High-precision time difference measuring circuit and measuring method suitable for taming crystal oscillator

Abstract

The invention discloses a high-precision time difference measurement circuit and measurement method suitable for taming a crystal oscillator, and the circuit comprises an MCU module, a GNSS second pulse signal module, an external high-precision crystal oscillator module, a differential-to-single-ended module, a frequency dividing circuit, a time-to-digital converter, and a power unit, and the GNSS second pulse signal module is connected with the frequency dividing circuit through the differential-to-single-ended module. The external high-precision crystal oscillator module is connected with the frequency dividing circuit, the output end of the frequency dividing circuit is connected with the time-to-digital converter, the time-to-digital converter is in communication connection with the MCU module, and the power supply unit is electrically connected with the MCU module, the GNSS second pulse signal module, the external high-precision crystal oscillator module, the differential-to-single-ended module, the frequency dividing circuit and the time-to-digital converter. According to the application, the single-channel measurement precision is high, the circuit size is small, and the circuit can be widely transplanted and applied to high-precision time keeping and time service systems in various fields.

Description

Technical Field

[0001] The present application relates to the technical field of time difference measurement, and in particular to a high-precision time difference measurement circuit and a measurement method suitable for taming a crystal oscillator. Background Art

[0002] With the development of GNSS and crystal oscillators, the accuracy of their respective clocks has reached a very high level. The demand for higher accuracy has driven people to explore technical methods that combine the long-term stability advantages of GNSS with the short-term temperature advantages of crystal oscillators, that is, to achieve higher-precision designs by taming crystal oscillators. With the development of digital circuits, crystal oscillator taming technology has become more and more mature, and there are more and more types. High-precision and high-stability frequency standards are widely used in various fields such as military and civilian.

[0003] The basic principle of taming a crystal oscillator is to compare the time difference of the input signal and use a certain control method to use the deviation to calibrate the frequency of the crystal oscillator output. There are many circuit implementation methods, such as using analog phase detection and filtering circuits to achieve time difference measurement, but this method has a complex circuit and has a greater impact on short-term stability. Summary of the invention

[0004] The present application provides a high-precision time difference measurement circuit and measurement method suitable for taming a crystal oscillator, which has high single-channel measurement accuracy and small circuit size, and can be widely transplanted and applied to high-precision timekeeping and timing systems in various fields.

[0005] The present application provides a high-precision time difference measurement circuit suitable for taming a crystal oscillator, comprising: an MCU module, a GNSS second pulse signal module, an external high-precision crystal oscillator module, a differential-to-single-ended module, a frequency division circuit, a time-to-digital converter and a power supply unit, wherein the GNSS second pulse signal module is connected to the frequency division circuit via the differential-to-single-ended module, the external high-precision crystal oscillator module is connected to the frequency division circuit, the output end of the frequency division circuit is connected to the time-to-digital converter, the time-to-digital converter is communicatively connected to the MCU module, and the power supply unit is electrically connected to the MCU module, the GNSS second pulse signal module, the external high-precision crystal oscillator module, the differential-to-single-ended module, the frequency division circuit, and the time-to-digital converter.

[0006] Furthermore, the differential-to-single-ended module uses a MAX3485 differential level conversion chip to convert the differential pulse-per-second signal output by the GNSS pulse-per-second signal module into a 3.3V single-ended signal.

[0007] Furthermore, the output frequency range of the external high-precision crystal oscillator module is between 10 MHz and 100 MHz.

[0008] Furthermore, the frequency division circuit adopts the EPM570T100 chip to realize the filtering output of the pulse 1PPS and the frequency division of the crystal oscillator output.

[0009] Furthermore, the time-to-digital converter adopts a GP22 chip.

[0010] The present invention also provides a measurement method using the high-precision time difference measurement circuit suitable for taming a crystal oscillator, comprising:

[0011] The GNSS differential second pulse signal output by the GNSS second pulse signal module is output to the differential to single-ended module to convert the differential second pulse signal into a 3.3V single-ended second pulse signal, which is then filtered through a frequency division circuit; the crystal oscillator signal output by the external high-precision crystal oscillator module to be tamed is output to the frequency division circuit for frequency division, and the reference clock signal after the crystal oscillator frequency division and the crystal oscillator signal to be tamed are output; wherein the single-ended second pulse signal is used as a reference signal, and the crystal oscillator signal to be tamed is a calibrated signal;

[0012] The frequency division circuit outputs the filtered single-ended second pulse signal, the reference clock signal after the crystal oscillator frequency division, and the crystal oscillator signal to be tamed to the time digital converter. The time digital converter compares the single-ended second pulse signal and the crystal oscillator signal to be tamed with the reference clock signal to obtain a time difference digital quantity signal. Then, the time digital converter transmits two types of time difference digital quantity signals to the MCU through the SPI serial port.

