A wireless crystal oscillator calibration method based on frequency offset estimation
Patent Information
- Application Number
- CN202611047500.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-15
- Publication Date
- 2026-10-16
AI Technical Summary
然而，传统无线晶振校准虽取消了有线探针，却仍存在多项技术短板
[0014] This invention utilizes communication principles to wirelessly calibrate the crystal oscillator in a chip. This eliminates the need for special considerations for crystal oscillator measurement during circuit board design and reduces the risk of chip damage caused by introducing external signals as a standard clock reference. Furthermore, because it employs wireless calibration, this invention can calibrate multiple devices simultaneously, significantly improving chip calibration efficiency.
Smart Images
Figure CN122932846A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wireless communication, and in particular to a wireless crystal oscillator calibration method based on frequency offset estimation. Background Technology
[0002] With the rapid development of information technology, the proportion of digital circuits in various electronic systems is constantly increasing. As the core of digital circuits, the accuracy of the clock largely determines the system's performance. Crystal oscillators, as the most common clock source, are hailed as the "heart" of digital circuits. In the field of wireless communication, the accuracy of the carrier frequency directly affects communication quality, and the clock signal provided by the crystal oscillator is usually the basis for carrier frequency generation; therefore, the importance of its accuracy is self-evident.
[0003] Existing crystal oscillator calibration methods mostly employ wired connections. These methods impose special requirements on the circuit board during calibration, typically requiring dedicated test points to calculate the deviation between the standard clock frequency and the crystal to be calibrated. Simultaneously, a dedicated pin must be designed within the chip to introduce the standard clock, which may damage parts of the circuitry due to excessively high voltage amplitude from the external clock input. Furthermore, the overall efficiency of the chip during the crystal oscillator calibration stage is not high due to limitations in the number of devices that wired calibration methods can simultaneously support.
[0004] To address these issues, the industry has gradually developed wireless crystal oscillator calibration methods. However, while traditional wireless crystal oscillator calibration eliminates wired probes, it still suffers from several technical shortcomings. Specifically, its initialization strategy relies solely on the average of the crystal's inherent capacitance and adjustable capacitance to determine the initial control word, failing to adequately consider frequency drift caused by PCB parasitic capacitance and operating temperature variations. This results in a larger initial frequency offset upon power-on. Consequently, the number of subsequent binary search iterations increases, and calibration time remains long, hindering improvements in mass production efficiency. Summary of the Invention
[0005] To address the aforementioned problems, this invention proposes a wireless crystal oscillator calibration method based on frequency offset estimation, aiming to simplify the requirements for external equipment during crystal oscillator calibration and improve calibration efficiency. The method includes the following steps:
[0006] S1. Construct and initialize a wireless crystal oscillator calibration system, which includes a host computer, a device to be calibrated, and a calibrated transmitting device; wherein:
[0007] The frequency points of the device to be calibrated and the calibrated transmitting device are set via the host computer.
[0008] Obtain the inherent parameters of the device to be calibrated, and initialize the crystal oscillator control word of the device to be calibrated according to the inherent parameters; the inherent parameters include the crystal's inherent load capacitance value, the adjustable capacitance value corresponding to the built-in crystal oscillator control word, the fixed parasitic capacitance value of the PCB trace, and the crystal temperature drift coefficient.
[0009] Configure the calibrated transmitting device to transmit a standard Bluetooth 2M data packet at preset intervals;
[0010] S2. After receiving a standard Bluetooth 2M data packet, the device to be calibrated performs the following operations:
[0011] Frequency offset is calculated in hardware using a fixed sequence of preambles;
[0012] Determine whether the frequency offset is within the preset standard frequency offset range. If yes, end the calibration and record the current crystal oscillator control word. If not, adjust the crystal oscillator control word using the binary search method and return to step S2 to continue execution.
[0013] The beneficial effects of this invention are:
[0014] This invention utilizes communication principles to wirelessly calibrate the crystal oscillator in a chip. This eliminates the need for special considerations for crystal oscillator measurement during circuit board design and reduces the risk of chip damage caused by introducing external signals as a standard clock reference. Furthermore, because it employs wireless calibration, this invention can calibrate multiple devices simultaneously, significantly improving chip calibration efficiency.
