CN105375921A - Accurate frequency control based on MEMS oscillator - Google Patents
Accurate frequency control based on MEMS oscillator Download PDFInfo
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- CN105375921A CN105375921A CN201410427718.9A CN201410427718A CN105375921A CN 105375921 A CN105375921 A CN 105375921A CN 201410427718 A CN201410427718 A CN 201410427718A CN 105375921 A CN105375921 A CN 105375921A
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Abstract
A microelectromechanical system (MEMS) oscillator provides an oscillator output signal with a first frequency which is different from the predetermined frequency of the output signal. An error determining circuit determines the frequency error relative to the predetermined frequency based on initial frequency offset and/or temperature and provides error information which indicates the difference between the first frequency and the predetermined frequency. The error information is used in the frequency conversion logic by a receiving system, and the frequency conversion logic uses an oscillator output signal as a frequency reference.
Description
Technical field
The present invention relates to generation oscillator signal, and relate more specifically to supply oscillator signal and corresponding thereto in the information that the accuracy of preset frequency is relevant.
Background technology
The such as contemporary electronic systems of radio device, tuner, micro controller unit (MCU) and so on generally includes the phase-locked loop (PLL) (or other circuit) that can carry out frequency inverted in system.Often to system supply frequency reference signal.In the past, the frequency reference signal to system supply has by the predetermined fixed frequency accurately manufacturing crystal resonator or obtain by using the freq converting circuit of such as PLL and so on to carry out electronics correct frequency error.Change than solving the error be associated with variations in temperature by regulating resonator load or adjusting frequency, thus produce fixing rate-adaptive pacemaker.
Based on the oscillator of MEMS (micro electro mechanical system) (MEMS) just more and more for generation of reference signal.MEMS typically refer to be incorporated with can the mechanical structure of movement at interior device.MEMS resonator can replace the source of traditional crystal (quartz) resonator as frequency reference signal in various electronic system.MEMS resonator has lot of advantages, such as, less size, with the manufacturing process of lot size semiconductor industrial manufacturing process compatibility and lower cost.A shortcoming based on the oscillator of MEMS is utilized to relate to frequency tuning.From can be different by cutting the quartz resonator accurately controlling its frequency, MEMS resonator frequency has intrinsic original frequency inaccuracy due to manufacturing tolerance.In addition, and can be different by the crystal oscillator increasing or reduce electric capacity to draw (adjustment) its frequency on resonator node, be very difficult to traction MEMS resonator frequency to offset manufacturing tolerance.Fractional-N phase lock loop (PLL) is generally used for using the frequency inverted ratio of PLL to be predetermined fixed frequency accurately by inaccurate MEMS frequency correction.Similarly, the MEMS oscillator of temperature stabilization needs to carry out frequency correction for temperature effect.
Fig. 1 shows prior art systems, and wherein, MEMS resonator 101 and MEMS oscillator holding circuit 102 combine to provide MEMS oscillator signal 106 to frequency correction PLL108.Frequency correction PLL108 is implemented as mark-NPLL usually.Correction of frequency errors circuit 112 supplies control information to allow PLL by guaranteeing that PLL108 has correct frequency inverted and compares and correct for the initial frequency drift of MEMS resonator and temperature effect to PLL108.Frequency correction PLL108 supplies precise frequencies reference signal 116, and this precise frequencies reference signal 116 has preset frequency known for receiving system 130.Frequency reference signal 116 can be accurate to such as 200/1000000000ths or be suitable for certain other accuracy of receiving system.Receiving system utilizes the frequency reference signal 116 in frequency inverted PLL132 to produce the system clock 134 used by the functional circuit 136 of receiving system.Frequency inverted PLL132 carrys out inversion frequency reference signal 116 based on expected frequency signal 138.This expected frequency signal can be multiplied by such as 117.6 to frequency inverted PLL132 instruction with reference to frequency.Therefore, frequency inverted PLL132 also may be implemented as mark-NPLL, to allow the non-integer ratio between system clock 134 and frequency reference signal 116.
But, use PLL to produce frequency reference signal 116 in conjunction with MEMS oscillator and there is multiple shortcoming.Particularly, PLL adds complexity, additional noise and power consumption.