[0013] The MCU calculates the time difference between the single-ended pulse-per-second signal and the crystal oscillator signal to be tamed according to the time difference digital quantity.

[0014] Furthermore, the MCU sets the register of the least significant bit LSB of the time digital converter through the serial port, and sets the bit width and the FIFO length at the same time.

[0015] Furthermore, the reference clock signal is 1 MHz.

[0016] Furthermore, the frequency division circuit divides the signal output by the tamed external high-precision crystal oscillator module by 10 8 The frequency is divided to obtain the crystal oscillator signal to be tamed.

[0017] Furthermore, the MCU uses the reference clock signal as the reference clock and combines the register configuration value of the least significant bit LSB to calculate the time corresponding to the digital quantity. The specific calculation formula is: t2-t1+K*2^16, t1 and t2 are the measurement moments of the reference clock signal and the crystal oscillator signal to be tamed, respectively, and K is the linear ratio between the time and the time difference digital quantity signal.

[0018] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0019] 1. This application takes into account that directly using the crystal oscillator output as the input of the time-frequency conversion module is likely to result in a large amount of module data and cumbersome processing. The output signal of the crystal oscillator is first divided and used as the input of the frequency division circuit, making the entire circuit small.

[0020] 2. This application converts the GNSS second pulse signal from differential to single-ended and performs filtering, with high measurement accuracy. In the frequency division circuit, 1MHz is specially designed as the clock reference of the time digital converter to ensure that even if the time interval between the two pulse signals is too large, it will not cause the time digital converter data overflow. The least significant bit LSB register is set to 216 to ensure that the digital quantity representation accuracy of the measured output is within 20ps. It can be widely transplanted and applied to high-precision timekeeping and timing systems in various fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0022] Figure 1 This is the overall functional block diagram of the circuit of this application;

[0023] Figure 2 The power supply circuit schematic diagram for this application;

[0024] Figure 3 A differential to single-ended circuit for this application;

[0025] Figure 4 This is the frequency division circuit schematic diagram of this application;

[0026] Figure 5 This is the circuit schematic diagram of the time-to-digital converter of this application;

[0027] Figure 6 This is the principle timing diagram of the time difference measurement implementation of this application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0029] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0030] Example 1

[0031] The overall circuit framework structure of the present invention is that one GNSS differential second pulse signal enters the time difference measurement circuit module after passing through the RS422 interface circuit, and the other is the output of the crystal oscillator to be tamed and enters the time difference measurement module after frequency division. The two input signals are measured by the time digital converter and the digital time difference signal is output. The power supply of the entire functional module adopts 5V input, which is converted into 3.3V and 1.8V secondary power supplies for each part of the digital circuit through the power management module.

[0032] The external power input of the present invention is a 5V power supply, and the power management module can be implemented by a power management chip TPS70302 or multiple linear LDOs, and according to the requirements of the time-frequency conversion circuit chip, 3.3V and 1.8V power supplies are generated for use by various digital circuits inside the module. Taking TPS70302 as an example, the input voltage of the chip is 5V, and the output end can achieve the conversion from 5V to 3.3V and 1.8V by matching the resistance of the feedback end and the output end, thereby realizing the power supply support for the subsequent digital circuit. The resistance matching of the feedback end and the output end needs to be selected according to the recommended working resistance of the chip, and the recommended value of the resistance between the feedback end and the ground is 30.1K. The resistance value of the output end and the feedback end needs to be calculated according to the required voltage and the principle of the same current flowing through the same path.

[0033] The GNSS differential pulse-per-second signal outside the module is input in RS422 differential level mode. The present invention uses the MAX3485 differential level conversion chip to convert the differential pulse-per-second signal into a 3.3V single-ended signal. The single-ended signal can be directly used by connecting to the frequency division and multiplication modules of the subsequent stage.

