JPS616903A - Digitally controlled temperature compensation crystal oscillator - Google Patents

Abstract

PURPOSE:To stabilize an oscillation output by giving a histeresis so as to eliminate chattering in applying digital encoding to temperature information. CONSTITUTION:An output voltage VA of a temperature detecting circuit 11 is inputted to a voltage shift circuit 13 in a temperature encoding circuit 12 and fed to a terminal A of a changeover switch 14. The voltage shift circuit 13 has a function shifting the inputted voltage VA by a prescribed minute quantity and its output voltage VB is fed to the other terminal B of the changeover switch 14. The switch 14 changes over the VA and VB alternately and gives them to an A/D coverting circuit 15 and a discriminating circuit 16. The discriminating circuit 16 compares a digital code corresponding to the VA with a digital code corresponding to the VB and when the both are coincident, the digital code is regarded as the temperature information at that point of time. The temperature information is inputted to a processing circuit 21 and used for the control of the oscillating frequency of the crystal oscillation circuit.

Description

Detailed Description of the Invention "Industrial Application Field" This invention encodes a detected temperature signal into a digital code, performs digital processing on the encoded information to generate a control signal, and uses the control signal to control a crystal oscillation circuit. This invention relates to a digitally controlled temperature-compensated crystal oscillator that obtains an oscillation output with a stable frequency against temperature changes by controlling the oscillation conditions of the oscillator.

``Prior art'' Temperature compensated crystal oscillators ('TCXOs) are based on the temperature characteristics of the resonant frequency of the crystal resonator. It is an oscillator that can obtain a stable oscillation frequency over a wide temperature range. Conventional TCXO configurations use analog processing for everything from temperature detection to oscillation frequency control, but due to limitations in compensation characteristics, it is difficult to obtain high compensation accuracy over a wide temperature range. It is.

For this reason, digitally controlled TCXOs, which are relatively easy to achieve high precision, are attracting attention.

A digitally controlled TCXO (hereinafter referred to as DTCX'O) converts a detected temperature signal into a digital code, performs digital processing on the encoded temperature information, and generates a control signal for temperature compensation. By controlling the oscillation frequency of the crystal oscillation circuit, an oscillation output with a frequency stable with respect to temperature can be obtained.

"Problems to be Solved by the Invention" As described above, when converting temperature into a digital code in a TCXO, the target temperature range is divided into minute intervals (hereinafter referred to as steps), and a series of steps are performed for each step. A method of matching digital codes is used. That is, for example, let the temperature between 200°C and 205°C be a 7-bit code string C1-10000QO, and the temperature between 20.5°C and 21.5°C.
The temperature of 0° C. is encoded as C2=1.000001. In such a case, if the temperature gradually changes and reaches the boundary point of the encoding step, that is, in the above example, near 205 degrees Celsius, the code string corresponding to the temperature will go back and forth between 01 and 02. A so-called chattering phenomenon often occurs. The temperature compensation reservoir control signal is encoded temperature information C.
.

An object of the present invention is to make it possible to eliminate chattering and obtain stable oscillation output by adding history characteristics when digitally encoding temperature information in a digitally controlled temperature compensated crystal oscillator. do.

[Means for Solving the Problem] According to the present invention, temperature is converted into voltage by a temperature detection circuit, and the output voltage of the temperature detection circuit is shifted by a constant minute amount by a voltage soft circuit. Periodically converting the output voltage of the temperature detection circuit and the output voltage of the voltage shift circuit into digital codes by an analog-to-digital conversion circuit,
A judgment circuit compares the digital code corresponding to the output voltage of the temperature detection circuit and the digital code corresponding to the output voltage of the voltage shift circuit, and if the two digital codes match, the digital code is used as the temperature information at that point in time. is input to a processing circuit, and the processing circuit generates a control signal to compensate for the temperature characteristics of the crystal oscillation circuit based on the temperature information input from the judgment circuit,
The control signal controls the oscillation frequency of the crystal oscillation circuit.

"Example" FIG. 1 shows an embodiment of the invention.

