CN110113045B - High-precision crystal-free self-correction clock system applied to USB slave equipment - Google Patents
High-precision crystal-free self-correction clock system applied to USB slave equipment Download PDFInfo
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- CN110113045B CN110113045B CN201910418421.9A CN201910418421A CN110113045B CN 110113045 B CN110113045 B CN 110113045B CN 201910418421 A CN201910418421 A CN 201910418421A CN 110113045 B CN110113045 B CN 110113045B
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- 238000001514 detection method Methods 0.000 claims abstract description 24
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
- G06F1/04—Generating or distributing clock signals or signals derived directly therefrom
- G06F1/08—Clock generators with changeable or programmable clock frequency
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/099—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/16—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop
- H03L7/18—Indirect frequency synthesis, i.e. generating a desired one of a number of predetermined frequencies using a frequency- or phase-locked loop using a frequency divider or counter in the loop
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Abstract
The invention discloses a high-precision crystal-free self-correction clock system applied to USB slave equipment, which aims to provide accurate clock signals for the USB slave equipment. The clock system comprises an SOF detection module (101), a correction module (102), an oscillator (103) and the like; firstly, when a slave device with a crystal-free oscillator is inserted into a USB master device, the master device supplies power to the slave device, meanwhile, a coarse control code and a fine control code are reset to initial values, and the oscillator outputs the lowest clock frequency; secondly, a correction module starts a primary correction mode to perform linear correction on the oscillator, so that an oscillator output frequency error enters a primary frequency tuning error range, an SOF (Start OF Frame) detection module correctly identifies the SOF, and finally a coarse control code is obtained; and finally, the correction module enters a secondary correction mode to perform secondary coarse adjustment and fine adjustment on the oscillator, and when the output frequency error of the oscillator enters a secondary frequency tuning error range, the correction work is completed, and the USB slave equipment normally works. The invention is suitable for USB interface chips, MCU control chips and the like.
Description
Technical Field
The invention mainly relates to the field of high-precision clock system design, in particular to a crystal-free self-correction high-precision clock generation circuit structure applied to USB slave equipment.
Background
The USB (Universal Serial BUS) interface is widely applied to the data transmission interface technology, and a high-precision clock source is needed to provide accurate clock signals for the interface, so that the data interaction function of USB master-slave equipment is ensured to be correct. For example, the low speed transmission mode requires a USB clock frequency range of 12 M+ -1.5%, the full speed transmission mode requires a USB clock frequency range of 48 M+ -0.25%, and the high speed transmission mode requires a USB clock frequency range of 480 M+ -0.05%. Therefore, in the conventional USB interface implementation, a crystal oscillator clock is generally used as an accurate clock reference source, and an internal clock frequency doubling module is combined to implement a high-precision target clock, for example, a phase-locked loop technology is used to double the reference clock to a target frequency for output. However, this implementation requires an external crystal and a resonant capacitor, which increases the BOM cost of the overall scheme, and also increases the layout area of the PCB, and additionally considers the problem of mutual crosstalk when designing the PCB with high-frequency signal processing, and increases the wiring difficulty, such as the BLE module design with USB interface.
In order to solve the technical problems, the invention provides a high-precision crystal-free self-correction clock system applied to USB slave equipment, which comprises an SOF detection module (101), a correction module (102) and an oscillator (103);
firstly, when a USB slave device with a crystal-free oscillator is inserted into a USB master device, the master device supplies power to the slave device, meanwhile, a coarse tuning control code and a fine tuning control code are reset to initial values, and the oscillator outputs a clock signal with the lowest frequency;
secondly, a correction module (102) enters a primary correction mode, the oscillator (103) is subjected to linear correction by adjusting the coarse control code, so that the output frequency deviation of the oscillator enters a primary tuning error range, an SOF detection module correctly identifies SOF, a corresponding coarse control code is obtained, and the primary correction mode is closed;
and finally, the correction module (102) enters a secondary correction mode, and the secondary coarse adjustment and fine adjustment of the frequency of the oscillator are respectively realized by adjusting the coarse adjustment control code and the fine adjustment control code on the basis of the coarse adjustment control code generated in the primary correction mode, so that the output frequency deviation of the oscillator enters a secondary tuning error range, a target frequency clock is obtained, and the correction work is completed.
In addition, in order to avoid power supply voltage jitter, clock deviation caused by factors such as temperature change of a working environment and the like causes communication failure of USB master-slave equipment, the self-correction clock system always detects clock frequency in the working process, and when the frequency deviation detects a set target value, a corresponding correction mode can be automatically started to correct the output clock frequency to be within a target range.
According to the high-precision crystal-free self-correction clock system, BOM (crystal oscillator and corresponding tuning capacitor) cost in an application scheme is reduced under the condition that normal communication of USB master-slave equipment data is met, meanwhile, test cost about a correction part in a chip test process is avoided, and design difficulty and wiring area of a PCB in the application process are simplified.
