TWI551036B - Method and circuit for detecting frequency deviation of oscillator - Google Patents

Description

Oscillation frequency offset detection method and oscillation frequency offset detection circuit

The invention relates to an oscillating circuit, in particular to an oscillating frequency offset detecting method and related circuits.

Please refer to FIG. 1. FIG. 1 is a graph showing an oscillation frequency and a corresponding temperature outputted by a crystal oscillator. When the temperature changes, the oscillation frequency output by the crystal oscillator is also offset. As shown in Fig. 1, the curve of the oscillation frequency and the corresponding temperature will exhibit an S-shape, i.e., an S-curve. This oscillating frequency shift can affect electronic devices, especially some systems or applications that require extremely stringent oscillator frequency offsets, such as the Global Positioning System (GPS).

A conventional compensation method uses a temperature compensated crystal oscillator (TCXO) to improve this problem. The principle of the temperature-compensated crystal oscillator is to pre-measure an S-curve of a crystal oscillator during production and store the S-curve in an additional wafer, and the wafer can calculate a inverse curve according to the S-curve. And generating a model of the inverse curve, and the inverse curve can completely cancel the S curve to compensate the original frequency offset of the crystal oscillator, but the cost of the temperature compensation crystal oscillator is much higher than a general crystal oscillator, and the The S-curve stored in the wafer is fixed, so as the number of uses and time increases, the S-curve of the crystal oscillator may change due to some factors, which may cause the wafer to be accurately compensated, that is, the conventional The temperature compensated crystal oscillator has a certain lifetime. Another conventional compensation method also requires pre-measuring the S-curve and then using an additional digital circuit to compensate for it. However, this approach requires a rather cumbersome control mechanism and also has a lifetime problem.

Therefore, there is a need for an innovative oscillating frequency offset detection mechanism that dynamically calculates the frequency offset of a crystal oscillator without pre-measuring the S-curve of the crystal oscillator, and then based on the resulting frequency offset. To compensate for the crystal oscillator.

An object of the present invention is to provide a method for detecting oscillation frequency offset and related circuits to solve the above problems.

An embodiment of the present invention discloses an oscillating frequency offset detecting method, including: receiving an oscillating signal having an oscillating frequency; generating a self-mixing signal according to the oscillating signal; and performing frequency division on the self-mixing signal to generate a Deactivating a self-mixing signal; determining a down-converting self-mixing frequency having a maximum energy in a specific frequency range of the down-converted self-mixing signal; and calculating the oscillation frequency based on the at least the oscillating frequency and the down-converting self-mixing frequency A frequency offset.

Another embodiment of the present invention discloses an oscillation frequency offset detecting circuit, comprising: a self-mixer, generating a self-mixing signal according to an received oscillation signal having an oscillation frequency; and a frequency dividing circuit, The self-mixing signal is frequency-divided to generate a down-converted self-mixing signal; and a control circuit is configured to determine a down-converting self-mixing frequency having a maximum energy in a specific frequency range of the down-converted self-mixing signal, at least according to the oscillation The frequency and the down-converted self-mixing frequency are used to calculate a frequency offset of the oscillation frequency.

With the above embodiments, the frequency offset of the crystal oscillator can be dynamically detected and compensated by a simple circuit to achieve the goals of accuracy, low cost, and long service life.

200‧‧‧Oscillating frequency offset detection circuit

201‧‧‧Digital Analog Converter

203, 305, 409‧‧‧ frequency mixer

205‧‧‧Self mixer

207‧‧‧ Frequency dividing circuit

209‧‧‧Gain Amplifier

210‧‧‧Control circuit

211‧‧‧ Analog Digital Converter

213‧‧‧ Frequency Calculator

215‧‧‧Operating circuit

216‧‧‧ crystal oscillator

217‧‧‧ frequency synthesizer

300‧‧‧Oscillation frequency offset compensation circuit

400, 601‧‧‧ signal transceiver circuit

401‧‧‧Power Amplifier

407‧‧‧Low noise amplifier

413‧‧‧Switching elements

600‧‧‧Electronic devices

602‧‧‧Antenna

603‧‧‧temperature sensor

605‧‧‧Transceiver controller

610‧‧‧ Signal Transceiver Module

611‧‧‧Storage device

Figure 1 is a graph of an oscillation frequency and a corresponding temperature output by a crystal oscillator.