Summary of the invention
In an embodiment, a kind of device comprises: MEMS (micro electro mechanical system) (MEMS) oscillator, for supplying MEMS oscillator output signal; And frequency error determination circuit, output signal with described MEMS oscillator the frequency error be associated for supplying.
In an embodiment, a kind of method comprises: use MEMS (micro electro mechanical system) (MEMS) oscillator to produce the oscillator output signal with first frequency.Determine the error signal of the difference indicating described first frequency and preset frequency.Described oscillator output signal and control information is supplied to receiving system.In described receiving system, determine the frequency inverted ratio of described oscillator output signal based on described control information and expected frequency information, and compare clocking in freq converting circuit based on described oscillator output signal and described frequency inverted.Described clock signal supplied by functional circuit to described receiving system.
In another embodiment, a kind of integrated circuit comprises: MEMS (micro electro mechanical system) (MEMS) oscillator, for supplying the oscillator output signal with first frequency.Error determination circuit provides the control information of the difference of the described first frequency of instruction and preset frequency.One or more error output of described integrated circuit are coupled to described error determination circuit to provide error signal.Reference signal lead-out terminal is coupled to provide described oscillator output signal.
In another embodiment, a kind of device comprises the first integrated circuit.Described first integrated circuit comprises: MEMS (micro electro mechanical system) (MEMS) oscillator, for supplying the oscillator output signal with first frequency; And error determination circuit, for providing the error signal of the difference of the described first frequency of instruction and preset frequency.Multiple lead-out terminals of described integrated circuit are coupled to described error determination circuit and described MEMS oscillator to provide described error signal and described oscillator output signal.Described device also comprises the second integrated circuit, and described second integrated circuit comprises: multiple input terminal, for receiving described error signal and described oscillator output signal; And freq converting circuit, for described oscillator output signal being transformed into different frequencies based on described error signal and expected frequency instruction.
Accompanying drawing explanation
By referring to accompanying drawing, the present invention may be better understood, and to those skilled in the art, multiple object of the present invention, feature and advantage will be apparent.
Fig. 1 shows prior art systems.
Fig. 2 shows the embodiment using MEMS oscillator and frequency error determination circuit to come supplied frequency control information and MEMS oscillator signal.
Fig. 3 A shows and uses ∑ Δ (sigmadelta) modulator to produce frequency error information.
Fig. 3 B shows the embodiment that pulse-width modulator produces frequency error information.
Fig. 3 C shows the embodiment producing and provide the analog signal of frequency error information.
Fig. 4 shows the embodiment of frequency inverted PLL.
Fig. 5 shows MEMS oscillator and the embodiment of frequency inverted PLL on identical integrated circuit.
Identical Reference numeral is used to indicate similar or identical item in different drawings.
Embodiment
The such as contemporary electronic systems of radio device, tuner, micro controller unit (MCU) and so on generally includes the mark-NPLL (or other circuit) that can carry out frequency inverted in system.Often to system supply frequency reference signal.On the single silicon substrate needing the system of frequency reference signal to be integrated into provide SOC (system on a chip) (SoC) to realize.Not there is a PLL for correcting the error be associated with MEMS resonator and provide the 2nd PLL of frequency inverted for receiving system, but in one embodiment, in receiving system (such as, SoC system) in single PLL in perform frequency inverted to MEMS oscillator reference signal, this frequency inverted take into account the error in MEMS signal.Therefore, in an embodiment, contrary with only providing oscillator output signal (frequency reference signal), MEMS oscillator circuit provides two kinds of signals.According to embodiment, frequency reference produces circuit provides MEMS oscillator to output signal, and has supplied following signal: this signal provides the frequency error information (comprising temperature effect) outputing signal with MEMS oscillator and be associated.
Fig. 2 shows the example embodiment with MEMS oscillator 201.MEMS oscillator 201 comprises MEMS resonator 203 and for keeping the oscillator holding circuit 205 of the vibration of MEMS resonator.MEMS oscillator 201 produces MEMS oscillator output signal 207.Due to manufacturing tolerance, MEMS oscillator signal export 207 usually and the target frequency that is designed to of MEMS oscillator depart from 1 ~ 2%.In addition, MEMS oscillator is subject to the impact of temperature.Therefore, two error sources frequency shift of comprising initial frequency drift and causing due to variations in temperature.
