 100 MHz third overtone is used as the oscillation frequency. However, at still higher frequencies exceeding 120 MHz, for example, the amplification factor of the amplifier portion is small and so the oscillation output cannot be amplified sufficiently. Consequently, it has been impossible to operate the circuit as an oscillator circuit.
Where one attempts to produce higher frequencies by making use of overtones higher than the third overtone, the following problems take place. The configuration of
FIG. 17
is integrated except for the quartz oscillator XL. As shown in the equivalent circuit of
FIG. 18
, the quartz oscillator XL can be represented as a series circuit of a resistor RX and an inductor LX. The other components in the form of an integrated circuit can be represented as a series circuit of a negative resistor RL and a capacitor CL. The frequency characteristics of the negative resistor RL are shown in
FIG. 19
, where the resistance value is plotted on the vertical axis and the frequency on the horizontal axis. Thus, the negative resistance RL of the third overtone oscillation is indicated. The values of resistive components of the quartz oscillator at the fundamental wave, third overtone, and fifth overtone are indicated by R
01
, R
03
, and R
05
, respectively. If the negative resistance RL is greater than that of the resistance RX in the negative direction, the circuit operates as an oscillator circuit. If a quartz oscillator of 30 MHz is used to generate the third overtone in the configuration of
FIG. 17
, the negative resistance RL decreases with frequency from a peak close to 30 MHz that is the oscillation frequency of the third overtone as shown in FIG.
19
. For example, at the oscillation frequency of 50 MHz of the fifth overtone, the negative resistance RL is smaller than the resistive component of RX of the quartz oscillator and, therefore, the oscillator circuit cannot be set into operation. For this reason, a coil LADD and a capacitive element CADD are sometimes connected between a capacitive element CD and a power-supply terminal VSS as shown in
FIG. 20
to produce the fifth overtone. However, it is necessary to provide the external coil LADD and capacitive element CADD, which in turn increases the circuit area. In addition, it is laborious to control the values of these added elements.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an oscillator circuit which is adapted for a piezoelectric oscillator which generates a weak oscillation output. The provided oscillator circuit operates at increased speed. It is another object of the invention to provide an integrated circuit which is used for oscillation and which is used to construct the above oscillator circuit.
An oscillator circuit in accordance with the present invention comprises: an amplifier portion consisting of plural CMOS inverters connected in cascade; a piezoelectric oscillator connected between the input and the output terminals of the amplifier portion; a first load capacitor connected between the input terminal of the amplifier portion and a terminal at a certain potential; a second load capacitor connected between the output terminal of the amplifier portion and the terminal at the certain potential; and a filter circuit included in the amplifier portion. The CMOS inverters have gate areas which decrease successively in going from the first stage to the last stage.
Preferably, the filter circuit is defined such that the negative resistance of the circuit formed by the amplifier portion, the feedback resistor, the first and second load capacitors has a peak at a given frequency.
Preferably, the filter circuit described above is in a signal path between the input and the output terminals of the amplifier portion. A capacitive element is connected with the input terminal of at least one of the above-described plural CMOS inverters. A resistor is connected between the input terminal of the CMOS inverter with which the capacitive element is connected and the output terminal.
The above-described filter circuit is preferably composed of a capacitive element and a resistor. In the preferred embodiment shown in
FIG. 1
, the capacitive element is connected between the input terminal of the amplifier portion and the input terminal of the first-stage CMOS inverter of the amplifier portion. The resistor is connected between the input and output terminals of the first-stage CMOS inverter.
In the above-described amplifier portion, the CMOS inverters desirably have the same channel length. The CMOS inverters have channel widths that decrease successively in going from the first stage to the last stage.
Another oscillator circuit in accordance with the present invention comprises: an amplifier portion consisting of first, second, and third CMOS inverters connected in cascade, said CMOS inverters having gate areas that decrease successively in going from the first stage to the last stage; a filter circuit consisting of a capacitive element and a resistor connected between the input and the output terminals of the first CMOS inverter, the capacitive element having one terminal connected with the input terminal of the first CMOS inverter and the other terminal acting as the input terminal of the amplifier portion; a piezoelectric oscillator connected between the input and output terminals of the amplifier portion; a feedback resistor connected between the input terminal of the amplifier portion and a terminal at a certain potential; and a second load capacitor connected between the output terminal of the amplifier portion and the terminal at the certain potential.
Preferably, each of the above-described oscillator circuits has a resistor connected to at least one of first and second signal paths to suppress the electric current flowing through the piezoelectric oscillator. The first signal path is formed by the input terminal of the amplifier with which the first load capacitor is connected and by the certain potential. The second signal path is formed by the output terminal of the amplifier with which the second load capacitor is connected and by the certain potential.
In each of the above-described oscillator circuits, the sources of the MOS transistors forming the CMOS inverters of the amplifier portion and the terminal at the certain potential are preferably connected with a power-supply potential via a current-limiting device. Desirably, the current-limiting device connects some of the plural MOS transistors in parallel. The others of the pl
Hasegawa Eiichi
Kimura Masahisa
Oyama Kazuhisa
Tsukagoshi Kunihiko
Lutzker Joel E.
Mis David C.
Nippon Precision Circuits Inc.
Schulte Roth & Zabel LLP
Vishev Anna
LandOfFree
Oscillator circuit and integrated circuit for oscillation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Oscillator circuit and integrated circuit for oscillation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Oscillator circuit and integrated circuit for oscillation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3086665