JP2010193240A - Synthesizer and receiving apparatus using the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synthesizer capable of reducing deterioration of a phase noise performance caused by a digital frequency control of the synthesizer to provide a receiving device having a satisfactory receiving characteristic, and to provide the receiving device using the same and an electronic apparatus. <P>SOLUTION: The synthesizer includes: a comparator to which a reference oscillation signal output from a reference oscillator is input; a filter connected to the output side of the comparator; an oscillator connected to the output side of the filter to output the oscillation signal; and a frequency divider for frequency-dividing the output signal from the oscillator on the basis of the control signal of a control unit. The comparator compares the output signal from the frequency divider and the output signal from the reference oscillator to output the signal expressing the comparison results to the filter. The control unit controls the frequency dividing ratio of the frequency divider at time interval T on the basis of the detected results of a detector for detecting temperature. The relationship between the time interval T and a cutoff frequency fc of the filter is as follows: 1/T≥fc. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a synthesizer that has a temperature characteristic of frequency and performs frequency correction for temperature so that the frequency changes discretely (digitally), a receiving device using the synthesizer, and an electronic apparatus. In particular, when a synthesizer is configured using a vibrator having a poor frequency temperature characteristic such as a MEMS (Micro Electro Mechanical Systems) vibrator, a great effect is exhibited.

  Hereinafter, a conventional synthesizer that performs temperature compensation of a reference oscillator that outputs a reference oscillation signal will be described with reference to FIG.

  FIG. 9 shows a block diagram of a conventional synthesizer 200. In FIG. 9, a conventional synthesizer 200 includes a first frequency divider 202 that divides a reference oscillation signal output from a reference oscillator 201, and a comparator that receives an output signal from the first frequency divider. 203 and a low-pass filter 204 that receives the output signal from the comparator 203 and outputs a signal voltage value having a frequency near DC. The synthesizer 200 further includes an oscillator 205 that outputs an oscillation signal as a local signal based on the signal voltage value output from the low-pass filter 204 and inputs the other signal to the second frequency divider 206. As the oscillator 205, a voltage controlled oscillator VCO (Voltage Controlled Oscillator) is often used. The synthesizer 200 further includes a second frequency divider 206 that divides the output signal from the oscillator 205 by the frequency division number designated by the control circuit 207 in accordance with the channel designation. The comparator 203 compares the output signal from the second frequency divider 206 with the output signal from the first frequency divider 202. The above is the configuration of a general synthesizer. The synthesizer 200 shown in FIG. 9 further includes a temperature sensor 208 that detects the ambient temperature and a second component based on the temperature detected by the temperature sensor 208. And a control circuit 207 for controlling the frequency division number of the frequency divider 206. As described above, the synthesizer 200 uses the temperature sensor 208 to correct the oscillation frequency shift caused by the ambient temperature change.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 03-209917

  However, for example, in the conventional synthesizer 200, when the ambient temperature is detected by the temperature sensor 208 at regular intervals and the second frequency divider 206 is controlled based on the detected temperature, the oscillation frequency of the synthesizer 200 is switched at regular intervals. As a result, the problem that the phase noise level of the synthesizer output increases has been newly found. This increase in noise level deteriorates equivalent C / N (Carrier Noise Ratio), and deteriorates the performance of the receiving apparatus and the electronic device.

  In addition, in order to reduce the phase noise of the output signal of the synthesizer 200, a new system for realizing randomness in the control circuit 207 or the like when the second frequency divider 206 is controlled at random. Therefore, there is a new problem that the circuit configuration becomes complicated.

  Therefore, the present invention provides a synthesizer capable of suppressing a deterioration in phase noise performance caused by such digital frequency control and realizing a receiver having good reception characteristics, a receiver using the same, and an electronic device. The purpose is to provide.

In order to achieve the above object, a synthesizer according to the present invention includes a comparator to which a reference oscillation signal output from a reference oscillator is input, a filter connected to the output side of the comparator, and a filter connected to the output side of the filter. The oscillator includes an oscillator that outputs an oscillation signal, and a frequency divider that divides the output signal of the oscillator based on a control signal from the control unit, and the comparator outputs an output signal from the divider and an output signal from the reference oscillator And a signal indicating the comparison result is output to the filter, and the control unit controls the frequency division ratio of the frequency divider based on the detection result of the temperature detecting detector by the time interval T,
The relationship between the time interval T and the cutoff frequency fc of the filter is a configuration that satisfies 1 / T ≧ fc.