Disclosure of Invention
The invention aims to solve the problems that: aiming at the problems existing in the prior art, the invention provides a high-precision crystal-free self-correction clock system applied to USB slave equipment, which comprises an SOF detection module, a correction module and an oscillator module, and can automatically complete clock correction without manual intervention, thereby providing accurate clock signals for the USB slave equipment; meanwhile, an external crystal is not required to provide a reference clock, so that the BOM cost of a product scheme is reduced; the correction module always detects clock frequency in the USB working Process, when the error exceeds a target range, the correction module immediately works, enters a corresponding correction mode to realize frequency correction, finally outputs a clock signal meeting the precision requirement of the USB clock, and shows the advantage of insensitivity to PVT (P: process-manufacturing technology, V: voltage-power supply Voltage, T: temp-environmental temperature).
In order to realize the technical problems, the invention provides the following solutions: the utility model provides a be applied to USB slave unit's high accuracy crystal-free self-correcting clock system which characterized in that: comprises an SOF detection module (101), a correction module (102) and an oscillator (103); the SOF detection module (101) receives the signal USB_DATA, outputs a signal SOF_FLAG to the correction module, and the correction module outputs a coarse control code and a fine control code to the oscillator (103); the oscillator (103) outputs a clock signal CLK_OUT and feeds back the clock signal CLK_OUT to the SOF detection module (101) and the correction module (102);
firstly, when a USB slave device with a crystal-free oscillator is inserted into a USB master device, the master device supplies power to the slave device, meanwhile, a coarse tuning control code and a fine tuning control code are reset to initial values, and the oscillator outputs a clock signal with the lowest frequency;
secondly, the correction module (102) enters a primary correction mode, the oscillator (103) is linearly corrected by adjusting the coarse control code, under the condition, the weight corresponding to the coarse control code is gradually increased by 1, and the coarse control code is adjusted according to the actual frequency deviation; when the output frequency error of the oscillator starts to enter a primary tuning error range, the SOF detection module correctly identifies the SOF, the coarse tuning control code is continuously adjusted to enable the output frequency of the oscillator to be continuously increased until the SOF detection module fails to identify the SOF, all coarse tuning control codes in the whole process from the first time of correctly identifying the SOF to the last time of correctly identifying the SOF are processed, a primary correction target coarse tuning control code is obtained, and the primary correction mode is closed;
finally, the correction module (102) enters a secondary correction mode, the secondary coarse adjustment and fine adjustment of the oscillator are respectively realized by adjusting the coarse adjustment control code and the fine adjustment control code on the basis of the coarse adjustment control code generated in the primary correction mode, for the secondary coarse adjustment stage, the output clock of the oscillator is counted on the basis of a time scale with 1ms interval between every two SOF identification bits, and when the counting result is larger than the upper limit value of the secondary coarse adjustment target counting value range, the frequency of the output clock of the oscillator is represented to be higher than the upper limit of the coarse adjustment frequency range, and the coarse adjustment weight needs to be reduced; when the counting result is smaller than the lower limit value of the secondary coarse adjustment target counting value range, the output clock frequency of the characterization oscillator is lower than the lower limit of the coarse adjustment target frequency range, and coarse adjustment weight needs to be increased; when the counting result is in the range of the target counting value of the secondary coarse adjustment, characterizing that the clock deviation is in the range of coarse adjustment errors, ending the secondary coarse adjustment stage, and obtaining a secondary correction coarse adjustment control code;
for the fine tuning stage, the period counting is carried out on the oscillator output clock based on the time scale with the interval of 1ms between the two SOF identification bits, when the counting result is larger than the upper limit value of the fine tuning target counting value range, the frequency of the oscillator output clock is higher than the upper limit of the fine tuning target frequency range, and the fine tuning weight is required to be reduced; when the counting result is smaller than the lower limit of the fine tuning target counting value range, the output clock frequency of the characterization oscillator is lower than the lower limit of the fine tuning target frequency range, and the fine tuning weight is required to be increased; and when the counting result is in the fine tuning target counting range, the clock deviation is represented in the fine tuning error range, the fine tuning stage is ended, and the correction work is completed.
The high-precision crystal-free self-correction clock system is characterized in that: in the whole USB master-slave data interaction process, the correction module is always in a frequency detection state; when detecting that the frequency deviation of the output clock of the oscillator exceeds the fine tuning error range but is within the coarse tuning error range, the correction module immediately enters fine tuning correction; when the frequency deviation of the output clock of the oscillator exceeds the coarse tuning error range, the correction module immediately enters a second-level coarse tuning correction; therefore, the system is insensitive to manufacturing process variations, supply voltage and temperature variations in the operating environment.
