JPH03113903A - Digital temperature compensation oscillator - Google Patents

Abstract

PURPOSE:To set an offset voltage from the outside of an air-tight package by containing an oscillator applying temperature compensation according to compensation data stored in a 1st memory into an air-tight package and giving data to a 2nd memory storing an offset data externally. CONSTITUTION:Components such as a voltage controlled oscillator (VCXO) 11-2nd memory 16 are contained in a metal-made air-tight package 19 and sealed. Then switches 17, 18 are so structured that they are fitted air-tightly to e.g. the air-tight package 19 and operated externally. When the VCXO 11 is operated, the temperature is detected by a temperature sensor 12 and the data is fetched in a CPU 13. The CPU 13 reads the temperature compensation data in response to the fetched temperature from a 1st memory. Then an offset data read from the 2nd memory 16 is adjusted and given to an A/D converter 15. The A/D converter 15 converts a given digital value into an analog value and the result is given to the VCXO 11 as a control voltage to compensate the oscillating frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a digital temperature-compensated oscillator with good frequency-temperature characteristics, and more particularly to setting an offset amount for offsetting the oscillation frequency by a certain value.

(Technical background of the invention and its problems) A crystal oscillator using a crystal resonator is generally known as an oscillator whose frequency is stable with respect to temperature.

A crystal resonator has substantially ideal chemical and physical characteristics as a piezoelectric material, has an extremely high Q as a resonator, and has good frequency stability.

However, in recent years, more precise frequency stability has been required for various electronic devices, and for example, the crystal oscillator used as the frequency standard for the mobile station of the currently planned car phone is subject to temperature fluctuations of -30°C to 80°C. It is required that the deviation be within ±2 ppm.

On the other hand, in a crystal resonator, when the oscillation conditions of the oscillation circuit are kept constant, the biggest factor that changes the frequency is temperature change. The frequency changes in a substantially cubic curve with respect to temperature changes of ~80°C, resulting in a frequency error of around 40 ppm.

Conventionally, oscillators with good frequency fluctuations relative to temperature changes, that is, good frequency-temperature characteristics, have been made using oven-type crystal oscillators in which the crystal oscillator is housed in a thermostatic oven, or in which a circuit network of thermistors and varicaps is connected in series with the crystal oscillator. There were oscillators using an indirect temperature compensation method, and oscillators using a direct temperature compensation method using a parallel circuit of a capacitor and thermistor connected in series with a crystal resonator.

However, the oven-type crystal oscillator has a problem in that it consumes a large amount of power, and it takes a long time to stabilize the temperature in the thermostatic oven after the power is turned on.

In addition, the indirect compensation method using a thermistor and the direct compensation method both provide approximate compensation, and there is a problem in that even if sufficient adjustment is made, a considerable frequency error remains uncompensated.

Furthermore, the relationship between the ambient temperature of the crystal oscillator and the frequency deviation is measured in advance and the compensation data is digitally stored.
A digital temperature compensation type oscillator that performs temperature compensation according to the compensation data has also been proposed.

Such a digital temperature-compensated oscillator has a quick start-up when the power is turned on, and if a large-capacity memory is used to store compensation data, short-term frequency stability can be significantly improved and accurate temperature compensation can be achieved. becomes possible.

On the other hand, in such a highly stable oscillator, long-term stability is also a problem, and for example, frequency fluctuations occur due to aging characteristics of the crystal resonator itself, aging of circuit elements, etc.

Regarding such long-term stability, it is particularly important to store the oscillator in an airtight container to improve moisture resistance, as humidity has a large effect.

Incidentally, in such an oscillator, it is inevitable that the center frequency will shift due to changes over time in relation to long-term stability. Therefore, a trimmer capacitor is provided for the purpose of adjusting the load capacitance of the crystal resonator and offsetting the oscillation frequency by a certain amount. However, with this type of device, it is necessary to drill a through hole in the container housing the oscillator to adjust the trimmer capacitor, and the internal electronic components are directly exposed to the influence of external humidity, resulting in a decrease in moisture resistance. There is.

Another idea is to house the oscillator in an airtight container, provide a variable resistor and a variable voltage source outside of the container, and use the airtight terminal to vary the voltage applied to the varicap that adjusts the load capacity of the crystal resonator. It is being

In this way, the oscillator can easily have an airtight structure, but there is a problem in that it requires external components with high precision and high stability.