  In order to achieve the above object, a receiving apparatus of the present invention includes a frequency converter that converts a frequency of a received signal, a reference oscillator, a comparator that receives a reference oscillation signal output from the reference oscillator, and a comparator. A filter connected to the output side of the filter, an oscillator connected to the output side of the filter and supplying an oscillation signal to the frequency converter, and a frequency divider that divides the output signal of the oscillator based on a control signal from the control unit And a detector for detecting the frequency fluctuation of the output signal from the oscillator or the received signal, and the comparator compares the output signal from the frequency divider with the output signal from the reference oscillator and indicates the comparison result. The controller outputs a signal to the filter, and the control unit controls the frequency division ratio of the frequency divider at the time interval T based on the detection result of the detector, and the relationship between the time interval T and the filter cutoff frequency fc is 1 / T ≧ It is a configuration of a receiving apparatus that meets or c.

  With the above configuration, the synthesizer and the receiving device of the present invention have a time interval T for controlling the frequency division ratio when performing frequency adjustment to change the frequency division number of the frequency divider in response to a temperature change. By making the relationship with the cut-off frequency fc of the filter satisfy 1 / T ≧ fc, it is possible to suppress an increase in phase noise and suppress deterioration in reception quality.

(Embodiment 1)
Hereinafter, the synthesizer of the first embodiment will be described. FIG. 1 is a block diagram of a receiving apparatus equipped with the synthesizer according to the first embodiment of the present invention.

  In FIG. 1, the synthesizer 100 includes a reference oscillator block 101, a PLL (Phase Locked Loop) block 102, and a control block 103.

  The reference oscillator block 101 includes a vibrator 104, a driver circuit 105 that drives the vibrator 104, and a load capacitor 106. In this embodiment, a MEMS vibrator made of silicon is used as the vibrator 104. The present invention including this embodiment is particularly effective when a resonator having poor frequency temperature characteristics such as a MEMS resonator is used (details will be described later).

  The PLL block 102 divides the output frequency fref from the reference oscillator block 101 by R to obtain fref / R, its output, and the output frequency fVCO from the second divider 112. / N phase and frequency are compared, the phase frequency comparator 108 that outputs the difference, the charge pump 109 that converts the output from the phase frequency comparator 108 into a current component, and the output of the charge pump 109 Among them, the low-pass filter 110 that extracts only components near the direct current, the oscillator 111 that inputs the oscillation signal to the frequency converter 116 based on the output from the low-pass filter 110, and the output frequency fVCO from the oscillator 111 are divided by N. and a second frequency divider 112 that outputs fVCO / N.

  As the oscillator 111, for example, a voltage-controlled oscillator VCO (Voltage Controlled Oscillator) or the like is used, and an oscillator whose frequency changes corresponding to a DC voltage.

  The low-pass filter 110 is also called a loop filter, and includes, for example, a capacitor portion that charges an input current (charge), a low-pass filter that passes a low frequency, and the like. The second frequency divider 112 may be an integer frequency divider described in the related art, or may be a fractional frequency divider capable of finer control. In the present embodiment, the latter fractional frequency divider is used.

  The control block 103 detects the temperature, and sends a control signal to the second frequency divider 112 based on the output signal from the temperature detection unit 113, and the frequency division number of the second frequency divider 112. And a memory 115 in which a frequency division number corresponding to the temperature is stored. Note that the control unit 114 controls the second frequency divider 112 with the frequency division number read from the memory 115. Of course, the control unit 114 also changes the frequency division number of the second frequency divider 112 based on the channel switching request signal.

  The temperature detection unit includes, for example, a semiconductor temperature sensor, a temperature sensor such as a thermistor, and an A / D converter that converts an analog signal into a digital signal.