Compared with the prior art, the invention has the advantages that:
1. the PVT (P: process-manufacturing Process, V: voltage-supply Voltage, T: temp-ambient temperature) characteristics of the clock system are increased. Compared with the traditional USB clock system, the high-precision crystal-free self-correction clock system is always in a clock frequency detection state in the working process, and when the clock frequency change is caused by the process, the power supply voltage or the ambient temperature, the correction module is immediately started when the clock frequency change exceeds the target frequency deviation range, and enters a corresponding correction mode to adjust the output frequency of the oscillator, so that the frequency precision of the USB clock is ensured to meet the application requirement;
2. the test cost is reduced. Compared with the traditional USB clock system and the crystal-free USB clock system described in FIG. 2, the self-correcting clock system of the invention adopts a self-correcting mode to carry out frequency adjustment in the working process, and the actual control code of each chip can select the corresponding control code to realize frequency correction based on the actual frequency characteristic, thereby avoiding the correction cost of realizing frequency correction in the middle measurement or the final measurement stage;
3. the application is simple, and the BOM cost is reduced. Compared with the traditional USB clock system, the self-correction clock system does not need an external crystal and a tuning capacitor, reduces BOM cost, simplifies PCB wiring difficulty and reduces PCB area.
Drawings
FIG. 1 is a schematic diagram of a high precision crystal-free self-correcting clock system of the present invention applied to a USB slave device;
FIG. 2 is a block diagram of a currently proposed crystal-free USB device clock system;
FIG. 3 is a detailed block diagram of the high-precision crystal-free self-correcting clock system of the present invention;
fig. 4 is a flowchart of the operation of the high precision crystal-less self-correcting clock system of the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and the specific examples.
Referring to fig. 1 and 3, the high-precision crystal-free self-correction clock system of the present invention includes a SOF detection module (101), a correction module (102), and an oscillator (103).
Referring to fig. 1 and 3, fig. 4 shows a specific embodiment of a self-correcting clock system, which is specifically described as follows:
when the USB slave device is inserted into the master device, the USB master device identifies the slave device and simultaneously supplies power to the slave device through the VBUS port; after the USB slave device is powered on, registers corresponding to the coarse control code and the fine control code of the oscillator (103) are reset to default values, and the lowest clock frequency is output at the moment. Meanwhile, the SOF detection module (101) starts to work and judges whether SOF can be correctly identified;
after the initialization is finished, the self-correction clock system enters a first-level correction mode, the weight of the coarse control code is gradually increased by 1, the linear adjustment of the frequency of the oscillator is realized, and the SOF detection module always detects SOF signals;
when the SOF detection module does not detect the SOF signal, the coarse control code weight is added with 1, so that the output frequency of the oscillator is improved; repeating the above operation until the SOF detection module correctly recognizes the SOF signal, and the corresponding Coarse control Code is Coarse_Code_1; the Coarse control Code weight continues to be increased, the oscillator output clock frequency continues to increase, and each time the SOF detection module correctly recognizes that the corresponding Coarse control Code for SOF is saved as coarse_code_j (j=1, 2, 3.). Along with the increase of the weight of the Coarse control Code, the output clock frequency of the oscillator exceeds the target frequency range of the USB clock, the SOF module cannot recognize the SOF signal, meanwhile, the corresponding Coarse control Code which can recognize the SOF at the previous time is stored as the coarse_code_N, the correction module finishes the primary correction mode, and all the stored Coarse control codes coarse_code_J (N=1, 2,3.
After the primary correction is finished, the self-correction clock system enters a secondary correction mode, a secondary coarse adjustment counter counts based on an oscillator output clock, and when the counting result is greater than the upper limit value of a secondary coarse adjustment counting range, the frequency of the oscillator output clock is higher than the target frequency, and coarse adjustment weight needs to be reduced; when the counting result is smaller than the lower limit value of the secondary coarse adjustment counting range, the output clock frequency of the characterization oscillator is lower than the target frequency, and coarse adjustment weight needs to be increased; when the counting result enters the secondary Coarse tuning counting range, the frequency deviation of the output clock of the characterization oscillator enters the secondary Coarse tuning frequency error range, and the corresponding Coarse tuning control Code is stored as Coarse_code_Sec.
When the secondary coarse adjustment of the secondary correction mode is finished, the self-correction clock system enters a fine adjustment correction mode, a fine adjustment counter counts based on an oscillator output clock, and when the counting result is larger than the upper limit value of a fine adjustment counting range, the frequency of the oscillator output clock is higher than the target frequency, and the fine adjustment weight needs to be reduced; when the counting result is smaller than the lower limit value of the fine tuning counting range, the output clock frequency of the characterization oscillator is lower than the target frequency, and the fine tuning weight is required to be increased; when the counting result enters the Fine tuning counting range, the frequency deviation of the output clock of the characterization oscillator enters the Fine tuning frequency error range, and the corresponding Fine tuning control Code is stored as Fine_code.