[Temperature detection circuit] 1 is composed of, for example, a negative temperature coefficient resistance element bridge, and converts temperature into voltage.The output voltage vA is input to the voltage soft circuit 13 in the temperature encoding circuit 12, and is also input to the changeover switch 14. is supplied to one terminal A of the. The 13 voltage shift circuits have the function of shifting the input voltage VA by a certain minute amount (Δ■), and the output voltage VB (=VA+ΔV) is set by the selector switch 1.
4, the other terminal B [supply. The changeover switch 14 is connected to the output voltage vA of the temperature detection circuit 11 and the voltage shift circuit 13.
The output voltage VB of
Then voltage V7. ．． VB is alternately converted into a digital code and supplied to the judgment circuit 16. As shown in FIG. 2, the judgment circuit 16 includes a temporary storage circuit 17 such as a D flip-flop, a coincidence judgment circuit 18, and a data launch circuit 19.
It is composed of a lot of things. As mentioned above, the A/D conversion circuit 15 encodes the voltages vA and v2 alternately, but if the corresponding digital codes are cA and cB, cA and cB are alternately stored and held in the temporary storage circuit 17. . While the code CA is stored in the temporary storage circuit 17, the A/D conversion circuit 15 encodes the voltage VB, and when the encoding operation is completed, the code cB is output. Id in the match judgment circuit 18
The code from the A/D conversion circuit 15 and the code from the temporary storage circuit 17 are compared to determine if the codes CA and CB match.
A mismatch is determined, and if they match, the matched code is input to the data latch circuit 19 and held. On the other hand, if the codes cA and CB do not match, the data latch circuit 19 holds the previous state.

The data held in the data latch circuit 19 is inputted to the processing circuit 21 as shown in FIG. The oscillation frequency of the circuit 22 is controlled to compensate for variations based on the temperature characteristics of the crystal oscillation circuit 22.

Operating clocks for each section are supplied from a clock supply circuit 23.

Next, temperature encoding circuit 12, ie voltage, shift circuit 1
3. The operations of the changeover switch 14, A/D conversion circuit 15, and determination circuit 16 will be explained in more detail.

FIG. 3 shows the encoding characteristics of the temperature encoding circuit 12, where the horizontal axis corresponds to the analog input voltage A, and the vertical axis corresponds to the digitally encoded output. The solid line in FIG. 3 is the encoding characteristic of the A/D conversion circuit 15, and its step boundary voltage is vI + v
2 + v3 + ..., the step interval (quantization step interval) is expressed as vs.

y,' = V1 + (+ 1) VS (1 is an integer)
shall be.

If selector switch 4 is connected to terminal A side, A
Since the output of the temperature detection circuit 11 is directly input to the /D conversion circuit 15, the encoding characteristic for the voltage vA is A, /
This corresponds to the encoding characteristic of the D conversion circuit 15, and is represented by the solid line in FIG.

On the other hand, when the selector switch 14 is connected to the terminal B side, the voltage ■AvC
The encoding characteristics for the A/D conversion circuit 15 are shifted by one Δ■ compared to the encoding characteristics of the A/D conversion circuit 15. If the step boundary voltages in this case are v1', ■2', ■3'..., then v
The relationship is i#-vi-Δ■. However, Δ■ is a shift voltage applied by the voltage shift circuit 13. Therefore, if the shift voltage Δ■ is set smaller than the step interval V, V i-+ <' V as shown by the broken line in FIG.
H'<V 1 .

Now, the output voltage VA of the temperature detection circuit 11 is vl<VA (
Consider the case where the voltage is at V2' and the temperature gradually changes and the voltage ■A increases. When Vl<VA<■2', the output sign of the A/D conversion circuit 15 is determined by the changeover switch 1.
No matter whether 4 is connected to the terminal A side or the terminal B side, both match as 01, so the output code of the judgment circuit 16 is 01.
becomes. When the voltage ■A increases and reaches V2'<VAT/2, the output sign of the A/D conversion circuit 15 remains C1, but the changeover switch 14 is connected to the terminal A side. is connected to the terminal B side, the output code of the A/D conversion circuit 15 becomes C2, and the two do not match. Therefore, the output of the judgment circuit 16 maintains the previous state C1. The voltage ■A increases further, and v2
<When VA<v3' is reached, selector switch] 4 is connected to terminal A
Since the output code of the A/D conversion circuit 15 is C2 in both cases of the side and the B side, the output of the determination circuit 16 also changes to code C2.

Even if the voltage ■A decreases and returns to V2'<VA<V2''-
As is clear from the above explanation, the output of the determination circuit 16 maintains the sign C2, and returns to the sign C1 when it decreases to (1) <vA<v2'. In other words, the characteristic of the temperature encoding circuit 12 is as shown by the arrow in FIG.
It has a history characteristic that changes along the solid line in the figure and changes along the broken line when descending.