[0015] This invention provides a novel crystal oscillator control word initialization strategy. The entire process eliminates the need for a target total equivalent load capacitance as a constraint, abandoning the traditional inverse calculation logic for tuning capacitance. This strategy generates the initial control word based on the device's actual inherent parasitic capacitance and the actual operating conditions of the current adjustable capacitance, thereby significantly reducing the initial frequency offset during crystal oscillator power-on initialization. This effectively narrows the frequency offset adjustment range for subsequent fine calibration, reduces the number of iterative tuning iterations, and shortens the overall calibration time. Attached Figure Description
[0016] Figure 1 This is a flowchart of a wireless crystal oscillator calibration method based on frequency offset estimation according to the present invention;
[0017] Figure 2 This is a schematic diagram of the structure of a wireless crystal oscillator calibration system according to the present invention. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] Please see Figure 1 This invention provides a wireless crystal oscillator calibration method based on frequency offset estimation, comprising the following steps:
[0020] S1. Construct and initialize a wireless crystal oscillator calibration system, which includes a host computer, a device to be calibrated, and a calibrated transmitting device. Initializing the wireless crystal oscillator calibration system includes:
[0021] The frequency points of the device to be calibrated and the calibrated transmitting device are set via the host computer.
[0022] Obtain the inherent parameters of the device to be calibrated, and initialize the crystal oscillator control word of the device to be calibrated according to the inherent parameters; the inherent parameters include the crystal's inherent load capacitance value, the adjustable capacitance value corresponding to the built-in crystal oscillator control word, the fixed parasitic capacitance value of the PCB trace, and the crystal temperature drift coefficient.
[0023] The calibrated transmitting device is configured to transmit a standard Bluetooth 2M data packet every 625μs. The standard Bluetooth 2M data packet has a data length of 37 bytes.
[0024] S2. After receiving a standard Bluetooth 2M data packet, the device to be calibrated performs the following operations:
[0025] Frequency offset is calculated in hardware using a fixed sequence of preambles;
[0026] Determine whether the frequency offset is within the preset standard frequency offset range. If yes, end the calibration and record the current crystal oscillator control word. If not, adjust the crystal oscillator control word using the binary search method and return to step S2 to continue execution.
[0027] In this invention, the device to be calibrated includes a Bluetooth SoC chip and an external crystal resonator; the Bluetooth SoC chip integrates a main control processor, a Bluetooth Low Energy RF transceiver module, and an adjustable capacitor array; the Bluetooth RF transceiver module is used to receive standard Bluetooth 2M data packets and calculate the carrier frequency offset using its internal preamble fixed sequence hardware, and writes the frequency offset value into a register; the main control processor reads the frequency offset value, determines whether it meets the preset standard frequency offset range, and adjusts the crystal oscillator control word using a binary search method to change the equivalent capacitance value of the adjustable capacitor array.
[0028] The standard Bluetooth 2M data packet refers to the link layer data packet that conforms to the BLE LE 2M PHY (Bluetooth Low Energy 2 Mbps Physical Layer) specification in Bluetooth Core Specification 5.0 and above.
[0029] In some embodiments, the wireless crystal oscillator calibration method proposed in this invention provides a novel crystal oscillator control word initialization strategy for initializing the crystal oscillator control word of the device to be calibrated.
[0030] Existing conventional crystal oscillator control word initialization schemes all use the crystal's nominal target total equivalent load capacitance as a constraint. This capacitance is substituted into the equivalent load calculation formula for the oscillator circuit (such as the standard load capacitance formula for the Pierce oscillator circuit) to inversely solve for the required tuning capacitance, and then converted to obtain the initial crystal oscillator control word. This scheme is highly dependent on the crystal's factory-specified load capacitance parameters. If there are batch deviations in the chip's inherent parasitic capacitance, PCB trace stray capacitance, or if the crystal's actual load characteristics deviate from the nominal value, it can easily lead to excessively large frequency offsets during the initialization phase, prolonging the convergence time of subsequent iterative calibrations. In extreme cases, it may even cause problems such as unstable crystal oscillator startup and exceeding calibration search limits.
[0031] To address the aforementioned shortcomings of existing technologies, this invention extracts the inherent parameters of the device to be calibrated. These inherent parameters include the inherent load capacitance of the crystal, the fixed parasitic capacitance of the PCB traces, the crystal temperature drift coefficient, and the adjustable capacitance value corresponding to the current original crystal oscillator control word of the device. A new initial crystal oscillator control word is then generated based on these inherent parameters.