2 is an architectural diagram of an exemplary embodiment of an oscillation frequency offset detecting circuit of the present invention.

3 is an architectural diagram of an exemplary embodiment of an oscillation frequency offset compensation circuit of the present invention.

FIG. 4 is a structural diagram of the oscillating frequency offset detecting circuit used in the signal transmitting and receiving circuit of the present invention.

FIG. 5 is a flow chart of an exemplary embodiment of an oscillation frequency offset detecting method of the present invention.

Fig. 6 is a view showing an electronic device using the signal transmitting and receiving circuit shown in Fig. 4.

Figure 7 is a flow chart of an exemplary embodiment of oscillation frequency offset compensation of the present invention.

Certain terms are used throughout the description and following claims to refer to particular elements. It should be understood by those of ordinary skill in the art that manufacturers may refer to the same elements by different nouns. The scope of this specification and the subsequent patent application do not use the difference of the names as the means for distinguishing the elements, but the difference in function of the elements as the criterion for distinguishing. The term "including" as used throughout the specification and subsequent claims is an open term and should be interpreted as "including but not limited to". In addition, the term "coupled" is used herein to include any direct and indirect electrical connection. Therefore, if a first device is coupled to a second device, it means that the first device can be directly electrically connected to the second device or indirectly electrically connected to the second device through other devices or connection means.

Please refer to FIG. 2, which is a block diagram of a first exemplary embodiment of an oscillation frequency offset detecting circuit according to the present invention. In the exemplary embodiment, the oscillating frequency offset detecting circuit 200 includes a digital-to-analog converter (DAC) 201, a frequency mixer 203, a self-mixer 205, and a a frequency divider 207, a gain amplifier 209, and a control circuit 210, wherein the control circuit 210 includes an analog-to-digital converter (ADC) 211, a frequency calculator 213, and An arithmetic circuit 215. The frequency mixer 203 is configured to mix an oscillation signal S _osc and an input signal S _in which an input frequency f _in is converted by the digital analog converter 201 to generate a mixed signal S _mix , wherein the oscillation signal S _osc has an oscillation frequency f _osc . Then, the mixed signal S _{mix is} transmitted to the self-mixer 205 (for example, using a coupling method), and the self-mixing device 205 self-mixes the mixed signal S _mix to generate a self-mixing signal S _sm , and then has a frequency dividing factor. The frequency dividing circuit 207 of N divides the self-mixing signal S _sm to generate a down- _converted self-mixing signal S _dcsm , and then _adjusts the amplitude of the down- _converted self-mixing signal S _dcsm to an appropriate range through a gain amplifier 209. In order to avoid the situation that the subsequent analog-to-digital converter 211 is underutilized or saturated, and outputting a gain amplification signal S _ga and sampling from the analog-to-digital converter 211 from an analog domain. Enters a digital domain and finally outputs an analog-to-digital converter signal _Sadc . Then, the frequency calculator 213 is used to calculate the analog-to-digital converter signal _Sadc to obtain a down- _converted self-mixing frequency f _dcsm having the maximum energy in a specific frequency range, and then at least according to the frequency reduction self-mixing via the operation circuit 215. The frequency f _dcsm , the frequency dividing factor N, and the oscillation frequency f _{osc are} used to find a frequency offset f _s . Wherein, the Fourier transform (Fourier transformer) can be used to calculate the analog-to-digital converter signal _Sadc to obtain a down- _converted self-mixing frequency f _dcsm having the maximum energy in a specific frequency range; or can be preset the frequency for a plurality of correlation patterns (pattern correlation) operation and the analog to digital converter signal S _adc, to calculate the specific frequency within the range having the maximum energy of the frequency down mixing frequencies from _f dcsm. It should be noted, however, that the present invention is not limited to the use of a particular method to calculate the down- _converted self-mixing frequency f _dcsm having the greatest energy in that particular frequency range. In fact, any other different approach that can achieve the dominant frequency should be The scope of the invention, for example, using a modified Fourier transform or using other computational methods similar to the type correlation operation. In this exemplary embodiment, a crystal oscillator 216 outputs a crystal oscillator having a frequency f _crystal of a crystal oscillator signal S _crystal, and after a frequency synthesizer (frequency synthesizer) 217 to the crystal oscillator frequency f _crystal Multiplying to the oscillating frequency f _osc , that is, outputting the oscillation signal S _osc , in other words, a frequency offset generated by the crystal oscillator signal S _crystal is also multiplied by the frequency synthesizer 217 to become a frequency doubling frequency offset, Note that the frequency offset f _s discussed and calculated in this embodiment refers to the frequency doubling frequency offset.

