JP2009194428A - Synthesizer, receiver using the same and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synthesizer capable of generating highly accurate oscillation frequencies. <P>SOLUTION: The synthesizer 1 includes: a comparator 4 for receiving a reference oscillation signal input from a reference oscillator 2; a voltage-controlled oscillator 5 to output an oscillation signal based on the output signal of the comparator 4; and a second frequency divider 6 for dividing the frequency of the output signal from the voltage-controlled oscillator 5 based on a control signal from a controller 7. The comparator 4 compares an output signal from the second frequency divider 6 with an output signal from the reference oscillator 2, and outputs a signal indicating results of comparison to the voltage-controlled oscillator 5. A value of frequency dividing ratio of the second frequency divider 6 is determined based on the use state of an electronic apparatus using the synthesizer 1, so that an error in oscillation frequency of the synthesizer due to a difference in temperature between a temperature detecting section 8 and an MEMS resonator 11 is eliminated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a synthesizer characterized by a temperature compensation method for an oscillation frequency, and a receiver or electronic device using the synthesizer.

  A conventional synthesizer that performs temperature compensation of the reference oscillator will be described below with reference to FIG. FIG. 6 shows a block diagram of a synthesizer 100 that performs temperature compensation of a conventional reference oscillator. In FIG. 6, a conventional synthesizer 100 includes a first frequency divider 102 that divides the reference oscillation signal output from the reference oscillator 101, and a comparator 103 connected to the output side of the first frequency divider 102. And a low-pass filter 104 that converts the output signal of the comparator 103 into a signal having a frequency close to DC. Furthermore, the synthesizer 100 is connected to the output side of the low-pass filter 104 and outputs a voltage-controlled oscillator 105 that outputs a local signal, a second frequency divider 106 that receives a part of the local signal, and an ambient temperature of the reference oscillator 101. A temperature detection unit 108 for detecting the temperature, an analog / digital converter 109 connected to the output side of the temperature detection unit 108 for converting temperature data output from the temperature detection unit 108 into a digital signal, and an analog / digital converter 109 Output data from the memory 110, a memory 110 in which a correction value according to temperature is recorded in advance, and a control unit 107 that reads a predetermined value from the memory 110 and changes the frequency division ratio of the second frequency divider 106. The output signal of the second frequency divider 106 is input to the comparator 103.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 3-209917

  However, in the conventional synthesizer 100, when the usage state of the electronic device changes, for example, when the electronic device power source changes from the off state to the on state, the temperature change of the reference oscillator 101 also increases instantaneously. . As a result, a temperature difference is generated between the temperature detection unit 108 and the reference oscillator 101 immediately after the usage state of the electronic device is changed. For this reason, in the method of indirectly detecting the temperature of the reference oscillator 101 via the temperature detection unit 108 and controlling the frequency division ratio of the second frequency divider 106, the actual frequency of the synthesizer 100 is determined from the desired oscillation frequency of the synthesizer 100. There was a problem that the oscillation frequency shifted.

  Therefore, an object of the present invention is to suppress the oscillation frequency of a synthesizer from shifting from a desired oscillation frequency when the usage state of an electronic device changes.

  In order to solve the above problems, a synthesizer of the present invention includes a comparator to which a reference oscillation signal output from a reference oscillator is input, an oscillator that outputs an oscillation signal based on the output signal of the comparator, and an output signal of the oscillator And a frequency divider that divides the signal based on the control signal from the control unit, and the comparator compares the output signal from the frequency divider with the output signal from the reference oscillator and outputs a signal indicating the comparison result. In the synthesizer that outputs to the oscillator, the value of the frequency division ratio of the frequency divider is determined with respect to the usage state of the electronic device that uses the synthesizer.

  With the above configuration, the synthesizer of the present invention has a frequency division ratio of the frequency divider determined in advance with respect to the usage state of the electronic device, so that the temperature from the temperature detection unit immediately after the usage state of the electronic device changes. The frequency division ratio of the frequency divider can be changed without using information. Accordingly, it is possible to provide a synthesizer capable of setting a desired oscillation frequency immediately after the usage state of the electronic device is changed.

  Further, when the synthesizer of the present invention is used as a local oscillator, temperature information from the temperature detection unit is not used so that a deviation between the frequency of the received signal and the synthesizer is within a frequency deviation ΔFopt that can be accepted by the receiving device, By changing the frequency dividing ratio of the frequency divider, it is possible to provide a receiving device and an electronic device with little deterioration in reception performance even when the usage state of the electronic device changes.