  Next, a problem when the synthesizer described in the related art is operated without using the configuration of the present invention will be described with reference to FIG. The reference numerals in FIG. 1 are used. FIG. 2 shows the frequency spectrum of the output signal of the synthesizer 100 at the moment when the second frequency divider 112 is switched (the vertical axis is the spectrum intensity, and the horizontal axis is the frequency).

  In FIG. 2, the peak indicated by A in the central portion is the peak of the original desired output signal, and other sub-peaks, for example, the portion B is unnecessary power called spurious and becomes a noise component. When there are many spurious portions, the quality of the output signal after the frequency converter 116 multiplies the output signal of the synthesizer 100 and the received signal deteriorates, and as a result, the reception performance deteriorates. That is, it is important to keep the spurious levels and the number of output signals of the synthesizer 100 small.

  The power ratio per unit frequency between the noise component such as spurious and the original desired signal (portion A in FIG. 4) is called phase noise. If this phase noise is high, in the output signal from the frequency mixer, which is the frequency converter 116, the desired signal (carrier) and the noise component ratio C / N (Carrier Noise Ratio) will also deteriorate. In addition, errors in the subsequent stage such as the demodulation unit also increase. For example, in the case of digital communication, the result is that the BER (Bit Error Rate), which is the error rate of the received signal, is deteriorated. In the case of a television, such deterioration of the BER causes disturbance in the received video. In the worst case, there may be a situation where reception is not possible. Such C / N, BER, and the like are measures for knowing the quality of the received signal.

  3 shows a frequency spectrum of a received signal of OFDM (Orthogonal Frequency Division Multiplexing), which is a modulation scheme used in the domestic digital television standard ISDB-T (Integrated Services Digital Broadcasting-Terrestrial). OFDM is a multi-carrier system and is composed of a plurality of carriers carrying information.

  Although only five lines are shown in FIG. 3, in practice, a signal is often composed of a set of 1000 or more carriers. In FIG. 3A, focusing on the carrier A2, in the state where the phase noise of the synthesizer is small, the spectrum spreads as shown in the figure, and the influence on the adjacent carriers A1 and A3 is small. However, when the phase noise of the local oscillation signal is deteriorated, the phase noise of the carrier A2 affects the adjacent carriers A1 and A3 as shown in FIG. This causes C / N degradation of the received signal.

  The fact that the phase noise of the oscillation signal of the synthesizer 100 is large, that is, the state as shown in FIG. 2, also affects the reception signal multiplied by the reception signal by the frequency converter 116. As a result, FIG. It will cause a situation like this. Note that FIG. 3 shows a diagram in which the actual signal and the spurious head value portion are connected by a line in order to show the phase noise for the sake of convenience.

  As described above, the phase noise performance of the synthesizer and the oscillator has a great influence on the entire system of the receiving device and the electronic device. As shown in FIG. 2, even if the phase noise is instantaneously deteriorated at the time of switching, the signal quality is lowered, temporary reception deterioration and reception inability are caused, and the image is interrupted or disturbed. End up.

  Next, the focus of the present invention and its features will be described. FIG. 4 is an enlarged view of the horizontal axis (frequency) of FIG. As shown in FIG. 4, the spurious periods are arranged at an interval of 1 / Tc that is the reciprocal of the control interval Tc of the second frequency divider 112. Focusing on this result, if Tc is decreased, 1 / Tc is increased, and the spurious frequency adjacent to the desired carrier frequency (A in the figure) is separated, and the influence is reduced (FIG. 5).

  Further, in the same band, the number of spurious in FIG. 5 is reduced as compared with the case of FIG. 4, and as a result, the phase noise performance is improved.

  Furthermore, due to the operation of the PLL, the noise level is suppressed by the effect of the low-pass filter 110 when it is separated from the center carrier frequency f0 by the cutoff frequency fc of the low-pass filter 110. Therefore, 1 / Tc is set to be smaller than fc. By increasing it, spurious is also suppressed, and the phase noise performance of the synthesizer 100 is greatly improved.

  If the control interval Tc is too small, there may be a problem that the current consumption of the circuit increases and the output frequency of the synthesizer 100 is not stable. The reason for the increase in current consumption is, for example, an increase in current in order to increase the speed of the A / D converter that constitutes the temperature detection unit 113 and to increase the response of the PLL block 102. Further, the reason why the output frequency is destabilized is that, as a result of enhancing the responsiveness of the PLL block 102, the fluctuation (overshoot) of the output frequency becomes large or it becomes difficult to converge.