(Object of the Invention) The present invention has been made in view of the above circumstances, and provides a digital temperature compensation system that allows externally setting an offset voltage that varies the oscillation frequency of a digital temperature compensated oscillator housed in an airtight container by a certain amount. The purpose is to provide a compensated oscillator.

(Summary of the Invention) The present invention stores an oscillator in an airtight container, which performs temperature compensation according to compensation data that is stored in a first memory by measuring the relationship between the ambient temperature and frequency deviation of the crystal oscillator in advance, and stores offset data in the airtight container. The present invention is characterized in that data is supplied from the outside to the stored second memory via the airtight container.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the block diagram shown in FIG. 1 and the perspective view shown in FIG.

In the figure, numeral 11 denotes a voltage controlled crystal oscillator (hereinafter referred to as CXO) whose oscillation frequency can be varied according to the value of the control voltage. And 12 is the temperature of VCXO11, more precisely the temperature of its crystal oscillator i! ! It is a temperature sensor that determines the temperature.

The temperature sensor 12 then digitizes the detected temperature data and inputs it to a one-chip microprocessor (hereinafter referred to as CPU) 13 in which a predetermined program is stored.

The CPU 13 stores temperature compensation data in advance according to the value of the signal from the temperature sensor 12.
The data at the corresponding address in the memory 14 is read out and supplied to the digital-to-analog converter 15 to be converted into an analog signal.

Then, the analog signal output from the digital-to-analog converter 15 is applied to the VCXOII to perform temperature compensation.

The offset data for varying the oscillation output of the VCXOII by a certain amount is, for example, an electrically erasable second data.
The information is stored in the memory 16 of the computer. Therefore C
The PU 13 reads the offset data from this second memory 16 and sets the offset voltage according to this content to V.
Give for CXOI 1.

The stored contents of the second memory 16 include the states of the contacts of the frequency increase switch 17 and the frequency decrease switch 18.
13, and the offset value is increased or decreased by a fixed amount each time a contact is closed, for example.

The VCXOII or the second memory 16 within the dashed line frame in FIG. 1 is housed and sealed in a metal airtight container 19 as shown in FIG. 2, for example.

The switches 17 and 18 are, for example, airtightly attached to the airtight container 19 and can be operated from the outside.

In this way, when the VCXOII operates, the temperature is detected by the temperature sensor 12 and taken into the CPU 13. C
The PU 13 reads temperature compensation data corresponding to the captured temperature from the first memory, adds or subtracts offset data read from the second memory 16 to the data, and supplies the data to the digital-to-analog converter 15. Digital-analog converter 1
5 converts the given digital value to analog and converts it to vcx.

11 as a control voltage to compensate for the oscillation frequency.

Then, when the frequency increase switch 17 or the frequency decrease switch 18 is operated, the state of the contact is determined by the CPU.
13 and stored in the second memory 16 is rewritten. In this case, the offset data may be increased or decreased in proportion to the time during which the contacts of the switches 17 and 18 are closed.

Note that the present invention is not limited to the above embodiments,
For example, in the above embodiment, the switch 1'7.18 is airtightly provided in the airtight container 19, but if only the terminal is provided in the airtight container 19 and the offset data is changed,
An L/T may also be used in which this terminal is short-circuited to the container 19 itself using a suitable conductive wire or the like to function as a switch. Makuga 1 Kobo no Sumizo 1
1+, +l, 1s-memozoto 8-ka Takeuchi・1Komoyo・1 (Effects of the Invention) As detailed above, according to the present invention, the digital temperature compensated It is possible to provide a digital temperature compensated oscillator in which an offset voltage for varying the oscillation frequency of the oscillator by a certain amount can be set from outside the airtight container.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a perspective view showing the oscillator of the above embodiment. 11 ・ l 2 ・ 13 ・ 14 ・ 15 ・ l 6 ・Voltage controlled oscillator (VCXO) ・Temperature sensor ・Microprocessor (CPU) ・First memory (temperature compensation data) ・Digital-to-analog converter ・Second Memory (offset data) 7. 18・Switch 9・Airtight container

Claims (1)

[Scope of Claims] An oscillator housed in an airtight container that performs temperature compensation according to compensation data that is digitally stored in a first memory by measuring the relationship between the ambient temperature and frequency deviation of the crystal oscillator in advance, A digital temperature-compensated oscillator comprising: a second memory for storing an offset amount of the oscillation frequency of the crystal oscillator; and a terminal for supplying data to the second memory from the outside via the airtight container.