Generator and method for generating controlled frequency

Abstract

To provide a frequency generator for generating a controlled frequency, an improving method therefor, a program, and a frequency generator system.SOLUTION: A frequency generator 300 comprises frequency ratio generators 100, 101, 102, a comparator 310, and a controlled oscillator 330 and has, as input, a controlled frequency 331. The controlled frequency is a generated frequency and thus effectively output of the frequency generator. The frequency ratio generators provide a frequency ratio signal 312. The frequency ratio generators comprise a resonator, determine a ratio between the controlled frequency and a resonance frequency of the resonator, and determine a ratio between two resonance frequencies of the resonator. At least one of the resonance frequencies is an overtone frequency. The comparator has, as input, the frequency ratio signal and a target ratio 311; compares the frequency ratio signal to a target ratio; and provides, as output, a comparison signal 315, which is the result of this comparison.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention

[0001] [Field of the Invention] The present invention relates to the field of generators and methods for generating a controlled frequency that is highly stable.

[0002] [Background of the Invention] Generating a signal having a controlled frequency can be a useful electronic component in a variety of electronic circuits with a wide variety of functionality.

[0003] A known circuit for generating a frequency is known from WO2013 / 066161A1, specifically FIG. 2.

[0004] WO2013 / 066161A1 includes a first oscillator for supplying a first oscillation signal, a second oscillator for supplying a second oscillation signal, a first controller for delivering a first control signal as a function of the phase difference between a first controller input and a second controller input of the first controller, a second controller for delivering a second control signal as a function of the phase difference between a first controller input and a second controller input of the second controller, a resonator, at least one second resonance frequency with a first phase shift that depends on the difference between the frequency of the second excitation signal and the second resonance frequency, and processing means for receiving the first oscillator signal and the second oscillator signal, determining their mutual ratio, looking up a frequency compensation factor in a pre-stored table, and outputting a compensated oscillation signal. An electronic oscillator circuit is disclosed.

[0005] In FIG. 2 of WO2013 / 066161A1, the divider setting of the feedback divider determines the ratio between the resonator frequency and the frequency output.

[0006] The disadvantage of the circuit in FIG. 2 of WO2013 / 066161A1 is that the frequency is not controllable. Further, the disadvantage is that the circuit has only one feedback loop. Having only one feedback loop means that all noise sources in that loop contribute to the phase noise of the output frequency. Therefore, the loop filter in this circuit must be a trade-off between a high bandwidth to track changes in the loop and a low bandwidth to attenuate all noise sources in the loop.

[0007] U.S. Patent Application Publication No. 2014 / 152354 (A1) discloses a method of adjusting the frequency of a generated signal to form an output signal, including forming the generated signal in a signal generator, comparing a feedback signal with a reference signal to generate a control signal in response to the comparison, where the feedback signal is generated using the output signal, generating the output signal by performing a frequency division operation according to the generated signal and a division factor, where the division factor is specified according to the control signal. The disadvantage of U.S. Patent Application Publication No. 2014 / 152354 (A1) is that the output signal may have phase noise, thereby making this method unsuitable for the requirements.

[0008] [Summary of the Invention] An object of the present invention is to overcome one or more of the disadvantages described above.

[0009] According to a first aspect of the present invention, there is provided a frequency generator for generating a controlled signal having a controlled frequency, - comprising a frequency ratio generator adjusted to generate a frequency ratio, the frequency ratio generator having - an input configured to receive a controlled signal, - A first control frequency divider (110) adjusted to generate a first divided signal (115) having a first divided frequency that is a controlled frequency substantially divided by a first frequency ratio signal. - A converter adjusted to generate an excitation signal (129) having the first divided frequency based on the first divided signal, the excitation signal being provided to a resonator for excitation of the resonator. - A connector for connecting to a resonator adjusted to generate a resonance signal having a first resonance frequency, the resonator being excited based on a controlled signal. - An output configured to provide a frequency ratio signal based on a first frequency ratio signal indicating a frequency ratio between the controlled frequency and the first resonance frequency. The frequency generator further includes - A comparator adjusted to generate a comparison signal based on a comparison of the frequency ratio with a target ratio. - A controlled oscillator circuit adjusted to generate a controlled signal having a controlled frequency based on the comparison signal.

[0010] The frequency ratio generator outputs a frequency ratio signal. The frequency ratio signal indicates the frequency ratio between the controlled frequency and the first resonance frequency. The resonator provides a relatively stable or fixed resonance frequency, which cannot be controlled over a wide range of frequencies. On the other hand, the controlled oscillator can provide such a wide range of frequencies or cannot be controlled at all. The frequency ratio can be set at a controlled ratio using the target ratio according to the present invention. Thus, the present invention provides the advantage of a controlled signal having a controllable frequency over a wide frequency range.

[0011] The target ratio can be set to any positive rational number. As an example, forward error correction in telecommunications requires additional bits to be inserted or extracted from the bit stream. Both bit streams have separate frequencies and thus typically their own clock signals. These clock signals are typically non-integer multiples of each other. This frequency generator advantageously enables the generation of a non-integer ratio between the controlled frequency and the resonant frequency.

[0012] The comparator handles signals at relatively low frequencies. These signals are in a relatively small band above DC. Thus, the comparator can be implemented in a DSP or CPU, providing the advantage that additional functions can be easily implemented without direct hardware impact. Thus, this frequency generator has the advantage of being highly adaptable to new or additional functionality.

[0013] For a detailed description of the frequency generator used as an element in the present invention, reference is made to the text filed as patent application NL2022646. This text is incorporated herein by reference in its entirety. Specifically refer to the embodiments in this text incorporating a resonator. Also specifically refer to the definitions and ranges applicable to the present invention.

[0014] The controlled signal is typically a low-phase noise signal in a frequency range of 8 kHz to 24 MHz, preferably 10 kHz to 22 MHz, more preferably 12 kHz to 20 MHz, and most preferably 14 kHz to 18 MHz, and in a range of less than 500 fs, preferably 200 fs, more preferably 100 fs, and most preferably 80 fs.

[0015] In one embodiment of the present invention, the frequency generator - includes an outer loop filter adjusted to generate a filtered comparison signal based on a comparison signal, The controlled frequency is based on the filtered comparison signal, A frequency ratio generator, a comparator, a comparison signal, an outer loop filter, a filtered comparison signal, a controlled oscillator, and a controlled signal form an outer loop, The outer loop filter filters the comparison signal, thereby preventing instability of the outer loop.

[0016] Loop instability can be detected from the unstable controlled frequency of the controlled signal. Typically, the frequency ratio generator has an inner loop, and the inner loop is a low-pass filter with a cut-off frequency. The outer loop filter is typically also a low-pass filter. Further, the cut-off frequency of the outer loop is selected low enough that the maximum amount of noise is removed, enabling the controlled oscillator to generate a controlled signal with a minimum amount of phase noise. On the other hand, the cut-off frequency should be selected high enough that changes in the outer loop due to, for example, temperature variations or hysteresis can be tracked, thereby keeping the controlled frequency stable. Additionally, the cut-off frequency should be selected high enough that start-up delay is minimized. Both loop filters typically also have an integrating behavior following a proportional behavior. The integrating behavior in a static or stable mode causes the loop of which the loop filter forms a part to exhibit no residual error, and advantageously, the accuracy of achieving the target ratio is increased.

[0017] In one embodiment of the present invention, the comparator includes a subtractor adjusted to provide a comparison signal based on subtracting a target ratio from a frequency ratio, and / or The comparator includes a divider adjusted to provide a comparison signal based on dividing a frequency ratio by a target ratio.

[0018] The subtractor may include an adder with a signal inverter on one input. The divider may include a multiplier with a reciprocal value supplied to one of its inputs. The measured ratio is typically compared to a target ratio. The target ratio can be predefined, set, or continuously changed by another feedback loop. The target ratio can be changed temporarily, continuously, or permanently, for example, to match the phase of a controlled frequency to the phase of a resonator's resonance signal.

[0019] As the frequency ratio is controlled, the frequency ratio will typically substantially reach or at least approach the target ratio during stable operation. Thus, it can be stated as follows. t = target ratio r = frequency ratio

[0020]

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[0021] The aforementioned conditions are typically met during stable operation, and the frequency ratio is normalized with respect to the target ratio. Thus, for stable operation, the subtractor and divider with an offset of -1 can be considered identical. The frequency ratio generator, and thus also the behavior of the frequency generator, can be different during startup or power-on, and especially while compensating for larger disturbances in the frequency generator, particularly in separate loops.

[0022] In one embodiment of the present invention, the frequency ratio generator is - a first controlled frequency divider adjusted to generate a first divided signal having a first divided frequency that is a controlled frequency substantially divided by a first frequency ratio signal, - A converter adjusted to generate an excitation signal having a first divided frequency based on a first divided signal, the excitation signal being provided to a resonator for excitation of the resonator, the converter, - A first frequency phase detector adjusted to generate a first phase difference signal based on a first frequency phase difference between the first divided frequency and a first resonance frequency, and a first inner loop filter adjusted to generate a first frequency ratio signal, wherein a first frequency ratio generator loop is formed by the first control frequency divider, the first divided signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter, and the first frequency ratio signal, and a second frequency ratio generator loop is formed by the first control frequency divider, the first divided signal, the converter, the excitation signal, the resonator, the resonance signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter, and the first frequency ratio signal, The first inner loop filter filters the first phase difference signal, thereby preventing instability of the frequency ratio generator loop.

[0023] The control frequency divider, such as the first control frequency divider, can be a digital control frequency divider. The control frequency divider can be a control multi-frequency divider or a control fractional frequency divider. The frequency phase detector, such as the first frequency phase detector, can be a frequency mixer, an analog multiplier, a digital circuit, or a logic circuit configured as a phase detector. Alternatively, the frequency phase detector can be a digital mixer, such as an XOR port mixer.