  Therefore, the control interval is always moved at the interval Tc that satisfies the condition of Tc ≦ 1 / fc (or 1 / Tc ≧ fc), and a time for moving beyond the Tc of the above condition is provided while considering the phase noise level. May be.

  Further, the size of the spurious shown in FIG. 2 tends to increase as the frequency moved in the control increases, and the present invention particularly relates to a vibrator having a poor frequency temperature characteristic, for example, in the present embodiment. In the MEMS vibrator using silicon as used, the effect is further exhibited. Hereinafter, this will be described in more detail.

  Generally, when the reference temperature is Tm0, the current temperature is Tm, the resonance frequency at the reference temperature is fr0, and the amount of change in resonance frequency when the temperature changes from Tm0 to Tm is δTm, the temperature changes from Tm0 to Tm. The frequency variation rate δfr / fr0 is expressed by (Equation 1).

  Here, α, β, and γ are referred to as primary, secondary, and tertiary frequency temperature coefficients, respectively. These vibrators having a small temperature coefficient are vibrators having good frequency temperature characteristics. Here, “^” is a symbol representing a power. “^ 2” means square.

  Here, for example, a crystal resonator is a resonator having a frequency temperature coefficient of 0 for the first order and a small second order and third order temperature coefficient. 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 equipment is also reduced, so the first order temperature coefficient is 0. This indicates that the frequency temperature characteristic of the vibrator is 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, in the operating temperature range (-30 to 85 ° C.), the frequency variation rate is about ± 20 to ± 100 ppm. The width of the frequency variation rate is caused by a minute difference in the cut angle.

  Unlike a quartz crystal, a silicon resonator, which is one of the MEMS resonators, has poor frequency temperature characteristics. The first-order temperature coefficient is large and is −30 ppm / ° C. Since the first-order temperature coefficient is dominant in the temperature range to be used, the frequency variation rate is considered below, ignoring the second-order and third-order temperature coefficients.

  The frequency fluctuation rate of the silicon resonator is ± 1725 ppm, which is 10 times or more larger than that of the crystal resonator, considering the entire temperature range to be used. In the synthesizer 100 used in the present embodiment, when the output frequency from the reference oscillator block 101 is shifted due to a temperature change or the like, the frequency is divided by the second frequency divider 112 of the synthesizer 100. By changing it, the output of the synthesizer 100 is set to a substantially constant value, or to an output value with a less influence level in the subsequent stage. Here, if the frequency fluctuation with respect to the temperature of the reference oscillator block 101 is large, the frequency correction width must be increased, and the spurious level is also increased.

  More preferably, the second frequency divider 112 of the present invention is a fractional frequency divider. The fractional frequency divider can reduce the frequency control amount per time as compared with the integer frequency divider. As described above, the spurious level can be reduced. The frequency may be corrected in several steps by reducing the control interval Tc as much as the frequency control amount at one time is reduced.

  In the synthesizer of the present invention, it is more preferable that the frequency control amount for one time be within the lock range of the PLL block 102. The lock range is generally a range in which the difference between the frequencies fVCO / N and fref / R compared by the phase frequency comparator 108 is small, that is, it is not necessary to perform the frequency comparison and only the phase comparison can be performed. Say.

  If the frequency difference to be compared is within this range, the PLL will immediately converge to a stable locked state. If the PLL lock operation starts from outside the lock range, for example, a PLL for a TV tuner takes about 1 msec to 100 msec until the PLL is locked. In this case, the control interval Tc needs to be at least as long as that time, and the condition of 1 / Tc ≧ fc, which is a condition of the present invention, may not be satisfied.

  If there is a case where control is performed from outside the lock range, the frequency of the output signal of the synthesizer 100 that changes by one control is outside the lock range of the synthesizer 100 and within the lock range. In some cases, the control time interval Tc is made different, and the frequency of the output signal of the synthesizer 100 that is changed by one control is within the lock range of the synthesizer 100, so that the control time interval Tc is shorter. Is preferred. As a result, it is possible to lock the frequency at an early stage and realize a synthesizer with a low phase noise level.