Therefore, except MEMS oscillator circuit 201, shown embodiment also comprises the MEMS error determination circuit 210 producing control information 221.Control information 221 and MEMS oscillator output signal 207 are provided, make it possible to use error signal combination expected frequency information and produce clock signal accurately in downstream, the expected frequency of this expected frequency information indicating system clock signal.MEMS error determination circuit 210 in shown embodiment comprise nonvolatile memory (NVM) 215, this NVM215 may be used for store relative to target frequency 1 ~ 2% frequency shift (FS).Initial frequency drift can be determined by the manufacture calibration of equipment.
MEMS oscillator also may be subject to the impact of temperature.Therefore, temperature sensor 217 can provide sensing temperature, and this sensing temperature is provided to frequency error computing circuit 219.The temperature effect with the frequency dependence of oscillator output signal can also be determined during manufacturing test.Plate carries heater or thermostat (oven) may be used for carrying out operating equipment with different temperature and determining how different temperature affects the frequency of oscillator output signal 207.Can serviceability temperature information in various manners.In one embodiment, frequency error computing circuit 219 provides index for the lookup table in NVM215 based on sensing temperature.Selected table entries provides the frequency error be associated with sensing temperature.Using this error as to change about the percentage such as at the determined initial frequency drift of specific predetermined temperature or absolute frequency changes and is stored in NVM215, or can store this error in any mode being suitable for identification error.In an embodiment, temperature-compensating is implemented as and represents the equation of temperature curve, and the one or more variablees be associated with specified temp can store in memory and for determining the compensation needed for specified temp.Therefore, this equation (such as, five rank compensated curves) can be used to determine frequency compensation based on temperature to temperature for frequency error.In such an embodiment, frequency error computing logic 219 using compensation curve determines frequency error, and provides this frequency error to the system of frequency of utilization reference signal.
Frequency error computing circuit 219 can be implemented as in separate hardware such as programme microcontroller or can with programming microcontroller and other combination of hardware realize.Initial frequency drift and temperature error can be merged by frequency error computing circuit 219, indicate the skew relative to target frequency with precentagewise, absolute frequency or any suitable mode, and provide this skew as error indicator 221.Such as, the initial frequency errors of MEMS oscillator can 10KHz slower in target frequency.Error in the temperature of current sensing can make MEMS oscillator slow 5KHz operation again.The pooled error of 15KHz can be provided as absolute frequency error information.Alternatively, control information can indicate that and reaches target frequency and require that the relative percentage of current oscillation output signal frequency increases or reduces.For some application, this relative percentage can have very meticulous granularity, such as, and 1,000,000,000 proportions by subtraction (ppb).
MEMS oscillator 201 and error determination circuit 210 can be placed on single integrated circuit 200.Integrated circuit 200 can comprise lead-out terminal 225 and 227, provides oscillator output signal 207 and frequency error information 221 by this lead-out terminal 225 and 227 to receiving equipment 230.
In an embodiment, control information 221 is provided as digital value.In an embodiment, the convergent-divergent of numeral can be factory program or can be selected by DLL (dynamic link library) 223.Therefore, for representing that the amount of bits of the resolution of frequency error can be optional.Selected amount of bits can depend on the ability of receiving system and the accuracy needed for receiving system.In addition, in various embodiments, the form carrying the signal of control information 221 can change.Such as, in one embodiment, the output format of control information 221 is 1 bit streams supplied from ∑ Delta modulator 301 to lead-out terminal 227, as shown in Figure 3A.Receiving equipment 230 (see Fig. 2) carries out average to obtain the frequency error information needed for frequency correction to digital stream.In another embodiment, by the such as I on one or more lead-out terminal 227
2 and so on standard serial interface or other serial line interfaces error signal is provided.In another embodiment, provide pulse width modulating signal by PWM logic 303, this pulse width modulating signal represents error signal and is supplied to lead-out terminal 227, as shown in Figure 3 B.In another embodiment, provide frequency error information with the form of analog voltage level, wherein, voltage level is corresponding with frequency error, as shown in FIG. 3 C.Therefore, the digital value from frequency error computing logic 219 is converted into analog signal and is supplied to lead-out terminal 227 in digital to analog converter 305.In another embodiment, parallel interface provides control information 221, and the lead-out terminal 227 in Fig. 2 represents multiple lead-out terminal.