[0024] A control frequency divider divides the frequency of a first input signal in response to a control signal, such as a first control signal. Typically, the control signal is a stabilized signal with low jitter to prevent the introduction of significant additional jitter in the control frequency divider. The control signal may include an offset. The divided signal, such as the first divided signal, typically includes jitter or noise introduced by the control frequency divider as a dominant noise source.

[0025] A frequency phase detector that detects the phase between the frequency of the divided signal and the frequency of a second input signal, such as a resonance signal, typically also introduces noise. Thus, the value (such as height) of the phase difference signal is typically dominated by the phase difference and typically further includes noise introduced by the control frequency divider and the frequency phase detector.

[0026] A loop filter, such as a first loop filter, filters the phase difference signal. The output signal of the loop filter is the control signal, which indicates a frequency ratio. The loop filter is typically a low-pass filter. The cut-off frequency of the loop filter is selected based on two limitations. If the cut-off frequency is selected too low, the loop will respond too slowly to disturbances in the loop, causing loop instability. If the cut-off frequency is selected too high, the loop will not sufficiently remove the noise in the phase difference signal, which may also cause loop instability. Loop instability can be detected from an unstable control signal. An unstable control signal may have a signal value that swings from one end of the range to the other end of the range, or may stagnate at one of the two ends. The cut-off frequency is typically selected low enough to still allow the control signal to adapt sufficiently quickly to any disturbances introduced in the loop while removing the maximum amount of noise from the phase difference signal.

[0027] The frequency ratio generator provides the advantage of a very stable frequency ratio measurement value. The frequency ratio generator according to the present invention has a feedback loop with an integration effect. The integration effect provides the advantage of removing low-frequency noise related to phase at 20 dB / decade. This effect in the frequency domain causes a 40 dB / decade removal, while known systems only have a 20 dB / decade removal.

[0028] Furthermore, in the frequency ratio generator, the temperature behavior of filtering components such as loop filters is approximately replaced by DC, and as a result, the effective bandwidth only changes slightly due to small deviations, while the actual center frequency does not change. In comparison, what is known in the art is a loop filter, and known loops hold a specific frequency, so these known loop filters are band-pass filters. When the components of a known loop filter change in value, for example, under the influence of temperature or aging deterioration, the center frequency of the known loop filter will change. Therefore, the circuit according to the present invention provides the advantage of increased temperature stability.

[0029] This frequency ratio generator has a resonator that provides a resonance signal, and provides an excitation signal to the resonator based on the divided signal. As will be described in more detail later, this circuit provides the advantage of not having to comply with the Barkhausen criterion. Not complying with this Barkhausen criterion has the effect of reducing phase noise.

[0030] Prior art loops that comply with the Barkhausen criterion can be likened to AM signal transmission. The present invention, which does not comply with the Barkhausen criterion, can be likened to FM signal transmission. FM signals are known to be less prone to interference. One such interference in the present invention can be small adjacent resonance frequencies. These small adjacent resonance frequencies can even cross, for example, under the influence of temperature changes. In particular in these cases, the fact that it is not necessary to comply with the Barkhausen criterion provides the advantage of a significant removal of the noise generated by the small adjacent resonance frequencies.

[0031] Generating a specific frequency with low phase noise requires a significant amount of power. The advantage provided by this frequency generator is that two independent frequencies, namely the controlled frequency and the resonance frequency, are loosely coupled via the frequency ratio, and both have low phase noise without doubling the power, while on the other hand, with much less power consumed by the circuit.

[0032] In one embodiment of the present invention, the phase difference signal has a magnitude based on the frequency phase difference, such as amplitude or value, and / or the control signal has a magnitude indicating the frequency ratio, such as amplitude or value. When the phase or control signal is an analog signal, the signal information is typically, advantageously, contained in the amplitude of the signal. When the phase or control signal is a digital signal, the signal information is typically, advantageously, contained in the digital value of the signal. The digital value can be a binary code, BCD code, Gray code, or a combination of these codes, or any other code having a defined value system.

[0033] ​In one embodiment of the present invention, the loop filter is a low-pass filter, and the low-pass filter preferably has a cut-off frequency that is advantageously below the frequency noise introduced by the control frequency divider and preferably above the ratio of the changes in the first and second frequencies. Further, the cut-off frequency should be advantageously selected such that the control signal is within a specified range and the circuit remains stable under varying conditions that cause disturbances in the circuit. The specified range is typically specified by the user. The specified range can also be determined based on the noise introduced by other functions in the circuit, such as the control frequency divider and the frequency phase detector. The specified range can also be affected by the variations in the first input signal and the second input signal.

[0034] In one embodiment of the present invention, the control frequency divider is a control fractional frequency divider. The phase difference between the divided signal and the second input signal can be caused by a static phase difference and / or a frequency difference and the elapsed time. In this embodiment, the use of the control fractional frequency divider advantageously enables improved frequency matching between the frequency of the divided signal and the second frequency. This is because the first frequency is divided with a higher granularity. Further, since the granularity is higher, the first frequency can advantageously be selected lower. The use of high frequencies has disadvantages such as crosstalk and increased energy loss.

[0035] The resonator may be a crystal resonator, and preferably, the resonance frequency is the overtone resonance frequency of the crystal resonator. The resonator is typically a resonator that enables resonance at different frequencies simultaneously. Crystal is an easily available and understandable solution for the resonator. The harmonic frequencies change in frequency under the influence of temperature in a similar manner to the fundamental frequency. In contrast, the overtone frequencies can change the frequency in a different manner under the influence of temperature. Furthermore, the different overtones of the crystal can change in frequency in different manners under the influence of temperature. Therefore, the different overtones can have different temperature gradients. Since the overtones of the crystal can be selected, the circuit can advantageously be designed to have a predefined temperature behavior based on the predefined behavior of the resonator.

[0036] As described, the temperature behavior can be different when at least one, but preferably two, of the divided frequencies are selected as overtone frequencies. The temperature can vary in the temperature range from -40°C to +125°C. Within this range, the temperature gradient for a specific overtone can vary.

[0037] In one embodiment of the present invention, the frequency ratio generator - a second controlled frequency divider adjusted to generate a second divided signal having a second divided frequency that is a controlled frequency substantially divided by a second frequency ratio signal; - a second frequency phase detector adjusted to generate a second phase difference signal based on a second frequency phase difference between the second divided frequency and the second resonance frequency; - a second inner loop filter adjusted to generate a second frequency ratio signal indicating a second frequency ratio based on the second phase difference signal; - an adder adjusted to generate an added signal supplied to the converter wherein the added signal has a first divided frequency and a second divided frequency, and the adder; - including a temperature compensator for compensating for changes in the resonance frequency of the resonator, the temperature compensator being - an input configured to receive a first frequency ratio and a second frequency ratio, - a first divider adjusted to generate a first division value based on the division of the first frequency ratio and the second frequency ratio, - a computer adjusted to calculate a compensation coefficient based on one or more values from the group consisting of a first phase difference signal, a second phase difference signal, the first frequency ratio, and the first division value, preferably including a look-up table, - including a redresser adjusted to generate a frequency ratio based on correcting a signal based on one or more of the group consisting of the first phase difference signal, the second phase difference signal, and the first frequency ratio using the compensation coefficient, The excitation signal is based on the added signal, A third frequency ratio generator loop is formed by a second control frequency divider, a second divided signal, a second frequency phase detector, a second phase difference signal, a second inner loop filter, and a second frequency ratio signal, A fourth frequency ratio generator loop is formed by a second control frequency divider, a second divided signal, a converter, an excitation signal, a resonator, a resonance signal, a second frequency phase detector, a second phase difference signal, a second inner loop filter, and a second frequency ratio signal, The second inner loop filter filters the second phase difference signal, thereby preventing instability of the frequency ratio generator loop.

[0038] The frequency ratio generator loops are in parallel and are evaluated simultaneously, and the influence of temperature is measured simultaneously. Known circuits may tend to measure the influence of temperature at intervals in time. This time interval causes inaccuracies in temperature in known circuits when the temperature changes over time. Thus, the ratio generator according to the present invention has the advantage of improved accuracy of temperature measurement.

[0039] In one embodiment of the present invention, the frequency ratio generator - includes a selector adjusted to select one or more of a group consisting of a first phase difference signal, a second phase difference signal, and a first frequency ratio based on one or more values of a group consisting of a first frequency ratio and a first division value; The redresser is adjusted to generate a frequency ratio based on correcting the selected frequency ratio using a compensation factor.

[0040] This embodiment of the ratio frequency generator advantageously uses the property of the resonator that it can resonate at multiple frequencies simultaneously. The resonator typically occupies more space compared to other elements of the circuit. Therefore, resonating at multiple frequencies using the resonator enables integration and miniaturization of the circuit.

[0041] Furthermore, the selector can advantageously select the most stable frequency ratio for a particular temperature, whereby the frequency ratio does not vary significantly due to temperature changes. Additionally, the redresser can base the compensation factor primarily on the parameter having the highest variation of values for a particular temperature range. The parameter can also be used to specify the temperature.