[0032] The crystal temperature drift coefficient is a nominal parameter of the crystal at the factory, or it is obtained by pre-calibrating the batch of crystals through high and low temperature tests, and stored in the non-volatile memory of the device to be calibrated.
[0033] In one optional implementation, initializing the crystal control word of the device to be calibrated according to its inherent parameters includes:
[0034] Read the current temperature value T from the temperature sensor in the device to be calibrated. The Bluetooth SoC chip of the device to be calibrated integrates a temperature sensor to collect the current operating temperature.
[0035] Based on the fixed parasitic capacitance of PCB traces, the inherent load capacitance of the crystal, and the adjustable capacitance, the fundamental equivalent capacitance is calculated, including:
[0036] ,
[0037] In the formula, Cbase is the basic equivalent capacitance value, C0 is the inherent load capacitance value of the crystal, Cx is the adjustable capacitance value corresponding to the crystal oscillator control word of the device to be calibrated, and Cp is the fixed parasitic capacitance value of the PCB trace.
[0038] By combining the current temperature value T with the crystal temperature drift coefficient, the basic equivalent capacitance value is compensated to obtain the temperature compensation capacitance correction amount, including:
[0039] ,
[0040] In the formula, Ct is the temperature compensation capacitor correction amount.
[0041] The overall tuning capacitance value is calculated based on the temperature compensation capacitor correction and the basic equivalent capacitance value, including:
[0042] ,
[0043] In the formula, Cinit is the value of the overall tuning capacitor.
[0044] The integrated tuning capacitor value is mapped to the adjustable capacitor array register value, and this value is written as the initial crystal oscillator control word into the device to be calibrated.
[0045] The entire process does not require the introduction of the target total equivalent load capacitance as a constraint, and abandons the traditional inverse calculation logic of tuning capacitance. This invention integrates the crystal temperature drift coefficient into the initialization modeling process in advance, and reuses the adjustable capacitor corresponding to the original control word of the device to jointly correct the initial tuning code. It can simultaneously compensate for the frequency offset caused by board-level parasitics, device individual discreteness and full-temperature drift, reduce the initial frequency offset range from the source, and significantly reduce the power-on initialization frequency offset.
[0046] Compared to traditional calibration initialization methods, this solution eliminates the need for constraint calculations based on the crystal's nominal target total equivalent load capacitance. It generates the initial control word by closely aligning with the device's inherent parasitic capacitance and the actual operating conditions of the adjustable capacitor. This significantly reduces the initial frequency offset during crystal oscillator power-on initialization, effectively narrowing the frequency offset adjustment range for subsequent fine calibration, reducing the number of iterative tuning iterations, and shortening the overall calibration time. Furthermore, this solution reduces the risk of crystal oscillator startup anomalies and capacitor array adjustment overflows caused by excessive initial frequency offset, improving the consistency and stability of crystal oscillator calibration for batch products.
[0047] This embodiment combines the inherent capacitance of the crystal with the capacitance superimposed on the crystal oscillator control word to set an initial value different from that of the prior art, thereby shortening the crystal oscillator calibration time. Specifically, the initial control word of the device to be calibrated is associated with the inherent capacitance of its crystal and the superimposed capacitance corresponding to the current crystal oscillator control word, thereby improving calibration efficiency.
[0048] Figure 2 This invention provides a wireless crystal oscillator calibration system.
[0049] exist Figure 2In this system, the PC is a host computer used for configuration and information retrieval; the gold device is a wireless transmitter that has undergone crystal oscillator calibration (i.e., a calibrated transmitting device); and the board under test (DUT) is a wireless receiver that has not undergone crystal oscillator calibration (i.e., a device to be calibrated). The wireless crystal oscillator calibration system includes several devices to be calibrated. The PC is connected to the UART interface of the device to be calibrated via a USB-to-UART converter module, used to send configuration commands and receive calibration result data.
[0050] In some embodiments, such as Figure 2 As shown, the PC configures the gold receiver to continuously transmit a standard Bluetooth 2M data packet with a data length of 37 bytes every 625 μs. The PC sets the gold receiver's transmit power as high as possible to ensure the quality of the received signal from the devices under calibration. Simultaneously, the PC sets all devices under calibration to receive at the same frequency as the gold receiver's transmit frequency, and the crystal oscillator control word of the devices under calibration is initialized according to the aforementioned strategy.
