JPH04302510A - Digital temperature-compensated oscillator - Google Patents

Abstract

PURPOSE:To make the oscillator inexpensive and small in size by decreasing the number of components. CONSTITUTION:The oscillation output of a clock oscillator 11 which varies in oscillation frequency monotonously with temperature is supplied as a gate signal to a counter 14, which counts the oscillation output of a voltage-controlled oscillator 15 and compensation data for compensating variation in the oscillation frequency due to the temperature variation of the voltage-controlled oscillator 15 according to the counter value are read out of a digital memory 16 and converted into analog data, which are supplied to the voltage-controlled oscillator 15, thereby controlling the oscillation frequency to a constant value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital temperature compensation oscillator that performs temperature compensation according to temperature compensation data stored in a digital memory, and more particularly to a simplified configuration.

0002

2. Description of the Related Art Generally, a crystal oscillator using a crystal resonator is known as an oscillator whose frequency is stable with respect to temperature. A crystal resonator has nearly ideal chemical and physical characteristics as a piezoelectric material, and has an extremely high Q as a resonator.
Frequency stability is also good. 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 the form of a substantially cubic curve with respect to temperature changes in degrees Celsius, resulting in a frequency error of around 40 ppm. Conventionally, oscillators with good frequency-temperature characteristics, i.e., the rate of frequency variation with respect to temperature changes, 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, oven-type crystal oscillators consume large amounts of power.
Moreover, after the power is turned on, there is a problem in that it takes a long time to consume until the temperature in the thermostatic chamber stabilizes. 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, a digital temperature-compensated oscillator has also been proposed in which the relationship between the ambient temperature of the crystal resonator and the frequency deviation is measured in advance, compensation data is stored in a digital memory, and temperature compensation is performed in accordance with the compensation data. . 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. However, such a digital temperature compensated oscillator generally has a complicated configuration and a large number of parts. For example, in this type of oscillator that uses a microprocessor to perform temperature compensation according to a program, in addition to the original temperature compensation oscillator, there is also a clock oscillator to operate the microprocessor, and an analog oscillator to convert the detected value of the temperature sensor into a digital signal. Requires a goo digital converter etc. For this reason, there are problems in that the number of parts is large, the cost is high, and the shape is also large.

0004

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a digital temperature-compensated oscillator that has a small number of parts, can be miniaturized, and is inexpensive. It is.

[0005]

[Means for Solving the Problems] The present invention provides the oscillation output of a clock oscillator whose oscillation frequency monotonically changes depending on the temperature to a counter as a gate signal, and counts the oscillation output of a voltage-controlled crystal oscillator by the counter. According to this count value, the compensation data is read from the digital memory that stores the compensation data that compensates for the change in oscillation frequency due to the temperature change of the voltage-controlled crystal oscillator, is converted into analog, and is applied to the voltage-controlled crystal oscillator to adjust the oscillation frequency. It is characterized by being controlled to a constant value.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to a block diagram showing the overall configuration shown in FIG. 1 and a block diagram of a clock oscillator shown in FIG. 2. In the figure, reference numeral 11 denotes a clock oscillator whose oscillation frequency monotonically changes depending on the temperature. This clock oscillator 11 is constructed by inserting a time constant circuit consisting of C and R into the feedback circuit of a ring oscillator in which two inverters 11a and 11b are connected in a ring as shown in FIG. Using a thermistor 12 whose resistance value changes depending on the
An oscillation frequency of about 0 KHz is obtained. The resistance value of the thermistor 12 shows a negative resistance that continuously decreases as the temperature rises, and the time constant of the feedback circuit of the clock oscillator also changes accordingly, so the oscillation frequency monotonically and significantly changes depending on the temperature. Change. The oscillation output of the clock oscillator 11 is then given as a clock signal to a CPU (central processing unit) 13, which is, for example, a one-chip microprocessor, to execute a preset program. In addition, the oscillation output of the clock oscillator 11 is sent to the counter 1.
4 to control the opening and closing of the input gate of the counter 14. The oscillation output of the voltage controlled crystal oscillator 15 is input to this counter 14, and the oscillation output of the voltage controlled crystal oscillator 15 is counted during the gate time controlled by the oscillation output of the clock oscillator 11. Therefore, the counter 14 is, for example, a binary counter with serial input and parallel output. This voltage controlled crystal oscillator 15 is a Colpitts-type several MH oscillator using transistors, for example.
In a crystal oscillator that obtains an oscillation output of 10 MHz to several tens of MHz, a voltage-capacitance conversion element, a so-called varicap, is connected in series with a crystal resonator. By controlling the voltage applied to the varicap, the load capacitance of the oscillation circuit is controlled and the oscillation frequency is changed. Therefore, the oscillation frequency of the clock oscillator 11 changes monotonically depending on the temperature, and the gate time also changes accordingly. On the other hand, the amount of change in the oscillation frequency of the voltage controlled crystal oscillator 15 is within a range that can be ignored relative to the change in the oscillation frequency of the clock oscillator 11. Therefore counter 1
The width of the gate time 4 increases or decreases depending on the temperature, and the count value becomes temperature data corresponding to the temperature. The count value of the counter 14 is then provided to the CPU 13 as temperature data. The CPU 13 reads temperature compensation data corresponding to the temperature data given from the counter 14 from the digital memory 16 according to a preset program, and reads out the temperature compensation data corresponding to the temperature data given from the counter 14,
It is applied to the digital-to-analog converter 17 via U13. The digital memory 16 has a voltage controlled crystal oscillator 15 in advance.
Temperature compensation data necessary to maintain the oscillation frequency at a constant frequency is stored for each temperature. The compensation data converted into analog by the digital-to-analog converter 17 is then applied to the voltage controlled crystal oscillator 15 to perform temperature compensation.

With this configuration, since the clock oscillator is used as a temperature sensor, there is no need for an analog-to-digital converter, and the oscillation output of the clock oscillator is used as the clock signal for the CPU. Easy to configure. When the operating clock frequency of the CPU is lowered, power consumption can be reduced, and noise components included in the oscillation output of the voltage-controlled crystal oscillator can also be reduced. Furthermore, since a counter is used, it is also possible to obtain a signal obtained by frequency-dividing the oscillation output of the voltage-controlled crystal oscillator from this counter. Note that the present invention is not limited to the above embodiments,
For example, in the above embodiment, temperature compensation is performed using the CPU, but instead of using the CPU, for example, the count value of the counter is taken out as a parallel output, and this signal is directly applied to the address terminal of the digital memory to obtain compensation data. It is also possible to selectively perform reading temperature compensation. In this case, there is an effect that the number of parts can be further reduced.

[0008]

As described in detail above, according to the present invention, it is possible to provide a digital temperature compensated oscillator that has a small number of parts, can reduce costs, and can be made compact.

[0009]

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a clock oscillator of the present invention.

[Explanation of symbols]

11 Clock oscillator 13 CPU 14 Counter 15 Voltage controlled crystal oscillator 16 Digital memory

Claims (1)

[Claims] 1. A clock oscillator whose oscillation frequency monotonically changes according to temperature, a counter to which the oscillation output of the clock oscillator is given as a gate signal, and a voltage-controlled crystal oscillator whose oscillation output is counted by the counter. A digital memory that stores compensation data for compensating for changes in oscillation frequency due to temperature changes of this voltage-controlled crystal oscillator and outputs compensation data corresponding to the count value of the counter, and converts the stored contents read from this digital memory into analog. and a digital-to-analog converter for supplying the voltage-controlled crystal oscillator to the voltage-controlled crystal oscillator.