KR100895029B1 - Frequency synthesizer - Google Patents

Abstract

A method and frequency synthesizer are provided for stabilizing the frequency of the frequency synthesizer via a reference oscillator unit coupled to a voltage controlled oscillator (VCO), the synthesizer being provided with a phase locked loop (PLL) for stabilizing the operation of the voltage controlled oscillator. The reference oscillator unit is a microelectromechanical system (MEMS) reference oscillator unit, the temperature of the microelectromechanical system reference oscillator unit is measured, and the output frequency is corrected according to the measured temperature using a frequency / temperature function. do.

Description

Frequency synthesizer {Frequency synthesizer}

The present invention relates to a method for stabilizing the frequency of a frequency synthesizer. In particular, the present invention relates to a method for stabilizing the frequency of a frequency synthesizer via a reference oscillator connected to a voltage controlled oscillator (VCO) using a phase locked loop (PLL). The invention also relates to a frequency synthesizer.

In typical modern radio transceivers the communication frequency is obtained from a reference oscillator. For example, in a wireless handset, the frequency based on the reference oscillator is used to initiate communication with a base station. After the connection is established, the frequency accuracy can be further improved by various synchronization methods, but the initial communication frequency must be accurate enough to enable the establishment of the initial communication.

In a typical transceiver architecture, the output of the reference oscillator is phase locked to the output of the VCO and the output of the VCO provides the desired Local Oscillator (LO) frequency.

An example of such PLL based frequency generation is shown in FIG. 1A. The output 13 of the phase comparator 12 is used to stabilize the operation of the VCO 14; The output frequency 15 of the VCO 14 will be the reference oscillator frequency 11 multiplied by the division factor N of the divider chain 16.

The basic PLL based frequency generation uses an integer counter chain as a frequency divider, but the fractional version divides two different dividing modulos, typically under the control of a sigma-delta converter, to approximate a continuous output frequency range. Use a fractional divider that alternates between

The PLL-based frequency generation shown in FIG. 1A may be developed into the frequency synthesizer shown in FIG. 1B when the division factor N is to be changed dynamically.

In addition to the requirement to provide long term frequency accuracy for the VCO, a low reference oscillator phase noise is required because the more the LO generated carrier contains low phase noise, the more likely the communication channel will be to provide error free information transfer. Because it is.

Reference oscillators are used as precision and stable frequency references in frequency synthesizers and are used to provide a precise and stable reference frequency to enable the generation of variable but stable frequencies that can be used as tunable LO-frequency.

An important requirement for the output frequency signal of the frequency synthesizer is stability, low phase noise and high thermal stability, for example with a low thermal coefficient, and additionally a requirement that a precise value for the output frequency can be selected quickly.

In wireless communication devices the reference oscillator is conventionally based on modifications. The stable and precise mechanical vibration of quartz resonators is suitable for the generation of oscillators with good long term (drift and aging) and short term (phase noise) stability. Moreover, the temperature dependence of the resonant frequency can be reduced to low values (less than a few ppm over the typical operating temperature range) by suitable modification preparation methods (eg AT-cut). The main drawbacks of the modified reference oscillator modules are their difficulty in monolithic integration with transceiver modules based on their rather large size and typically high integration solutions. Modern micromachining makes it possible to manufacture small mechanical resonators (microelectromechanical systems = MEMS) with resonant frequencies ranging from several kHz to GHz. Examples of such microresonators based on the surface or bulk micromachining of silicon are described in 2002 in Boston / London, Artec House, H. second. It is presented in De Los Santos, "Designing RF MEMS Circuits for Wireless Communications." Advantages of microresonators include the small size, low power consumption and the potential for increased levels of integration between resonators, oscillator electronics and device packages. Both monolithic integration and system-on-chip approaches are viable solutions for increasing the integration level of a reference oscillator. Monolithic integration of micromachined resonators and integrated circuits can encourage more complex microelectro-mechanical circuits and provide complete on-chip frequency synthesizers.

However, the basic complexity in using silicon-based microresonators in frequency synthesizers results from their large temperature coefficient, typically df / dT of -10 to -30 ppm / K. This temperature dependency is too great for baseline applications if left unknown. The compensation of the temperature dependence is therefore necessary to make the microresonators suitable as frequency references for frequency synthesizers.