Referring again to Fig. 2, received reference frequency (oscillator output signal) is adjusted to the clock signal of the expected frequency of the functional circuit 233 had in receiving system by receive frequency change-over circuit 231.Functional circuit 233 comprises the multiple time control circuits (clockedcircuit) being coupled to clock signal, such as, and bistable multivibrator (flip-flop).Freq converting circuit 231 utilize by receiving system with numeral or analog form receive control information and expected frequency frequency is adjusted to expected frequency value.But, not receive given frequency reference signal (such as, predetermined or target frequency is accurate to) with 200/1000000000ths, but receiving system receives the reference signal with variable frequency, this variable frequency may change 1 ~ 2% relative to initial frequency drift and may change due to temperature.Therefore, control information and expected frequency information must be merged to provide expected frequency by receiving system by rights.Such as, system 230 may need the clock signal 235 of faster than object reference clock frequency 117.3 times.Because reference frequency departs from target frequency, therefore multiplication factor 117.3 is adjusted up or down suitable amount to consider the error existed in the frequency of the reference clock signal received.Such as, control information can make the factor 117.3 adjust 1.23% up or down to consider the inaccuracy in reference clock frequency, and making to just look like frequency reference signal is equally carried out frequency inverted accurately.Therefore, receiving system is determined to change for the appropriate frequency of reference signal based on control information and expectation clock frequency.By using receiving system PLL and providing control information to receiving system, the frequency inverted PLL of receiving system can be used produce clock signal 235 accurately, and the frequency correction PLL found in prior art can be eliminated, thus save power, preventing noise and complexity.Although describe PLL in various embodiments herein, and can require to use other freq converting circuits according to the ability of receiving system.
In an embodiment, such as at place of factory when determining temperature compensation information and initial frequency drift, output format (serial, walk abreast, simulation etc.) is programmable.Can programme via control interface 223 pairs of output formats, and the control bit of programming can be stored in NVM to control output format subsequently.In an embodiment, control interface 223 is one or more input terminals, and the aspect able to programme of quiescent voltage value determination error signal on one or more lead-out terminal.Therefore, the attribute of error signal can be pin-programmable.Control interface can manufacture calibration or test period or utilize lead-out terminal 227 when equipment becomes more Iarge-scale system a part of after a while.
Fig. 4 shows for using fractional-N phase lock loop to produce a kind of scheme of the clock signal with expected frequency as the freq converting circuit 231 for generation of expected frequency.The frequency of the frequency using mark-NPLL to allow signal to produce has non-integer relationship with the reference frequency of supplying from oscillator 201.Arrange to frequency divider control circuit 403 supplied frequency that can comprise ∑ Delta modulator.Frequency divider control circuit produces the divider control 405 for frequency divider 407 based on expected frequency signal 404, with the frequency allowing PLL to produce system expectation.This divider control 405 is also incorporated with on one or more holding wire to the control information 221 (see Fig. 2) that receiving circuit 230 provides.This allows receiving system to consider the error of the reference signal produced due to temperature error and/or initial offset.In this way, without the need to repeating PLL.
Fig. 5 shows the reference clock comprising MEMS oscillator 201 and error logic 210 and produces circuit and the embodiment of receiving system on identical integrated circuit 500.Although do not use lead-out terminal 225 and 227 in the 5 embodiment of figure 5, control information can be provided by any one mode in mode as herein described (serially, PWM, simulation).The advantage with the single PLL for providing both error correction and frequency inverted based on expected frequency is still present in the system shown in Fig. 5.
The various methods utilizing the MEMS oscillator signal supplied together with frequency error information are described.The description of the invention set forth herein is illustrative, and is not intended to limit the scope of the present invention set forth in claims.When not departing from the scope of the present invention set forth in claims, based on the description of setting forth herein, embodiment disclosed herein can be carried out other and changes and amendment.