  Further, when it is necessary to converge to the locked state at a high speed from outside the range of the lock range due to channel switching or the like, it is more preferable to switch the cutoff frequency of the low-pass filter to a high value. This is because the higher the cutoff frequency of the low-pass filter, the shorter the convergence time from outside the lock range. Realization of switching between cut-off frequency for temperature compensation and cut-off frequency for high-speed lock, for example, have two low-pass filters and switch with a switch such as a PIN diode, or change the constant of one low-pass filter This can be achieved by switching. The latter can be realized by making the cutoff frequency variable by, for example, configuring the capacitance portion with a varicap or switching the capacitance with a switch.

  More specifically, when the temperature compensation control period is 1 msec, the cut-off frequency fc must be 1 kHz or less using the present invention. However, for example, in the case of a tuner for digital television, in order to realize a convergence time from outside the lock range of several to several tens of msec, the cutoff frequency of the filter is often set to several kHz or more. By switching the cut-off frequency of the low-pass filter, it is possible to achieve both of them. Since the mobile phone system requires a convergence time that is one digit or more faster than that of a television, the effect of switching the cut-off frequency is further increased.

  When the synthesizer of the present invention is used in a multicarrier system such as OFDM, the relationship between 1 / Tc, which is the reciprocal of the control interval Tc, and the OFDM carrier interval Δfcar is 1 / Tc ≠ n × Δfcar or m × It is more preferable that (1 / Tc) ≠ Δfcar. This means that the influence on the reception performance is less when the control interval Tc is determined so that the spurious does not coincide with other carriers.

(Embodiment 2)
An example of the receiving apparatus used in this embodiment is shown in FIG. The receiving device 120 used in the present embodiment is obtained by mounting the synthesizer 100 of the present embodiment on a domestic digital television broadcast receiving system. Note that most of the synthesizer 100 is built in the RF-IC 117, but there is an external one such as the vibrator 104.

  In addition, some circuits such as the memory 115 and the temperature detection unit 113 are built in the BB-IC 119. In the present embodiment, the basic operation of the synthesizer 100 is the same as that of the first embodiment, but the configuration of the temperature detection unit 113 is different. The temperature detector 113 is not a temperature sensor or the like that directly detects the temperature, but is a detector that detects the frequency variation of the output signal from the oscillator 111, that is, the output signal of the synthesizer 100.

  In the case where the MEMS vibrator having poor frequency temperature characteristics as described in Embodiment 1 is used as the vibrator 104, this frequency fluctuation is considered to be a fluctuation caused by the vibrator 104, and the frequency of the vibrator 104 is considered. The temperature can be calculated backward from the temperature characteristics. Actually, the frequency dividing number of the second frequency divider 112 corresponding to the frequency fluctuation is written in the memory 115 for control.

  Next, the configuration and operation of the receiver will be described with reference to FIG. The television signal received by the antenna 121 passes through the first frequency filter 122 that removes the interference wave. For example, in the case of a television receiver mounted on a mobile phone, a signal emitted from the mobile phone itself becomes the strongest interference wave with respect to the television receiver, and a frequency filter for removing this is arranged.

  Next, the output signal from the first frequency filter 122 passes through a low noise amplifier 123 for amplifying the signal, and further passes through a second frequency filter 124 for removing an interference wave. The second frequency filter 124 removes an interference wave that could not be completely removed by the first frequency filter 122 or another interference wave whose intensity is relatively weak. Next, the output signal from the second frequency filter 124 passes through the balun 125 that converts the unbalanced signal into a balanced signal, and is input to the front end unit 118 of the RF-IC 117.

  In the front end unit 118, the signal is further amplified by a low noise amplifier, or directly input to a frequency converter (frequency mixer) 118, synthesized with a local oscillation signal that is an output of the synthesizer 100, and an intermediate frequency (IF: Intermediate Frequency). ).