It is an object of the present invention to eliminate the disadvantages of the prior art and to provide an improved method and improved frequency synthesizer for stabilizing the frequency of a frequency synthesizer.

The present invention provides an LO frequency synthesizer structure in which a MEMS reference oscillator unit with a nonzero temperature coefficient is used for frequency stabilization and the temperature-dependent nature of the reference frequency is described at the synthesizer level.

The present invention is based on the principle that the resonator temperature is measured to electronically compensate for the temperature dependence and the resulting temperature dependent frequency shift. By measuring the temperature T of the MEMS resonator as shown in FIG. 1C and by using a known frequency versus temperature function f _r (T), the resonant frequency is the stability of the prior art frequency synthesizer according to FIG. 1B. It is a precisely defined amount that can be used to improve the performance.

In a preferred embodiment the temperature measurement is based on exciting two modes in a MEMS resonator with different temperature coefficients. By examining the frequency shift of the two modes, the change in temperature can be measured and electrically compensated. The method has the following advantages: 1) no temperature sensor is required to eliminate the temperature transient hysteresis associated with the temperature difference between the temperature sensor and the resonator; 2) the frequency measurement is direct and accurate for digital realization. And 3) no additional sensors are needed since the resonator is also a sensor. This simplifies manufacturing and reduces cost.

Features of the invention are provided in more detail in the appended claims.

The main advantage of the methods provided in the present invention is that the rather large (but predictable) temperature dependence of the MEMS-oscillator is directly taken into account in frequency synthesis, so that the long term stability for the reference oscillator when the oscillator itself operates without compensation And low phase noise can be further optimized. Using the methods described above, the MEMS-referenced oscillator can be integrated (in unity) as part of a wireless transceiver module.

The objects, features and advantages of the present invention described above and additional objects, features and advantages will become more clearly understood from the following description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.

1A is a block diagram of a typical PLL based frequency synthesizer where the VCO generates the LO frequency.

1B is a simplified block diagram of a frequency synthesizer.

1c is a simplified block diagram of a frequency synthesizer according to the present invention.

2A is a block diagram of a frequency synthesizer according to a preferred embodiment of the present invention.

2B is a block diagram of a simplified frequency synthesizer according to an embodiment of the present invention.

2C is a block diagram of a frequency synthesizer according to another embodiment of the present invention.

3A and 3B show two oscillation modes observed for a square plate resonator with different temperature coefficients.

4 discloses measured frequency coefficients for two square plate vibration modes.

5A and 5B show two methods for simultaneously detecting two square plate vibration modes.

Figure 6 illustrates a preferred embodiment of the present invention implemented with temperature information extracted from two mode measurements.

The present invention relates to a method for stabilizing a frequency of a frequency synthesizer by using a reference oscillator coupled to a voltage controlled oscillator (VCO) using phase locked loops (PLL) or frequency comparison control, wherein a reference MEMS oscillator stabilizes the VCO. By measuring the temperature T of the MEMS resonator and using its known frequency versus temperature function f _r (T), the output frequency can be defined precisely which can be used as reference in frequency synthesizers. It becomes the amount that became.

In the following three stabilization methods are provided for MEMS-oscillator-based frequency synthesizers.

According to a first method, referring to the block diagram shown in FIG. 2A, VCO 24 generates an LO-frequency (eg at 1 GHz) f _LO . MEMS-referenced oscillator 21 is typically operated at significantly lower frequencies (eg at 10 MHz). The VCO output frequency is divided in the divider 25 to equalize the divider's output frequency 28 with the MEMS-referenced oscillator frequency. Their relative phase is detected by phase detector 22 and after low pass filtering (LPF) 23 the result is used to stabilize the VCO 24. This loop forms a basic PLL, as previously described.

The frequency of the MEMS reference oscillator 21 is not stable with temperature, but its temperature-dependent frequency offset can be compensated for by changing the divider 25.