The operation of the input signal S _in and the oscillation signal S _osc mixed by the frequency mixer 203 to generate the mixed signal S _mix can be expressed by the following formula: S _in =cos(2 πf _in t )

S _osc =cos(2 πf _osc t )

S _mix =cos(2 πf _in t )*cos[2 π ( f _osc ) t ]

When the frequency offset f _{s is added} to the oscillation signal S _osc , the operation of mixing the frequency mixer 201 to generate the mixed signal S _mix can be expressed by the following program:

The operation of mixing the mixed signal S _mix by the mixer 205 to generate the self-mixing signal S _sm can be expressed by the following formula: let a = c = cos[2 π ( f _in - f _osc - f _s ) t ]

b = d =cos[2 π ( f _in + f _osc + f _s ) t ]

then

among them

Ad + bc =cos[2 π *2(2 f _osc +2 f _s ) t ]+cos(2 π *2 f _in t )

Therefore, according to the derivation of the above relationship, the self-mixing signal S _sm generates five frequency components, that is, a first frequency, a second frequency, a third frequency, a fourth frequency, and a fifth frequency, wherein the first A frequency is a DC component, the second frequency is 2*f _in , that is, twice the input frequency f _in , the third frequency is 2*f _osc +2*f _s -2*f _in , and the fourth frequency is 2 *f _osc +2*f _s , the fifth frequency is 2*f _osc +2*f _s +2*f _in , and among the five frequency components, the third, fourth, and fifth frequencies have a frequency The information of the offset f _s , that is, can be used as information for calculating the frequency offset f _s .

Since the present exemplary embodiment wants to perform frequency domain and time domain conversion using the convenience of digital signal processing to detect or even compensate the frequency offset fs, the self-mixing signal Ssm is required. First converted to the digital definition domain, however, since the output oscillation signal Sosc is frequency multiplexed by the frequency synthesizer 217 to the oscillation frequency fosc, the oscillation frequency fosc is at a very high frequency, and with the current technology The analog digital converter of the specific number of bits that need to be sampled at such a high frequency in this embodiment cannot be produced in practice, so the self-mixing signal Ssm must first pass through the frequency dividing circuit 207 to remove the frequency factor N. Performing a frequency reduction process to reduce the frequency of the mixed signal Ssm to a reasonable frequency range, that is, all five frequency components of the mixed signal Ssm are down-converted by the frequency dividing factor N, and then proceed Gain amplification and analog digital conversion processing, followed by the analog digital converter signal Sade. It should be noted that any method for calculating, detecting, or compensating for frequency offset using the above equations or algorithms of the present invention, regardless of the digital or analog circuit architecture, is within the scope of the present invention, and does not limit the final need. The multi-leaf conversion is accomplished by digital signal processing. After entering the digit definition field, we can simply use a frequency calculator to calculate any of the third, fourth, and fifth frequencies after the down-conversion, and then calculate the frequency offset by the operation circuit 215. The amount of shift fs.