Claims (22)
1. a method, comprising:
Micro-electromechanical system (MEMS) oscillator is used to produce the oscillator output signal with first frequency;
Determine the error signal of the difference indicating described first frequency and preset frequency;
Described oscillator output signal and control information is supplied to receiving system;
Based on described control information and expected frequency information, determine the frequency inverted ratio of oscillator output signal described in described receiving system;
Based on described oscillator output signal and described frequency inverted ratio, clocking in the freq converting circuit in described receiving system; And
Described clock signal supplied by functional circuit to described receiving system.
2. method according to claim 1, also comprises: programme to one or more attributes of described error signal.
3. method according to claim 2, wherein, described one or more attribute comprises the zoom factor for described control information.
4. method according to claim 2, wherein, described one or more attribute comprises the output format of described control information.
5. method according to claim 2, wherein, described one or more attribute is programmable via communication interface.
6. method according to claim 1, also comprises: the one or more lead-out terminals to integrated circuit provide described control information.
7. method according to claim 6, also comprises: use described one or more lead-out terminal to carry out serial and provide described control information.
8. method according to claim 1, also comprises: provide the simulation of described control information to indicate, and wherein, described simulation instruction provides as voltage, and the voltage level of analog signal is corresponding with described control information.
9. method according to claim 1, wherein, described control information comprises the initial frequency drift of described oscillator output signal relative to described preset frequency.
10. method according to claim 1, also comprises:
In temperature sensor, determine temperature and the instruction to sensing temperature is provided;
Based on the instruction to sensing temperature, determine the frequency error of the described oscillator output signal caused by temperature; And
Described frequency error in described oscillator output signal caused by temperature is incorporated in described control information.
11. methods according to claim 10, also comprise: the described frequency error caused by temperature and initial frequency drift are merged in described control information.
12. methods according to claim 1, also produce MEMS oscillator output signal on the first integrated circuit and supply described MEMS oscillator output signal and described control information to the described freq converting circuit on the second integrated circuit.
13. 1 kinds of integrated circuits, comprising:
Micro-electromechanical system (MEMS) oscillator, for supplying the oscillator output signal with first frequency;
Error determination circuit, for providing the control information of the difference of the described first frequency of instruction and preset frequency;
One or more error output of described integrated circuit, are coupled to described error determination circuit to provide error signal; And
Reference signal lead-out terminal, for providing described oscillator output signal.
14. integrated circuits according to claim 13, wherein, one or more attributes of described error signal are programmable.
15. integrated circuits according to claim 14, wherein, described one or more attribute comprises the zoom factor for described control information.
16. integrated circuits according to claim 14, wherein, described one or more attribute comprises the output format of described control information.
17. integrated circuits according to claim 14, also comprise: one or more input terminal, and wherein, the quiescent voltage value on described one or more input terminal determines described one or more attribute of described control information.
18. integrated circuits according to claim 13, wherein, described one or more lead-out terminal comprises the serial line interface being coupled to described control information logic, to provide described control information by described serial line interface.
19. integrated circuits according to claim 13, wherein, described one or more lead-out terminal comprises the lead-out terminal being coupled to described error determination circuit and indicating to provide the simulation of described control information, and described simulation instruction is what to provide as the voltage level corresponding with described control information.
20. integrated circuits according to claim 13, wherein, described control information comprises the initial frequency drift of described oscillator output signal relative to described preset frequency.
21. integrated circuits according to claim 13, also comprise:
Temperature sensor, for providing the instruction to sensing temperature;
Nonvolatile memory, stores the information corresponding with initial frequency drift and the frequency error that causes due to temperature; And
Wherein, frequency determination logic is coupled to described temperature sensor and described nonvolatile memory, and is configured to provide described control information based on the frequency error caused by temperature and initial frequency drift.
22. 1 kinds of devices, comprising:
First integrated circuit, comprising:
Micro-electromechanical system (MEMS) oscillator, for supplying the oscillator output signal with first frequency;
Error determination circuit, for providing the error signal of the difference of the described first frequency of instruction and preset frequency; And
Multiple lead-out terminals of described integrated circuit, are coupled to described error determination circuit and described MEMS oscillator to provide described error signal and described oscillator output signal respectively;
Second integrated circuit, comprising:
Multiple input terminal, for receiving described error signal and described oscillator output signal respectively; And
Freq converting circuit, for being transformed into different frequency based on described error signal and expected frequency instruction by described oscillator output signal.
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Cited By (1)
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Application publication date: 20160302 |