  Hereinafter, the synthesizer of the present embodiment will be described with reference to FIG. In FIG. 1, a synthesizer 1 includes a first frequency divider 3 to which a reference oscillation signal (fREF1 = 10 MHz) output from a MEMS (Micro-Electro-Mechanical Systems) oscillator 2 is input, and a first frequency divider 3. A comparator 4 to which a signal after frequency division (fREF2 = 5 MHz) is input, a voltage controlled oscillator 5 that outputs an oscillation signal based on the output signal of the comparator 4, and a part of the oscillation signal of the voltage controlled oscillator 5 are The second frequency divider 6 that is input and the control unit 7 that controls the frequency division ratio of the second frequency divider 6 based on the temperature data from the temperature detection unit 8. The output signal is input to the comparator 4. The comparator 4 compares the input signal from the second frequency divider 6 with the input signal from the first frequency divider 3, and outputs a signal indicating the comparison result to the voltage controlled oscillator 5.

  In the above description, “based on the output signal of the comparator 4” means that at least the output result of the comparator 4 is received indirectly or directly, and the output is passed through another circuit block. The voltage controlled oscillator 5 may receive it. In the present embodiment, the output of the comparator 4 is converted into a current component by the charge pump 9, the output signal of the charge pump 9 is input to the loop filter 10, and only the component near the direct current is taken out by the loop filter 10 to control the voltage. Supply to the oscillator 5. The loop filter 10 is constituted by a charged portion of the current (charge) from the comparator 4 by a capacitor and a low-pass filter that passes a low frequency.

  Based on the output signal of the temperature detection unit 8 for detecting the temperature, the control unit 7 sends a control signal with an appropriate integer frequency division number M and fractional frequency division number N to the second frequency divider 6 to obtain the second frequency division. The frequency dividing ratio of the frequency divider 6 is changed. That is, the second frequency divider 6 includes an integer part to which the frequency dividing number M is input and a fractional part to which the frequency dividing number N is input. Further, when changing the frequency channel received by the electronic device equipped with the synthesizer 1, the electronic device transmits a channel switching signal to the control unit 7, and the control unit 7 that has received the channel switching signal is based on the channel after switching. The frequency division ratio of the second frequency divider 6 is changed to the frequency division ratio.

  Note that the MEMS vibrator 11 included in the MEMS oscillator is composed of, for example, silicon or a compound thereof as a main material. For example, in the case of a vibrator made of silicon, the temperature characteristic is very large as about −30 ppm / ° C. in terms of the first-order frequency temperature coefficient. It is necessary to frequently perform such temperature control. Details of the frequency temperature coefficient will be described later (Equation 1). In addition, a receiving apparatus (to be described later, FIG. 2) equipped with the synthesizer 1 includes a synthesizer 1 and a signal processing unit (not shown) connected to the output side of the synthesizer 1. The signal processing unit, for example, mixes the received signal received by the antenna (not shown) and the oscillation signal from the synthesizer 1, performs frequency conversion, and then demodulates the signal.

  Note that an electronic device (not shown) on which the synthesizer 1 is mounted includes the receiving device and a display unit (not shown) connected to the output side of the signal processing unit in the receiving device.

  As an example, a television receiver using the synthesizer 1 of the present embodiment will be described with reference to FIG. In FIG. 2, the synthesizer 1 of the present embodiment is formed on the same semiconductor IC 12 including the temperature detection unit 8 and mounted on the base substrate 13. Further, the MEMS vibrator 11 is used as a constituent element of the reference oscillator and is mounted on the base substrate 13. By using the MEMS vibrator 11, it is possible to reduce the size of the receiving device. For example, the crystal resonator has a size of 2.5 × 2.0 mm, but the resonator using the MEMS resonator 11 can have a size of 1.0 × 1.0 mm to 0.3 mm × 0.3 mm. Also, regarding the height, the vibrator using the MEMS vibrator 11 is less than half of the quartz vibrator. This is because, for example, when the MEMS vibrator 11 is made of silicon, it can be formed by a semiconductor process such as RIE (Reactive Ion Etching) or photolithography. Moreover, the said size is a typical example and has a possibility of being able to be made smaller compared with the case where the piezoelectric single crystals, such as the conventional quartz, are used. In addition, since the size of a small television receiving device mounted on a mobile phone is as small as 9 × 9 mm to 8 × 8 mm, the above-described size effect is very large. An example of other components will be described. The base board 13 has a first filter 15 to which a reception signal received by the antenna 14 is input, and an LNA (Low Noise Amplifier) to which an output signal of the first filter 15 is input. 16, a second filter 17 to which an output signal of the LNA 16 is input, and a balun 18 to which an output signal of the second filter 17 is input. The output signal of the balun 18 is input to the semiconductor IC 12.