The cause of the chattering phenomenon is various fluctuations near the step boundary, that is, the output voltage of the temperature detection circuit 11 ■A
This is due to fluctuations in the A/D conversion circuit 15, internal noise in the A/D conversion circuit 15, fluctuations in the reference voltage, etc. The above-mentioned history characteristics are added to the encoding characteristics, and the difference between the step boundary voltages when the voltage rises and when the voltage falls, that is, the shift voltage Δ by the voltage shift circuit 13
If (2) is set larger than the fluctuation voltage, the chattering phenomenon can be eliminated. There is no restriction on the positive or negative sign of the shift voltage ΔV; when Δ■>0, the step boundary shifts to the low voltage side as explained in Fig. 3, and when Δ■<0, the step boundary shifts to the high voltage side. However, all encoding characteristics exhibit historical characteristics.

Practically speaking, it is preferable for the history characteristic to be small, so the absolute value of the shift voltage ΔV may be set to be sufficiently smaller than the step interval V5 and larger than the fluctuation voltage. For example, if the maximum voltage of the output vA of temperature detection circuit 1 is 3V,
When encoding with bits, v5 is 11.76 mV. If the shift voltage Δ■ is about 115 of ■5, ΔV
= 2.3 mV, whereas the fluctuation voltage is generally 1 mV or less, so chattering can be completely eliminated.

The shift voltage ΔV can be obtained by dividing the reference voltage input to the A/D conversion circuit 15.
3 can be constructed by an analog adder circuit using an operational amplifier. Since the changeover switch 14 can be constructed from a semiconductor element such as an il'1M0S transistor, it can be mounted together with the temperature encoding circuit 12 and the id processing circuit 21 on an integrated circuit.

As for the configuration of the temperature encoding circuit 12, it is also possible to use a parallel configuration, for example, as shown in FIG. 4, without using the changeover switch 14 for the voltages A and VB. The output voltage ■A of the temperature detection circuit 11 is supplied to the voltage shift circuit 13, and
The signal is supplied to the A/D conversion circuit 15. The output of the voltage shift circuit 13 is A/D conversion circuit 15, and the analog digital signal having the same characteristics is simultaneously encoded and sent to the judgment circuit 16'.
are input simultaneously. The judgment circuit 16' is composed of only the match judgment circuit 18 and the data launch circuit 19 except for the temporary storage circuit 17 in the structure shown in FIG. The match determination circuit 18 determines whether the output codes of the 9 A/D conversion circuits 15 and 15' match or do not match, and the data launch circuit 19 is operated. It is clear that the configuration shown in FIG. 4 also provides encoding characteristics with a history similar to that shown in FIG.

In this case, two analog-to-digital conversion circuits are required, but the encoding operation speed is fast, and one temporary storage circuit is required.
8 is required.

"Effects of the Invention" As explained above, the digitally controlled temperature compensated crystal oscillator according to the present invention can eliminate the chattering phenomenon inherent in digital systems by simply adding a simple circuit, and provides a stable frequency source. Therefore, it can be applied to carrier wave sources, clock sources, etc. of various communication devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a digitally controlled temperature-compensated crystal oscillator according to the present invention, FIG. 2 is a block diagram showing an example of the configuration of the judgment circuit 16, and FIG. 3 is a block diagram showing an example of the configuration of the judgment circuit 16. FIG. 4, a diagram showing the characteristics, is a block diagram showing another example of the configuration of the temperature encoding circuit. 11... Temperature detection circuit 12... Temperature encoding circuit 13... Voltage shift circuit 14... Changeover switches 1, 5, 15'... Analog-digital conversion circuit 16, 16'... Judgment Circuit 21... Processing circuit 22... Crystal oscillation circuit 23... Operating clock supply circuit 17... Temporary storage circuit 18... Match determination circuit 19... Data launch circuit

Claims (1)

[Claims] (1) A temperature detection circuit that generates a voltage corresponding to temperature;
A voltage shift circuit receives the output voltage of the temperature detection circuit and shifts the voltage by a constant minute amount that is larger than the fluctuation of the voltage and sufficiently smaller than the quantization step interval of the analog-to-digital conversion means; the analog-to-digital conversion means for periodically converting each output voltage of the circuit and the voltage shift circuit into digital codes;
The digital code corresponding to the output voltage of these temperature detection circuits is compared with the digital code corresponding to the output voltage of the voltage shift circuit, and if the two match, a decision is made to output the digital code as temperature information at that point in time. A circuit, a processing circuit that inputs temperature information from the judgment circuit and outputs a control signal to compensate for fluctuations based on the temperature characteristics of the crystal oscillation circuit, and a control signal from the processing circuit that determines the oscillation frequency. A digitally controlled temperature-compensated crystal oscillator comprising the above-described controlled crystal oscillator circuit.