In this embodiment, the fourth frequency after down-conversion can be used as the target, that is, (2/N)*(f _osc +f _s ), since the frequency offset f _s is usually small, we are The fourth frequency (2/N)*(f _osc +f _s ) after frequency reduction must be found in a specific range around the known (2/N)*f _osc , and the specific range does not need to be too Big. In other words, in this particular range, the frequency with the largest energy is the fourth frequency after the frequency reduction. After obtaining the fourth frequency (2/N)*(f _osc +f _s ) after down- _conversion , the operation circuit 215 is used to perform a simple operation on the fourth frequency after the down-conversion (here, multiplying N) After dividing by 2 and subtracting f _osc ), the frequency offset f _{s is obtained} . It should be noted that the order of operations is different from the above-described examples, but simple changes that can achieve the same object are included in the scope of the present invention.

In another embodiment, the third frequency after down-conversion can be used as the target, that is, (2/N)*(f _osc +f _s -f _in ), similarly, we are known (2 /N)*(f _osc -f _in ) around the specific range, the third frequency (2/N)*(f _osc +f _s -f _in ) after the down-conversion can be found, and the specific The range does not need to be too large. In other words, in this particular range, the frequency with the largest energy is the third frequency after the frequency reduction. After obtaining the third frequency (2/N)*(f _osc +f _s -f _in ) after down- _conversion , the operation circuit 215 is used to perform a simple operation on the third frequency after down-conversion (here) To multiply N by 2, and subtract f _osc and add f _in ), the frequency offset f _s can be obtained. What is different from the above embodiment is that a frequency component of f _in is added, and the advantage is that F _in is known and can be arbitrarily changed, so in practical applications, this embodiment has more flexibility in band selection, such as having a large amount of noise in a certain frequency band, and the band range is just right. If the frequency bands to be calculated overlap, then f _in can be used to avoid such noise. It should be noted that if only the fourth frequency is detected without using the third and fifth frequencies, it is not affected by the input frequency f _in . In this case, the embodiment shown in FIG. 2 does not require the input signal S _in , and the frequency offset f _s can be obtained only by self-mixing with the signal having the oscillation frequency S _osc , in other words, the frequency mixer 203 can be omitted in this case, and this design change is also within the scope of the present invention.

Please refer to FIG. 3, which is a block diagram of an exemplary embodiment of an oscillation frequency offset compensation circuit of the present invention. Operation of the oscillation frequency offset compensation circuit 300 is to be compensated down from the mixed signal _S dcsm converted to analog to digital converter signal S _adc the digital domain in the form of ^e jωt of (where ω = 2 * π * ( ±f _s ), and f _s is the aforementioned frequency offset), which is input to a frequency mixer 305 located on the normal signal receiving path, thereby compensating for the analog digital converter signal S _adc . Please note that the above-mentioned oscillation frequency offset compensation operation is merely illustrative and not a limitation of the present invention. In fact, any frequency offset obtained based on the oscillation frequency offset detection mechanism shown in FIG. 2 is performed. The oscillation frequency offset compensation operation is within the scope of the present invention.

Please refer to FIG. 4, which is a block diagram of an exemplary embodiment of an oscillating frequency offset detecting circuit used in a signal transceiving circuit according to the present invention. As shown in FIG. 4, a portion of the circuit components of the oscillating frequency offset detecting circuit 200 are shown in FIG. 4 to reveal the technical features shared by the components without affecting the disclosure of the present technology. As shown, the power amplifier 401, the frequency mixer 203, and the digital analog converter 201 in the signal transceiver circuit 400 constitute a signal transmission path, and the low noise amplifier 407, the frequency mixer 409, and the analogy in the signal transceiver circuit 400. The digital converter 211 forms a signal receiving path. In addition, the signal transceiving circuit 400 further includes a frequency mixer 205, a switching element 413, a frequency calculator 213, and a frequency mixer 307 (which can also be regarded as a compensation unit). In a frequency offset detection mode, the switching element 413 couples the signal receiving path to the frequency calculator 213, so that the frequency mixers 203, 205 and the frequency calculator 213 form a picture as shown in FIG. The oscillation frequency offset detecting circuit can detect the oscillation frequency offset of the oscillation frequency S _osc . For example, the frequency offset detected at different temperatures can be stored in a storage device (for example, In non-volatile memory, in other words, a look-up table of temperature and corresponding frequency offset can be established in the non-volatile memory so that it can be compensated directly by comparing the lookup table. The frequency offset does not require repeated calculation of the frequency offset. For example, when the crystal oscillator 216 is again operated on the previously detected temperature, the control circuit 210 directly uses the stored frequency offset corresponding to the temperature. Move without having to perform additional signal processing and numerical calculations. However, it should be noted that the above examples are for illustrative purposes only, and any simple changes that achieve the same objectives described above are intended to be included within the scope of the present invention.