[0034] The crystal oscillator input signal outside the module is the output of a high-precision constant temperature crystal oscillator, and its output frequency range is between 10MHz and 100MHz. The present invention takes the 100MHz design as an example. Considering that if the crystal oscillator output is directly used as the input of the time-frequency conversion module, it is easy to cause a large amount of module data and cumbersome processing, the output signal of the crystal oscillator is first divided and used as the input of the frequency division circuit. At the same time, this signal is also used as the reference clock of the time digital converter.

[0035] The frequency division circuit is implemented by using the EPM570T100 chip, which realizes two functions: one is the filtering output of the pulse 1PPS; the other is the frequency division of the crystal oscillator output 100MHz. It uses 3.3V power supply, and its input is the above two external input signals; its output is 1 GNSS 1PPS_1 signal, 1 crystal oscillator divided 1PPS_2 signal, and 1 shaped 1MHz signal. Its frequency division function needs to be implemented through JTAG port programming, so it is also equipped with a JTAG circuit unit.

[0036] The time digital converter uses the GP22 chip. Compared with the previous generation TDC chip, this type of chip has a higher resolution and can achieve a maximum accuracy of 20ps, which is more suitable for high-precision time difference measurement circuits. The chip uses an SPI communication module, which can communicate with various MCU units in the back stage of the time difference measurement, and transmit the digital time difference signal to the back stage. Taking into account the resolution of the conversion and the size of the digital quantity, the input reference clock of the chip is the 1MHz signal of the tamed crystal oscillator on the module. GP22 has 4 groups of STOP inputs, and the present invention uses 2 of them. One STOP is the second pulse signal 1PPS_1 of the GNSS; the other STOP is the second pulse signal 1PPS_2 after the crystal oscillator is divided. Both signals can be compared with the reference clock. After comparison, the two types of digital quantities transmitted by GP22 through the SPI serial port can be calculated to obtain the time difference between the two signals.

[0037] After designing each circuit unit according to the above requirements, the hardware circuit of the present invention has been realized, and the specific principle of its time difference measurement needs to be realized in combination with software and hardware. The software is in two parts, one part is the frequency division circuit, which needs to apply the phase-locked loop module and frequency division module in EPM570T100, and after 10E8 frequency division, the required crystal oscillator second pulse signal 1PPS_2 is obtained. At the same time, the MCU sets the LSB setting register, bit width, and FIFO length of GP22 through the serial port. Taking into account the STOP data storage width of GP22, the present invention specially designs 1MHz as the clock reference of GP22 in the frequency division circuit to ensure that even if the time interval between the two pulse signals is too large, it will not cause GP22 data overflow. At the same time, the LSB setting register is set to 216 to ensure that the digital quantity representation accuracy of the measured output is within 20ps.

[0038] Example 2

[0039] Figure 1 This is the overall functional block diagram of the circuit of the present invention. The overall function of the circuit of the present invention is to externally input 2 different time models, with the GNSS second pulse signal as the reference and the external high-precision crystal oscillator as the calibrated crystal oscillator signal. After the GNSS second pulse signal passes through the differential to single-ended circuit, it can be connected to the frequency division and filtering circuit for conversion, and then output without changing the frequency; the crystal oscillator to be tamed is also connected to the frequency division circuit module, and divided into 1MHz and 1PPS output of the crystal oscillator. The 3-way signal passing through the frequency division circuit enters the time-frequency converter, and through the STOP1 and STOP2 dual-channel combined measurement, accurate time difference measurement is achieved, and the time difference measurement result is transmitted to the subsequent MCU unit in the form of digital quantity. That is, the time difference measurement is completed. The accuracy of the time difference measurement is concentrated in the frequency converter.

[0040] Figure 2The figure is the schematic diagram of the power supply circuit. The figure shows the schematic diagram of the power management circuit for TPS70302 as an example. The input voltage of the chip is DVS5+, that is, the external 5V input voltage. The front-end C4 and C5 are 0.22uF tantalum capacitors, which perform front-end filtering on the power input. VDD3V3 and VDD1V8 are the output voltages after passing through the power management chip. Resistors R13 and R24 are resistors between the feedback terminal and the ground. The recommended value is 30.1K, and the reference voltage of the FB pin is 1.224V. According to the voltage-current formula, the current flowing through R13 and R24 is 1.224V / 30.1K=0.04066mA, so the current flowing through R2 and R20 is also 0.04066mA, so the output voltage corresponding to the Vout2 pin can be obtained as 0.04066mA*(53.6K+30.1K), which is approximately equal to 3.3V. Similarly, the output voltage corresponding to the Vout1 pin is 1.8V, which meets the power requirements of subsequent circuits.