  Although the driver circuit 105 for driving the vibrator 104 and the load capacitor 106 are not shown, the driver circuit 105 is added inside the RF-IC 117 and the load capacitor 106 is added externally. The signal converted to the intermediate frequency IF is input to a BB-IC (Base Band IC) 119, that is, a demodulation IC. On the demodulation side, signal processing such as deinterleaving and error correction code decoding is performed to demodulate the data. Here, deinterleaving is to release interleaving for rearranging data during modulation in order to reduce burst errors. Moreover, in systems such as ISDB-T for domestic use and DVB-H for overseas use, Viterbi code and Reed-Solomon code are adopted as error correction codes.

  The signal that has entered the demodulator is first subjected to Viterbi code decoding. Thereafter, the Reed-Solomon code is decoded. In this case, in order to obtain a so-called error-free state with almost no error, the BER after the Viterbi code is decoded is equal to or lower than a certain value (for example, BER). = 2 × 10 ^ −4 or less). BER (Bit Error Rate) means a bit error rate, and is a measure for knowing the quality of an output signal from the frequency converter 118, that is, a received signal.

  With the above processing, processing from reception to data demodulation is completed. In the present embodiment, the demodulator including the BB-IC 119 as a main constituent circuit has been described as being included in the receiving device 120. However, the present invention is not limited to this, and a portion that does not include the demodulator is used as the receiving device 120. Also good. In this case, the electronic device side has a demodulation unit.

  Actually, even a television receiver for home use or a television receiver for a mobile phone may use a portion that does not include a demodulator as a receiver. In this case, the control block 103 is not included in the BB-IC 119. Although not shown, in order to view an image, an MPEG decoder (not shown) is further required on at least a display to display, that is, a display unit and an output side of the receiving device 120. The data that has been decoded to the Reed-Solomon code by the demodulator is input to the MPEG decoder as an MPEG-TS signal, and the image signal is reproduced and displayed as an image.

  By using the receiving device of this embodiment, the built-in synthesizer has the same effect as that of Embodiment 1, but it is also possible to use a small vibrator such as a MEMS vibrator. Miniaturization can be achieved. In addition, since a detector for detecting frequency fluctuation is used as the temperature detection unit 113, a temperature error due to the difference in the location of the temperature sensor and the vibrator 104 is reduced as compared with the case where the temperature sensor as described in Embodiment 1 is used. It can be kept low.

  An example of the temperature detection unit 113 will be described with reference to FIG. In FIG. 7, the temperature detector 113 detects an error between the frequency fca of the received signal and the frequency flo from the PLL block 102, obtains temperature fluctuation information from the frequency error, and obtains the temperature fluctuation information from the controller 114. It is sent to. That is, if the frequency temperature characteristic of the vibrator 104 is known, the current temperature can be determined from the frequency difference, and the frequency division number of the second frequency divider 112 can be controlled via the control unit 114. It becomes. For example, the temperature information calculated from the frequency difference and the numerical value information of the frequency division number are stored in the memory 115 in advance, read out in response to a call from the control unit 114, and the frequency divider of the second frequency divider 112 is read. Set the number.

  Note that the frequency division number may be directly calculated without converting the frequency error output from the temperature detection unit 113 into temperature information. In this case, if the frequency error output from the temperature detection unit 113 is ΔF and the minimum setting unit of the frequency division number is Δdiv, the control unit 114 adds the frequency division number of the second frequency divider 112 by ΔF / Δdiv. Good. In order to realize this control, the control unit 114 may control the frequency division number based on the correspondence table of ΔF and ΔF / Δdiv stored in the memory 115, or may be an internal CPU or logic circuit (see FIG. May be used to calculate ΔF / Δdiv from ΔF and control the frequency division number.

  Next, frequency error detection will be described. In FIG. 7, the received signal (frequency fca) is multiplied by the output (frequency flo) of the PLL block 102 by the frequency converter 118 and converted into signals of frequencies | flo−fca | and | fla + fca |. Next, if | flo + fca | is removed by a low-pass filter (not shown), only a signal having a frequency | flo-fca | remains. Here, fca is shifted from the carrier frequency fca0 of the signal originally desired to be received by the frequency difference Δfca1 between the local oscillation signal of the broadcast station and the output signal of the first synthesizer unit 101. That is, fca = fca0 + Δfca1. Here, Δfca1 takes a positive value when the difference is on the positive side, and takes a negative value when the difference is on the negative side. Further, flo is a value obtained by adding Δft, which is a frequency fluctuation attributed to the frequency temperature characteristic of the vibrator 104, to the carrier frequency fc0 of the signal to be originally received, that is, flo = fca0 + Δft.