The previously known fractional-N divider technique, which can be tuned continuously, can conveniently be used to adjust the counting of the divider chain 25. It can be realized using, for example, a sigma-delta modulator technique that continuously adjusts the count module N of the frequency divider stage. Using the sigma-delta modulator 27 to adjust the divider 25, the VCO frequency can be formed to be N + x [n] times the reference frequency and become nearly continuously adjustable. have. N represents the module integer setting of the frequency divider and x [n] is the phase detector output signal 28 used to control the sigma-delta modulator 27.

Based on the measured (29) temperature (T) of the MEMS reference oscillator 21 and the T-dependence (f (T)) of the MEMS reference oscillator 21, the sigma-delta modulator 27 is Logic circuit 30 is used to generate an x [n] 32 signal that compensates for the temperature-induced output frequency offset of MEMS reference oscillator 21.

The compensation is due to the sigma-delta modulator 27 adjusting the modulo N of the divider chain 25. The logic circuit 30 may advantageously use a lookup table 31 which provides the necessary correction control signal x (n) selected using the measured temperature T of the reference oscillator 21. The manufacturing tolerance offset of the reference frequency may likewise be calibrated and used to additionally adjust x [n] in the same manner using, for example, a two-dimensional lookup table 31 or a suitable combining algorithm.

The MEMS reference oscillator 21 is realized using the techniques described later. Long term stability and low phase noise for the reference oscillator can be provided using a single MEMS-oscillator based on bulk acoustic wave (BAW) operation. If desired, improved performance for the reference oscillator can be realized using two or more MEMS components in which the properties are optionally combined. For example, long term stability and low phase noise for the reference oscillator can be obtained by combining the characteristics of the two MEMS-components.

A block diagram of the second method is shown in FIG. 2B. That is the case where the VCO 44 can generate a signal with the spectral purity (phase noise) required by itself and the reference oscillator 41 is only needed to provide the long term frequency stability.

In this case, the VCO feedback loop can be formed in a narrower band and a constant integer-N division is added to the divider 43 to produce a reference frequency from the reference oscillator 41 and an output to be mixed in the mixer 42. Can be used). The mixer 42 outputs the sum and difference frequencies of the mixed frequencies but after low pass filtering 48 only the low frequency difference frequency between the reference frequency fr and the divided VCO output frequency fVCO / N. (fbeat = fr-fVCO / N or fVCO / N-fr) is maintained and can be used to generate a control signal for the VCO that adjusts the VCO to output the desired frequency. It is important to note that the VCO output signal need not be a constant multiple of the reference signal. By appropriate selection of the difference frequency fbeat, fine adjustment of the output frequency fVCO = N · (fr-fbeat) is possible. This can be used to digitally compensate for temperature induced changes in the reference oscillator.

The VCO control signal 49 is generated by logic circuitry 45 to generate a tuning voltage for the VCO that additionally corrects for the reference oscillator temperature dependent frequency offset and / or offsets found during calibration. Additional correction control voltages may be added to this control signal.

The mixing method described above can only be used if the relative frequency sense of the frequencies does not change. Another more general method uses the single common signal to directly count the two relative low frequency signals fr and fVCO / N to control the counters to the gate to control the frequency difference and its sense. To decide. This clock can be any one of the signals, for example.

The logic circuit 45 outputs a tuning control voltage 49 that depends on the frequency difference in this manner to make the difference frequency between the divided VCO output frequency and the reference frequency closer to the desired frequency difference. .

The voltage dependent on the measured oscillator temperature T and any calibration correction can be additionally adjusted to adjust the tuning voltage for the VCO 44, advantageously simply by using lookup tables and a DAC. In the same manner as previously described for the first method, the lookup tables may include both correction values and correction correction values that depend on the known temperature dependent operation of the MEMS reference oscillator.

An advantageous embodiment of this method uses the control signal 50 and the logic circuit to control the VCO by analog methods using the frequency difference and to change the frequency divider of the frequency divider counter chain 43. 45) to digitally adjust the integer counter chain for temperature and calibration correction.

Each time a synthesizer divider dispenses using integer values (e.g. for channel selection), the logic circuitry can quickly provide the channel selection if it is provided with the information of the desired channel, In an example the logic circuit 45 may directly provide the temperature corrected N needed for the desired channel to provide fast channel selection.