[0042] In one embodiment of the present invention, the frequency ratio generator - a third control frequency divider adjusted to generate a third divided signal having a third divided frequency that is a controlled frequency substantially divided by a third frequency ratio signal; - a third frequency phase detector adjusted to generate a third phase difference signal based on a third frequency phase difference between the third divided frequency and a third resonance frequency; - a third inner loop filter adjusted to generate a third frequency ratio signal indicating a third frequency ratio based on the third phase difference signal. The added signal also has a third divided frequency, The input of the temperature compensator is further configured to receive a third frequency ratio, The temperature compensator further - includes a second divider adjusted to generate a second division value based on the division of the first frequency ratio and the third frequency ratio, When dependent on Embodiment 6, the selector is further adjusted to make a selection based on one or more values from the group consisting of the third phase difference signal, the second frequency ratio, and the third frequency ratio, and also based on one or more values from the extended group consisting of the second frequency ratio, the third frequency ratio, and the second division value, The computer is further adjusted to calculate a compensation coefficient based on one or more values from the group extended with the third phase difference signal, the second frequency ratio, the third frequency ratio, and the second division value, The redresser is adjusted to generate a frequency ratio based on correcting the selected frequency ratio using the compensation coefficient, A fifth frequency ratio generator loop is formed by the third control frequency divider, the third divided signal, the third frequency phase detector, the third phase difference signal, the third inner loop filter, and the third frequency ratio signal, A sixth frequency ratio generator loop is formed by the third control frequency divider, the third divided signal, the converter, the excitation signal, the resonator, the resonance signal, the third frequency phase detector, the third phase difference signal, the third inner loop filter, and the third frequency ratio signal, The third inner loop filter filters the third phase difference signal, thereby preventing instability of the frequency ratio generator loop.

[0043] This embodiment advantageously enables measuring the hysteresis behavior of the resonator during operation. Known circuits tend to compensate for hysteresis in the resonator by designing the countermeasures from a theoretical point of view. Therefore, this embodiment provides the advantage of improved accuracy due to hysteresis measurement.

[0044] In one embodiment of the present invention, the selector of the frequency ratio generator is - to select one of a group consisting of a first frequency ratio, a second frequency ratio, and a third frequency ratio, wherein the selected ratio is based on one or more values of a group consisting of a first frequency ratio, a second frequency ratio, a third frequency ratio, a first division value, and a second division value, or - to select two or more weighted combinations of a first frequency ratio, a second frequency ratio, and a third frequency ratio, wherein the weighted combination is based on one or more values of a group consisting of a first frequency ratio, a second frequency ratio, a third frequency ratio, a first division value, and a second division value, and is adjusted to perform the selection.

[0045] The aforementioned advantages regarding the selector also apply to this more sophisticated embodiment of the selector. Further, this version of the selector enables a more balanced combination with the weighted combination. For example, the weighted combination advantageously enables the mixing and matching of various performance aspects such as Allan variance or phase noise.

[0046] In one embodiment of the present invention, the first division value is based only on the first frequency ratio signal and the second frequency ratio signal, the second division value is based only on the first frequency ratio signal and the third frequency ratio signal, the selector is adjusted to select one or more of a limited group consisting of a first phase difference signal, a second phase difference signal, and a third phase difference signal, and / or The computer is adjusted to calculate a compensation factor based on one or more values from a limited group consisting of a first division value and a second division value. This embodiment advantageously limits the amount of selection in various groups to the signals and / or ratios most suitable for providing a compensation factor, such as with respect to changes in the parameters of various components due to temperature changes.

[0047] In one embodiment of the present invention, the frequency ratio generator includes an analog / digital converter adjusted to generate a digital resonance signal based on a resonance signal, and the digital resonance signal is supplied to at least a first frequency phase detector. Operating on the input signal in the digital or analog domain can advantageously be done in one of those domains. Typically, the resonator is an easily available analog component. More typically, the frequency phase detector is easier to implement in the digital domain. The ADC advantageously provides a coupling of the analog and digital domains, benefiting from availability on the one hand and ease of implementation on the other.

[0048] In one embodiment of the present invention, the converter of the frequency ratio generator includes a digital / analog converter adjusted to generate an excitation signal based on a divided signal. The digital control frequency divider is easier to implement and can be easily controlled. The resonator is an analog component. Adding a DAC between the digital control frequency divider and the resonator provides the advantage of combining two advantageous partial solutions in the digital and analog domains respectively.

[0049] In one embodiment of the present invention, the comparator is - a scaler adjusted to generate a scaled signal that is a frequency ratio signal scaled by a scaling factor, and / or - including a shifter adjusted to generate a shifted signal that is a scaled signal shifted by a shift value, The comparison signal is based on the shifted signal.

[0050] The controlled oscillator typically has an input for controlling the controlled frequency of the controlled signal. The input signal supplied to the input of the controlled oscillator is based on the comparison signal. Depending on the embodiment, other signals can be combined, such as being added to, subtracted from, divided by, and multiplied by the comparison signal. The comparison signal can also be manipulated, such as being filtered, before becoming the input signal. Typically, when the input to the controlled oscillator is zero, the controlled frequency will have a specific ground frequency or center frequency. And if it is shifted from zero by any amount in the positive or negative direction, a positive or negative frequency change will occur respectively. Applying the scaler and shifter provides the option to manipulate the signal so that it is suitable as the input signal for the most common controlled oscillators. Further, the scaler and shifter provide the advantage of introducing an additional offset. The additional offset can be used, for example, in a communication system that requires some additional space to insert signaling into a bitstream.

[0051] The controlled oscillator can be implemented in many different embodiments. The controlled oscillator can be a voltage-controlled oscillator and optionally includes the output of a DAC that provides a signal for the control input of the voltage-controlled oscillator. The controlled oscillator can also be a fully digital PLL.

[0052] In one embodiment of the present invention, the frequency generator is - a phase acquisition circuit adjusted to generate a phase difference signal based on the phase difference between a controlled frequency and a reference signal having a reference frequency, - including a PLL adjusted to generate an offset signal based on the phase difference signal, The controlled frequency is also based on the offset signal.

[0053] Adding a PLL, preferably a digital PLL, enables tracking of the phase and frequency of an external signal having a specific frequency. The external signal can have significant phase jitter, such as a carrier wave for a telecommunication protocol. The frequency generator can advantageously generate a very stable controlled signal having a very stable controlled frequency. The controlled frequency is typically controlled such that it can be used as a reference while receiving communication carried by the carrier wave.

[0054] As an advantage of this embodiment when implemented for most in the digital domain, the frequency generator allows various noise sources, such as external signals, resonators, and controlled oscillators, to be identified and at least partially compensated through the architecture of the frequency generator loop, particularly loop filters. For example, resonators are typically affected by temperature and cause changes in resonance in the range of tens of kHz. During this time, the controlled oscillator typically generates phase noise in the range of hundreds of kHz or even in the range of hundreds of MHz, which can be caused by the Fermi sea, Brownian motion, etc.

[0055] Resonators and controlled oscillators are typically elements implemented in the analog domain. Most of the frequency generator, advantageously implemented in the digital domain, may require implementation in dedicated hardware but may also allow part of the implementation to be done in software.

[0056] The loop including the resonator or oscillator generally complies with the Barkhausen criterion. The Barkhausen criterion includes the following constraints. 1. The absolute value of the loop gain is equal to 1; and 2. The phase shift of the loop is 2πx;

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[0057] The Barkhausen criterion typically implies additional design constraints regarding the resonator loop. Loops that comply with the Barkhausen criterion are typically difficult to design and introduce additional phase noise. Typically, loops that include a normal amplifier to make the loop comply with the Barkhausen criterion introduce significant phase noise and consume significant power. The controlled oscillator is the only element in the frequency generator that can comply with the Barkhausen criterion. Thus, this embodiment provides the advantages of low power and low phase noise introduction.

[0058] In a further embodiment of the present invention, if it includes a shift value, the shift value is an offset signal, or if it includes a filtered comparison signal, the filtered comparison signal is indirectly based on the offset signal.

[0059] In a first option, the offset signal is supplied through an outer loop filter, while in a second option, the offset signal is not supplied through the outer loop filter. In the context of this text, the terms directly and indirectly based on a signal mean whether the input signal contributes to the resulting signal, either directly or through the loop. The first option advantageously limits the number of filters in the system. The second option advantageously allows the offset signal to be added to the signal controlling the controlled oscillator, either filtered or unfiltered. The filter applied to the offset signal can advantageously be designed to suit specific needs for filtering the offset signal. This is particularly advantageous because the offset signal typically has noise in a band of hundreds of kHz or even in a band of hundreds of MHz, having the controlled oscillator as the main noise source, while the filtered comparison signal typically has noise in a band of tens of Hz, having the resonator as the main noise source.

[0060] According to another aspect of the present invention, in a method for generating a controlled signal having a controlled frequency, - receiving a resonance signal having a first resonance frequency from a resonator; - providing a first ratio signal indicating a first frequency ratio signal between the controlled frequency and the first resonance frequency; - generating a first phase difference signal (155) based on a first frequency phase difference between a first divided frequency and the first resonance frequency; - filtering the first phase difference signal to generate a first frequency ratio signal; - basing the frequency ratio on the first frequency ratio signal; - providing a target ratio; - generating a comparison signal based on a comparison of the frequency ratio with the target ratio; - generating a controlled signal having a controlled frequency based on a comparison signal; - generating a first divided signal (115) having a first divided frequency that is the controlled frequency substantially divided by a first frequency ratio signal; - generating an excitation signal (129) having the first divided frequency based on the first divided signal, the excitation signal being provided to a resonator for excitation of the resonator; - outputting the controlled signal, a first frequency ratio generator loop is formed by the first divided signal, a first phase difference signal, and the first frequency ratio signal; a second frequency ratio generator loop is formed by the first divided signal, the excitation signal, the resonator, the resonance signal, the first phase difference signal, and the first frequency ratio signal; the filtering step filters the first phase difference signal, thereby preventing instability of the frequency ratio generator loop.

[0061] According to another aspect of the present invention, a frequency generator system includes - a frequency generator chip including a frequency generator according to any of the above embodiments, - a resonator for connecting to the frequency generator chip for generating a resonance signal, and - an oscillator for connecting to a controlled oscillator circuit for generating an oscillation signal.