  Therefore, to be precise, | flo−fca | = Δft−Δfca1. Here, since Δfca1 is a very small value compared to Δft, that is, Δft >> Δfca1, it is possible to set | flo−fca | = Δft. That is, | flo-fca | corresponds to detecting frequency variation information according to the temperature of the vibrator 104, and the temperature detection unit 113 functions as a temperature sensor.

  Next, a specific method for detecting a frequency error will be described. Basically, a frequency error is detected by signal processing a predetermined known signal included in the received signal. As shown in FIG. 8, in the case of one-segment broadcasting, a signal called a guard interval signal (GI in the figure) is inserted in advance in a received signal at the time of transmission from a broadcasting station. The guard interval signal is generated by copying a certain portion of an effective signal (effective symbol) including image data.

  That is, one symbol includes an effective symbol and a guard interval signal. By inserting such a guard interval signal, a correlation between the received signal and a signal delayed for a certain period (for example, a period corresponding to an effective symbol) is obtained (how much the signal is similar) ), A correlation peak output is output for each period in which the guard interval signal is detected (because it is a copy, it is determined that the signals are similar).

  Correlation processing is realized by performing convolution integration of signals, and digital signal processing is obtained by negating the exclusive OR (XOR) of each bit (Bar of XOR) and adding them. . By using the correlation output thus detected, an error between the received signal and the local oscillation output from the PLL block 102 can be detected and used as a frequency variation.

  In addition, as a method for detecting a frequency error from the correlation output described above, the following method can be used for a signal subjected to quadrature modulation. When the received signal is an I signal, in addition to the correlation output (hereinafter referred to as correlation output 1), the Q signal that is orthogonal to the I signal is correlated with the I signal. In this method, a correlation output (correlation output 2) is obtained, and a frequency difference is detected from the ratio. Here, saying that two signals are orthogonal means that the convolution integral value of the two signals becomes zero.

  Examples of the signal to be compared with the local oscillation output from the PLL block 102 include a signal and a clock used in another system. For example, a GPS (Global Positioning System) signal may be used.

  Other methods for detecting temperature include a method of using a frequency discriminator that outputs an input frequency change as an amplitude change, a frequency counter that directly counts the frequency, and the like. In this method, since the frequency is converted to a low frequency, the frequency difference information can be detected with high accuracy and a simple circuit configuration regardless of the carrier frequency (for example, regardless of the 770 MHz).

In the first and second embodiments described above, a silicon vibrator having a semiconductor material as a base material is used as the vibrator 104, but another example of the MEMS vibrator is a polycrystal. Examples include a silicon vibrator, a so-called FBAR (Film Bulk Acoustic Resonator) based on a thin film piezoelectric material such as AlN, ZnO, and PZT, and a vibrator 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, in FBAR using AlN, a vibrator using thickness longitudinal vibration (vibration in the same direction as the applied electric field) is used, which is about −25 ppm / ° C., and in ZnO, about −60 ppm / ° C. Further, even in a vibrator using SAW, in a case where 36 ° y-cut lithium tantalate is used as a base material, in a case where about -35 ppm / ° C. is used and a base material is 64 ° y-cut lithium niobate, It becomes about -72 ppm / ° C. Many of these vibrators can be made smaller than a crystal vibrator, and can be used by adopting the configuration of the present invention. Further, an effect such as integration with a semiconductor IC can be obtained. In particular, the silicon vibrator has many merits such as that a lot of semiconductors are formed on a silicon substrate, so that it can be formed together with IC formation. In addition, since a piezoelectric thin film material (FBAR material) such as AlN or ZnO can be oriented and formed on a semiconductor substrate, the effect of integration is great.

  Since the synthesizer of the present invention has good phase noise characteristics even when a MEMS resonator advantageous for miniaturization is used as a reference oscillator, it can be used for a communication terminal, a television receiver, or the like.