  Here, in FIG. 2, a temperature difference occurs between the temperature detection unit 8 and the MEMS vibrator 11 due to the positional relationship between them. The cause of the temperature difference includes, in addition to the positional relationship, thermal conductivity of the MEMS vibrator 11, the semiconductor IC 12, the base substrate 13, and the like. This means that a temperature difference occurs depending on the speed at which heat is transmitted. In addition, this temperature difference is particularly likely to increase when a sudden temperature change occurs. Therefore, the temperature detected by the temperature detection unit 8 and the actual temperature of the MEMS vibrator 11 are different, and the frequency is corrected to the wrong frequency at the time of temperature correction. As a result, the oscillation frequency of the synthesizer 1 deviates from a desired value, that is, the frequency of the signal to be received, causing reception degradation. In particular, in the case of a synthesizer using a MEMS vibrator having a poor frequency temperature characteristic, that is, a frequency oscillator having a large frequency temperature coefficient, the frequency correction error due to the temperature difference is large, and the reception characteristic is significantly deteriorated. Become.

  Therefore, when the ambient temperature of the MEMS vibrator 11 changes abruptly at the moment when the usage state of the electronic device changes, the synthesizer 1 of the present embodiment has frequency division ratio data corresponding to this usage state in advance. Yes. When the electronic device enters the use state, the control unit 7 refers to the frequency division ratio data and changes the frequency division ratio of the second frequency divider 6 in FIG. That is, the synthesizer 1 of the present embodiment changes the frequency division ratio of the second frequency divider 6 without referring to the temperature data obtained from the temperature detection unit 8 at the moment when the usage state of the electronic device changes. Will do. Thereby, it is possible to suppress a deviation in the oscillation frequency of the synthesizer 1 due to a temperature difference between the MEMS vibrator 11 and the temperature detection unit 8. If this is an electronic device at the time of mass production, of course, the arrangement of parts and the types of members are the same (same thermal conductivity), and the current value, which is an element of heat generation, also defines the state of use. This is achieved by being able to determine uniquely.

  As an electronic device, for example, an example of a usage state when a mobile phone is considered is shown in Table 1.

  In Table 1, Case 1 in the use state is a case where the power supply of the mobile phone is turned on from the off state. In this case 1, since current starts to flow simultaneously to the ICs in the mobile phone, it is assumed that the temperature around the receiving device in FIG. Case 2 in use is a case where the mobile phone has changed from a standby state to a call state. In case 2 in this (Table 1), it is assumed that a large current suddenly starts to flow through the power amplifier, which is one of the transmission side circuits of the RF circuit, and the temperature around the receiving device suddenly rises. Is done. In Table 1, use case 3 is a case where the television reception function is turned on from the standby state of the mobile phone. In the case 3, it is assumed that current starts to flow all at once in the RF circuit and baseband circuit necessary for receiving the television signal, and the temperature around the receiving device suddenly rises. In Table 1, the use case 4 is a change from the call state of the mobile phone to the standby state, and the use case 5 is the change from the mobile phone TV reception function to the standby state. This is the case. In both cases, since a relatively large current that has been flowing to necessary components in the mobile phone does not flow suddenly, it is assumed that the ambient temperature of the receiving apparatus rapidly decreases. In Table 1, use case 6 is when the power of the mobile phone and the TV reception function are turned on simultaneously from the power-off state of the mobile phone. In this case 6, it is assumed that the current starts to flow simultaneously to each IC in the mobile phone from the state in which the power supply of the mobile phone is off, and the temperature around the receiving device suddenly rises.

  In the above cases 1 to 6, since the ambient temperature of the receiving device changes abruptly due to a change in use state, a temperature difference is generated between the MEMS vibrator 11 and the temperature detecting unit 8 having different physical positions in the receiving device. Will occur. An example of the temperature change of the MEMS vibrator 11 and the temperature detector 8 in the case 6 of Table 1 is shown in FIG. 3 shows that the MEMS vibrator 11 is arranged closer to the device serving as the heat source than the temperature detection unit 8, or the environmental temperature is better tracked in relation to the heat capacity (according to the ambient temperature). The temperature is likely to change). In the graph of FIG. 3, the horizontal axis represents time, and the vertical axis represents the temperatures of the MEMS vibrator 11 and the temperature detection unit 8. In FIG. 3, the use state of the mobile phone changes as shown in Case 6 of (Table 1) at the instant of time t0. As a result, the temperature around the receiving device rises rapidly. As a result, the temperature of the MEMS vibrator 11 and the temperature detection unit 8 itself starts to rise. However, as shown in FIG. 3, the MEMS vibrator 11 and the temperature detecting unit 8 have different temperature profiles with respect to time depending on the positional relationship and the heat capacity. In the example of FIG. 3, the temperature of the MEMS vibrator 11 rises more rapidly than the temperature of the temperature detector 8. The temperatures of the MEMS vibrator 11 and the temperature detection unit 8 are greatly different during a certain time T. As a result, when the frequency division ratio of the second frequency divider 6 is adjusted based on the temperature data of the temperature detector 8, a desired oscillation frequency cannot be obtained. In order to prevent this, the synthesizer 1 of the present embodiment has a database of the usage state of the electronic device and the value of the frequency division ratio of the second frequency divider corresponding thereto. An example of this database is shown in (Table 2).

