JP2604600B2 - Digital temperature compensated oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature-compensated oscillator for compensating a fluctuation in an oscillation frequency due to a temperature change based on digitally encoded temperature information, and in particular, at the time of startup. The present invention relates to a digital temperature-compensated oscillator having improved stability.

(Prior art) As a means of suppressing fluctuations in the oscillation frequency of a voltage controlled oscillator (VCO) due to changes in external temperature, a temperature sensor whose oscillation frequency fluctuates greatly due to temperature is used, and the temperature from the digitally encoded temperature sensor is used. There is a digital temperature-compensated oscillator which performs frequency temperature compensation based on information to obtain a predetermined oscillation frequency. Since a voltage controlled oscillator generally uses a crystal oscillator (VCXO), the VCXO will be described below.

FIG. 2 (a) is a block diagram of a conventional digital temperature compensation type oscillator. The temperature compensation circuit includes a temperature sensor 1 including an oscillator which sensitively detects an external temperature change and changes the frequency. A digital control circuit 2 for converting the temperature information into a digital code and generating a temperature compensation code; and a D / D converter for converting the temperature compensation code generated by the control circuit 2 into an analog signal to generate a temperature compensation voltage (frequency control voltage). It has an A-converter circuit 3 and a voltage-controlled crystal oscillator (VCXO) 4 that is an oscillation source that generates a reference pulse signal and that is subject to temperature compensation.

The digital control circuit 2 has a ROM that stores a table in which the control voltage and the temperature in each temperature range of the (VCXO) 4 to be compensated correspond one-to-one. FIG. 2 (b) is a block diagram showing an example of the digital control circuit in FIG. 2 (a) in more detail, wherein the gate circuit 2 is opened and closed by an output pulse of the temperature sensor 1.
-1, a frequency divider 2-2 for dividing a part of the signal from the VCXO4 and transmitting the divided signal to the other input of the gate 2-1, and a digital encoding of the number of pulses counted by the gate circuit 2-1. And a digital control section 2-3 for generating a temperature information signal corresponding to the pulse code at that time. The digital control section 2-3 stores each temperature and a compensation voltage to be output for each temperature. It has a ROM 2-4 that stores a table corresponding one-to-one.

FIG. 3 is a structural explanatory view showing an example of the D / A converter circuit in FIG. 2, which is at least as many as flip-flops having a clear terminal CL for resetting, for example, D-type flip-flops 11 to 18. The ladder-type resistor 20 includes resistors 31 to 38 connected in series. The connection point of each series resistor of the ladder type resistor 20 is configured to connect the output of each of the D-type flip-flops 11 to 18 through voltage dividing resistors 21 to 28 of a required value.

In the above configuration, with each allowed to the corresponding input to the input terminals D ₁₁ to D ₁₈ of the digital control circuit 2 8-bit D-type flip-flop temperature compensation code from 11 to 18,
A clock signal is input to the clock signal input terminal CK. When a digital code corresponding to the temperature information is input to the input terminals D ₁₁ to D _18, the output terminal Q of the D-type flip-flops corresponding to the "1" bit among the bits High level example becomes 5V The bit “0” is at a low level, for example, 0V. The output voltage from each output terminal Q is a ladder type resistor
The voltage is divided at 20, and the temperature compensation code bits "0" and "1"
The corresponding voltage is the output V of the D / A converter circuit 3.
_OUT , that is, the temperature compensation voltage of VCXO4. Each D
Although the voltage at each output terminal Q is high when the input bits of the flip-flops 11 to 18 are high, the voltage at the output V _OUT is higher than that of the D-type flip-flop 11 due to the voltage dividing action of the ladder resistor 20. The output voltage is the highest and the one for the D flip-flop 18 is the lowest.

Further, different DC voltages can be obtained depending on the combination of these flip-flops which become High output. The compensation code that can be expressed by 8 bits is 00000000 to 11111111.
There are 256 ways.