[0062] According to another aspect of the present invention, in a computer program product including a computer-readable medium having computer-readable code embodied therein, the computer-readable code, when executed by a suitable computer or processor, causes the computer or processor to perform the - providing a first ratio signal, - generating a comparison signal, - generating a controlled signal; - outputting an excitation signal; - outputting a controlled signal, and is configured to perform.

[0063] According to another aspect of the present invention, in a computer program product including a computer-readable medium having computer-readable code embodied therein, the computer-readable code, when executed by a suitable computer or processor, causes the computer or processor to be configured to perform the method specified in an embodiment according to the present invention.

[0064] The present invention will become apparent and will be more clearly understood by referring to the embodiments described as examples in the following description and to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0065]

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[0066] The figures are purely schematic and are not drawn to scale. In the figures, elements corresponding to elements already described may have the same reference numerals.

Description of Reference Numerals

[0067] 100…Frequency ratio generator of the first embodiment, 101…Frequency ratio generator of the second embodiment, 102…Frequency ratio generator of the third embodiment, 104…First input signal, 105…Third input signal, 106…Fourth input signal, 107…(First) control signal, 108…Second control signal, 109…Third control signal, 110…(First) control frequency divider, 111…Second control frequency divider, 112…Third control frequency divider, 115…(First) divided signal, 116…Second divided signal, 117…Third divided signal, 120…Adder, 121…Added signal, 125…Digital / analog converter (DAC), 129…Excitation signal, 130…Resonator, 135…Second input signal, 140…Analog / digital converter (ADC), 145…Digital second signal, 150…(First) frequency phase detector, 151…Second frequency phase detector, 152…Third frequency phase detector, 155…(First) phase difference signal, 156…Second phase difference signal, 157…Third phase difference signal, 160…(First) loop filter, 161…Second loop filter, 162…Third loop - loop filter, 200... subsystem of the first embodiment, 201... subsystem of the second embodiment, 210... first circuit including a resonator, 211... second circuit including a resonator, 220... (first) divider, 221... second divider, 225... first display, 226... second display, 230... subtractor, 235... subtracted signal, 300... frequency generator of the first embodiment, 301... frequency generator of the second embodiment, 310... comparator, 311... target ratio, 312... frequency ratio signal, 315... comparison signal, 320... outer loop filter, 321... filtered comparison signal, 330... controlled oscillator circuit, 331... controlled signal, 340... phase acquisition circuit, 341... reference signal, 345... phase difference signal, 350... digital PLL, 355... offset signal, 356... adder, 357... oscillator control signal, 1000... computer program product, 1010... computer-readable medium, 1020... computer-readable code [Embodiments for Carrying Out the Invention]

[0068] [Detailed Description of Exemplary Embodiments] The following figures may detail various embodiments. It is possible to combine the embodiments to achieve enhanced or improved technical effects. These combined embodiments may be explicitly mentioned throughout the text, may be suggested in the text, or may be implicit.

[0069] FIG. 1 schematically shows a first embodiment of a frequency generator 300. The frequency generator includes frequency ratio generators 100, 101, 102, a comparator 310, and a controlled oscillator 330.

[0070] The frequency ratio generators have a controlled frequency 331 as an input. The controlled frequency is the generated frequency and is thus in fact the output of the frequency generator. The frequency ratio generators provide a frequency ratio signal 312.

[0071] The frequency ratio generator includes a resonator. The frequency ratio generator determines the ratio between a controlled frequency and the resonant frequency of the resonator. Further, the frequency ratio generator is capable of determining the ratio between two resonant frequencies of the resonator, at least one of those resonant frequencies being a harmonic frequency. Typically, the resonator varies with temperature and exhibits the effect of hysteresis. The frequency ratio signal can be stabilized or compensated for temperature. The frequency ratio signal can be stabilized or compensated for hysteresis. The frequency ratio signal can be stabilized or compensated for any other effects of the resonator or any other component in the frequency ratio generator or in the frequency generator.

[0072] The comparator has the frequency ratio signal and the target ratio 311 as inputs. The target ratio typically has a predefined value or is selected from a set of predefined values. The predefined value is typically determined by the manufacturer, preferably during the manufacture of the frequency ratio generator or the resonator by in-line characterization. The comparator compares the frequency ratio signal with the target ratio and provides as output a comparison signal 315 which is the result of this comparison. Typically, the comparison of the frequency ratio signal with the target ratio is performed by subtraction.

[0073] The controlled oscillator has as input a signal based on the comparison signal. The input signal can be a filtered comparison signal with an offset 357, a filtered comparison signal 321, the comparison signal, or any other signal based on the comparison signal. The output of the controlled oscillator is the controlled frequency 331.

[0074] The controlled oscillator is typically an oscillator having a center frequency. The controlled oscillat The device is typically highly stable with respect to hysteresis. Typically, when the oscillator control signal is 0, the controlled frequency is equal to the center frequency. Any change in the oscillator control signal, whether it is negative or positive, changes the controlled frequency. The change in the controlled frequency is typically linear over a predefined range. Scaling and shifting to obtain an appropriate signal as input for the controlled oscillator are advantageously done in a comparator. The controlled oscillator can be implemented using a varicap, an LC network, or can be implemented entirely in the digital domain.

[0075] The frequency generator optionally includes an outer loop filter 320. The outer loop filter takes a comparison signal as input. The outer loop filter outputs a filtered comparison signal 321. The outer loop filter filters the comparison signal, thereby preventing instability of the outer loop. The outer loop is formed by at least a frequency ratio generator, a comparator, an outer loop filter, and a controlled oscillator.

[0076] The frequency generator optionally includes an adder 356. The adder takes as a first input the filtered comparison signal, the comparison signal, or a signal based on the comparison signal. The adder takes an offset signal 355 as a second input. The adder adds the two input signals to provide an added signal. The oscillator control signal may be equal to the added signal or may be based on the added signal. This offset signal can be used to shift the added signal into an appropriate range as input for the controlled oscillator. The offset signal can also be used to introduce an offset onto the oscillator control signal to control the controlled frequency. The offset signal can also be used to introduce an offset, typically a time offset, onto the oscillator control signal to control the phase of the controlled frequency.

[0077] It is to be assumed that the frequency ratio generator is stable and a zero-offset signal is provided. Further, it is to be assumed that the controlled frequency is slightly too high. The frequency ratio generator will output a frequency ratio signal indicating the ratio between the resonant frequency of the resonator and the controlled frequency. This frequency ratio will be slightly too high. The comparator will compare the target ratio with the frequency ratio and will conclude that the frequency ratio is slightly too high. The result of this comparison will be indicated in the comparison signal. Typically, the comparison signal will be slightly too low compared to its desired setting point. An optional outer loop filter may filter the comparison signal. If the outer loop filter includes an integrating function, the error in the controlled frequency can be reduced to zero. A signal based on the comparison signal is provided to the controlled oscillator. The controlled oscillator will react to a signal that is slightly too low based on the slightly too low comparison signal by lowering the controlled frequency and thereby stabilizing the controlled frequency to the desired frequency. The controlled frequency is at least partially specified by the setting of the target ratio. An optional offset signal provides an additional means for controlling the controlled frequency. The offset signal can be injected either before or after the optional outer loop filter in the loop.

[0078] The embodiment of the present invention in FIG. 1 may use the embodiment of the frequency ratio generator shown in FIG. 3.

[0079] The embodiment of the present invention in FIG. 1 may use the embodiment of the frequency ratio generator shown in FIG. 4 in combination with the subsystem shown in FIG. 6 to provide a temperature-compensated frequency generator. If the frequency ratio generator is temperature-compensated and the other parts of the frequency generator are implemented in the digital domain as much as possible, the frequency generator is particularly insensitive to temperature variations.

[0080] The embodiment of the present invention in FIG. 1 can use the embodiment of the frequency ratio generator shown in FIG. 5 in combination with the subsystem shown in FIG. 7 to provide a frequency generator compensated for temperature and hysteresis. If the frequency ratio generator is compensated for temperature and hysteresis and the other parts of the frequency generator are implemented in the digital domain as much as possible, the frequency generator is particularly insensitive to temperature variations and hysteresis.

[0081] FIG. 2 schematically shows a second embodiment of the frequency generator 301. This frequency generator includes the elements, signals, and features of the first embodiment. Further, this frequency generator includes a phase acquisition circuit 340 and a PLL 350.

[0082] The phase acquisition circuit has, as inputs, a controlled signal having a controlled frequency and a reference signal 341 having a reference frequency. The phase acquisition circuit identifies the phase difference between the controlled frequency and the reference frequency and outputs this difference as a phase difference signal 345.

[0083] The phase acquisition block can be implemented as a counter, with one input used as a clock signal for counting the zero crossings of the other signal. The number of crossings is related back to the phase between the signals.

[0084] The PLL has, as inputs, a controlled signal and a phase difference signal. The PLL generates a phase-locked signal based on the controlled signal and the phase difference signal. The phase-locked signal can be seen as an offset signal 355. The PLL is preferably a digital PLL or a fully digital PLL. The controlled frequency signal is typically used as a clock input to the digital PLL.

[0085] When a phase acquisition circuit and a digital PLL are added, the phase of the controlled frequency is locked to the phase of the reference frequency. This embodiment typically tracks a remotely generated reference frequency and then locally stabilizes this reference frequency, such that a local reference in the form of a controlled frequency exhibits very low frequency jitter. Thus, this frequency generator compensates for or removes any disturbances injected between the source of the reference signal and the frequency generator. Exemplary applications can be found in telecommunications such as smartphones or satellite phones, printed circuit boards such as larger printed circuit boards, systems synchronized to atomic clocks, navigation systems, and the like.

