JPS63108806A - Crystal oscilator with digital temperature compensation - Google Patents

Abstract

PURPOSE:To eliminate influence due to the change in the lapse of time of a volume or a variable capacitor and to improve stability, by providing an arithmetic circuit which calculates an adjusting signal at the front of a D/A converter which converts a temperature compensating signal. CONSTITUTION:A bit of temperature information from a temperature detecting element is inputted from a terminal 1, and it is converted to a digital signal at an A/D converter 2. A temperature data converted to the digital signal is inputted to a first memory circuit 3 where the bit of temperature information of a crystal oscillator for temperature is stored in a ROM, and the compensating signal is outputted. The compensating signal is inputted to the arithmetic circuit 4. The arithmetic circuit 4 performs addition or subtraction, and calculates it with a data signal for fine adjustment from an adjusting circuit 5. The output of the arithmetic circuit 4 is converted to an analog signal at the D/A converter 7, and is outputted from a terminal 8, and is inputted to a variable capacitance diode, etc., then, the frequency of the crystal oscillator can be compensated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a digital temperature-compensated crystal oscillator whose frequency is finely adjusted using a digital signal.

[Prior art 1] In recent years, when performing temperature compensation in an oscillation circuit using a crystal resonator, an analog signal generated from a temperature sensing circuit 20 that senses temperature with a temperature sensing element and generates temperature information is converted to an A/D converter. 21, the temperature characteristics of the crystal resonator 23 are stored in advance in the ROM circuit 22, a temperature compensation signal corresponding to the temperature is digitally output, and this digital signal is converted to a digital signal by the D/A converter 23. Variable capacitance diode 2 converted into an analog signal and connected in series with crystal oscillator 24
A digital temperature-compensated crystal oscillator (D-TCXO) that compensates for the temperature by inputting the input signal to the D-TCXO has been announced.

At this time, a variable capacitance diode 25 is used to finely adjust the frequency.
Use the volume 26 to adjust the analog signal added to the
Adjustments were made by connecting a variable capacitor in series or parallel to the variable capacitance diode 25. 27 is an oscillation circuit. FIG. 3 is a block diagram showing a conventional example. A signal from a temperature sensing element such as a thermistor is converted into a digital signal by an A/D converter 21. Digital signal is ROM circuit 2
2 outputs a digital signal of the temperature characteristic information of the crystal resonator already stored, that is, a temperature compensation signal corresponding to the temperature signal.

However, the volume and variable capacitor change over time, and there is a risk that the frequency may change over time.

[Problem to be Solved by the Invention J The present invention does not convert the temperature compensation signal into an analog signal, but finely adjusts it in the digital signal state.
An arithmetic circuit is provided between the OM circuit and the A/D converter, a fine adjustment signal is given as a digital signal, and the arithmetic circuit calculates and adjusts the fine adjustment signal.

[Configuration of the present invention] The configuration of the present invention converts temperature information from a temperature sensing element using an A/D converter, and compensates according to the temperature information from a memory circuit in which temperature characteristics of a crystal resonator are stored in advance. In a digital temperature compensated crystal oscillator that outputs a signal and converts the temperature compensated signal with a D/A converter to compensate for the temperature of the crystal resonator, the D
1. A digital temperature-compensated crystal oscillator, characterized in that an arithmetic circuit for calculating an adjustment signal is provided in front of a /A converter.