  The “case” in the leftmost column in (Table 2) represents a change in the usage state of (Table 1).

  The database shown in (Table 1) and (Table 2) may be configured to be recorded in a memory unit included in the control unit 7, for example. In short, the database of (Table 1) and (Table 2) may be recorded in the memory unit accessible by the control unit 7. The control unit 7 obtains information about the usage state from the electronic device at the moment when the usage state of the electronic device changes, and stores the database recorded in the memory unit from the usage state before and after the change. Search for which use state change case matches. Then, the control unit 7 acquires the frequency division ratio data of the second frequency divider 6 corresponding to the matched case, and changes the frequency division ratio of the second frequency divider 6. Thereby, at the moment when the usage state of the electronic device is changed, the frequency division ratio of the second frequency divider 6 can be changed to an optimum value without using the temperature data of the temperature detection unit 8, so that the temperature detection unit 8 and the MEMS It is possible to suppress an oscillation frequency error caused by a temperature difference from the vibrator 11.

  In addition, when the final ultimate temperatures assumed in the cases 1 to 6 are T1 to T6, it is clear that T1, T2, T3, T6> T4, T5. When a MEMS vibrator made of silicon having a primary frequency temperature coefficient of −30 ppm / ° C. is used, since the temperature coefficient is negative, the resonance frequency of the MEMS vibrator is lowered when the temperature is high. Become. Therefore, since it is necessary to set the frequency dividing number of the second frequency divider 6 large, the relationship is N1, N2, N3, N6> N4, N5.

  In the case of the present embodiment, the cases 1, 3, 6 also have a relationship of T 1 <T 3 <T 6 in the case, and the frequency division number of the second frequency divider 6 is N 1. The relationship <N3 <N6 holds.

  In FIG. 3, as a method of determining the fixed time T, the temperature difference ΔTemp between the MEMS vibrator 11 and the temperature detection unit 8 is set to fall within a predetermined temperature difference ΔTop. Here, the predetermined temperature difference ΔTop is preferably set to such an extent that ΔTemp does not affect the receiving system. In other words, ΔTemp causes the resonance frequency of the MEMS vibrator 11 (the oscillation frequency of the reference oscillator 2) to fluctuate, and the fluctuation causes the frequency of the local oscillation output of the synthesizer 1 to be the same as the original received signal. It fluctuates and a frequency difference ΔF occurs with the frequency of the received signal. Accordingly, it is preferable that the predetermined temperature difference ΔTop is set so that the reception state does not deteriorate. Here, examples of the problem that the reception state deteriorates include a state in which, in the case of television reception, noise is generated in the image, data cannot be synchronized, and reception itself cannot be performed. Further, the frequency difference ΔFopt corresponding to ΔTop (ΔF when ΔTemp = ΔTop) also depends on the receiving system configuration (referring to the configuration of the “signal processing unit” in the claims), but ΔF ≦ By suppressing the frequency difference ΔF within the range of ΔFopt, desired reception performance can be maintained. In the present embodiment, in order to satisfy this condition, it is further possible to adjust the frequency division ratio of the second frequency divider (for example, Table 2) in various reception state cases (for example, Table 1). This is preferable.

  In the configuration example of ISDB-T which is a domestic television system, for example, ΔFopt can be set to ± 25 kHz. If the carrier frequency is 770 MHz, ± 25 kHz corresponds to a variation of ± 32.5 ppm. Here, considering a MEMS resonator made of silicon, the frequency fluctuation of ± 32.5 ppm is about ± 1.1 ° C. as the temperature fluctuation because of the first-order frequency temperature coefficient of −30 ppm / ° C. It corresponds to the fluctuation of. What is necessary is just to set (DELTA) Top so that it may become in this range. Here, if ΔTop is defined as an absolute value, it can be used without considering the sign. Here, although ΔFopt = ± 25 kHz, it is not limited to this value. This value is an item determined at the time of system design and may be determined according to each system (details will be described later).