[0086] The scenario described above to explain the outer loop stabilization function can be applied in a manner similar to the embodiment of the frequency generator shown in FIG. 2.

[0087] Furthermore, it is assumed that the frequency ratio generator is stable and a zero-offset signal is provided. Furthermore, it is assumed that the controlled frequency lags slightly with respect to the reference signal. The phase acquisition block will detect the phase difference between the controlled frequency and the reference frequency. The PLL will typically use a high Q value to filter the phase difference signal representing the phase difference. The resulting signal from the PLL will be injected as an offset signal into the outer loop to increase the controlled frequency. As soon as the phase acquisition circuit detects that there is no phase difference in between, the phase difference signal will indicate the absence of a phase difference. The resulting signal from the PLL, injected as an offset signal into the outer loop, will decrease the controlled frequency and remain in phase with the reference signal. Thus Then, the phase of the controlled frequency will be locked to the phase of the reference signal. The filtering of the PLL, typically using a high Q value, will remove the phase jitter in the reference signal. Therefore, this embodiment provides the advantage of providing a controlled frequency with low, for example, extremely low phase jitter. Therefore, this frequency generator can remove any disturbances (such as jitter) in the reference frequency to provide a local control signal having a very stable frequency and a controlled frequency with low phase jitter.

[0088] The embodiment of the present invention in FIG. 2 may use the embodiment of the frequency ratio generator shown in FIG. 3.

[0089] The embodiment of the present invention in FIG. 2 may use the embodiment of the frequency ratio generator shown in FIG. 4 in combination with the subsystem shown in FIG. 6 to provide a frequency generator compensated for temperature. If the frequency ratio generator is compensated for temperature and the other parts of the frequency generator are implemented in the digital domain as much as possible, the frequency generator is particularly insensitive to temperature variations.

[0090] The embodiment of the present invention in FIG. 2 may use the embodiment of the frequency ratio generator shown in FIG. 5 in combination with the subsystem shown in FIG. 7 to provide a frequency generator compensated for temperature and hysteresis. If the frequency ratio generator is compensated for temperature and hysteresis and the other parts of the frequency generator are implemented in the digital domain as much as possible, the frequency generator is particularly insensitive to temperature variations and hysteresis.

[0091] FIG. 3 schematically shows a first embodiment of the frequency ratio generator 100. The frequency ratio generator includes a control frequency divider 110, a frequency phase detector 150, and an inner loop filter 160. The control frequency divider may also be labeled as the first control frequency divider. The frequency phase detector may also be labeled as a phase detector, the first phase detector, or the first frequency phase detector. The inner loop filter may also be labeled as the first inner loop filter, the first loop filter, or the loop filter.

[0092] The control frequency divider takes the first input signal 104 and the control signal 107 as inputs and provides the divided signal 115 as an output. Typically, the first input signal is the controlled signal 331. The control signal may also be labeled as the first control signal. The divided signal may also be labeled as the first divided signal. The first input signal is a periodic signal having a first frequency, typically the controlled frequency. The control signal is typically a signal having a large amount of energy at a lower frequency, such as substantially close to 0 Hz.

[0093] The control frequency divider generates a divided signal. The divided signal is a periodic signal having a divided frequency. The divided frequency is related to the first frequency based on the magnitude of the control signal. The magnitude of the signal can be the amplitude of the signal, the value of the signal, or any other characteristic of the signal representing a measured value. In the case where the control signal is an analog signal, the magnitude is typically the amplitude of the signal. In the case where the control signal is a digital signal, the magnitude is typically the value of the signal. Typically, the relationship between the input and output of the control frequency divider is

[0094]

Equation

[0095] The phase detector takes the divided signal and the second input signal 135 as inputs and provides the first phase difference signal 155 as an output. The second input signal is a periodic signal having a second frequency. The first phase difference signal may also be labeled as the phase difference signal.

[0096] The magnitude of the phase difference signal is related to the phase difference between the divided frequency and the second frequency. Typically, depending on the implementation of the phase detector, the magnitude of the phase difference signal may have a minimum value at a phase difference of 0 degrees, -90 degrees, or 90 degrees.

[0097] The loop filter takes the phase difference signal as an input and provides a control signal as an output. The loop filter is typically a low-pass filter. The loop filter stabilizes a loop or feedback loop formed by the control frequency divider, the divided signal, the frequency phase detector, the phase difference signal, the loop filter, and the control signal. The first control signal may be output as the frequency ratio signal 312.

[0098] It is desired to assume that the first frequency has not changed. Further, it is desired to assume that the divided frequency is slightly higher compared to the second frequency and that the divided signal and the second input signal are in phase. The phase detector will detect an increasing phase difference between the two signals. This is because the second input signal will begin to lag compared to the divided signal. As the phase difference increases, the magnitude of the phase difference signal will increase. With some delay, attenuation, and / or reduction resulting from being implemented as a low-pass filter, the loop filter will increase the magnitude of the control signal. The increase in the control signal will cause the first frequency to be divided by a larger magnitude, thus a larger number, and a lower divided frequency will be provided. Thus, any difference in frequency between the second frequency and the divided frequency will be reduced and / or minimized with a negative feedback loop. Further, since the divided frequency tracks the second frequency, the magnitude of the control signal will indicate the ratio between the first frequency and the second frequency.

[0099] In another scenario, it is desired to assume that the first frequency is increasing. Further, it is desired to assume that the second frequency is stable. Since the first frequency is increasing and the magnitude of the control signal is stable, the divided frequency will increase. The phase detector will detect an increasing phase difference between the two signals. This is because the second input signal will start to lag compared to the divided signal. As the phase difference increases, the magnitude of the phase difference signal will increase. With some delay, attenuation, and / or reduction resulting from being implemented as a low-pass filter, the loop filter will increase the magnitude of the control signal. The increase in the control signal will cause the first frequency to be divided by a larger magnitude, and thus a larger number, providing a lower divided frequency, which will be substantially the divided frequency before the increase in the first frequency. Thus, regardless of how the first frequency changes, the divided frequency will remain substantially the same as the second frequency due to the negative feedback loop. Further, since the divided frequency tracks the second frequency, the magnitude of the control signal will indicate the ratio between the first frequency and the second frequency, and that ratio will increase in this situation and will continue to increase

[0100] Typically, since both the first and second frequencies are changing, there can be combinations of the above scenarios.

[0101] To obtain an initial lock, the divided frequencies need to be relatively close to a second frequency, such as the resonant frequency of a resonator that generates the second frequency; otherwise, the lock procedure for obtaining an initial lock can become extremely complex and time-consuming. If the first or second frequency, or a combination of the first and second frequencies, moves faster than the resonator loop can track, the lock can be lost. Preferably, the first frequency should not change too quickly in order to allow for a faster change in the second frequency. Slow frequency movement of the first and second frequencies over a relatively wide range enables the lock to be maintained. Fast frequency movement of the first and second frequencies over a relatively narrow range also enables the lock to be maintained.

[0102] For some circuits, it may be known how much the frequency moves. By combining that knowledge with the circuit, it becomes possible to select a resonator and design other elements in the loop to maintain the lock during operation. As a rule of thumb, if the loop's dynamic frequency tracking is slower than the combination of changes in the first and second frequencies, the lock will be lost.

[0103] FIG. 4 schematically shows a second embodiment of the frequency ratio generator 101. This circuit includes all the features described with respect to FIG. 3. This circuit may further include a second control frequency divider 111, an adder 120, a DAC 125, a resonator 130, an ADC 140, a second phase detector 151, and a second loop filter 161.

[0104] The first control frequency divider 110 takes the first input signal 105 and the first control signal 108 as inputs and provides the first divided signal 115 as an output. The second control frequency divider takes the third input signal 105 and the second control signal 108 as inputs and provides the second divided signal 116 as an output. The adder takes the first and second divided signals as inputs and provides the added signal 121 as an output. This added signal is the sum of the first and second divided signals.

[0105] An optional DAC takes the added signal as an input and provides, as an output, an excitation signal 129 suitable for resonating the resonator. This offers the advantage of having many of the functions of the circuit in the digital domain, while only requiring a single DAC to provide the excitation signal, which is typically an analog signal, to the resonator, which is typically a crystal or crystal oscillator. Further, the frequency divider is typically implemented in the digital domain, offering the advantages of ease of implementation and introduction of limited phase noise. The introduction of limited phase noise is substantially due to the fact that a controlled digital fractional frequency divider has a higher granularity compared to an integer frequency divider.

[0106] In an alternative embodiment, two DACs are present at each input of the adder, whereby the adder is an analog adder. In another alternative embodiment, the circuit does not have a DAC within the loop. In yet another embodiment, the DAC is between the first loop filter output and the first control frequency divider, and preferably, a second DAC is between the second loop filter output and the second control frequency divider.

[0107] An optional ADC takes the second input signal as an input and provides, as an output, a digital second signal 145. This offers the advantage of having many of the functions of the circuit in the digital domain, while only requiring a single ADC to receive the second input signal, which is typically an analog signal, from the resonator, which is typically a crystal. In an alternative embodiment, two ADCs are between each phase detector and the loop filter. In yet another embodiment, two ADCs are between each loop filter and the control frequency divider. while only requiring a single ADC to receive the second input signal, which is typically an analog signal, from the resonator, which is typically a crystal. In an alternative embodiment, two ADCs are between each phase detector and the loop filter. In yet another embodiment, two ADCs are between each loop filter and the control frequency divider.

[0108] The first frequency phase detector 150 receives the first divided signal 115 and the digital second signal 145 as inputs and provides the first phase difference signal 155 as an output. The second frequency phase detector 151 receives the second divided signal 116 and the digital second signal 145 as inputs and provides the second phase difference signal 156 as an output. The first loop filter 160 receives the first phase difference signal as an input and provides the first control signal 107 as an output. The second loop filter 161 receives the second phase difference signal as an input and provides the second control signal 108 as an output.