This method for fast channel selection at the transceiver is not limited to the method shown in FIG. 2B and can be used whenever correction values are adjusted to change the counter chain. Thus, this method can also be used with the preferred embodiment. In a preferred embodiment, although not shown, a three-dimensional table is used instead of a two-dimensional correction table to provide correction values for all combinations of manufacturing calibration correction, reference oscillator temperature correction and the channel select frequency offsets.

Providing temperature, calibrated or channel corrected N values to the counter chain can be accomplished in many other ways that will be apparent to those skilled in the art. For example, in addition to modifying the modulo of the counter chain or using fractional methods, the count value of the counter itself adds counts at a regular rate to increase or decrease the output frequency or Can be changed. This method, which is often used in phase accumulators to provide a fixed phase offset, can be easily modified for continuous phase changes, which in fact provides a controlled increase or decrease of the output frequency.

2C is a block diagram of a frequency synthesizer according to another embodiment of the present invention in which an offset synthesizer is used for temperature stabilization of the VCO 55 output frequency. The VCO produces an LO-frequency (eg at 1 GHz) f _LO . MEMS-referenced oscillator 51 provides a reference frequency, typically 10 MHz. The VCO output frequency is divided in the divider 54 and the divided VCO output is mixed with the reference oscillator using a mixing phase detector 52. The mixer output is filtered with a low pass filter 53 to obtain f1 = fVCO-fr. The second mixer 57 is used to add an offset frequency foffset provided by the oscillator 58 to the signal. The resultant frequency f2 = f1-foffset is obtained after filtering with the second low pass filter 56. When the phase loop is locked, the frequency f2 is zero and the VCO output is equal to fVCO = N · (fr + foffset).

The frequency of the MEMS reference oscillator 51 is not stable with temperature, but its temperature-dependent frequency offset can be compensated by adjusting the foffset. Based on the measured temperature T of the MEMS reference and the T-dependency f (T) of the MEMS reference 51, the logic circuit 60 and the lookup table 59 control the offset oscillator 58. It is used to The offset oscillator may be a MEMS oscillator (eg flexural oscillator) or VCO with a wide tuning range.

) 모드 진동(f0=12.1 MHz에서, Q=60000)을 도시한 것이다. 상기 확장 진동 모드는 원래의 정방형 모양을 유지하는 2-D 플레이트 팽창으로서 특징지워진다. 상기 라메 모드는 실리콘 온 인슐레이터(SOI) 웨이퍼의 깊은 반응 이온 식각에 의해 형성될 수 있다. 상기 공진기에 대한 전기 접촉은 전체 장치가 하나의 마스크와 함께 제조될 수 있도록 코너 앵커링(anchoring)(T-형 코너 앵커링)으로 행해질 수 있다. 상기 확장 모드는 부가적으로 브이. 카아자카리, 티. 마틸라, 에이. 오자, 제이. 키이하마키, 에이치. 카텔루스, 엠. 코스켄부오리, 피. 란타카리, 아이. 티토넨 및 에이치. 세빠의, (2003년 6월, 보스톤) 트랜스듀서03에서 발행된 논문, "정방형-확장 모드 단일-수정 실리콘 마이크로기계 RF-공진기"에서, 낮은 위상 잡음을 획득하는데 매우 적합한 것으로 나타났다. 도 4는 서로 상이한, 상기 두 모드들에 대한 측정된 온도 의존성을 나타낸 것이다.According to another embodiment of the invention, the silicon resonator is excited simultaneously in two modes, each mode having a different temperature coefficient. An example of a useful resonator structure showing these two types of modes is shown in FIG. 3. Figure 3a shows the expansion mode oscillation (q = 120000 at f0 = 13.1 MHz) in the plate and Figure 3b shows the lame (

) Mode oscillation (f0 = 12.1 MHz, Q = 60000). The extended vibration mode is characterized as a 2-D plate expansion that maintains the original square shape. The lame mode may be formed by deep reactive ion etching of a silicon on insulator (SOI) wafer. Electrical contact to the resonator may be done with corner anchoring (T-shaped corner anchoring) so that the entire device can be manufactured with one mask. The extended mode is additionally V. Kaazakari, T. Matilla, a. Come on, Jay. Kiihamaki, H. Catelus, M. Koskenbuori, P. Lantakari, child. Titonen and H. In Sepha's (Boston, June 2003), a paper published in Transducer03, "Square-extended mode single-modified silicon micromechanical RF-resonators," was found to be well suited for obtaining low phase noise. 4 shows the measured temperature dependence for the two modes, which are different from each other.