In addition, in a normal signal transmission and reception mode, the signal transmission path is used to transmit a transmission signal S _tx , and the signal reception path is used to receive a reception signal S _rx , and the switching element 413 couples the signal reception path to the frequency. The mixer 305 compensates when the temperature changes to cause the oscillation frequency to shift.

5 is a flow chart of a first exemplary embodiment of the method for detecting an oscillation frequency offset according to the present invention. If the same result is substantially achieved, it is not necessarily required to follow the sequence of steps in the flow shown in FIG. The steps shown in Figure 5 do not have to be performed continuously, that is, other steps can be inserted therein. Moreover, some of the steps in Figure 5 may be omitted in accordance with different embodiments or design requirements. The oscillating frequency offset detecting method 500 includes the following steps: Step 501: Receive an input signal having an input frequency; Step 503: Receive an oscillating signal having an oscillating frequency; Step 505: Receive the oscillating signal and the input signal Mixing to generate a mixed signal; Step 507: self-mixing the mixed signal to generate the self-mixing signal; Step 509: De-frequencying the self-mixing signal to generate a down-converted self-mixing signal; Step 511: Finding The down-converted self-mixing frequency having the maximum energy in a specific frequency range of the self-mixing signal; step 513: calculating the frequency offset according to the oscillating frequency, the input frequency, and the down-converted self-mixing frequency.

Since the flow of the oscillation frequency offset detecting method shown in FIG. 5 can be easily understood by referring to the above description of the oscillation frequency offset detecting circuit 200, the description thereof will be omitted here for brevity. It should be noted that, as mentioned above, the input signal S _in may not be used in a design change, in which case steps 501, 505 may be omitted, and step 513 may be modified to: according to the oscillation frequency and the drop The frequency is self-mixed to calculate the frequency offset.

Fig. 6 is a view showing an electronic device using the signal transmitting and receiving circuit shown in Fig. 4. As shown in FIG. 6, the electronic device 600 includes a signal transceiver circuit 601 and an antenna 602. The signal transceiver circuit 601 includes a signal transceiver module 610, a storage device 611, and the foregoing crystal oscillator 216 and control circuit 210. . The signal transmitting and receiving circuit 601 includes the circuit structures shown in FIG. 4 and FIG. 2 (that is, the signal transmitting and receiving circuit 601 has the capability of detecting and compensating the oscillation frequency offset in addition to the original signal transmitting and receiving function), and another A temperature sensor 603 and a transceiver controller 605 are included. The signal transceiver circuit 601 can detect the oscillation frequency offset of the crystal oscillator 216 in a detection mode, and can compensate for signal transmission and/or oscillation frequency offset in a normal mode. In this embodiment, the temperature sensor 603 can detect a temperature T of the crystal oscillator 216 and transmit it to the control circuit 210 through the transceiver controller 605 (eg, to the arithmetic circuit 210 in the control circuit 210). Next, the control circuit 210 stores the correspondence between the obtained oscillation frequency offset fs and the temperature T sensed by the temperature sensor 603 to a storage device (for example, non-volatile memory) 611. After the storage device 611 stores the corresponding relationship between the frequency offset f _s and the temperature T, the control circuit 210 can directly read the corresponding frequency offset from the storage device 611 according to the temperature T, and via the aforementioned frequency. The mixer 305 performs frequency offset compensation.

