JP3960016B2 - Digitally controlled temperature-compensated crystal oscillator and electronic device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digitally controlled temperature-compensated crystal oscillator, and more particularly to a digitally controlled temperature-compensated crystal oscillator used in a communication device that employs a modulation method using digital phase modulation and an electronic device using the same.
[0002]
[Prior art]
Generally, in a communication device, a TCXO (temperature compensated crystal oscillator) is used as a reference oscillator for stabilizing the frequency of a local oscillator. Some TCXOs include a varactor diode and use a VCXO (voltage controlled crystal oscillation circuit) that can change an oscillation frequency according to a voltage applied thereto. As a method for temperature compensation, there is an analog method in which a network is formed by a thermistor and the voltage generated by the network is used. On the other hand, compensation data corresponding to the temperature is digitally stored in advance in the storage device, the compensation data is read according to the ambient temperature, converted to analog by the D / A converter, and provided in the VCXO. There is also a digital method for stabilizing the frequency by applying it to a varactor diode or the like.
[0003]
In such a conventional digital system, since the ambient temperature must be detected discretely, the voltage applied to the varactor diode also changes stepwise. As a result, the VCXO oscillation frequency changes stepwise, and a steep oscillation frequency change is caused during temperature compensation. The steep oscillation frequency change of the VCXO causes a steep frequency change even in a local oscillator using the VCXO as a reference frequency, which may cause an error in the phase modulation of the communication apparatus.
[0004]
As a countermeasure against this, it is only necessary to prevent a sharp frequency change when performing VCXO temperature compensation. For example, Japanese Patent Laid-Open No. 7-202568 (hereinafter referred to as Conventional Example 1) and Japanese Patent Laid-Open No. No. 29742 (hereinafter referred to as Conventional Example 2) discloses countermeasures.
[0005]
In the conventional example 1, in addition to the detection of the ambient temperature at regular intervals for temperature compensation, the temperature change during that period is electrically stored at short time intervals, and the stored information is appropriately weighted. Thus, the voltage applied to the varactor diode is not stepped by adding to the temperature compensation signal. That is, the temperature compensation voltage discontinuity is interpolated with a voltage change proportional to the gradient of the ambient temperature.
[0006]
On the other hand, the conventional example 2 discloses a configuration in which a voltage change is made gentle and continuous by applying a voltage for temperature compensation to a varactor diode through a delay circuit. A number of prior art examples in which an integration circuit, a smoothing circuit, an LPF, or the like is used in place of the delay circuit have been disclosed, though not listed.
[0007]
[Problems to be solved by the invention]
By the way, in a general VCXO, the gradient of the ambient temperature and the gradient of the temperature compensation voltage at that time do not necessarily match. For example, the slope of the ambient temperature when changing from 0 ° C. to 1 ° C. and the slope of the ambient temperature when changing from 30 ° C. to 31 ° C. are the same, but the slope of the temperature compensation voltage to be applied to the varactor diode at that time Are not the same. Therefore, in the conventional example 1, there is a possibility that the change of the temperature compensation voltage applied to the VCXO cannot always be continuous.
[0008]
On the other hand, in the case of the conventional example 2, when the ambient temperature changes suddenly, the slope of the temperature compensation voltage applied to the VCXO becomes steep even if a delay circuit is used. There remains the possibility of errors. Increasing the time constant of the delay circuit can make the slope gentle, but conversely, when the temperature change is small, there is a problem that it takes a long time for temperature compensation. Further, in order to increase the time constant, it is necessary to increase the capacitance of the capacitor of the time constant circuit, but there is a problem that this leads to an increase in the size and cost of the delay circuit.