[0041] Figure 3 The schematic diagram of differential to single-ended circuit is shown in Figure 2. The circuit is a differential to single-ended circuit. The circuit uses the MAX3485 half-duplex communication chip, whose communication rate can reach 10Mbps and whose power supply voltage is 3.3V. The external differential signal is connected to the input end of the differential chip through pins 6 and 7 respectively. The direction of the chip is controlled by pin 2 RE. Since 1PPS only has a unidirectional transmission from differential to single-ended, pin 2 can be directly pulled down. On the way, R114, R120, and R126 are termination resistors for signal matching for data transmission, which are generally used as debugging resistors. The resistance value can be adjusted according to the actual situation of the matching resistor at the signal source end and the transmission line resistance. The present invention selects the resistance value as shown in the figure according to actual needs.

[0042] Figure 4 The frequency division circuit is implemented by using the EPM570T100 chip, which has 100 pins. The circuit power supply is 3.3V, and the program download is realized through JTAG. The input signal can be divided internally. After the crystal oscillator 100MHz signal is input, it is divided by 100 times and 10 times respectively. 8 By dividing the frequency by multiples, we can get two homologous frequency outputs of 1MHz and 1PPS_2.

[0043] Figure 5The schematic diagram of the circuit of the time digital converter is shown in FIG. The time digital converter adopts the GP22 chip, which is a chip specially used for time digital conversion and is widely used in the field of time difference measurement. The GP22 chip has a higher resolution and can achieve a maximum accuracy of 20ps, which is more suitable for the present invention to solve the problem of measurement accuracy. The power supply of the chip is a plurality of groups of 3.3V power supplies and 1.8V power supplies, which respectively supply power to different modules in the chip. When designed and used, all power supplies must be supplied. It can be connected to the external control chip MCU through the on-chip MISO, MOSI, SCK, and SSN to pass the calculated time difference digital quantity to the subsequent stage. The two input signals of the time difference to be measured are respectively connected to STOP1 and STOP2. After the time difference digital quantity of STOP1 and STOP2 is measured by the combination, there is a linear correspondence between the time difference digital quantity and the time. According to the 1MHz reference clock input by REFCLKP and the configuration value of the LSB register, the time corresponding to the digital quantity can be calculated. If the LSB register configuration of the present invention is valid as 16BIT, the time corresponding to each LSB transmitted is 1 / 1MHz / 2^16=15.25ps, that is, every time the digital value changes by 1, it represents a change of 15.25ps in the time difference measurement. This design value is less than the highest resolution of GPX2, which can ensure that the chip works at the highest resolution. In addition, other reset, interrupt and other control signals on the chip are connected to the external MCU to realize chip control and status feedback, such as RSTIDXP pin, internal count reset, high level is valid. DISABLEP pin, channel disabled, high level is valid. INTERRUPT pin will be pulled low when the test is completed to notify the user to collect data.

[0044] Figure 6 This is the schematic diagram for time difference measurement, which is used to measure the time difference between 1PPS_1 and 1PPS_2, where t1, t2, N, and N+K are all data transmitted to the MCU unit through the serial port. N represents the Nth capture of 1PPS_1, 1MHz is the reference clock, and the calculation formula for the time difference digital quantity of the two channels is t2-t1+K*2^16 least significant bits LSB, t1 and t2 are the measurement moments of the reference clock signal and the crystal oscillator signal to be tamed, respectively, and K is the linear ratio between time and the time difference digital quantity signal.

[0045] In summary, the present application takes into account that directly using the crystal oscillator output as the input of the time-frequency conversion module is likely to result in a large amount of module data and cumbersome processing. The output signal of the crystal oscillator is first divided, and used as the input of the frequency division circuit, so that the entire circuit is small in size. The GNSS second pulse signal is converted from differential to single-ended and filtered, with high measurement accuracy. 1MHz is specially designed as the clock reference of the time digital converter in the frequency division circuit to ensure that even if the time interval between the two pulse signals is too large, it will not cause the time digital converter data overflow. The least significant bit LSB register is set to 216 to ensure that the digital quantity representation accuracy of the measured output is within 20ps. It can be widely transplanted and applied to high-precision timekeeping and timing systems in various fields.