[0109] Typically, the first divided frequency and the second divided frequency are different frequencies, both of which are the resonance frequencies of the resonator. Thus, this resonator is typically a resonator that enables resonance at different frequencies simultaneously. Typically, this resonator is a crystal resonator. Further, typically, at least one of the resonances is a harmonic resonance, and preferably, both resonances are harmonic resonances.

[0110] As described above, when at least one of the first and second divided frequencies is selected as a harmonic frequency, the temperature behavior can be different. The temperature can vary in a temperature range from -40°C to +125°C. Within this range, the temperature gradient for a particular harmonic can vary.

[0111] Either the first control signal or the second control signal can be selected as the frequency ratio signal. Typically, the first control signal and the second control signal are combined to compensate for the effects of temperature, particularly the temperature on the resonator. This combination is then provided as the frequency ratio signal as the output. Using this combination, it is possible to select the control signal that varies the least with respect to a specific temperature. As shown in and described with respect to FIG. 6, the first and second control signals can be split to provide a temperature indication that enables compensation for any temperature effects of the frequency generator, the frequency ratio generator, and particularly the resonator. The compensation is typically predefined, for example, during manufacturing, by providing the frequency ratio generator with settings for estimating compensation factors for the first and second control signals, and / or, preferably, other signals inside the frequency ratio generator, in order to provide a compensated frequency ratio signal.

[0112] FIG. 5 schematically shows a third embodiment of the frequency ratio generator 102. This frequency ratio generator includes all the features described with respect to FIG. 4. This circuit may further include a third control frequency divider 112, a third phase detector 152, and a third loop filter 162.

[0113] The first control frequency divider 110 takes the first input signal 105 and the first control signal 108 as inputs and provides the first divided signal 115 as the output. The second control frequency divider takes the third input signal 105 and the second control signal 108 as inputs and provides the second divided signal 116 as the output. The third control frequency divider takes the fourth input signal 106 and the third control signal 109 as inputs and provides the third divided signal 117 as the output. The adder takes the first, second, and third divided signals as inputs and provides the added signal 121 as the output. This added signal is the sum of the first, second, and third divided signals.

[0114] The first frequency phase detector 150 receives the first divided signal 115 and the digital second signal 145 as inputs and provides the first phase difference signal 155 as an output. The second frequency phase detector 151 receives the second divided signal 116 and the digital second signal 145 as inputs and provides the second phase difference signal 156 as an output. The third frequency phase detector 152 receives the third divided signal 117 and the digital third signal 145 as inputs and provides the third phase difference signal 157 as an output. The first loop filter 160 receives the first phase difference signal as an input and provides the first control signal 107 as an output. The second loop filter 161 receives the second phase difference signal as an input and provides the second control signal 108 as an output. The third loop filter 162 receives the third phase difference signal as an input and provides the third control signal 109 as an output.

[0115] Typically, the first divided frequency, the second divided frequency, and the third divided frequency are different frequencies, all being the resonance frequencies of the resonator. Thus, this resonator is typically a resonator that enables resonance at different frequencies simultaneously. Typically, this resonator is a crystal resonator. Further, typically, at least two of the resonances are overtone resonances, and preferably, all of the resonances are overtone resonances.

[0116] As described above, when at least one of the first and second divided frequencies is selected as an overtone frequency, the temperature behavior can be different. The temperature can vary in a temperature range from -40°C to +125°C. Within this range, the temperature gradient for a particular overtone can vary.

[0117] Any one of the first control signal, the second control signal, or the third control signal may be selected as the frequency ratio signal. Typically, the first control signal, the second control signal, and / or the third control signal are combined to compensate for the effects of temperature and / or hysteresis, particularly the effects of temperature and hysteresis on the resonator. This combination is then provided as the frequency ratio signal as an output. Using this combination, it is possible to select the control signal that varies the least for a particular temperature. As shown in and described with respect to FIG. 7, it is possible to divide the first and second control signals to provide a first display, and to divide the first and third control signals to provide a second display. Both or at least one of them make it possible to compensate for any temperature effects of the frequency generator, the frequency ratio generator, and particularly the resonator. When both displays are subtracted, they make it possible to compensate for any hysteresis effects of the frequency generator, the frequency ratio generator, and particularly the resonator. The compensation is typically predefined, for example, during manufacturing, by providing the frequency ratio generator with settings for estimating compensation factors for the first, second, and third control signals, and / or, preferably, other signals inside the frequency ratio generator, in order to provide a compensated frequency ratio signal.

[0118] FIG. 6 schematically shows a subsystem 200 for compensating for the effects of temperature. This subsystem includes frequency ratio generators 101, 102 according to any of the embodiments of the present invention that include a resonator and provide a control signal 107 and a second control signal 108 as in FIGS. 1 and 2. This subsystem further includes a control signal splitter 220 that is adjusted to generate a split control signal 225 based on the splitting of the control signal by the second control signal. The split control signal is the temperature display 225. Using this temperature display, it is possible to apply temperature compensation to the frequency ratio signal in a separate unit to provide a frequency ratio compensated for temperature.

[0119] FIG. 7 schematically shows a subsystem 201 for compensating for the effects of temperature and hysteresis. This system includes a resonator and a frequency ratio generator 211 according to any of the embodiments of the present invention that provides a control signal 107, a second control signal 108, and a third control signal 109. This subsystem further includes a first control signal splitter 220 that is adjusted to generate a divided control signal 225 based on the splitting of the control signal by the second control signal. The first divided control signal is the first temperature indication 225. This system further includes a second control signal splitter 221 that is adjusted to generate a second divided control signal 226 based on the splitting of the control signal by the third control signal. The second divided control signal is the second temperature indication 226.

[0120] This system optionally includes a subtractor 230 that is adjusted to generate a subtracted signal 235 based on subtracting the second divided control signal from the first divided control signal. Typically, the first divided control signal and the second divided control signal have individual minimum temperature activities. The subtracted signal is a temperature indication and / or a hysteresis indication. Based on this subtracted signal, the first, second, and / or third control signals can be corrected with respect to the effects of temperature and hysteresis, particularly from the resonator. Further, it is possible to compensate the frequency ratio signal in a separate unit for temperature and hysteresis to provide a frequency ratio compensated for temperature and hysteresis.

[0121] The embodiment in FIG. 4, in combination with the feature that this embodiment is adjusted to resonate at two individual resonance frequencies (the resonance frequencies are selected to have individual activity dips, first and second control signals respectively indicating first and second ratios), would be suitable for measuring changes in the temperature of a resonator, preferably a crystal resonator. The individual minimum temperature activities in the context of this application are the minimum values that exhibit their minimum frequency changes at separate or individual temperatures. This minimum change may be related to the frequency of another signal. This embodiment offers the advantage that it is possible to measure temperature changes of the resonator over the entire temperature range with high accuracy. As another advantage, dividing the first ratio by the second ratio provides a ratio that is independent of the first frequency. Thus, any temperature-dependent variations of the first frequency can be eliminated.

[0122] Furthermore, the embodiment in FIG. 4 can be extended to include a third loop as shown in FIG. 5. The third loop includes a third control frequency divider 112, a third phase detector 152, and a third loop filter 162, all of which are adjusted in a similar manner as for the first and second loops. Furthermore, this embodiment is extended with a first control signal divider that generates a first divided control signal by dividing a control signal by a second control signal. Furthermore, this embodiment is extended with a second control signal divider that generates a second divided control signal by dividing a control signal by a third control signal. Furthermore, this embodiment is extended with a subtractor that is adjusted to generate a subtracted signal based on subtracting the second divided control signal from the first divided control signal, and the subtracted signal indicates the temperature of the resonator. Furthermore, at least the first divided control signal and the second divided control signal have individual minimum temperature activities.

[0123] This embodiment provides the advantage of being able to measure the temperature change of a resonator over the entire temperature range with high precision. As another advantage, the ratio division provides the divided ratios, and these ratios are independent of the first frequency. Thus, any temperature-dependent variations in the first frequency can be eliminated or at least minimized. Further, any behavior of the resonator that changes the resonance frequency of the resonator, such as time-dependent behavior, for example, hysteresis, can be compensated for.

[0124] The frequency measurement technique used enables a measurement accuracy of about 0.1 ppb at a speed of 1 k samples / second. This leads to the system being advantageously able to measure small temperature changes of a resonator, such as a crystal, at a stable first frequency. The small temperature changes can be in the range of millikelvin. Further, the system is typically able to respond sufficiently fast to changes.

[0125] In one embodiment of the frequency ratio generator, an offset is added to the phase difference signal. This enables locking the loop at different angles. For example, if the frequency phase detector has a minimum output signal regarding a 0-degree phase shift on its input, the offset will lock the loop at an angle other than 0 degrees. For example, if the frequency phase detector has a minimum output signal regarding a 90-degree phase shift on its input, the offset will lock the loop at an angle other than 90 degrees.

[0126] In one embodiment, a resonator such as a crystal oscillator, a crystal, or a crystal resonator can be used, and it is read out indirectly. This indirect reading can introduce a phase shift. This introduced phase shift can be corrected along with the introduction of the offset described above.

[0127] Typically, one or more of the signals can be normalized to simplify further calculations using these signals.

[0128] In one variant form of the frequency generator, the frequency ratio signal is based on the first phase difference signal, the second phase difference signal, and / or the third phase difference signal. The selection from each of these phase difference signals or the respective weights can also be based on the first control signal, the second control signal, and / or the third control signal. This variant form offers the advantage that the inner loop signal is filtered only by the inner loop filter and the outer loop signal is filtered only by the outer loop filter. Each of those filters, especially the outer loop, can be adjusted to meet the specific requirements of that loop. The requirements for each loop typically balance the stability of the loop and the agility with respect to external changes.