  Note that (Table 1) shows an example of the usage state, and the same effect can be obtained even when the synthesizer of the present embodiment is applied to other changes in the usage state. Further, in (Table 1), a table in which specific usage states of electronic devices are described is used. However, in practice, a number or the like may be assigned to each usage state for management. For example, when the power-off state of the mobile phone is managed by the number “1” and the power-on state of the mobile phone is managed by the number “2”, the electronic device notifies the control unit 7 of the use state of the electronic device. A number may be used.

  An example of the time change of the frequency division ratio of the second frequency divider 6 in the synthesizer 1 of the present embodiment will be described with reference to FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the frequency division ratio of the second frequency divider 6. FIG. 4 shows an example in which the mobile phone is in a power-off state until time t0, and at the instant of time t0, the mobile phone is changed to a power-on state and a television reception function on state. At the instant of time t0, the usage state of the mobile phone changes, and accordingly, the frequency division ratio of the second frequency divider 6 is instantly changed to the frequency division ratio A. Thereby, an oscillation frequency error of the synthesizer 1 due to a temperature difference between the temperature detection unit 8 and the MEMS vibrator 11 can be suppressed. At the instant of time t0, after the control unit 7 changes the division ratio of the second divider 6 to the predetermined division ratio A, based on the temperature data obtained from the temperature detection unit 8, The control unit 7 changes the frequency division ratio of the second frequency divider 6. However, this is executed after the elapse of a certain time (a certain time T in FIG. 4) after which the temperature difference between the temperature detection unit 8 and the MEMS vibrator 11 is substantially eliminated after the time t0. Thereby, after the usage state of the electronic device changes, the accuracy of the oscillation frequency of the synthesizer 1 after the lapse of the predetermined time can be improved.

  The demodulation operation of the television signal may be started during the lapse of the predetermined time. This is because the synthesizer of this embodiment can output an oscillation frequency with high accuracy even immediately after a change in the usage state of a mobile phone (for example, the predetermined time). Further, if it is not necessary to shorten the time until the start of the demodulation operation of the television signal, the demodulation operation of the television signal may be started after the predetermined time has elapsed.

  It should be noted that, after the predetermined time has elapsed from time t0, the control unit 7 changes the frequency division ratio of the second frequency divider 6 based on the temperature information obtained from the temperature detection unit 8 and is selected in the first period. The frequency division ratio data of the 2 frequency divider 6 is recorded, and with reference to the recorded data, the second frequency divider 6 used when the use state of the mobile phone changes from the standby state to the call state next time. It is good also as a structure which corrects a circumference ratio. Actually, the value of the frequency division ratio of the second frequency divider 6 corresponding to the usage state of the electronic device is set in advance and recorded in the memory unit or the like. It is also assumed that the set division ratio value deviates from the ideal division ratio value. In such a case, if the synthesizer has the above-described configuration, the frequency division ratio of the second frequency divider 6 can be corrected to an ideal value later. As a result, the synthesizer of the present embodiment can realize a highly accurate oscillation frequency in the actual use state. As an example of the frequency division ratio correction method, for example, an average of a plurality of frequency division ratio data recorded in a period after the predetermined time has elapsed since the use state of the mobile phone changed from the standby state to the call state It is conceivable to calculate the value. The control unit 7 uses this average value as a frequency division ratio at the next change from the standby state to the call state. The frequency division ratio data used for calculating the average value may use only the frequency division ratio data for a predetermined period after the predetermined period has elapsed. This is because the use of the frequency division ratio data immediately after the usage period changes and the predetermined period has elapsed is the most reliable in correcting the frequency division ratio data used when the usage state changes. Further, by limiting the number of data used for correcting the frequency division ratio to that within a predetermined period, the number of data that needs to be recorded can be reduced, so that the size of the memory unit can be reduced.