Figure 7 is a flow chart of an exemplary embodiment of an oscillation frequency offset compensation method of the present invention. If the same result can be substantially achieved, it does not necessarily need to be performed in the order of steps in the flow shown in FIG. 7, and the steps shown in FIG. 7 do not have to be performed continuously, that is, other steps can be inserted therein. . Moreover, some of the steps in Figure 7 may be omitted in accordance with different embodiments or design requirements. The oscillating frequency offset compensation method 700 can be performed by the electronic device 600 shown in FIG. 6 and includes the following steps: Step 703: Detecting the temperature of the crystal oscillator; Step 705: Determining the frequency offset at the current temperature T Is it known? If yes, go to step 711, if no, go to step 707; step 707: detect the oscillation frequency offset under temperature T; step 709: store the temperature T and the corresponding oscillation frequency offset f _s correspondence; 711: Compensating for the oscillation frequency offset in the digital definition domain.

Please note that the present invention can also detect the temperature T and the corresponding oscillation frequency offset in real time, and then directly enter step 711 to perform compensation without storing, that is, in another embodiment of the present invention, step 709 Can be omitted.

The oscillation frequency offset detecting circuit of the present invention is not limited to detecting the oscillation frequency offset caused by the temperature T, but it can detect the frequency offset caused by any factor, for example, the crystal oscillator itself. Aging or process drift that occurs when a crystal oscillator is manufactured. The frequency offset detection and compensation mechanism disclosed by the present invention can dynamically detect and compensate the frequency offset of the crystal oscillator through a simple circuit, or directly compare the previously recorded lookup table to obtain a corresponding The compensation value below the temperature is such that the goal of precision, low cost and long service life is achieved.

In addition, in the embodiment of the present invention, the circuits may have various implementation manners. For example, the control circuit 211 may use a hardware description language (Verilog or VHDL) to complete the entire circuit or use a central control circuit (CPU). Software, or a micro-controller (controller) with firmware, can directly complete the above operations, flowcharts and other operations. Those skilled in the art should be able to easily derive other changes. For example, if the mixed signal is self-mixed twice, another self-mixing frequency can be found in the vicinity of other times of oscillation frequency, and then corresponding The present invention can still be implemented by the operation; for example, the self-mixing object is changed from the mixed signal to the input signal, and the corresponding operation can be performed to easily complete the present invention.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

200‧‧‧Oscillating frequency offset detection circuit

201‧‧‧Digital Analog Converter

203‧‧‧ frequency mixer

205‧‧‧Self mixer

207‧‧‧ Frequency dividing circuit

209‧‧‧Gain Amplifier

210‧‧‧Control circuit

211‧‧‧ Analog Digital Converter

213‧‧‧ Frequency Calculator

215‧‧‧Operating circuit

216‧‧‧ crystal oscillator

217‧‧‧ frequency synthesizer

Claims (18)