[0129] In one variant form of the frequency generator, the outer loop filter 320 and the adder 356 are exchanged, whereby the offset signal also passes through the outer loop filter. This variant has the advantage of further filtering the offset signal to further stabilize this signal. The original configuration, as shown in FIG. 2, only filters the signal through the PLL and offers the advantage of reaching or approaching an optimal balance between the stability and agility of the loop formed by the controlled oscillator and the PLL, and also of the loop formed by the controlled oscillator, the phase acquisition circuit, and the PLL.

[0130] Throughout this description, it may be necessary to scale and shift signals and / or inverted signals to facilitate the collaboration between the various blocks referred to and shown in the figures. For example, the frequency ratio signal and the target ratio are typically inverted in a comparator to become a comparison signal, which is suitable for being processed by the rest of the system.

[0131] FIG. 8 schematically shows an embodiment of a non-transitory computer-readable storage medium including a computer program product 1000, a computer-readable medium 1010, and / or a computer-readable code 1020. The computer-readable code implements the methods referred to throughout this description of the invention.

[0132] The signal can be a periodic signal. A periodic signal repeats after every period. The amount of repetition per second is equal to the frequency. Further, the signal can have a maximum magnitude such as an amplitude or value, an average signal level, and an RMS level. The signal in the context of this text can be an analog signal such as a voltage signal, a current signal, a power signal, and / or an energy signal. The signal in the context of this text can also be a digital signal representing a voltage signal, a current signal, a power signal, and / or an energy signal. The frequency ratio is a frequency ratio signal.

[0133] The control frequency divider can be a digital control frequency divider. The control frequency divider can be a control multi-frequency divider. The control multi-frequency divider provides an output signal having an output frequency equal to the value obtained by dividing the input frequency of the input signal by n, where n is a number in the set N. In equation form, it is as follows.

[0134]

Equation

[0135] Alternatively, the control frequency divider can be a control fractional divider. In equation form, it is as follows.

[0136]

Equation

[0137]

Equation

[0138] An exemplary embodiment of a digital control multi-frequency divider is when the divider switches between division numbers N and N + 1. A prerequisite is that when the divided signal is supplied to the resonator, this resonator has a reasonable quality factor Q. By switching between N and N + 1, fractions such as N + 3 / 4 or N + 5 / 7 are possible.

[0139] The implementation of such a digital control multi-frequency divider can be done by adding an accumulator with a configurable maximum value. In the example of N + 3 / 4, an accumulator with a maximum capacity of 4 and a repeatedly added number of 3 will have a carry in 3 out of 4 cycles. Whenever there is a carry, the divider should perform division by the number N + 1, and at any other time, the divider should perform division by N. This technique can be classified as shaping.

[0140] Higher-order shaping can be performed by adding another accumulator and a small differentiator. As a result, for higher-order shaping, the digital control frequency divider can perform division by any of N - 1, N, N + 1, or N + 2. With higher-order shaping, the spectral behavior becomes a sharper roll-off, thereby reducing the noise in the loop. Higher-order shaping provides the circuit with the advantage of a more stable frequency ratio.

[0141] It is possible to shift the edges of a signal, such as the output of a digital control multi-frequency divider, using a DTC (Digital to Time Converter). The digital control multi-frequency divider divides N, which alternates in some pattern, by division by N + 1, while the DTC interpolates the edges so that they are almost exactly in time. Therefore, the DTC can reduce the jitter introduced in the circuit and provide the advantage of a more stable circuit and / or frequency ratio.

[0142] The two methods described above are a digital control multi-frequency divider and a DTC, which have separate performances in terms of noise and accuracy. The digital control multi-frequency divider provides a divided signal, and the loop stability and optionally the accuracy depend on filtering by a loop filter and, if present, a resonator. On the other hand, the DTC provides much better initial accuracy but has the drawback of adding a large noise component spectrally. Which advantages or disadvantages are dominant is not easily specified. This is because their advantages and disadvantages vary with the behavior of other circuit components, especially other circuit components in the loop and the signals provided to the circuit.

[0143] The frequency phase detector can be a frequency mixer, an analog multiplier, a digital circuit, or a logic circuit configured as a phase detector. The frequency phase detector, phase detector, or phase generates an output signal such as a phase difference signal, which represents the difference in phase between two input signals, such as between the divided signal and a second input signal. Depending on the type of frequency phase detector, it may be necessary to phase shift the input signal to provide an output signal that can be used to lock onto the loop. As an example, a logic circuit phase detector made from an ex-OR logic gate typically locks the loop with a 90° phase shift between the input signals.

[0144] The inner loop filter and the outer loop filter stabilize the inner and outer loops, respectively. The inner loop filter and the outer loop filter can further stabilize their respective loops in consideration of the input signals provided to the frequency ratio generator and the frequency generator, respectively. When a resonator is present, the inner loop filter and the outer loop filter can further stabilize the circuit in consideration of the behavior of the resonator. The inner loop filter and the outer loop filter can be primary or secondary filters. The loop filter is typically a low-pass filter. The cut-off frequency of the loop filter is typically a balance between the accuracy and speed of disturbance correction in the circuit. When the cut-off frequency is low, the jitter allowed through each loop filter is reduced, providing higher accuracy. On the other hand, when the cut-off frequency is high, a faster response to changes in the circuit, such as temperature changes, is provided. Also, the behavior of each loop lock in the circuit can be affected by the selection of each loop filter, particularly the cut-off frequency. An important factor in designing the loop filter is to consider the loop gain. Each loop filter is typically implemented as a PID controller.

[0145] The resonator has a fundamental frequency, which is the lowest frequency of resonance. Furthermore, the resonator can resonate at harmonic frequencies, which follow the following relationship.

[0146]

Number

[0147] Furthermore, the resonator can resonate at overtone frequencies, which follow the following relationship.

[0148]

Number

[0149] The resonant frequency of a crystal, crystal oscillator, or crystal resonator can be an even or odd harmonic and associated overtones. Typically, odd harmonics and associated overtones are used to resonate the crystal.

[0150] Note that the figures are purely schematic and not drawn to scale. In the figures, elements corresponding to elements already described may have the same reference numbers.

[0151] It will be understood that the present invention applies also to a computer program adapted to carry out the present invention, in particular to a computer program on or in a carrier. The program can be in any form of object code, such as source code, object code, intermediate source code, and partially compiled forms, or any other form suitable for use in the implementation of the method according to the present invention. It will also be understood that such a program can have many different architecture designs. For example, the program code implementing the functionality of the method or system according to the present invention can be subdivided into one or more subroutines. Many different ways of distributing functionality among these subroutines will be apparent to those skilled in the art. These subroutines can be stored together in one executable file to form a self - contained program. Such an executable file can contain computer - executable instructions, such as processor instructions and / or interpreter instructions (e.g., Java interpreter instructions). Alternatively, one or more or all of the subroutines can be stored in at least one external library file and can be linked statically or dynamically, e.g., at runtime, to the main program. The main program includes at least one call to at least one of the subroutines. The subroutines can also include function calls to each other. One embodiment related to a computer program product includes computer - executable instructions corresponding to at least one respective processing step of the methods described herein. These instructions can be subdivided into subroutines and / or stored in one or more files that can be linked statically or dynamically. Another embodiment related to a computer program product includes computer - executable instructions corresponding to at least one respective means of the systems and / or products described herein.These instructions can be subdivided into subroutines and / or stored in one or more files that can be linked statically or dynamically.

[0152] A carrier of a computer program can be any entity or device capable of carrying that program. For example, the carrier can include a ROM, such as a CD ROM or a semiconductor ROM, or a magnetic recording medium, such as a hard disk and the like. Further, the carrier can be a transmissible carrier, such as an electrical or optical signal, which can be transmitted via an electrical or optical cable or by radio or other means. When the program is embodied in such a signal, the carrier can be constituted by such a cable or other device or means. Alternatively, the carrier can be an integrated circuit in which the program is embedded, the integrated circuit being adapted to execute the relevant method or used in the execution of that method.

[0153] The above embodiments are not intended to limit the present invention, but rather to illustrate it, and it should be noted that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those recited in the claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention may be implemented using hardware comprising several individual elements and using a computer appropriately programmed. In device claims listing several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0154] Examples, embodiments, or optional features should not be understood as limiting the claimed invention, whether shown as non-limiting or not.

Claims

1. A frequency generator (300, 301) for generating a controlled signal (331) having a controlled frequency, a frequency ratio generator (100, 101, 102) arranged to generate a frequency ratio, said frequency ratio generator (100, 101, 102) comprising: an input configured to receive the controlled signal; a first controlled frequency divider (110) adapted to generate a first divided signal (115) having a first divided frequency that is substantially the controlled frequency divided by a first frequency ratio signal; a converter adapted to generate an excitation signal (129) having the first divided frequency based on the first divided signal, the excitation signal being provided to the resonator for excitation of the resonator; and a resonator (130) tuned to generate a resonance signal having a first resonance frequency, the resonator being excited by the excitation signal; a first frequency phase detector (150) adapted to generate a first phase difference signal (155) based on a first frequency phase difference between the first divided frequency and the first resonant frequency; a first inner loop filter (160) tuned to generate the first frequency ratio signal; an output configured to provide a frequency ratio signal (312) based on the first frequency ratio signal (107) indicative of the frequency ratio between the controlled frequency and the first resonant frequency; a first frequency ratio generator loop is formed by the first controlled frequency divider, the first divided signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter, and the first frequency ratio signal; a second frequency ratio generator loop is formed by the first controlled frequency divider, the first divided signal, the converter, the excitation signal, the resonator, the resonance signal, the first frequency phase detector, the first phase difference signal, the first inner loop filter, and the first frequency ratio signal; the first inner loop filter filters the first phase difference signal, thereby preventing instability in the frequency ratio generator loop; The frequency generator further comprises: a comparator (310) adapted to generate a comparison signal (315) based on a comparison of said frequency ratio with a target ratio (311); a controlled oscillator circuit (330) adapted to generate the controlled signal having the controlled frequency based on the comparison signal.