[0046] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A high-precision time difference measurement circuit suitable for taming a crystal oscillator, characterized in that: include: An MCU module (1), a GNSS second pulse signal module (2), an external high-precision crystal oscillator module (3), a differential-to-single-ended module (4), a frequency division circuit (5), a time-to-digital converter (6) and a power supply unit (7), wherein the GNSS second pulse signal module (2) is connected to the frequency division circuit (5) via the differential-to-single-ended module (4), the external high-precision crystal oscillator module (3) is connected to the frequency division circuit (5), an output end of the frequency division circuit (5) is connected to the time-to-digital converter (6), the time-to-digital converter (6) is communicatively connected to the MCU module (1), and the power supply unit (7) is electrically connected to the MCU module (1), the GNSS second pulse signal module (2), the external high-precision crystal oscillator module (3), the differential-to-single-ended module (4), the frequency division circuit (5), and the time-to-digital converter (6).

2. A high-precision time difference measurement circuit suitable for taming a crystal oscillator according to claim 1, characterized in that: The differential-to-single-ended module (4) uses a MAX3485 differential level conversion chip to convert the differential pulse-per-second signal output by the GNSS pulse-per-second signal module (2) into a 3.3V single-ended signal.

3. A high-precision time difference measurement circuit suitable for taming a crystal oscillator according to claim 1, characterized in that: The output frequency range of the external high-precision crystal oscillator module (3) is between 10 MHz and 100 MHz.

4. A high-precision time difference measurement circuit suitable for taming a crystal oscillator according to claim 1, characterized in that: The frequency division circuit (5) adopts the EPM570T100 chip to realize the filtering output of the pulse 1PPS and the frequency division of the crystal oscillator output.

5. A high-precision time difference measurement circuit suitable for taming a crystal oscillator according to claim 1, characterized in that: The time-to-digital converter (6) adopts a GP22 chip.

6. A measurement method using the high-precision time difference measurement circuit suitable for taming a crystal oscillator according to any one of claims 1 to 5, characterized in that: include: The GNSS differential second pulse signal output by the GNSS second pulse signal module is output to the differential to single-ended module to convert the differential second pulse signal into a 3.3V single-ended second pulse signal, which is then filtered through a frequency division circuit; the crystal oscillator signal output by the external high-precision crystal oscillator module to be tamed is output to the frequency division circuit for frequency division, and the reference clock signal after the crystal oscillator frequency division and the crystal oscillator signal to be tamed are output; wherein the single-ended second pulse signal is used as a reference signal, and the crystal oscillator signal to be tamed is a calibrated signal; The frequency division circuit outputs the filtered single-ended second pulse signal, the reference clock signal after the crystal oscillator frequency division, and the crystal oscillator signal to be tamed to the time digital converter. The time digital converter compares the single-ended second pulse signal and the crystal oscillator signal to be tamed with the reference clock signal to obtain a time difference digital quantity signal. Then, the time digital converter transmits two types of time difference digital quantity signals to the MCU through the SPI serial port. The MCU calculates the time difference between the single-ended pulse-per-second signal and the crystal oscillator signal to be tamed according to the time difference digital quantity.

7. The measuring method of a high-precision time difference measuring circuit suitable for taming a crystal oscillator according to claim 6, characterized in that: The MCU sets the register of the least significant bit LSB of the time digital converter through the serial port, and sets the bit width and FIFO length at the same time.

8. The measuring method of a high-precision time difference measuring circuit suitable for taming a crystal oscillator according to claim 6, characterized in that: The reference clock signal after the crystal oscillator frequency division is 1 MHz.

9. The measuring method of a high-precision time difference measuring circuit suitable for taming a crystal oscillator according to claim 6, characterized in that: The frequency division circuit divides the signal output by the tamed external high-precision crystal oscillator module (3) by 10 8 The frequency is divided to obtain the crystal oscillator signal to be tamed.

10. The measuring method of a high-precision time difference measuring circuit suitable for taming a crystal oscillator according to claim 6, characterized in that: The MCU uses the reference clock signal as the reference clock and combines the register configuration value of the least significant bit LSB to calculate the time corresponding to the digital quantity. The specific calculation formula is: t2-t1+K*2^16, t1 and t2 are the measurement moments of the reference clock signal and the crystal oscillator signal to be tamed, respectively, and K is the linear ratio between the time and the time difference digital quantity signal.

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