However, in the D / A converter used in the above-mentioned conventional digital temperature compensated oscillator, since the reset signal is input to the clear terminal CL of each D-type flip-flop, the entire circuit is reset at power-on or the like. In this case, the output Q of each D-type flip-flop is all at the low level, and the compensation code in which all the bit values are “0” is D /
Join A converter. Although this differs depending on the code code and the method of expressing the temperature, since “00... 00” is generally set at the lowest temperature or the highest temperature, this code is a compensation code for one of the extreme temperatures. And the oscillation output according to this is output from the VCXO. Generally, it is extremely rare that the ambient temperature is such an extreme value in the reset state.
For example, if a compensation code of "00... 00" representing -30.degree. C. is applied when the ambient temperature is + 25.degree. C., there occurs a problem that the oscillation frequency is controlled to be shifted by the error. That is, there is a disadvantage in the frequency stability at the time of startup that the oscillation frequency largely deviates from the rated frequency.

(Purpose of the Invention) The present invention has been made in order to solve the drawbacks of the D / A converter circuit in the conventional digital temperature compensated oscillator as described above. It is an object of the present invention to provide a digital temperature-compensated oscillator having a frequency in which the deviation of the oscillation frequency of the VCXO is minimized and the starting stability is improved.

(Summary of the Invention) In order to achieve the above object, a digital temperature compensated oscillator of the present invention digitally codes external temperature change information detected by a temperature sensor by a digital control circuit and generates the digital temperature change information by a digital control circuit. The digital temperature compensation code is converted into an analog signal by a D / A converter circuit to generate a temperature compensation voltage (frequency control voltage), and the temperature compensation voltage is applied to the VCXO to constantly set the VCXO oscillation frequency to a reference value. In a digital temperature-compensated oscillator, the D / A converter is provided with a predetermined temperature compensation voltage (for example, a compensation at 25 ° C.) at a reset such as when a power switch is turned on regardless of an external temperature. Voltage).

Embodiment Hereinafter, a digital temperature compensated oscillator according to the present invention will be described in detail.

FIG. 1 is an explanatory diagram of the configuration of a D / A converter circuit used in a digital temperature compensated oscillator according to the present invention, which is an improvement of the D / A converter circuit of the digital temperature compensated oscillator shown in FIG. . Accordingly, the description of the configuration and operation of the entire temperature-compensated crystal oscillation circuit is omitted because it is the same as that of the conventional example.

This D / A converter circuit 3 is a D-type flip-flop D
FF1 to DFF8 and a ladder-type resistor 9 connected to the output terminal Q of each of the D-type flip-flops DFF1 to DFF8. Each of the D-type flip-flops DFF1 to DFF8 has an input terminal D for inputting an 8-bit temperature compensation code from the digital control circuit 2, a clock input terminal CK for inputting a clock signal, and an output terminal Q. A preset terminal PR is provided for the first D-type flip-flop DFF1, and a clear terminal CL is provided for the second to eighth D-type flip-flops DEF2 to DEF8. The ladder-type resistor 9 is composed of resistor groups 2R1-R1, 2R2-R2,... 2R8-R8 that divide the output voltages of the D-type flip-flops DFF1 to DFF8 to different values.

The clock signal is input to each clock input terminal CK, the reset signal is input to the preset input terminal PR in the first D-type flip-flop DFF1, and is input to the second to eighth D-type flip-flops DFF2 to DFF8. . Each D
The output terminals Q of the flip-flops DFF1 to DFF8 are connected to the resistor groups 2R1-R1, 2R2-R2,.
The output V _OUT of the ladder resistor 9 is connected to the control input terminal of the VCXO 4 as a compensation voltage, being connected to 2R8-R8, respectively.

Each D-type flip-flop DFF1 from the digital control circuit 2
Of Temperature compensation code D ₁ to D ₈ of 8 bits input to ～DFF8, temperature compensation code D ₁ is the most significant bit, D ₈ is the least significant bit. The temperature compensation code that can be represented by 8 bits is
There are 256 ways from 00000000 to 11111111, and the compensation code at normal temperature 25 ° C. is the 128th 10000000, and the first D
By providing the preset terminal PR to the type flip-flop DFF1, the most significant bit is set to "1" as an initial condition, and the other D-type flip-flops are set to "0". Therefore, the compensation code at the time of reset is set to "10000000", that is, a temperature of 25 ° C.

