Oscillators – Frequency stabilization – Temperature or current responsive means in circuit
Patent
1997-01-23
1998-09-01
Nelms, David C.
Oscillators
Frequency stabilization
Temperature or current responsive means in circuit
331158, H03L 700, H03B 532
Patent
active
058015965
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to the structure of a temperature compensation type quartz oscillator, particularly to one suitable for a small digital temperature compensation type quartz oscillator for incorporation in a portable telephone set or the like.
2. Background Technology
Demand is strong for smaller quartz oscillators for incorporation in portable telephone sets, automobile telephone sets and the like. Moreover, while analog temperature compensation type quartz oscillators used to be the main type, digital temperature compensation type quartz oscillators are recently receiving increasing attention for their frequency precision and ease of production.
The frequency regulation method is fundamentally the same in a digital temperature compensation type quartz oscillator as in an analog temperature compensation type quartz oscillator. Specifically, the oscillating frequency is maintained constant by varying the load capacitance of quartz oscillation means in accord with the temperature characteristics of the quartz oscillator or in accord with deviation from a reference frequency from a base station.
Means usable for changing the load capacitance in the temperature compensation operation of a digital temperature compensation type quartz oscillator include means for directly operating switch and capacitor circuity with a digital code and means for converting a digital code to analog voltage by a D/A converter and varying the capacitance value of a variable capacitance diode using this voltage.
It is extremely difficult to vary the load capacitance slowly with the former means using switch and capacitor circuity. Since the frequency compensation of the quartz oscillator therefore occurs abruptly at the time of temperature change, a telephone set using this means has the problem of producing FM noise.
On the other hand, the latter means using the D/A converter is easily able to achieve slow variation of the load capacitance by insertion of an integrating circuit (low-pass filter) between the D/A converter and the variable capacitance diode or by slowing the operation of the D/A converter itself and therefore does not have the problem of producing FM noise.
Because of this, means using a D/A converter and a variable capacitance diode is used in the temperature compensation operation of the ordinary digital temperature compensation type quartz oscillator.
Means using a variable capacitance diode is also used in the case of setting the oscillating frequency to the base station reference frequency, partly for the reason that the external input signal used in the setting operation is an analog signal intended for use with a variable capacitance diode.
FIG. 11 is a circuit diagram showing an example of the structure of a conventional digital temperature compensation type quartz oscillator. In this FIG. 11, the oscillation inverter and the like are designated using circuit symbols and the temperature information generation section and the like using blocks.
As shown in FIG. 11, a quartz oscillator 1, an oscillation inverter 3 and a feedback resistor 5 are connected in parallel to constitute quartz oscillation means 2, and a direct current blocking capacitor 23 for temperature compensation and a variable capacitance diode 25 for temperature compensation are connected in series to constitute temperature compensation control means 6. One terminal of the temperature compensation direct current blocking capacitor 23 is connected to the input terminal of the oscillation inverter 3, the anode of the temperature compensation variable capacitance diode 25 is connected to the other terminal of the temperature compensation direct current blocking capacitor 23, and the cathode of the temperature compensation variable capacitance diode 25 is connected to a high-potential side power supply +Vcc.
A direct current blocking capacitor 27 for external frequency control and a variable capacitance diode 29 for external frequency control are connected in series to constitute an external frequency control me
REFERENCES:
patent: 4015208 (1977-03-01), Hammer et al.
patent: 4415870 (1983-11-01), Zumsteg
patent: 5530458 (1996-06-01), Vig et al.
Citizen Watch Co. Ltd.
Nelms David C.
Phan Trong
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