[0009]
An object of the present invention is to solve the above-described problems. A digitally controlled temperature-compensated crystal oscillator in which an abrupt change in oscillation frequency does not occur by gently changing the temperature-compensated voltage applied to the VCXO, and the same. The electronic device used is provided.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a digitally controlled temperature compensated crystal oscillator according to the present invention comprises a storage means for outputting digital temperature compensation data corresponding to a measured temperature, and the digital temperature compensation data output from the storage means is converted to an analog voltage. In a digitally controlled temperature compensated crystal oscillator having a D / A converting means for converting, and a voltage controlled crystal oscillation circuit whose oscillation frequency changes based on an analog voltage output from the D / A converting means,
The D / A conversion means includes a pulse arithmetic circuit, a 1-bit D / A converter controlled based on an output of the pulse arithmetic circuit, and an output of the 1-bit D / A converter in its own current With an analog integrator that integrates the output sequentially to produce a new output,
The pulse arithmetic circuit calculates the number of driving times of the 1-bit D / A converter from a difference between the latest digital temperature compensation data and the immediately preceding digital temperature compensation data.
[0011]
In the digitally controlled temperature compensated crystal oscillator of the present invention, the D / A conversion means includes a low-pass filter that removes a high frequency component from the output of the analog integrator.
[0012]
In the digitally controlled temperature compensated crystal oscillator of the present invention, the pulse arithmetic circuit is realized by software processing using an MPU.
[0013]
Further, the digitally controlled temperature compensated crystal oscillator of the present invention is characterized in that the portion excluding the crystal resonator of the voltage controlled crystal oscillation circuit, the storage means, and the D / A conversion means are integrated into a single chip. .
[0014]
In addition, an electronic device according to the present invention is characterized by using the digitally controlled temperature compensated crystal oscillator.
[0015]
With this configuration, in the digitally controlled temperature compensated crystal oscillator of the present invention, the rapid change of the oscillation frequency at the time of temperature compensation is eliminated, and the occurrence of phase modulation error in the communication device using this is greatly reduced. be able to.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a block diagram of an embodiment of a digitally controlled temperature compensated crystal oscillator of the present invention. In FIG. 1, a digital control temperature compensation crystal oscillator 1 includes a temperature sensor 2 that detects an ambient temperature and outputs it as an analog voltage, an A / D converter 3 that converts a voltage output from the temperature sensor 2 into a digital value, a digital A storage device (ROM) 4 that stores temperature compensation data and outputs digital temperature compensation data corresponding to a digital value corresponding to the ambient temperature output from the A / D converter 3, and output from the storage device 4 immediately before The stored digital temperature compensation data is temporarily stored, and the number of times of driving a 1-bit D / A converter 6 to be described later is calculated from the difference between the digital temperature compensation data and the latest digital temperature compensation data output from the storage device 4, and output data ( A bit sequence) and a data (bit sequence) input from the pulse calculation circuit 5 in accordance with a predetermined timing. 1-bit D / A converter 6 that performs 1-bit D / A conversion by value, analog integrator 7 that integrates the analog voltage output from 1-bit D / A converter 6 with the output immediately before itself, analog integrator 7 includes a low-pass filter (LPF) 8 that removes a high-frequency component from the signal output from 7 and a VCXO 9 that is a voltage-controlled crystal oscillation circuit that is frequency-controlled by the voltage output from the low-pass filter 8. Among these, the storage device 4 constitutes a storage means, and the D / A conversion means is composed of four components: a pulse arithmetic circuit 5, a 1-bit D / A converter 6, an analog integrator 7, and a low-pass filter 8. 10 is constituted. In the digitally controlled temperature compensated crystal oscillator 1, all the digital processing units of the D / A conversion means 10 are composed of logic elements, and no MPU (Micro Processing Unit) or the like is used.