Simultaneous and independent detection of the two vibrations is shown in FIGS. 5A and 5B. 5a and 5b includes a square plate, electrodes ELE1-ELE4 providing capacitive coupling on all sides of the plate, voltage sources U _in and U _bias connected to the electrodes and an output voltage An acoustic wave mode (BAW) silicon resonator is shown. With the differential electrode configuration shown in FIG. 5A, the two modes can be detected using the same electrodes. This provides the maximum signal amplitude for both modes but complicates the oscillator electronics. The configuration shown in FIG. 5B uses different electrodes with different biases (differential polarities for other lam-electrodes) to excite and / or excite the lam-mode and extended-mode. The drive electronics are simpler and the two modes have good isolation, but the configuration is not optimal for signal power. For simplicity, the electrode size for the two modes is shown to be the same but the actual implementation may use larger electrodes for the mode used to generate the reference frequency and more for the mode used to generate the temperature information. Small electrodes can be used.

An alternative to detecting the two modes in the same resonator is to drive one resonator in plate extension mode and two in close thermal contact (eg on the same substrate) to drive the other resonator in lame mode. To make resonators. Since these resonators are on the same silicon substrate, the resonator temperatures are highly correlated. The advantage of this configuration is that the modes are electrically and mechanically isolated and the oscillator electronic components are simplified.

Other microresonator configurations can also be used to generate the temperature information. For example, it is possible to obtain the temperature information from twisted and curved beam oscillation modes, because these two modes also have different temperature dependencies. Alternatively, two resonators formed of different materials with different temperature dependencies can be used.

The temperature information needed for frequency compensation can be generated as follows: The two modes resonate at frequencies f1 and f2. Both modes are simultaneously excited and the pulses generated by the two resonances are detected as previously described and counted at counter1 and counter2, respectively. When the counter 1 stored N1 cycles, the counter 2 stored N2 = f2 / f1N1 cycles at the same time. Keeping N1 fixed, the temperature can be obtained.

This temperature information can be used by the present invention to correct the output frequency of the frequency synthesizer according to the first method, its simplified form and the third method. While other temperature measurement methods can likewise be used to implement frequency correction, the two-mode method is particularly suitable for use with MEMS reference oscillators.

The two-mode method can be used directly to form the reference oscillator used for the high frequency synthesizer as shown in FIG. The illustrated synthesizer uses a reference oscillator and a fractional-N phase-locked loop. The reference oscillator 71 has two frequency outputs 72 and 73 with different temperature dependence. The frequency output 72 is designed to have low phase noise. These outputs 72 and 73 are counted to counter 1 74 and counter 2 75. The counter is used by logic circuitry 77 to calculate the oscillator temperature as previously described. The temperature information along with the stored calibration information in the memory 76 is used to calculate the correct division factor N in the frequency divider 83 resulting in the desired LO frequency given by fVCO = N · f1. Since f1 is temperature dependent, the required dispensing factor N may be a fraction rather than an integer.

The desired frequency is synthesized using VCO 80 to generate the LO frequency. The VCO output frequency is divided in the divider 83 to make the output frequency 81 of the divider equal to the MEMS-referenced oscillator frequency 72. The dividing factor in the divider 83 is changed in the fractional sigma-delta modulator 82 in the manner previously described. The logic 77 circuitry is used to control the sigma-delta modulator to obtain fractional divisions. The relative phase between the reference oscillator signal 72 and the divided signal 81 is detected by a phase detector 78 and after low pass filtering in the LPF 79, the result of the phase comparison stabilizes the VCO 80. It is used to This loop forms a basic PLL, as previously described.