  FIG. 5 shows another example of the change over time of the frequency division ratio of the second frequency divider 6 in the synthesizer 1 of the present embodiment. In the graph of FIG. 5, the horizontal axis represents time, and the vertical axis represents the frequency division ratio of the second frequency divider 6. FIG. 5 shows an example in which the mobile phone is in a standby state until time t0, and the mobile phone is changed to a call state at the instant of time t0. At the instant of time t0, the usage state of the mobile phone changes, and accordingly, the frequency division ratio of the second frequency divider 6 is instantly changed to the frequency division ratio B. Next, at the instant of time t1, the frequency division ratio of the second frequency divider 6 is instantaneously changed to the frequency division ratio C. Next, at the instant of time t2, the frequency division ratio of the second frequency divider 6 is instantaneously changed to the frequency division ratio D. Next, at the instant of time t3, the frequency division ratio of the second frequency divider 6 is instantaneously changed to the frequency division ratio D. As described above, when the temperature change of the MEMS vibrator 11 during the predetermined time T in which the temperature difference is generated between the temperature detection unit 8 and the MEMS vibrator 11 is gentle compared to the case of FIG. As shown in FIG. 5, the value of the frequency division ratio may be changed stepwise. With such a configuration, the accuracy of the oscillation frequency of the synthesizer 1 can be improved. As a specific method for realizing the above configuration, as an example, the frequency division ratio data of the second frequency divider 6 corresponding to the use state of the electronic device and the timing data of the division ratio change are previously stored in the memory unit. It is possible to record in (Table 3) shows an example of this database.

  The “case” in the leftmost column in (Table 3) represents a change in the usage state of (Table 1). The database of (Table 3) is recorded in a memory unit accessible by the control unit 7.

  The control unit 7 changes the frequency division ratio of the second frequency divider 6 at an optimal timing with reference to the timing data of the frequency division ratio change in (Table 3). As a result, a synthesizer with high oscillation frequency accuracy can be realized.

  Note that the value of the frequency division ratio of the second frequency divider 6 that is predetermined for the usage state of the electronic device may be corrected based on the temperature information of the temperature detection unit 8. Specifically, based on the temperature data obtained from the temperature detector 8 immediately before the time t0 (time when the usage state of the electronic device changes) in FIG. 4 or FIG. This means that the value of the frequency division ratio of the second frequency divider 6 is corrected. This is because the temperature change profile of the MEMS vibrator 11 after the usage state change of the electronic device is expected to be different depending on the temperature of the MEMS vibrator 11 before the use state change. Therefore, based on the temperature data obtained from the temperature detector 8 immediately before the use state of the electronic device changes, the predetermined division ratio value of the second divider 6 is corrected. A synthesizer with high oscillation frequency accuracy can be realized. As a specific correction method, a method of using a correction formula (approximation formula) derived in consideration of the thermal resistance of each component in the electronic device can be considered.

  As another means for using the temperature data immediately before the usage state of the electronic device changes, frequency division ratio data is recorded in advance in the memory unit for each temperature as shown in (Table 4). A method is also conceivable.

  “Case” in the leftmost column in (Table 4) represents a change in usage state in (Table 1).

  The database of (Table 4) is recorded in a memory unit accessible by the control unit 7. Then, after receiving the signal corresponding to the state change from the electronic device, the control unit 7 based on the temperature data immediately before receiving the signal indicating the state change, from the database of (Table 4), the second frequency divider 6 The frequency division ratio data of the second frequency divider 6 is changed based on the read frequency division ratio data. As a result, a synthesizer with high oscillation frequency accuracy can be realized.

  The synthesizer 1 of the present embodiment may have a database such as (Table 2) to (Table 4) for each oscillation frequency to be output. As a result, a synthesizer with high accuracy can be realized even at a plurality of oscillation frequencies.

  As described above, in the embodiment of the present invention described above, the output of the voltage controlled oscillator 5 is used as the output of the synthesizer 1, but a frequency divider may be inserted after the voltage controlled oscillator 5 to obtain the output of the synthesizer 1. Thereby, the oscillation frequency of the voltage controlled oscillator 5 can be increased, and the size of the voltage controlled oscillator 5 can be reduced.

  The temperature detector 8 may be, for example, a semiconductor transistor based on a temperature characteristic of a current flowing through a semiconductor, a so-called a thermistor using a characteristic that changes its resistance value with respect to temperature, Examples include those using thermocouples that use electromotive force.

  In the present invention, a particularly large effect is exhibited for a vibrator having poor frequency temperature characteristics. This is because the worse the frequency temperature characteristic, the larger the error of the synthesizer oscillation frequency due to the actual temperature difference between the MEMS vibrator 11 and the temperature detector 8 in FIG.

  This frequency temperature characteristic is expressed by the following equation. When the reference temperature is T0, the current temperature is T, the resonance frequency at the reference temperature T0 is f, and the amount of change in the resonance frequency of the vibrator when the temperature is changed from T0 to T is δf, the frequency variation rate with respect to the temperature is ( It is expressed by Equation 1).