Block diagram of the synthesizer of the present invention Diagram showing increase of phase noise (occurrence of spurious) Diagram showing the effect of increasing phase noise (OFDM example) Explanatory diagram of relationship between spurious and control interval Explanatory diagram of spurious when control interval is small Block diagram of receiving apparatus of the present invention The synthesizer of the present invention and some other circuit block diagrams Illustration of guard interval signal Illustration of prior art

DESCRIPTION OF SYMBOLS 100 Synthesizer 101 Reference oscillator block 102 PLL block 103 Control block 104 Oscillator 105 Driver circuit 106 Load capacity 107 First frequency divider 108 Phase frequency comparator 109 Charge pump 110 Low pass filter 111 Oscillator 112 Second frequency divider 113 Temperature Detection unit 114 Control unit 115 Memory 116 Frequency converter

Claims (14)

A comparator to which the reference oscillation signal output from the reference oscillator is input;
A filter connected to the output side of the comparator;
An oscillator connected to the output side of the filter and outputting an oscillation signal;
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 filter.
The control unit controls a frequency division ratio of the frequency divider based on a detection result of a detector that detects a temperature at a time interval T;
The relationship between the time interval T and the cutoff frequency fc of the filter is a synthesizer that satisfies 1 / T ≧ fc. There are a plurality of time intervals T at which the control unit controls the frequency divider,
2. The synthesizer according to claim 1, wherein a relationship between a minimum time interval Tmin among the plurality of existing time intervals T and a cutoff frequency fc of the filter satisfies 1 / Tmin ≧ fc. The synthesizer according to claim 1, wherein the reference oscillator is a MEMS vibrator. The synthesizer according to claim 1, wherein the frequency divider is a fractional frequency divider. 2. The synthesizer according to claim 1, wherein the frequency of the output signal of the oscillator that is changed by a single control is within a lock range of the synthesizer. The time interval T differs between the case where the frequency of the output signal of the oscillator that changes by one control is outside the lock range of the synthesizer and the range of the lock range. The synthesizer according to claim 2, wherein the synthesizer is shorter. 2. The cut-off frequency of the filter is switched between a case where the frequency of the output signal of the oscillator, which is changed by a single control, is outside the lock range of the synthesizer and within the lock range. The synthesizer described in 1. A synthesizer used in a multi-carrier system, wherein the relationship between the carrier interval Δfcar of the multi-carrier system and the time interval Tc is (1 / Tc) ≠ n × Δfcar or m × (1 / Tc) ≠ Δfcar The synthesizer according to claim 1, wherein m and n are integers. A frequency converter that converts the frequency of the received signal;
A reference oscillator;
A comparator to which a reference oscillation signal output from the reference oscillator is input;
A filter connected to the output side of the comparator;
An oscillator connected to the output side of the filter to supply an oscillation signal to the frequency converter;
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 filter.
The control unit controls a frequency division ratio of the frequency divider based on a detection result of a detector that detects a temperature at a time interval T;
The relationship between the time interval T and the cut-off frequency fc of the filter satisfies 1 / T ≧ fc. A frequency converter that converts the frequency of the received signal;
A reference oscillator;
A comparator to which a reference oscillation signal output from the reference oscillator is input;
A filter connected to the output side of the comparator;
An oscillator connected to the output side of the filter to supply an oscillation signal to the frequency converter;
A frequency divider that divides the output signal of the oscillator based on a control signal from a control unit;
A detector that detects a frequency variation of an output signal from the oscillator or a received signal,
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 filter.
The control unit controls a frequency division ratio of the frequency divider based on a detection result of the detector at a time interval T;
The relationship between the time interval T and the cut-off frequency fc of the filter satisfies 1 / T ≧ fc. The receiving device according to claim 10, wherein the detector detects a frequency variation of the reference oscillation signal based on a reference symbol included in the reception signal. The receiving device according to claim 10, wherein the detector detects a frequency variation of the reference oscillation signal based on a guard interval signal included in the received signal. The receiving device according to claim 9, wherein the reference oscillator is a MEMS vibrator. The receiving device according to claim 9 or 10, and
A signal processing unit connected to the output side of the frequency converter;
An electronic apparatus comprising: a display unit connected to an output side of the signal processing unit.

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