[0017]
Here, the pulse calculation circuit 5 will be described. The pulse calculation circuit 5 includes a storage unit that stores the digital temperature compensation data output from the storage device 4 immediately before. When new digital temperature compensation data is output from the storage device 4, the difference from the previous digital temperature compensation data stored in the storage unit is calculated. At the same time, the new digital temperature compensation data is stored in the storage unit in place of the immediately preceding digital temperature compensation data for the time when the next digital temperature compensation data is input. The immediately preceding digital temperature compensation data is deleted at this point. In this way, each time new digital temperature compensation data is input, the difference from the previous digital temperature compensation data is calculated. Further, the difference in the digital temperature compensation data means the difference in voltage to be applied to the VCXO 9, so that the voltage difference is divided by the amplitude (ΔT) of the output voltage of the 1-bit D / A converter 6 to 1 bit. The number of times (number of pulses) for driving the D / A converter 6 is calculated. Then, 1-bit data of 1 or 0 corresponding to the number is continuously output. Whether the output data becomes 1 or 0 depends on whether the ambient temperature has increased or decreased.
[0018]
Next, the 1-bit D / A converter 6 will be described. The 1-bit D / A converter 6 outputs a predetermined voltage (+ ΔV or −ΔV) for a predetermined time (ΔT) based on the 1-bit data input from the pulse calculation circuit 5. If the input 1-bit data is 1, the 1-bit D / A converter 6 outputs + ΔV for the time of ΔT. On the other hand, if the input 1-bit data is 0, the 1-bit D / A converter 6 outputs −ΔV for the time of ΔT. Then, as shown in FIG. 2, this is repeated by the number of pulses calculated by the pulse calculation circuit 5. After this repetition is completed, + ΔV and −ΔV are alternately output a predetermined number of times every ΔT. In order to continue the temperature compensation, the next measurement of the ambient temperature and the calculation of the number of pulses are performed until the last output from the 1-bit D / A converter 6 is finished, and when the last output is finished. At the same time, a cycle for driving the next 1-bit D / A converter 6 is started.
[0019]
As described above, the voltage of + ΔV or −ΔV is continuously supplied from the 1-bit D / A converter 6 for the time corresponding to the number of pulses corresponding to the data input from the pulse calculation circuit 5 every time the ambient temperature is measured. After that, the + ΔV and −ΔV voltages are alternately output a predetermined number of times. Therefore, when the output voltage of the 1-bit D / A converter 6 is integrated, an analog voltage corresponding to the voltage to be applied to the VCXO 9 calculated by the pulse calculation circuit 5 is obtained.
[0020]
Next, the analog integrator 7 will be described. The analog integrator 7 holds its current output voltage inside. When a voltage of + ΔV or −ΔV is output from the 1-bit D / A converter 6 every ΔT, the voltage is internally stored each time. Accumulated as a new output by adding to the voltage held at. Therefore, as shown in FIG. 2, the output voltage of the analog integrator 7 rises with a constant slope when + ΔV is continuously output from the D / A converter 6, and becomes + ΔV from the D / A converter 6. When -ΔV is alternately output, the levels are almost constant to cancel each other, and when −ΔV is continuously output from the D / A converter 6, it is lowered with a constant slope. For example, as described above, when the output of + ΔV is output from the 1-bit D / A converter 6 for a time of 6 × ΔT, and then + ΔV and −ΔV are alternately output for a total time of 6 × ΔT, The output of the integrator 7 rises with a constant slope during the first 6 × ΔT, and then remains at a substantially constant level during the subsequent 6 × ΔT.
[0021]
In the example of FIG. 2, the output of + ΔV is first output from the 1-bit D / A converter 6 for a time of 6 × ΔT, and then + ΔV and −ΔV are alternately output for a total time of 6 × ΔT, Next, an output of + ΔV is output for a time of 4 × ΔT, and then + ΔV and −ΔV are alternately output for a total time of 6 × ΔT, and further, an output of −ΔV is output for a time of 8 × ΔT, and then + ΔV And −ΔV are alternately output for a total time of 6 × ΔT.