An oscillating frequency offset detecting method includes: receiving an oscillating signal having an oscillating frequency; generating a self-mixing signal according to the oscillating signal; and performing frequency division on the self-mixing signal to generate a down-converted self-mixing signal; And a frequency-down self-mixing frequency having a maximum energy in a specific frequency range of the down-converted self-mixing signal; and calculating a frequency offset of the oscillation frequency based on at least the oscillating frequency and the down-converting self-mixing frequency. The method for detecting an oscillating frequency offset according to claim 1, further comprising: receiving an input signal having an input frequency; wherein the step of generating the self-mixing signal according to the oscillating signal comprises: omitting the oscillating signal And the input signal is mixed to generate a mixed signal, and the mixed signal is self-mixed to generate the self-mixing signal; and the step of calculating the frequency offset comprises: according to the oscillation frequency, the input frequency, and the frequency reduction The frequency offset is calculated from the mixing frequency. The oscillating frequency offset detecting method according to claim 1, wherein the oscillating signal is generated by a crystal oscillator, and the oscillating frequency offset detecting method further comprises: detecting the crystal oscillator a temperature; and storing the frequency offset and corresponding to the temperature. The method for detecting an oscillating frequency offset as described in claim 3, further comprising: directly using the stored frequency offset when the crystal oscillator is again operated at the temperature the amount. The oscillating frequency offset detecting method of claim 1, wherein the step of determining the down-converted self-mixing frequency having the maximum energy in the specific frequency range of the down-converted self-mixing signal comprises: causing the falling The frequency self-mixing signal enters a digit field; and the down-converted self-mixing frequency having the maximum energy of the down-converted self-mixing signal in a specific frequency range is calculated. The method for detecting an oscillating frequency offset according to claim 5, wherein the step of calculating the down-converted self-mixing frequency of the down-converted self-mixing signal having the maximum energy comprises: performing the down-converted self-mixing signal The Fourier transform is used to calculate the down-converted self-mixing frequency with the largest energy in a particular frequency range. The method for detecting an oscillating frequency offset according to claim 5, wherein the step of calculating the down-converted self-mixing frequency of the down-converted self-mixing signal having the maximum energy further comprises: performing the down-converted self-mixing signal A type correlation operation calculates the down-converted self-mixing frequency having the largest energy in a particular frequency range. The oscillating frequency offset detecting method of claim 1, wherein the down-converted self-mixing signal is generated by dividing the self-mixing signal by a dividing factor; and calculating the oscillating frequency The step of frequency offset includes multiplying the down-converted self-mixing frequency by the dividing factor and dividing by 2, and comparing the oscillation frequency to obtain the frequency offset. The method for detecting an oscillation frequency offset according to claim 1, wherein the specific frequency is The enclosure is located in a fixed range around 2 times the oscillation frequency. An oscillating frequency offset detecting circuit includes: a self-mixer for generating a self-mixing signal according to an received oscillating signal having an oscillating frequency; and a frequency dividing circuit for performing the self-mixing signal Decoupling to generate a down-converted self-mixing signal; and a control circuit for determining a down-converted self-mixing frequency having a maximum energy in a specific frequency range of the down-converted self-mixing signal, and based at least on the oscillation frequency and The down-converting self-mixing frequency calculates a frequency offset of the oscillating frequency. The oscillating frequency offset detecting circuit of claim 10, further comprising: a frequency mixer for mixing the oscillating signal and the received input signal having an input frequency to generate a mixed signal Wherein the self-mixer self-mixes the mixed signal to generate the self-mixing signal; and the control circuit further calculates the frequency offset according to the oscillation frequency, the input frequency, and the down-converted self-mixing frequency. The oscillating frequency offset detecting circuit according to claim 10, further comprising: a temperature detector for detecting a temperature of the crystal oscillator; and a storage device for storing the frequency offset The amount corresponds to the temperature. The oscillating frequency offset detecting circuit of claim 12, wherein the control circuit directly uses the stored frequency offset when the crystal oscillator is again operated at the temperature. The oscillating frequency offset detecting circuit of claim 10, wherein the control circuit comprises: an analog-to-digital converter for causing the down-converted self-mixing signal to enter a digit field; and a frequency calculator, The down-converted self-mixing frequency having the maximum energy for calculating the down-converted self-mixing signal. The oscillating frequency offset detecting circuit according to claim 14, wherein the frequency calculator performs a Fourier transform on the down-converted self-mixing signal to calculate the down-converted maximum energy in a specific frequency range. Mixed frequency. The oscillating frequency offset detecting circuit according to claim 14, wherein the frequency calculator performs a pattern correlation operation on the down-converted self-mixing signal to calculate a maximum in a specific frequency range. This frequency of energy is self-mixing frequency. The oscillating frequency offset detecting circuit of claim 10, wherein the down-converted self-mixing signal is generated by dividing the self-mixing signal by the frequency dividing circuit having a frequency dividing factor; and The control circuit includes: an arithmetic circuit for multiplying the down-converted self-mixing frequency by the dividing factor and dividing by 2, and comparing the oscillation frequency to obtain the frequency offset. The oscillating frequency offset detecting circuit according to claim 10, wherein the specific frequency range is located in a frequency range around 2 times the oscillating frequency.