2. an outer loop filter (320) adapted to generate a filtered comparison signal (321) based on the comparison signal; the controlled frequency is based on the filtered comparison signal; an outer loop is formed by the frequency ratio generator, the comparator, the comparison signal, the outer loop filter, the filtered comparison signal, the controlled oscillator, and the controlled signal; the outer loop filter filters the comparison signal, thereby preventing instability of the outer loop; 2. The frequency generator of claim 1.

3. The comparator is based on subtracting the target ratio from the frequency ratio. and / or a subtractor arranged to provide said comparison signal based on said the comparator including a divider adapted to provide the comparison signal based on dividing the frequency ratio by the target ratio; 3. A frequency generator according to claim 1 or 2.

4. said frequency ratio generator comprising: a second controlled frequency divider (111) adapted to generate a second divided signal (116) having a second divided frequency that is substantially the controlled frequency divided by the second frequency ratio signal (108); a second frequency phase detector (151) adapted to generate a second phase difference signal (156) based on a second frequency phase difference between the second divided frequency and the second resonant frequency; a second inner loop filter (161) adapted to generate, based on the second phase difference signal, the second frequency ratio signal indicative of the second frequency ratio; a summer (120) adapted to generate a summed signal (121) that is supplied to the converter, the summed signal having the first divided frequency and the second divided frequency; and a temperature compensator for compensating for changes in a resonant frequency of the resonator, the temperature compensator comprising: an input configured to receive the first frequency ratio and the second frequency ratio; a first divider (220) adapted to generate a first divided value based on a division of the first frequency ratio by the second frequency ratio; a computer configured to calculate a compensation factor based on one or more values ​​from the group consisting of the first phase difference signal, the second phase difference signal, the first frequency ratio, and the first division value, the computer preferably including a look-up table; a redresser adapted to generate the frequency ratio based on straightening a signal based on one or more of the group consisting of the first phase difference signal, the second phase difference signal, and the first frequency ratio using the compensation coefficient; the excitation signal is based on the summed signal; a third frequency ratio generator loop is formed by the second controlled frequency divider, the second divided signal, the second frequency phase detector, the second phase difference signal, the second inner loop filter, and the second frequency ratio signal; a fourth frequency ratio generator loop is formed by the second controlled frequency divider, the second divided signal, the converter, the excitation signal, the resonator, the resonance signal, the second frequency phase detector, the second phase difference signal, the second inner loop filter, and the second frequency ratio signal; 4. The frequency generator of claim 3, wherein the second inner loop filter filters the second phase difference signal, thereby preventing instability in the frequency ratio generator loop.

5. said frequency ratio generator comprising: a selector adapted to select one or more of the group consisting of the first phase difference signal, the second phase difference signal, and the first frequency ratio based on one or more values ​​of the group consisting of the first frequency ratio and the first division value; 5. The frequency generator of claim 4, wherein the redresser is tuned to generate the frequency ratio based on correcting the selected frequency ratio with the compensation factor.

6. said frequency ratio generator comprising: a third controlled frequency divider (112) adapted to generate a third divided signal (117) having a third divided frequency that is substantially the controlled frequency divided by a third frequency ratio signal; a third frequency phase detector (152) adapted to generate a third phase difference signal (157) based on a third frequency phase difference between the third divided frequency and the third resonant frequency; a third inner loop filter (162) adapted to generate the third frequency ratio signal indicative of the third frequency ratio based on the third phase difference signal; the summed signal also has the third divided frequency; the input of the temperature compensator further configured to receive the third frequency ratio; the temperature compensator further comprising: a second divider (221) adapted to generate a second divided value based on a division of the first frequency ratio by the third frequency ratio; When dependent on claim 5, the selector is further adapted to select also on the basis of one or more values ​​from the group consisting of the third phase difference signal, the second frequency ratio, and the third frequency ratio, and also on the basis of one or more values ​​from an extended group consisting of the second frequency ratio, the third frequency ratio, and the second division value; the calculator is further adapted to calculate the compensation coefficient based on one or more values ​​of the third phase difference signal, the second frequency ratio, the third frequency ratio, and a group expanded by the second division value; the redresser is adjusted to generate the frequency ratio based on correcting the selected frequency ratio with the compensation factor; a fifth frequency ratio generator loop is formed by the third controlled frequency divider, the third divided signal, the third frequency phase detector, the third phase difference signal, the third inner loop filter, and the third frequency ratio signal; a sixth frequency ratio generator loop is formed by the third controlled frequency divider, the third divided signal, the converter, the excitation signal, the resonator, the resonance signal, the third frequency phase detector, the third phase difference signal, the third inner loop filter, and the third frequency ratio signal; 6. The frequency generator of claim 4, wherein the third inner loop filter filters the third phase difference signal, thereby preventing instability in the frequency ratio generator loop.

7. The selector of the frequency ratio generator selecting one of the group consisting of the first frequency ratio, the second frequency ratio, and the third frequency ratio, wherein the selected ratio is based on one or more values ​​of the group consisting of the first frequency ratio, the second frequency ratio, the third frequency ratio, the first division value, and the second division value; or 7. The frequency generator of claim 6, adapted to select a weighted combination of two or more of the first frequency ratio, the second frequency ratio, and the third frequency ratio, the weighted combination being based on one or more values ​​of the group consisting of the first frequency ratio, the second frequency ratio, the third frequency ratio, the first divide value, and the second divide value.

8. the first division value is based only on the first frequency ratio signal and the second frequency ratio signal; the second division value is based only on the first frequency ratio signal and the third frequency ratio signal; the selector is adapted to select one or more of a limited group consisting of the first phase difference signal, the second phase difference signal, and the third phase difference signal; and / or the calculator being adapted to calculate a compensation factor based on one or more values ​​from a limited group consisting of the first divided value and the second divided value; A frequency generator according to any one of claims 4 to 7.

9. 9. The frequency generator of claim 1, wherein the frequency ratio generator includes an analog-to-digital converter (140) arranged to generate a digital resonance signal (145) based on the resonance signal, the digital resonance signal being supplied to at least the first frequency phase detector.

10. 10. The frequency generator of claim 1, wherein the converter of the frequency ratio generator comprises a digital-to-analog converter (125) arranged to generate the excitation signal based on the divided signal.

11. The comparator, a scaler arranged to generate a scaled signal, the frequency ratio signal being scaled by a scaling factor; and / or a shifter arranged to generate a shifted signal, the scaled signal being shifted by a shift value; 11. A frequency generator as claimed in any preceding claim, wherein the comparison signal is based on the shifted signal.

12. a phase acquisition circuit (340) adapted to generate a phase difference signal (345) based on the phase difference between the controlled frequency and a reference signal (341) having a reference frequency; a PLL (350) adapted to generate an offset signal (355) based on the phase difference signal; the controlled frequency is also based on the offset signal. A frequency generator according to any one of claims 1 to 11.

13. at least when dependent on claim 11, the shift value being the offset signal; or At least when dependent on claim 2, the filtered comparison signal is indirectly based on the offset signal.

13. The frequency generator of claim 12.

14. 1. A method for generating a controlled signal having a controlled frequency, comprising: receiving a resonant signal from a resonator having a first resonant frequency; providing a first ratio signal indicative of a first frequency ratio between the controlled frequency and the first resonant frequency; generating a first phase difference signal (155) based on a first frequency phase difference between the first divided frequency and the first resonant frequency; filtering the first phase difference signal to generate the first frequency ratio signal; whereby instability in the frequency ratio generator loop is prevented; and basing a frequency ratio on the first frequency ratio signal; providing a target ratio; generating a comparison signal based on a comparison of the frequency ratio with the target ratio; generating the controlled signal having the controlled frequency based on the comparison signal; generating a first divided signal (115) having a first divided frequency that is substantially the controlled frequency divided by the first frequency ratio signal; generating an excitation signal (129) having the first divided frequency based on the first divided signal, the excitation signal being provided to the resonator for excitation of the resonator; and outputting the controlled signal. a first frequency ratio generator loop is formed by the first divided signal, the first phase difference signal, and the first frequency ratio signal; a second frequency ratio generator loop is formed by the first divided signal, the excitation signal, the resonator, the resonance signal, the first phase difference signal, and the first frequency ratio signal; The method of claim 1, wherein the filtering step filters the first phase difference signal, thereby preventing instability in the frequency ratio generator loop.

15. A frequency generator chip including a frequency generator according to any one of claims 1 to 14; a resonator for coupling to said frequency generator chip for generating said resonant signal; an oscillator for connecting to said controlled oscillator circuit for generating an oscillating signal; 2. A frequency generator system comprising:

16. A computer program product (1000) including a computer readable medium (1010) having computer readable code (1020) embodied therein, said computer readable code, when executed by a suitable computer or processor, causing said computer or processor to perform the method of claim 14. providing a first ratio signal; basing the frequency ratio; generating a comparison signal; generating said controlled signal; outputting an excitation signal; and outputting the controlled signal.

17. A computer program product (1000) comprising a computer readable medium (1010) having computer readable code (1020) embodied therein, the computer readable code being configured, when executed by a suitable computer or processor, to cause the computer or processor to perform the method of claim 14.

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