[0022]
Here, FIG. 3 shows a block diagram of an internal configuration example of the analog integrator 7. In FIG. 3, an analog integrator 7 includes a first switch 11 provided on the input side, a voltage adder 12 in which an output of a first switch and a second voltage holder described later is connected to the input side, a voltage A first voltage holder 13 for holding the output of the adder 12, a second switch 14 provided between an output of the first voltage holder 13 and an input of a second voltage holder 15 described later; The second voltage holding unit 15 is provided between the second switch 14 and the input side of the voltage adder 12. For the output of the analog integrator 7, the output of the first voltage holder 13 is used. The first switch 11 and the second switch 14 can be realized using a semiconductor such as a MOSFET.
[0023]
FIG. 4 shows a circuit diagram of a specific example of the voltage adder 12. In FIG. 4, a voltage adder 12 is a combination of resistors R1, R2 and R3 and an inverting adder composed of an operational amplifier Q1, and resistors R4 and R5 and an inverting amplifier composed of an operational amplifier Q2, and the resistors R1 to R5 are all the same. By making the value, an added value of the voltages input from the two input terminals IN1 and IN2 is output from the output terminal OUT. Note that the configuration of the inverting adder and the inverting amplifier is general as a circuit using an operational amplifier, and thus description of the operation is omitted.
[0024]
Returning to FIG. 3, the operation of the analog integrator 7 configured as described above will be described. First, it is assumed that the same voltage value is held in the first voltage holder 13 and the second voltage holder 15. Here, when a voltage of + ΔV or −ΔV is output from the 1-bit D / A converter 6 for the time of ΔT, first, the first switch 11 is turned on. At this time, the second switch 14 remains off. The output of the 1-bit D / A converter 6 is input to the voltage adder 12 via the first switch 11, where it is added to the voltage output from the second voltage holder 15 to hold the first voltage. Is input to the device 13. The first voltage holder 13 holds and outputs a newly input voltage instead of the voltage held so far. Thereafter, the first switch 11 is turned off. Next, the second switch 14 is turned on by shifting the time so that it is not turned on simultaneously with the first switch 11, and the output of the first voltage holder 13 is input to the second voltage holder 15. The second voltage holding unit 15 holds the input voltage, that is, the current output voltage of the analog integrator 7. Then, the second switch 14 is turned off. This series of operations is performed within the time ΔT during which the voltage is output from the 1-bit D / A converter 6, and integration is performed. The same operation is performed every time the voltage from the 1-bit D / A converter 6 is updated, and the integration is continued.
[0025]
The output of the analog integrator 7 is macroscopically steep and has no large voltage change, but microscopically there is a steep voltage change of + ΔV or −ΔV, and therefore includes a high-frequency component. Therefore, the output of the analog integrator 7 is input to the VCXO 9 via the low-pass filter 8 for removing high frequency components.
[0026]
Thus, in the digitally controlled temperature compensated crystal oscillator 1 of the present invention, the change in the voltage applied to the VCXO 9 at the time of temperature compensation has a constant slope both when it rises and when it falls. Therefore, the relationship between the time interval (ΔT) of the output of the 1-bit D / A converter 6 and the amplitude (ΔV) of the output voltage per bit is set to have a slope that does not cause an error in the phase modulation of the communication apparatus. By setting to, the oscillation frequency of the VCXO 9 does not change steeply, and the occurrence of phase modulation errors in the communication apparatus using the digitally controlled temperature compensated crystal oscillator 1 can be greatly reduced. In addition, since the digital processing unit of the D / A conversion means 10 is realized with only logic elements, the degree of circuit integration is reduced, and a digitally controlled temperature compensated crystal oscillator is configured relatively quickly, in a small size and at low cost. Can do.
[0027]
In the above embodiment, the 1-bit D / A converter 6 outputs + ΔV and −ΔV alternately for a time of 6 × ΔT after outputting + ΔV several times continuously, for example. The length of the alternately output portion can be freely set.
[0028]
Further, this portion may be omitted. In this case, the measurement interval of the ambient temperature is shortened, but the frequency is increased, and the stability of the oscillation frequency is increased.