The reference oscillator 71 is designed such that the output signal 72 firstly has low phase noise and secondly only has high temperature stability. The desired LO frequency is synthesized using a voltage controlled oscillator with a low quality factor, and thus is coupled to the reference oscillator for good stability to provide a low jitter LO signal, necessary for carrier signals and other uses. It is fixed.

Any reference oscillator frequency shift is corrected using fractional division of the VCO frequency using a fractional-N modulator.

Stored calibration values and known temperature dependencies are used by the logic circuit to control the fractional-N modulator.

The fractional-N PLL may advantageously be implemented using a sigma-delta modulator. This technique has been demonstrated to provide nearly continuous frequency tuning and to meet the GSM phase noise specification.

It is apparent to those skilled in the art that other embodiments of the invention are not limited to the examples described above, but may vary within the scope of the appended claims.

Claims (23)

A method for stabilizing the frequency of a frequency synthesizer via a reference oscillator unit coupled to a voltage controlled oscillator (VCO), wherein the synthesizer is provided with a phase locked loop (PLL) for stabilizing the operation of the voltage controlled oscillator. The reference oscillator unit is a microelectromechanical system (MEMS) reference oscillator unit, The temperature of the microelectromechanical system reference oscillator unit is measured, Output frequency is corrected according to the measured temperature using a frequency / temperature function. The oscillator of claim 1, wherein the voltage controlled oscillator generates a local oscillator frequency, the voltage controlled oscillator output frequency is divided such that it is equal to the microelectromechanical system reference oscillator frequency, and their relative phase is detected to detect the voltage controlled oscillator. Used to tune, A frequency divider is used to compensate for temperature-dependent reference frequency offset errors. 3. The tunable (fractional-N) divider is realized using sigma-delta modulator technology, and using the sigma-delta modulator feedback to the divider, the voltage controlled oscillator frequency is N + x. [n] times the reference frequency, where N represents an integer setting of the frequency divider and x [n] is an input sequence for guiding the sigma-delta modulator, the microelectromechanical system oscillator (T) Based on the measured temperature T of and the reference frequency T-dependence fr (T), a logic circuit is used to generate x [n] which compensates for the temperature-induced offset of the reference frequency. Method for stabilizing the frequency of a frequency synthesizer. The oscillator of claim 2, wherein the voltage controlled oscillator can generate a signal with spectral purity (phase noise) required by itself and the reference oscillator is required to provide long term frequency stability, the reference frequency fr And the difference between the divided VCO frequency (fVCO / N) is determined by counting a beat frequency (fr-fVCO / N), and then the frequency difference is determined by the measured T and known to produce the correct tuning voltage for the VCO. A method for stabilizing frequencies of a frequency synthesizer, characterized in that it is combined with a function fr (T). The oscillator of claim 2, wherein the voltage controlled oscillator can generate a signal with spectral purity (phase noise) required by itself and the reference oscillator is required to provide long term frequency stability, the reference frequency fr And the difference between the divided VCO frequencies fVCO / N is equal to the two frequencies fr and fVCO / N using one of the signals for clocking the counting of both the frequencies fr and fVCO / N. Is determined by direct counting and then the frequency difference is combined with the measured T and a known function fr (T) to produce the correct tuning voltage for the VCO. Way. The method of claim 1, wherein temperature compensation for the frequency of the reference oscillator unit is performed using an oscillator that can be tuned. The method of claim 1, wherein an offset synthesizer is used for temperature stabilization of the VCO 55 output frequency, wherein the VCO generates a Local Oscillator (LO) frequency, and the microelectromechanical system-reference oscillator (51). Provides the reference frequency, the VCO output frequency is divided in a divider 54 and the divided VCO output is mixed with the reference oscillator using a mixing phase detector 52, and the output of the mixing phase detector is filtered using low pass filter 53 to obtain f1 = fVCO / N-fr, a second mixer 57 is used to add the offset frequency provided by oscillator 58 to the signal, And a resulting frequency (f2 = f1-foffset) is obtained after filtering with the second low pass filter (56). The method of claim 1, wherein the temperature is measured by exciting two modes in a microelectromechanical system resonator with