  "^" Is a symbol representing a power, 10 is a base, and -11 is an exponent. In addition, α, β, and γ are called primary, secondary, and tertiary frequency temperature coefficients, respectively. More specifically, δf / f represents a frequency variation rate when the temperature changes from T0 to T. For example, a crystal resonator is a resonator having a frequency temperature coefficient of 0 for the first order and a small temperature coefficient for the second and third order. In general, the temperature coefficient becomes smaller as it becomes first order, second order, and third order, and the influence on the frequency temperature characteristic in the operating temperature range of the electronic device becomes smaller, so the first order temperature coefficient is zero. This means that the frequency-temperature characteristics of the vibrator are very good. Each temperature coefficient of the quartz crystal changes depending on a cut angle when the quartz crystal plate is cut out from the quartz ingot (the lump after the quartz crystal is pulled up). Due to its good frequency-temperature characteristics, the most widely used crystal resonator is an AT-cut crystal resonator. For example, the frequency variation rate is about ± 20 to ± 100 ppm in the operating temperature range (−40 to 85 ° C.). The width of the frequency variation rate is caused by a minute difference in the cut angle. On the other hand, most MEMS vibrators have poor frequency temperature characteristics. For example, a silicon vibrator has a large first-order temperature coefficient of −30 ppm / ° C. The first order temperature coefficient is dominant. In the operating temperature range of −40 ° C. to 85 ° C., this is 30 × 125 = 3750 ppm, which is very bad compared with about ± 20 to ± 100 ppm of the AT-cut quartz resonator.

  Therefore, the present invention is particularly effective in the configuration using the MEMS vibrator than the configuration using the more general crystal vibrator.

In the present embodiment, a silicon vibrator having a semiconductor material as a base material is used as the MEMS vibrator. However, as another example of the MEMS vibrator, a polysilicon vibrator having the same semiconductor material is used. The thing using is mentioned. In addition, there are those called FBAR (Film Bulk Acoustic Resonator) based on thin film piezoelectric materials such as AlN, ZnO and PZT, and those based on other thin film materials such as SiO ₂ . Examples thereof include SAW (Surface Acoustic Wave) vibrators using surface acoustic waves and vibrators using boundary waves propagating on the boundary between different substances. Among these vibrators, there are few that have frequency temperature characteristics comparable to those of AT-cut quartz vibrators, and most of them have a primary temperature coefficient (cannot be ignored). For example, FBAR using AlN is a vibrator using thickness longitudinal vibration (vibration in the same direction as the applied electric field), has a temperature coefficient of −25 ppm / ° C., and ZnO has a temperature coefficient of about −60 ppm / ° C. Have Moreover, even in the vibrator using SAW, the one using 36 ° y-cut lithium tantalate for the base material is about -35 ppm / ° C., and the one using 64 ° y-cut lithium niobate for the base material is It has a temperature coefficient of about -72 ppm / ° C.

  In the present embodiment, a temperature-compensated synthesizer using a PLL (Phase Locked Loop) has been described as the first synthesizer unit. However, a DLL (Delay Locked Loop) or an ADPLL (All Digital PLL) is used. May be. Further, a DDS (Direct Digital Synthesizer) that does not constitute a loop may be used. As an example of DDS, there is a method of generating signals of various frequencies by D / A (Digital / Analog) conversion of signal information stored in a memory in advance. Further, a frequency divider may be directly connected after the reference oscillator to adjust the frequency. In the configuration example, the second frequency divider 6 is arranged after the reference oscillator 2, the second frequency divider is adjusted, and the frequency is adjusted. Further, a configuration in which the load impedance of the reference oscillator is adjusted may be used. The configuration example is a configuration example in which a plurality of capacitors having a switch function are used as the load capacity of the reference oscillator, and the frequency is adjusted by switching the load capacity discretely by switching the switches. Although various temperature compensation synthesizers have been described above, the temperature compensation method may be any method that can achieve frequency adjustment with a predetermined frequency adjustment width.

  As an effect of the present embodiment, when a phase or frequency lock loop such as a PLL is used, there is an effect that the convergence time until the lock can be shortened. A PLL will be described as an example. In the operation of the PLL, first, the frequency is drawn (frequency lock operation), and then the phase is drawn (phase lock operation). This is performed by comparing the signals of the first frequency divider 3 and the second frequency divider 6 with the comparator 4 of FIG. 1 as described above. Usually, when the frequencies of the two signals are greatly different, there is a problem that it takes time until the frequency is locked. In the case of the present embodiment, the first signal is used in accordance with the use state of the electronic device. Since the frequency divider is set in advance, the initial frequency difference can be reduced, and the time required for frequency lock and phase lock can be shortened. This makes it possible to establish a good reception state earlier.