[0051] After correctly receiving a standard Bluetooth 2M data packet, the device to be calibrated will report the frequency offset information, calculated by the hardware using a fixed preamble sequence, to its main control processor. The main control processor then compares this frequency offset information with a preset frequency offset range.
[0052] If the reported frequency deviation is greater than the set frequency deviation range, the crystal oscillator control word is adjusted to increase the crystal oscillator frequency using the binary division method, and the next standard Bluetooth 2M data packet is received.
[0053] If the reported frequency offset is less than the set frequency offset range, the crystal oscillator control word is adjusted to reduce the crystal oscillator frequency using the binary division method, and the next standard Bluetooth 2M data packet is received.
[0054] If the reported frequency offset is within the set frequency offset range, the current crystal oscillator control word is recorded and the calibration process ends.
[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A wireless crystal oscillator calibration method based on frequency offset estimation, characterized in that, Includes the following steps: S1. Construct and initialize a wireless crystal oscillator calibration system, which includes a host computer, a device to be calibrated, and a calibrated transmitting device; wherein: The frequency points of the device to be calibrated and the calibrated transmitting device are set via the host computer. Obtain the inherent parameters of the device to be calibrated, and initialize the crystal oscillator control word of the device to be calibrated according to the inherent parameters; the inherent parameters include the crystal's inherent load capacitance value, the adjustable capacitance value corresponding to the built-in crystal oscillator control word, the fixed parasitic capacitance value of the PCB trace, and the crystal temperature drift coefficient. Configure the calibrated transmitting device to transmit a standard Bluetooth 2M data packet at preset intervals; S2. After receiving a standard Bluetooth 2M data packet, the device to be calibrated performs the following operations: Frequency offset is calculated in hardware using a fixed sequence of preambles; Determine whether the frequency offset is within the preset standard frequency offset range. If yes, end the calibration and record the current crystal oscillator control word. If not, adjust the crystal oscillator control word using the binary search method and return to step S2 to continue execution.
2. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 1, characterized in that, Initializing the crystal oscillator control word of the device to be calibrated according to its inherent parameters includes: Read the current temperature value T of the temperature sensor in the device to be calibrated; Calculate the basic equivalent capacitance value based on the fixed parasitic capacitance value of PCB traces, the inherent load capacitance value of crystal, and the adjustable capacitance value. By combining the current temperature value T with the crystal temperature drift coefficient, the basic equivalent capacitance value is compensated to obtain the temperature compensation capacitance correction amount; The integrated tuning capacitance value is calculated based on the temperature compensation capacitor correction and the basic equivalent capacitance value. The integrated tuning capacitance value is then mapped to the adjustable capacitor array register value and written as the initial crystal oscillator control word into the device to be calibrated.
3. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 2, characterized in that, Based on the fixed parasitic capacitance of PCB traces, the inherent load capacitance of the crystal, and the adjustable capacitance, the basic equivalent capacitance value is calculated as follows: ， In the formula, Cbase is the basic equivalent capacitance value, C0 is the inherent load capacitance value of the crystal, Cx is the adjustable capacitance value corresponding to the crystal oscillator control word of the device to be calibrated, and Cp is the fixed parasitic capacitance value of the PCB trace.
4. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 2, characterized in that, The basic equivalent capacitance is compensated by combining the current temperature value T with the crystal temperature drift coefficient, including: ， In the formula, Ct is the temperature compensation capacitor correction amount, and Cbase is the basic equivalent capacitance value.
5. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 2, characterized in that, The overall tuning capacitance value is calculated based on the temperature compensation capacitor correction and the basic equivalent capacitance value, including: ， In the formula, Cinit is the overall tuning capacitor value, Ct is the temperature compensation capacitor correction amount, and Cbase is the basic equivalent capacitor value.
6. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 1, characterized in that, The calibrated transmitter is configured to transmit a standard Bluetooth 2M data packet every 625μs. The standard Bluetooth 2M data packet has a data length of 37 bytes.
7. The wireless crystal oscillator calibration method based on frequency offset estimation according to claim 1, characterized in that, The number of devices to be calibrated is greater than or equal to 2.