[0029]
Alternatively, for example, when + ΔV is output six times, + ΔV and −ΔV are alternately output for a time of 6 × ΔT, and when + ΔV is output twice, + ΔV and −ΔV are alternately output for a time of 10 × ΔT. It may be controlled so that the total number of driving pulses of the 1-bit D / A converter 6 in the measurement of the ambient temperature at one time becomes the same. In this case, the time interval between the measurement of the ambient temperature and the resulting temperature compensation is constant.
[0030]
In the above embodiment, the 1-bit D / A converter 6 is a 1-bit D / A converter in a narrow sense that outputs + ΔV or −ΔV based on the input 1-bit data. Defined. However, a 1-bit D / A conversion that takes in a part for calculating the number of pulses in the pulse calculation circuit 5 and calculates the number of pulses internally for a plurality of bits of input data and outputs a predetermined number of times + ΔV or -ΔV A container may be used, and there is no substantial difference.
[0031]
In the above embodiment, the low-pass filter 8 for removing high frequency components is provided between the analog integrator 7 and the VCXO 9, but the output voltage per bit of the 1-bit D / A converter 6 is When the amplitude (ΔV) is small, the generation of high frequency is reduced.
[0032]
FIG. 5 shows a block diagram of another embodiment of the digital temperature compensated crystal oscillator of the present invention. 5, parts that are the same as or equivalent to those in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.
[0033]
In FIG. 5, the digital temperature compensation crystal oscillator 20 includes an MPU 21 instead of the pulse arithmetic circuit 5, and the A / D converter 3, the storage device 4, and the 1-bit D / A converter 6 are connected to the MPU 21. ing. The MPU 21 includes a storage device for primary storage of software and data for performing pulse calculation and controlling the 1-bit D / A converter 6. In the digital temperature-compensated crystal oscillator 20, the D / A conversion means 22 is constituted by the MPU 21, the 1-bit D / A converter 7, the analog integrator 8, and the low-pass filter 8.
[0034]
In the digital temperature compensated crystal oscillator 20 configured as described above, the MPU 21 takes in a digital value corresponding to the ambient temperature output from the A / D converter 3 and converts it into the digital temperature compensation data stored in the storage device 4. Based on this, the difference between the latest digital temperature compensation data and the previous digital temperature compensation data is calculated, and the number of pulses for driving the 1-bit D / A converter 6 is calculated to generate driving data, The 1-bit D / A converter 6 is used to drive.
[0035]
As described above, when the digital processing unit of the D / A conversion unit is realized by software processing using the MPU, the MPU and the storage device incorporated in a communication device such as a mobile phone as the MPU or the storage device are used. Therefore, the cost of the digital temperature compensated crystal oscillator can be reduced by reducing the number of parts.
[0036]
In each of the above embodiments, each circuit element is individually configured. However, the VCXO 9 excluding the crystal unit, the storage unit, and the D / A conversion unit are a digital / analog mixed circuit, but are integrated into one chip. It can also be integrated. As a result, a significant reduction in size can be realized.
[0037]
By the way, in the present invention, as shown in each of the above embodiments, a circuit for converting inputted numerical information into time-series information for each bit is referred to as a pulse arithmetic circuit. A device that outputs + ΔV or −ΔV voltage for each bit of sequence information is called a 1-bit D / A converter. In this regard, for example, input numerical information is converted into time-series information for each of a plurality of bits by a pulse arithmetic circuit, and each of the plurality of bits represents even three or more numerical values. However, it is possible to consider a configuration in which a binary voltage of + ΔV or −ΔV is output by judging that it has only two meanings. However, even in such a case, it is clear that even if it is a plurality of bits, it has substantially 1-bit information, and does not depart from the scope of the present invention.