  In this embodiment, ΔFopt = ± 25 kHz is described, and this is determined at the time of design and is not limited to this value. However, this will be described in detail below. The Japanese digital television broadcasting system (ISDB-T) uses orthogonal frequency division multiplexing (OFDM) (Orthogonal Frequency Division Multiplexing). Its reception bandwidth is about 5.6 MHz, which is divided into 13 frequency segments. 12 segments (full segment) are used for home television, and one segment (one segment) is used for mobile television such as mobile phones. In addition, for example, in Mode 3, 433 carriers are arranged side by side at a carrier interval of about 1 kHz to constitute one reception channel. By previously embedding a known signal for synchronization in these carriers and correcting the frequency, it is possible to substantially eliminate the frequency difference ΔF. As a result, the frequency can be corrected to half the interval of the carrier in which the known signal is embedded. However, if the frequency that can be corrected is increased too much, it takes time for the correction or a load is imposed on the circuit. Therefore, it is determined at the time of design by a trade-off with them. When applied to the present embodiment, ΔTop may be set as a predetermined temperature difference in accordance with ΔFopt in the present embodiment, which is a correctable frequency determined from them. In the present embodiment, in consideration of these, ΔFopt = ± 25 kHz.

  Since the synthesizer of the present invention can realize a highly accurate oscillation frequency, the synthesizer can be used for a receiving device or an electronic device having excellent receiving characteristics.

Block diagram of an example of a synthesizer of the present invention Conceptual diagram of an example of a receiving apparatus using the synthesizer of the present invention Conceptual diagram of an example of a receiving apparatus using the synthesizer of the present invention Conceptual diagram of an example of a receiving apparatus using the synthesizer of the present invention The graph which shows an example of the time change of the frequency division ratio of the synthesizer of this invention Block diagram of a conventional synthesizer

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Synthesizer 2 Reference oscillator 3 1st frequency divider 4 Comparator 5 Voltage control oscillator 6 2nd frequency divider 7 Control part 8 Temperature detection part 9 Charge pump 10 Loop filter 11 MEMS vibrator 12 Semiconductor IC
13 Base substrate 14 Antenna 15 First filter 16 LNA
17 Second filter 18 Balun

Claims (10)

In a synthesizer that outputs an oscillation signal,
Based on the usage state of the electronic device using the synthesizer,
A synthesizer in which a correction amount of the oscillation frequency of the synthesizer is determined. A comparator to which a reference oscillation signal is input;
An oscillator that outputs an oscillation signal based on the output signal of the comparator;
A frequency divider that divides the output signal of the oscillator based on a control signal from a control unit;
The comparator compares the output signal from the frequency divider with the output signal from the reference oscillator and outputs a signal indicating the comparison result to the oscillator,
Based on the usage state of the electronic device using the synthesizer,
The synthesizer according to claim 1, wherein a value of a frequency division ratio of the frequency divider is determined. It has a temperature detector that detects the temperature,
When the usage state of the electronic device is changed,
The synthesizer according to claim 2, wherein the control unit changes a frequency division ratio of the frequency divider based on a usage state of the electronic device and temperature data detected by the temperature detection unit. When the usage state of the electronic device is changed,
The control unit changes a frequency division ratio of the frequency divider based on a usage state of the electronic device,
The synthesizer according to claim 3, wherein the frequency division ratio of the frequency divider is changed based on temperature data detected by the temperature detection unit. The value of the frequency division ratio determined for the usage state of the electronic device is:
4. The synthesizer according to claim 3, wherein the control unit is corrected based on past frequency division ratio data of the frequency divider changed based on a usage state of the electronic device and a temperature signal of the temperature detection unit. The timing at which the control unit changes the frequency division ratio of the frequency divider to a value of the frequency division ratio determined for the usage state of the electronic device is predetermined. Synthesizer. A reference oscillator for outputting the reference oscillation signal;
The synthesizer according to claim 2, wherein the reference oscillator includes a vibrator formed of a MEMS element. A synthesizer according to claim 1;
And a signal processing unit connected to the output side of the synthesizer. The oscillation frequency of the synthesizer after being corrected by the correction amount of the oscillation frequency of the synthesizer;
The difference from the frequency of the received signal is
The receiving device according to claim 8, wherein the correction amount of the oscillation frequency of the synthesizer is determined so as to be within an upper limit value of a frequency correction amount that can be corrected by the signal processing unit. A receiving device according to claim 8;
An electronic apparatus having a display unit connected to the output side of the receiving device.