[Operation and Embodiment 1] FIG. 1 <a) is a block diagram showing an embodiment of the present invention. Temperature information from a temperature sensing element such as a thermistor is input from a terminal 1, and is converted from an analog signal to a digital signal by an A/D converter 2. The temperature data converted into a digital signal is stored in the ROM as the temperature information of the crystal resonator corresponding to the temperature.
The compensation signal is input to the first memory circuit 3 stored in the memory circuit 3, and the compensation signal is output. A compensation signal (compensation data) obtained from the ROM circuit is input to the arithmetic circuit 4. This arithmetic circuit 4 performs addition or subtraction and performs arithmetic operations with the fine adjustment data signal. The data signal for fine adjustment is a latch circuit or RO
This is an N-bit signal for finely adjusting the frequency output from the adjustment circuit 5 consisting of M circuits. The number of bits N may be large if the variable range is large, and may be small if the variable range is small. A signal for controlling the amount of fine adjustment is input from terminal 6. If the adjustment circuit 5 is a latch circuit, it is fine when the power is turned on and used after making fine adjustments, but if the power is turned off for transportation etc. after fine adjustment and then turned on again, the data will be lost. Therefore, a ROM circuit is provided. The arithmetic circuit output is converted into an analog signal by a D/A converter 7, output from a terminal 8, and input to a variable capacitance diode or the like to compensate for the frequency of the crystal resonator.

FIG. 1(b) shows the frequency-temperature characteristics of the digital temperature-compensated crystal oscillator according to the present invention. The vertical axis is the frequency deviation,
The horizontal axis is temperature. Before inputting the adjustment signal to the arithmetic circuit, the deviation at the 00th position l was on the negative side, as shown by the dotted line, but when the adjustment signal was input to the arithmetic circuit, the deviation 0 line became a solid line, and the deviation has a good balance between positive and negative sides, and can be kept within standard deviations.

FIG. 2 is a block diagram showing another embodiment of the present invention,
The first memory circuit 3 stores temperature characteristic information of the crystal sensor, and there is an arithmetic circuit 5 between the first memory circuit 3 and the D/A converter 4, and the first memory shown in FIG. It is the same as the circuit 5, and is branched from the input of the first memory circuit 5 to the second memory circuit 10.
transmits temperature information to. When temperature information is transmitted to the second memory circuit 10, it outputs a compensation signal at the address of that temperature, but if this is used as a fine adjustment signal, the compensated signal can be further adjusted as shown in FIG. 2(b). It is possible to compensate and achieve flat temperature characteristics. Curve A is the conventional temperature characteristic, and by applying an adjustment signal from the second storage circuit to the arithmetic circuit, it was possible to reduce the frequency deviation as in song IB.

[Effect 1 of the present invention] According to the present invention, it has become possible to eliminate the influence of changes over time in the volume and variable capacitor, which were caused by fine adjustments made after conversion to analog, which were conventionally performed. As a result, stability could be improved.

Furthermore, temperature information is transmitted to the second memory circuit, making it possible to perform more fine-grained compensation and improving stability.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1(a) is a block diagram showing an embodiment of the present invention.
Figure (b) is a frequency temperature characteristic diagram according to the present invention, and Figure 2 (a)
) is a block diagram showing another embodiment, FIG. 2(b) is a frequency temperature characteristic according to another embodiment, and FIG. 3 is a conventional D-TC.
It is a block diagram of XO. 2: A/D converter, 3: Memory circuit, 4: Arithmetic circuit, 7:... ...D/A converter patent applicant Kinseki Co., Ltd. Figure 3 Procedural Amendment (Issued by 岨) February 26, 1985 Commissioner of the Patent Office Akio Kuroda Tono Ta 1, Indication of Case Patent Application No. 254527 of 1988 2. Name of the invention Digital temperature-compensated crystal excavator 3. Relationship with the person making the amendment Patent applicant Postal code 201 Telephone number (03) 489-2311
Figure 1(a) of the drawing is corrected as shown in the attached sheet.

Claims (1)

[Claims] Temperature information from the temperature sensing element is converted by an A/D converter, and a compensation signal is output from the first storage circuit in which the temperature characteristics of the crystal resonator are stored in advance in accordance with the temperature information.
A digital temperature compensation crystal oscillator that performs temperature compensation of a crystal resonator by converting it with a /A converter, characterized in that an arithmetic circuit that operates with an adjustment signal is provided in front of the D/A converter. crystal oscillator.