[0038]
FIG. 6 shows a perspective view of one embodiment of the electronic device of the present invention. In FIG. 6, a mobile phone 30 which is one of electronic devices includes a casing 31, a printed circuit board 32 disposed therein, and the digitally controlled temperature compensated crystal oscillator 1 of the present invention mounted on the printed circuit board 32. It has.
[0039]
Since the cellular phone 30 configured as described above uses the digitally controlled temperature-compensated crystal oscillator 1 of the present invention, it is possible to reduce the occurrence of phase modulation errors during temperature compensation.
[0040]
In FIG. 4, a mobile phone is shown as an electronic device. However, the electronic device is not limited to a mobile phone, and any device using the digitally controlled temperature compensated crystal oscillator of the present invention may be used. .
[0041]
【The invention's effect】
According to the digitally controlled temperature-compensated crystal oscillator of the present invention, the number of times of driving a 1-bit D / A converter, which will be described later, is calculated as a D / A conversion means from the difference between the latest digital temperature compensation data and the immediately preceding digital temperature compensation data. A 1-bit D / A converter that is controlled based on its output, and an analog integrator that sequentially integrates the output with its current output to produce a new output. By providing, it is possible to prevent a sharp change in the oscillation frequency during temperature compensation.
[0042]
Further, according to the electronic device of the present invention, the occurrence of phase modulation error can be reduced by using the digitally controlled temperature compensated crystal oscillator of the present invention.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a digitally controlled temperature compensated crystal oscillator of the present invention.
2 is a waveform diagram showing outputs of a 1-bit D / A converter and an analog integrator in the digitally controlled temperature compensated crystal oscillator of FIG. 1. FIG.
3 is a block diagram showing a configuration of an analog integrator in the digitally controlled temperature compensated crystal oscillator of FIG. 1. FIG.
4 is a circuit diagram showing a voltage adder in the analog integrator of FIG. 3. FIG.
FIG. 5 is a block diagram showing another embodiment of the digitally controlled temperature compensated crystal oscillator of the present invention.
FIG. 6 is a perspective view showing an embodiment of the electronic device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,20 ... Digital control temperature compensation crystal oscillator 2 ... Temperature sensor 3 ... A / D converter 4 ... Memory | storage device 5 ... Pulse arithmetic circuit 6 ... 1 bit D / A converter 7 ... Analog integrator 8 ... Low-pass filter 9 ... VCXO
10, 22 ... D / A conversion means 21 ... MPU
30 ... Mobile phone

Claims (5)

Storage means for outputting digital temperature compensation data corresponding to the measured temperature, D / A conversion means for converting the digital temperature compensation data output from the storage means into an analog voltage, and output from the D / A conversion means In a digitally controlled temperature compensated crystal oscillator having a voltage controlled crystal oscillation circuit whose oscillation frequency changes based on an analog voltage,
The D / A conversion means includes a pulse arithmetic circuit, a 1-bit D / A converter controlled based on an output of the pulse arithmetic circuit, and an output of the 1-bit D / A converter in its own current An analog integrator that sequentially integrates the output and produces a new output. The pulse arithmetic circuit calculates the 1-bit D / D from the difference between the latest digital temperature compensation data and the immediately preceding digital temperature compensation data. A digitally controlled temperature compensated crystal oscillator characterized in that the number of times of driving of the A converter is calculated.   2. The digitally controlled temperature compensated crystal oscillator according to claim 1, wherein the D / A conversion means includes a low-pass filter that removes a high-frequency component from the output of the analog integrator. The digitally controlled temperature-compensated crystal oscillator according to claim 1 or 2, wherein the pulse arithmetic circuit is realized by software processing using an MPU. 4. The digital circuit according to claim 1 , wherein a portion excluding the crystal resonator of the voltage controlled crystal oscillation circuit, the storage unit, and the D / A conversion unit are integrated into a single chip. 5. Control temperature compensated crystal oscillator. 5. An electronic apparatus using the digitally controlled temperature compensated crystal oscillator according to claim 1 .

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