After the correction is completed, the output clock frequency of the oscillator meets the precision requirement of the frequency of the USB clock, and the USB master-slave equipment performs normal data communication. In the USB process, the self-correction clock system always monitors the frequency of the oscillator output clock, and when detecting that the frequency deviation of the oscillator output clock exceeds the fine adjustment error range but is within the coarse adjustment error range, the correction module immediately enters fine adjustment correction; when the frequency deviation of the output clock of the oscillator exceeds the coarse tuning error range, the correction module immediately enters a second-level coarse tuning correction; therefore, the self-correction system is insensitive to manufacturing process variations, power supply voltage and temperature variations in the operating environment.
Schematic diagrams and implementations of the above modules refer to all implementations with this functionality. The circuit shown in the above figures is only an example, and the circuit change caused by simply replacing the device is also within the protection scope of the present invention, and the protection scope of the present invention shall be subject to the claims.
Claims (2)
1. The utility model provides a be applied to USB slave unit's high accuracy crystal-free self-correcting clock system which characterized in that: comprises an SOF detection module (101), a correction module (102) and an oscillator (103); the SOF detection module (101) receives the signal USB_DATA, outputs a signal SOF_FLAG to the correction module, and the correction module outputs a coarse control code and a fine control code to the oscillator (103); the oscillator (103) outputs a clock signal CLK_OUT and feeds back the clock signal CLK_OUT to the SOF detection module (101) and the correction module (102);
firstly, when a USB slave device with a crystal-free oscillator is inserted into a USB master device, the master device supplies power to the slave device, meanwhile, a coarse tuning control code and a fine tuning control code are reset to initial values, and the oscillator outputs a clock signal with the lowest frequency;
secondly, the correction module (102) enters a primary correction mode, the oscillator (103) is linearly corrected by adjusting the coarse control code, under the condition, the weight corresponding to the coarse control code is gradually increased by 1, and the coarse control code is adjusted according to the actual frequency deviation; when the output frequency error of the oscillator starts to enter a primary tuning error range, the SOF detection module correctly identifies the SOF, the coarse tuning control code is continuously adjusted to enable the output frequency of the oscillator to be continuously increased until the SOF detection module fails to identify the SOF, all coarse tuning control codes in the whole process from the first time of correctly identifying the SOF to the last time of correctly identifying the SOF are processed, a primary correction target coarse tuning control code is obtained, and the primary correction mode is closed;
finally, the correction module (102) enters a secondary correction mode, the secondary coarse adjustment and fine adjustment of the oscillator are respectively realized by adjusting the coarse adjustment control code and the fine adjustment control code on the basis of the coarse adjustment control code generated in the primary correction mode, for the secondary coarse adjustment stage, the output clock of the oscillator is counted on the basis of a time scale with 1ms interval between every two SOF identification bits, and when the counting result is larger than the upper limit value of the secondary coarse adjustment target counting value range, the frequency of the output clock of the oscillator is represented to be higher than the upper limit of the coarse adjustment frequency range, and the coarse adjustment weight needs to be reduced; when the counting result is smaller than the lower limit value of the secondary coarse adjustment target counting value range, the output clock frequency of the characterization oscillator is lower than the lower limit of the coarse adjustment target frequency range, and coarse adjustment weight needs to be increased; when the counting result is in the range of the target counting value of the secondary coarse adjustment, characterizing that the clock deviation is in the range of coarse adjustment errors, ending the secondary coarse adjustment stage, and obtaining a secondary correction coarse adjustment control code;
for the fine tuning stage, the period counting is carried out on the oscillator output clock based on the time scale with the interval of 1ms between the two SOF identification bits, when the counting result is larger than the upper limit value of the fine tuning target counting value range, the frequency of the oscillator output clock is higher than the upper limit of the fine tuning target frequency range, and the fine tuning weight is required to be reduced; when the counting result is smaller than the lower limit of the fine tuning target counting value range, the output clock frequency of the characterization oscillator is lower than the lower limit of the fine tuning target frequency range, and the fine tuning weight is required to be increased; and when the counting result is in the fine tuning target counting range, the clock deviation is represented in the fine tuning error range, the fine tuning stage is ended, and the correction work is completed.
2. The high precision crystal-less self-correcting clock system of claim 1, wherein: in the whole USB master-slave data interaction process, the correction module is always in a frequency detection state; when detecting that the frequency deviation of the output clock of the oscillator exceeds the fine tuning error range but is within the coarse tuning error range, the correction module immediately enters fine tuning correction; when the frequency deviation of the output clock of the oscillator exceeds the coarse tuning error range, the correction module immediately enters the second-level coarse tuning correction.
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