In the above configuration, a clock input CK of the 8-bit temperature compensation code D ₁ to D ₈ kept the Low level input to the input terminal D of the D-type flip-flop DFF1～DFF8, followed by a clock input from the Low When the level is changed to the high level, a temperature compensation code appears at the output terminals Q of the D-type flip-flops DFF1 to DFF8. The temperature compensation code appearing at each output terminal Q has a voltage value of, for example, 5 V at a high level and 0 V at a low level. Each voltage value is applied to the input terminal R _IN -1~R _IN -8 ladder resistor 9, a voltage value corresponding to the temperature compensation code appears on the output voltage terminal V _OUT. This voltage value is applied to the subsequent VCXO4 as a compensation voltage. This operation is the same as that described in the related art.

When the reset input is set to the high level, the first D-type flip-flop DFF1 is preset, and the other D-type flip-flops DFF2 to DFF8 are cleared. This results in the same result as when the compensation code 10000000 at the normal temperature of 25 ° C. is input. The compensation voltage at the normal temperature of 25 ° C. appears at the output terminal _VOUT, and is applied to the control voltage terminal of the next stage VCXO4.
In this example, the reason why the compensation voltage at room temperature 25 ° C is applied to the VCXO4 at the time of reset is that the temperature of 25 ° C is the center of the compensation temperature range of the digital temperature-compensated oscillator -30 ° C to + 80 ° C. Is at 25 ° C, whatever the temperature in the compensation temperature range
This is because an error between the oscillation frequency of the VCXO and the rated frequency can be reduced.

When it is desired to set the compensation code at the time of reset to a code having a temperature other than 25 ° C., each of the D-type flip-flops DFF1 to DFF8 is set according to the bit value corresponding to the code.
Is set to be preset or cleared. For example,
When using in an area where the average temperature is low or in an area where the average temperature is high, if the average temperature is set, it is possible to respond to the ambient temperature more quickly, and when the compensation temperature range is different from the above embodiment. For example, when the temperature is between −40 ° C. and + 60 ° C., a code corresponding to the intermediate temperature + 10 ° C. may be generated.

Further, in the embodiment of the present invention, the present invention is not limited to the above-described 8-bit case, but is applicable to any bit, and is not limited to a D-type flip-flop and may be any circuit element having a similar function. It will be obvious that any may be used.

(Effect of the Invention) As described above, according to the digital temperature compensated oscillator of the present invention, the initial condition of the flip-flop is set to correspond to the preset temperature compensation code at the time of reset. This prevents the temperature compensation voltage of the VCXO from becoming a voltage corresponding to an extreme one in the set temperature range in the initial state such as when the power is turned on, and allows the VCXO to reach the steady state at the rated frequency in a shorter time. ,
This is effective in quickly increasing the stability at the time of startup.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of a D / A converter circuit used in a digital temperature compensated oscillator according to the present invention. FIGS. 2 (a) and 2 (b) are block diagrams of a conventional digital temperature compensated oscillator. FIG. 3 is a block diagram of a D / A converter used in a conventional digital temperature compensated oscillator. 1 ... temperature sensor, 2 ... digital control circuit, 3 ... D /
A converter, 4 VCXO, DFF1 to DFF8 D flip-flop, 2R1 to 2R8 ... resistor, R1 to R8 ... resistor, 9
... Ladder type resistor

Claims (1)

(57) [Claims] 1. Digitally processing ambient temperature information and D /
A digital temperature-compensated oscillator that controls a voltage-controlled oscillator (hereinafter, referred to as a VCO) via an A-conversion circuit and controls a frequency variation due to a change in ambient temperature. The D / A converter includes a flip-flop and a ladder. A number of flip-flops corresponding to the number of bits of digital processing, each of which has an input terminal for inputting each bit output of a digitized temperature compensation code, and a clock. The flip-flop has a clock input terminal for inputting a signal and a clear terminal for inputting a reset signal or a preset terminal for inputting a reset signal. The clock input terminals of the flip-flops are connected in parallel with each other, and the clear terminal and the preset terminal When the reset signal is input, the flip-flop outputs a digital value corresponding to predetermined temperature information. The ladder-type resistor has an input terminal connected to an output terminal of each flip-flop, and an output terminal outputting a frequency control voltage to the VCO. Wherein a digital signal corresponding to the predetermined temperature information is output when a reset signal is input to the VCO through the ladder-type resistor to control the VCO.