different temperature coefficients, and by examining the frequency shift of the two modes, a change in temperature can be measured. Method for stabilizing the frequency of a frequency synthesizer. The method of claim 1, wherein the correction value selected by the temperature measurement, regardless of the method, is continuously added or subtracted at a constant rate in the phase accumulator in the PLL counter chain to increase or decrease the output frequency depending on the temperature. Characterized by a method for stabilizing the frequency of a frequency synthesizer. A frequency synthesizer provided with a reference oscillator unit connected to a voltage controlled oscillator (VCO) for stabilizing the frequency of the frequency synthesizer, wherein the synthesizer is provided with a phase locked loop (PLL) for stabilizing the operation of the voltage controlled oscillator. To The reference oscillator unit is a microelectromechanical system (MEMS) reference oscillator unit, and the frequency synthesizer is adapted to measure the temperature of the microelectromechanical system reference oscillator unit and in accordance with the measured temperature using a frequency / temperature function. And means for compensating the output frequency. 11. The apparatus of claim 10, wherein the reference oscillator unit is a micromechanical bulk acoustic wave (BAW) silicon resonator having a square plate and electrodes for capacitive coupling arranged on all sides of the plate, wherein the vibration mode is in the original square shape. A frequency synthesizer characterized by a two-dimensional plate expansion holding. 11. The apparatus of claim 10, further comprising: means for generating a local oscillator frequency, means for dividing the voltage controlled oscillator output frequency to be equal to the microelectromechanical system reference oscillator frequency, and detecting their relative phases and tuning the voltage controlled oscillator And means for making a frequency synthesizer. 13. The frequency synthesizer of claim 12, comprising a divider for compensating for temperature-dependent reference frequency offset errors. 13. The frequency synthesizer of claim 12, wherein the tunable (fractional-N) divider is a sigma-delta modulator. 13. The frequency synthesizer of claim 12, wherein the voltage controlled oscillator has means for generating a signal having spectral purity (phase noise) required by itself and the reference oscillator is required to provide long term frequency stability. . 12. The microelectromechanical system of Claim 10, wherein an offset synthesizer is used for temperature stabilization of said VCO 55 output frequency, said frequency synthesizer comprising a VCO generating a Local Oscillator (LO) frequency. A reference oscillator 51 provides the reference frequency, wherein the VCO is for dividing the VCO output frequency in the divider 54 and the divided VCO output is mixed with the reference oscillator using a mixing phase detector 52. The output of the mixing phase detector is filtered with a low pass filter 53 to obtain f1 = fVCO / N-fr, and the second mixer 57 adjusts the offset frequency provided by the oscillator 58. Means for obtaining the resulting frequency (f2 = f1-foffset) which is used to add to the signal and is filtered with a second low pass filter 56 . 12. The microelectromechanical system reference oscillator unit has two modes with different temperature coefficients such that the temperature is measured by exciting the two modes in a microelectromechanical system resonator with different temperature coefficients. A frequency synthesizer characterized in that a change in temperature can be measured by examining the frequency shift of two modes. 18. The frequency synthesizer of claim 17, comprising an electrode configuration for simultaneously detecting the two modes. 19. The frequency synthesizer of claim 18, wherein the electrode configuration comprises means for detecting two modes with identical electrodes. The method of claim 18, wherein the electrode configuration is lame (

And different electrodes with different biases (inverted polarity with respect to other lam-electrodes) to excite) -mode and extended-mode. 19. The frequency synthesizer of claim 18, wherein the electrode configuration comprises different resonators for the excitation of the two modes. 11. The frequency synthesizer of claim 10, wherein the frequency synthesizer comprises a frequency reference oscillator and a phase-locked loop (fractional-N PLL), the reference oscillator providing frequencies f1 and f2 used to generate temperature information, The oscillator is designed such that the signal frequency (f1) has a low phase noise and the desired frequency is synthesized by a voltage controlled oscillator (VCO). 11. The frequency synthesizer of claim 10, wherein the frequency synthesizer includes a three-dimensional table to provide correction values for all combinations of manufacturing calibration corrections, reference oscillator temperature corrections, and channel select frequency offsets.

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